https://wiki.diyfaq.org.uk/api.php?action=feedcontributions&user=81.187.135.98&feedformat=atomDIYWiki - User contributions [en]2024-03-19T08:40:50ZUser contributionsMediaWiki 1.35.9https://wiki.diyfaq.org.uk/index.php?title=Oscillating_tools&diff=13035Oscillating tools2010-03-22T17:14:52Z<p>81.187.135.98: </p>
<hr />
<div>==Introduction==<br />
The oscillating tool, is a concept that was originally made popular by the German manufacturer Fein with their Multimaster range of tools. In recent years, a number of similar tools based on the multimaster concept have become available. This article serves not only as a FAQ for this particular class of tool, it also documents the level of interoperability between the blades and accessories for the various makes. <br />
<br />
==What is it?==<br />
Its a small versatile tool designed to perform a wide range of tasks. They can be used for cutting, sanding, rasping, polishing, scraping and a number of other tasks. They make very effective tools for performing awkward cutting operations that are almost impossible with any other tool. <br />
<br />
Most tools on the market are mains-operated but Bosch also make a cordless (Li-Ion powered) model.<br />
<br />
[[Image:Mm-multimaster-top.jpg|A Fein Multimaster Top (variable speed) with plunge cut blade mounted]]<br />
<br />
==How does it work?==<br />
An oscillating tool, looks a little reminiscent of a detail sander, and in fact they do make very good detail sanders. However that is where the similarity ends. Rather than having a fixed sanding pad that orbits, they have a tool attachment post. The various tools are then firmly bolted or clipped to the post. When running, the tool post rotates a very small amount in alternate directions, at a very high frequency (typically 20,000 oscillations per minute). <br />
<br />
[[Image:Mm-tool-post.jpg|240px|Blade Mounting Tool post]]<br />
<br />
Its this oscillation that does the actual work. The end of a saw blade for example will swing back and fourth by a couple of millimetres. With its fine teeth, this is enough to cut any rigidly held material it comes into contact with. An abrasive will similarly work back and forth over a surface.<br />
<br />
==What can it do?==<br />
One of the unique abilities of this type of tool is the way in which it can cut. Equipped with the appropriate blade it can simply plunge into the surface of the material that is being cut, without touching or damaging anything adjacent to the thing being cut. Unlike for example plunge cutting with a chisel, the cut has a very fine kerf. This makes it ideal for a number of jobs:<br />
<br />
* Cutting floorboards prior to lifting - precise neat cuts can be plunged into a board directly above a joist with no risk to pipes or cables under the floor. <br />
* Flush cutting; many of the blades include an offset of "crank" that enables them to cut flush with a surface. This is ideal for cropping pipes against a wall, or undercutting a door frame to allow a wood floor to slide under the jamb. Undercutting skirting. <br />
* Cutting objects, such as pipework, in confined spaces e.g. cutting copper pipe where there is insufficient access for a pipeslice, hacksaw, sabre saw etc: one can even cut a section out of a damaged pipe in an excavated chase.<br />
* Cutting grout out from between ceramic wall tiles (either using a grit-edged blade or an old wood or metal blade) to pry away a single tile (or small group of tiles) for access or repair.<br />
* Sanding, scraping, polishing etc<br />
* Rasping - a carbide rasp will quickly eat through rotten wood, tile glue residue, old putty etc.<br />
<br />
==Who will find a use for one?==<br />
<br />
Anyone doing general DIY, Handymen, Tilers, Glazers, Plumbers, Electricians. <br />
<br />
==Safety==<br />
Multitools are one of the safer power tools to use. When fitted with a blade, they have a unique ability to not cut human flesh even if deliberately applied to the skin, this is because the skin simply tends to vibrate and move with the blade rather than being abraded against it. (For this reason, surgical tools that use the same cutting technique are often used as bone saws, and also for more mundane jobs like removing plaster casts). <br />
<br />
When sanding, one must still take adequate protection from the dust. <br />
<br />
Ear protection is also advised for prolonged use, since they produce a fairly loud noise with much of the sound concentrated into a narrow frequency band that quickly dulls the hearing. <br />
<br />
<br />
==The Tools==<br />
<br />
{| border="1" cellpadding="6" cellspacing="0" style="text-align:left,top"<br />
|-<br />
!colspan="2"|Oscillating tool blades<br />
|-<br />
| [[Image:Mm-narrow-plunge.jpg]]<br />
(universal mounting)<br />
| A narrow plunge cut blade for wood and plastics etc. Ideal for floorboard lifting, cutting holes for electrical back boxes in plasterboard etc. This one is a "Bi-metal" type that can be used on composites and some non ferrous metals. <br />
|-<br />
| [[Image:Mm-wideblade.jpg]]<br />
(universal mounting)<br />
| A wide plunge cut blade for wood and plastics etc. Uses as above - but for wider cuts. <br />
|-<br />
| [[Image:Mm-wood-plunge-coarse.jpg]]<br />
(universal mounting)<br />
| This is a wood and plastics cutting plunge cutting blade. This one has larger more aggressive teeth for fast cutting. These are best suited to cutting things that are well supported and fixed, like floorboards since otherwise they tend to just catch and vibrate the work!<br />
|-<br />
| [[Image:Mm-scraper.jpg]]<br />
(Fein mounting)<br />
| A Sharp untoothed scraper blade. These are designed for getting under sticky stuff - scraping glue residue, or adhesive backed plastics off hard surfaces. <br />
|-<br />
| [[Image:Mm-unvented-sanding.jpg]]<br />
(Fein mounting)<br />
| A hook and loop sanding backing pad designed for the felt backed sanding pads. Note that unlike traditional delta pads these have a slight radius to each side that matches the arc of rotation of the machine. This enables you to sand right up to an adjacent surface with no risk of straying onto it, or hammering against an edge as you would with a traditional delta sander.<br />
|-<br />
| [[Image:Mm-vented-sanding.jpg]]<br />
(Fein mounting)<br />
| A vented version of the sanding pad designed for use with vacuum extraction. <br />
|-<br />
| [[Image:Mm-dust-cowl.jpg]]<br />
| The original Multimaster and many of the clones don't have any built in ducting for dust extraction. They typically have an additional cowl that bits against the side of the machine and under the tool post. A felt washer maintains a close seal between the cowl and the back of the sanding pad. While no sander has perfect dust collection, this is one of the more effective collection systems you will encounter. Mess is also reduced since the oscillating action tends to drop the dust straight down rather than throwing it into the air as much as other sanding actions. <br />
|-<br />
| [[Image:Mm-hss-segment.jpg]]<br />
(universal mounting)<br />
| This is a depressed centre HSS segment saw for cutting woods, composite, and metals. The depressed centre will allow flush cutting, and the segment allows you to cut up to neat finish at an edge without the traditional overcut one associates with a circular blade. Note that one is better off using a round blade if this close cutting facility is not required, since the teeth near the segment will tend to wear first, and this is the most useful bit of the blade.<br />
|-<br />
| [[Image:Mm-hss-segment-flat.jpg]]<br />
(universal mounting)<br />
| This is a flat version of the above. The flat blade can't cut flush to a surface, but can in some cases cut a little deeper. These blades are often a little cheaper than the depressed centre versions. <br />
|-<br />
| [[Image:Mm-hss-circle.jpg]] <br />
(universal mounting)<br />
| A circular HSS blade. Ideal for general cutting from any part of the blade. Note that since the tool does not rotate the blade in use, it is worth rotating it manually from time to time to spread the tooth wear around all the teeth. <br />
|-<br />
| [[Image:Mm-hss-broken-flat.jpg]]<br />
(Fein mounting)<br />
| Even broken blades can be worth keeping if the mounting part is still serviceable!<br />
|-<br />
| [[Image:Mm-carbide-segment.jpg]]<br />
(Fein mounting)<br />
| A carbide edged segment saw. These are ideal for cutting ceramics, glass, cast iron and other hard materials. Particularly good for neatly cutting holes in the middle of tiles or tiles that are already fixed to the wall - say when cutting in electrical accessory boxes, or making access to shower valves. They are also very effective for removing old grout from between tiles. For even longer life, there are diamond versions of these available. <br />
|-<br />
| [[Image:Mm-carbide-rasp.jpg]]<br />
(Fein mounting)<br />
| The carbide rasp is also a very handy tool for tilers, It allows the quick and effective removal of old set tile adhesive for example. Combined with this and the carbide segment saw, removing broken or damaged tiles for replacement becomes very straightforward. <br />
<br />
The rasp is also effective at removing badly flaked old paint, or putty residue from window frames when re-glazing. <br />
<br />
Can be used on wood for coarse shaping, or for quickly removing rotten wood from window frames etc prior to filling. <br />
|-<br />
| [[Image:Mm-mini-bladeholder.jpg]]<br />
(Fein mounting)<br />
| This is an adaptor blade designed for holding mini blades and rasps. These are aimed at detail work, and are handy for activities such as model making, and sharpening of small tools. <br />
|-<br />
| [[Image:Mm-mini-blades.jpg]]<br />
| A variety of blades and rasps for use with the above tool holder. <br />
|-<br />
<br />
|}<br />
<br />
==Tool Interchangeability==<br />
One of the disadvantages of oscillating tools is the cost of the blades, combined with the fact they are easily damaged if not treated with care (attempting to plunge a wood blade against a nail or masonry for example will very quickly reduce it to something that ceases cutting wood and attempts to burn its way though!<br />
<br />
The rise in availability of similar tools however has meant that blade prices have fallen, and there there are new sources of blades. Hence the question arises regarding blade interchangeability. <br />
<br />
Most brands produce the basic plunge cutting and scraping blades. Many also have the carbide blades. However Fein still produce the widest range of blades with some very specialist blades as well as the more run of the mill ones.<br />
<br />
Initial reports seem to suggest that blade quality is generally good, regardless of the source. <br />
<br />
<br />
{| border="1" cellpadding="6" cellspacing="0" style="text-align:left,top"<br />
|-<br />
! Machine<br />
! Blade Mounting<br />
|-<br />
| Original Fein Multimaster<br />
| [[Image:Mm-tool-screws.jpg]]<br />
[[Image:Mm-blade-fixing.jpg]]<br />
<br />
The original Multimaster used a basic screw fixing for the blades without any further registration lugs or pins. The blades simply had a 10mm mounting hole that sat over the flange on the tool post, and the fixing screw with clamp plate tightended down onto them. This system allowed the blade to be installed at any angle. However it does require the screw to be securely done up with the supplied allen wrench, or the blade position can wander in use. <br />
<br />
One advantage of the earlier Fein machine mounting is that it allows use of all the various blade designs available. <br />
|-<br />
| Current Multimaster<br />
| The current models use a quick release blade fixing system that retains a stud with a lever action mechanism. The tool post also has registration lugs that engage with notches cut around the periphery of the main 10mm mounting hole. Hence the new machines can use Fein blades, and universal blades. <br />
|-<br />
| Bosch Multitool<br />
| Bosch do a couple of tools, a green bodied DIY class machine that is mains powered, and a blue "pro" range cordless tool. These have a ring of registration pins that match the Bosch blade patten:<br />
[[Image:Mm-bosch-plunge.jpg]]<br />
<br />
Bosch tools can hence use Bosch blades and universal blades. <br />
|-<br />
| Ferm, Powercraft (Aldi) <br />
| The Ferm and Aldi Powercraft branded tool has a similar arrangement to the Bosch system but with fewer pins:<br />
[[Image:Mm-ferm-scraper.jpg]]<br />
<br />
As a result these tools can use their own branded blades, as well as Bosch, and universal ones. <br />
|-<br />
| Rockworth (Makro and other places)<br />
| These relatively low cost tools use the same mounting as the original Fein multimaster. Hence can use any blades. <br />
|-<br />
|}<br />
<br />
<br />
==See also==<br />
<br />
* [[Special:Allpages|Wiki Contents]]<br />
* [http://www.diyfaq.org.uk/contents.html#powertools Power Tool FAQ]<br />
* [[Special:Categories|Wiki Subject Categories]]<br />
<br />
<br />
[[Category:Tools]]</div>81.187.135.98https://wiki.diyfaq.org.uk/index.php?title=Wallwart&diff=9849Wallwart2008-08-15T23:43:10Z<p>81.187.135.98: Case of AC, DC, V and spacing.</p>
<hr />
<div>[[image:Wallwart fe 153-2.jpg|400px]]<br />
<br />
How to choose a '''wallwart''' for your small appliance.<br />
<br />
<br />
==What's a wallwart?==<br />
A wallwart is a small plug-in power supply commonly used to run small appliances at low voltage. The power supply and mains plug are one and the same item.<br />
<br />
==How to choose==<br />
When picking a wallwart for an appliance, 4 things matter:<br />
* voltage<br />
* AC, DC or rectified AC<br />
* current<br />
* regulated or unregulated<br />
<br />
<br />
===Voltage===<br />
Wart voltage needs to match appliance voltage. Sometimes it must be precise, sometimes small variation is ok.<br />
* Lighting needs correct voltage<br />
* Motors will run ok with a bit less, although a bit slower. They may overheat and fry with a bit higher voltage<br />
* Computer speakers are fine with a bit less voltage, though max power output may be reduced a bit<br />
<br />
====The Voltage gotcha====<br />
There is one thing to beware of. Warts with switchable voltage will store power at the highest voltage setting in their reservoir capacitor, so if you switch a wart from say 12 V off load (which will be anything from 15 V - 19 V) to 5 V then connect up an appliance containing logic circuitry, your appliance will be hit with over triple rated voltage, and probably die instantly.<br />
<br />
When switching voltage down on an adjustable wart, unplug it and short the output to discharge it before using it on a lower voltage appliance.<br />
<br />
<br />
===AC, DC or rectified AC===<br />
For an explanation of AC, DC & rectified AC, see [[Electricity Basics#AC, DC & Rectified AC|here]].<br />
<br />
====AC====<br />
Appliances requiring AC warts can be run happily from AC, DC or rectified AC. Neither AC warts nor appliances expecting AC warts are common, they are most often telecoms equipment. AC warts have few uses.<br />
<br />
If an appliance expecting AC is powered by a DC wart,<br />
* lightbulbs should use the same voltage DC as the expected AC voltage.<br />
* electronic appliances should use a DC wart of voltage: AC wanted voltage x 1.4<br />
<br />
AC symbol: '''~'''<br />
<br />
====DC====<br />
DC warts will happily run all small appliances, regardless of whether the appliance expects AC, DC or rectified AC.<br />
<br />
DC symbol: '''='''<br />
<br />
====Rectified AC====<br />
Most small appliances will run happily on rectified AC, but not all. Most likely to object are audio equipment (severe hum), motors (death by overheating) and miniature equipment (no room for a reservoir capacitor, major malfunctions).<br />
<br />
Rectified AC symbol: [[image:recdc2.gif]]<br />
<br />
===Current===<br />
Wart current rating must be the same as or more than the appliance current consumption.<br />
<br />
There's just one situation in which higher current rating can cause a problem. If the wart current rating is a lot higher than the appliance (say 3x as high), and the wart is unregulated, it will put out above specified voltage, and some appliances can object to this. If you're using an unregulated wart of excessive current rating, best check the output voltage with a [[multimeter]].<br />
<br />
<br />
===Regulated or unregulated===<br />
Regulated warts stay at the same voltage output under all conditions. Unregulated warts give the rated voltage under full load, but voltage will be quite a lot higher with light load or no load.<br />
<br />
Also regulated warts give a smooth flat output free of ripple. (Ripple causes hum in some audio equipment.) Unregulated warts on the other hand usually produce a lot of ripple.<br />
<br />
Some electronics must have a regulated supply, and some doesn't mind unregulated. Generally speaking, <br />
* anything with logic ICs requires regulated, and is likely to let the magic smoke out if given an unregulated supply (or even 1v more than rated voltage)<br />
* Motors and lamps are usually fine with unregulated, though there are occasional exceptions.<br />
<br />
Regulated supplies will run anything, if their other specs are right for the job. The more common unregulated supplies will run a lot of things, but can destroy some more sensitive appliances.<br />
<br />
<br />
==Electromagnetic and electronic==<br />
[[image:Wallwart sm 152-2.jpg|thumb|Electronic wallwart]]<br />
<br />
There are 2 types of wallwart. Most use an iron core transformer, and these are several times the size of a standard plug.<br />
<br />
Some are a similar size to an ordinary plug, and these are electronic warts. Electronic warts are small and light, and more or less always regulated. The downsides of electronic warts are lower reliability and higher price.<br />
<br />
==Multipurpose warts==<br />
Multipurpose warts are available to suit many appliances. These typically have:<br />
* several selectable voltages, eg 3 V, 4.5 V, 6 V, 9 V, 12 V.<br />
* switchable polarity<br />
* an assortment of power connectors<br />
<br />
Cheap unregulated 300mA warts of this type are common. The number of appliances they can run increases if the wart is also regulated. Regulated supplies do cost more.<br />
<br />
1 A 12 V variable regulated supplies are used where its desired to maximise the variety of appliances that can be run.<br />
<br />
==Wart reduction==<br />
Sometimes its possible to run 2 or more appliances off one wart to reduce clutter. The wart will need to be the right voltage for both appliances, and its current rating must be at least the current requierments of both appliances added. Ways to connect 2 appliances include:<br />
* make a plug-in adaptor from 3 connectors<br />
* Join a 2nd DC lead to the first<br />
<br />
Another approach to wart reduction is to use a power supply with multiple simultaneously usable output voltages. Then almost everything can be run off the one supply. Such supplies are too big to be built in wart format, and not often seen. <br />
<br />
Its also possible to use installed [[Low Voltage Wiring|low voltage wiring]] to distribute low voltage, removing the need for most warts.<br />
<br />
Finally, some appliances can be run off a computer's built in power supply. These provide 12 V, 5 V and 3.3 V. In some cases one can obtain other voltages from them, eg 7 V, but 7 V comes with issues.<br />
<br />
==Extension leads==<br />
As well as the usual bulky mains extension leads, it's also possible to extend the low voltage side of a wart. The result is far less visually intrusive. Speaker wire is good to extend the output of almost all warts. Such leads can help run multiple appliances from one wart, as long as the necessary specs are met.<br />
<br />
===Ampacity===<br />
Most speaker wire is 1 A rated, which is more than enough for pretty much any wart.<br />
<br />
===Voltage drop===<br />
The voltage drop for 0.5 mm wire is 90 mV per metre per amp. Thus a 300 mA supply would drop 27 mV or 0.027 V per metre of flex. If a drop of 0.3 V is acceptable, an 11 m extension is fine.<br />
<br />
===Invisible wire===<br />
When low voltage extension leads are wanted to be invisible, enamelled copper wire may be used. This is great for tucking into corners and cracks. Its available in reels from any electronic component supplier. 0.3 mm is good for most wallwart extensions, and is as good as invisible to people standing up if its at floor level.<br />
<br />
Enamelled copper wire has very thin varnish for insulation, and the insulation deteriorates if moved. Thus the wire needs to be either fixed completely immobile, or else treated as if uninsulated, and the 2 wires kept apart all the way.<br />
<br />
Uninsulated wire or wire with fragile insulation should be protected from pets if over 6 V is used. Many animals are much more prone to shock than humans.<br />
<br />
==Changing the voltage==<br />
The output voltage of a wart can be reduced either with [[Droppers|dropper diodes]] or a regulator. Use of regulators is a bit beyond DIY territory, but is fairly simple if you have basic electronic knowledge, and use a 78 series regulator or a variable LM317.<br />
<br />
Droppers and regulators can be used to provide multiple voltages, and thus run multiple appliances off one supply.<br />
<br />
==When an appliance has no markings==<br />
Usually appliances have the supply requirement marked on them. Sometimes the marking is only shallow embossment in the plastic, and needs light at an angle to be visible.<br />
<br />
When there are no markings, the fun begins. Following these steps will usually get it working, but is not risk free, and a percentage of dead appliances will occur. Experiment at your own risk.<br />
<br />
Its better to use a DC wart, but rectified AC will work in the majority of cases.<br />
<br />
===Batteries===<br />
If it takes batteries, the same voltage wart should work fine. Occasionally an appliance needs a higher voltage wart, either due to an inbuilt regulator, diode, or a desire to reduce power consumption when on batteries.<br />
<br />
===Diode===<br />
In electronic appliances, usually the first thing the power input encounters is a protection diode. Usually this is wired across the supply so that the wrong polarity causes a short. Thus the diode polarity will tell you the required power input polarity.<br />
<br />
Less often the diode is series wired.<br />
<br />
Even less often a bridge rectifier is used instead. The presence of one of these means the appliance will work on DC, rectified AC or even AC, and that polarity doesn't matter.<br />
<br />
<br />
===Reservoir capacitor===<br />
In electronic appliances the power input usually goes to a relatively large cylindrical electrolytic capacitor with a voltage marking. The power supply will be below the capacitor voltage rating at all times. The reservoir cap rating can't pin down the voltage exactly, since sometimes the cap rating is well above working voltage, usually to increase reliability.<br />
<br />
===IC===<br />
Appliances using an IC will have a specific voltage rating for the IC. Googling the right markings on the chip can usually find this. <br />
<br />
Occasionally applying the right voltage doesn't work, if so check the chip supply pins voltage - if its much lower than the wart voltage, there may be a regulator in the way. If so the appliance will want a higher voltage supply. Measure the voltage drop between wart and IC, and your wart will then need to be IC rated voltage + 20% + measured Vdrop.<br />
<br />
===Final option===<br />
When all else fails, start with 1.5 V and increase voltage until the appliance works properly. You can use batteries for this voltage test if a variable wart isn't available.<br />
<br />
<br />
==Connectors==<br />
[[image:DC power plug 157-3.jpg|thumb|DC plug]]<br />
<br />
Most low voltage appliances use these DC plugs, but they come in various sizes, and there is no standardisation on polarity.<br />
<br />
1970s appliances often use 3.5 mm TRS plugs to deliver power. These momentarily short during insertion, so the supply must tolerate this. Most do, but certainly some wallwarts don't. With iron warts, the smaller it is the more likely it is to be short tolerant.<br />
<br />
<br />
Please write more.<br />
<br />
==See Also==<br />
* [[Special:Allpages|Wiki Contents]]<br />
* [[Special:Categories|Wiki Subject Categories]]<br />
* [[Electricity Basics]]<br />
<br />
<br />
[[Category:Electrical]]<br />
[[Category:Appliances]]<br />
[[Category:Basics]]</div>81.187.135.98https://wiki.diyfaq.org.uk/index.php?title=Talk:RCD&diff=3607Talk:RCD2007-05-27T09:48:01Z<p>81.187.135.98: Explaination of and question on "What does it not do?" change.</p>
<hr />
<div>As well as switchon surges there are bulb blowing surges, which can also pop RCDs. The momentary high current amplifies the less than perfect current balancing of real world RCDs plus cable capacitance has an unequal effect on current flow, since the L-E capacitance is across 0-330v while N-E is across close to zero voltage.<br />
[[User:NT|NT]] 09:06, 26 May 2007 (BST)<br />
<br />
Yup, there is lots more to go in the trip section. Personally I have never experienced bulbs taking out the RCD (MCBs certainly, and even rewireable fuses on occasion), but I expect this is far more likely on an already sensitised device. I must do some sums on stray capacitances dotted about, and see exactly how much influence they can actually make, before going overboard on these topics - I expect for most users of the article, the section on "tell me how to find and fix the problem" is going to be the most useful. <br />
<br />
--[[User:John Rumm|John Rumm]] 16:25, 26 May 2007 (BST)<br />
<br />
There is also something else missing, some RCDs are senstive to pulsateing DC faults and some not. You may wish to consider the content of this file http://hvacity.danfoss.com/pdf_files/rcd.pdf<br />
<br />
Clarified the 2nd para of "What does it not do?". I had to read it two or three times before I worked out what it was saying. It also assumes that the drill body is conductive, many are plastic these days and double insulated. The drill bit and chuck would be live though.<br />
<br />
Question: Will and RCD trip if its monitored live or neutral wires are connected to an unprotected supply. I suspect it might as some extra current will flow thus upsetting the current balance at the RCD. I agree that the RCD cannot disconnect the unprotected supply but it could cut the power to the drill, possibly misleading the user into thinking *all* power has been cut.<br />
<br />
--Dave Liquorice 10:47, 27 May 2007 (BST)</div>81.187.135.98https://wiki.diyfaq.org.uk/index.php?title=RCD&diff=3606RCD2007-05-27T09:40:11Z<p>81.187.135.98: 2nd para of "What does it not do?" clarified.</p>
<hr />
<div>=RCD=<br />
<br />
A '''Residual Current Device''' or '''RCD''' is a circuit protective device designed to protect users from electric shock. They are also used in any circumstance where it is not possible to achieve normal operation of traditional protective devices (like Fuses, and MCBs), because the earth loop impedance is too high. <br />
<br />
==What Does it do?==<br />
A RCD detects a fault condition which would typically only be seen when a person is receiving an electric shock from the circuit. When this situation is detected it automatically isolates the circuit. <br />
<br />
This gives greatly enhanced shock protection from both direct contact (i.e. contact with an exposed live wire - say touching a flex you have just damaged with a power tool), and indirect contact (e.g. when the metal casing of an appliance becomes live due to an internal fault). RCD protection is particularly important to protect users in high risk locations where they may be more susceptible to electric shock; such as bathrooms, pool areas, saunas, or simply when they may be using power tools or appliances outside (basically anywhere the user can be expected to be wet, barefoot, or in good contact with earth).<br />
<br />
==What does it '''not''' do?==<br />
A standard RCD does not offer any overcurrent protection, and so it will not clear short circuits, or faults that result in an appliance drawing excessive current. <br />
<br />
When using a RCD protected supply to feed a power tool, they will offer no protection should you make contact with another live, non-protected, circuit with the tool. So if you drill into a non-RCD protected live cable, the RCD powering the drill will not detect any current flowing from wall cable to drill body, and from there to the user. Neither can it switch this current off.<br />
<br />
While RCDs act on the majority of shock situations, they won't protect you from all of them (e.g. a shock received by making contact with both live and neutral connections of a circuit while otherwise being well isolated from earth). Even when a RCD does operate, it can take up to two cycles of the mains (i.e. 40mS or even more for low leakage situations). RCD does not therefore eliminate the risk of shock, but rather reduces it.<br />
<br />
==How does it work?==<br />
RCDs are current balance devices. They measure any current imbalance in the flow in and out of a circuit or appliance via its Live and Neutral conductors (or on three phase circuits, the combined sum of currents in all phases and neutral). Should the current imbalance exceed the tripping threshold for the device, it will activate and disconnect the circuit. <br />
<br />
For more information see [http://en.wikipedia.org/wiki/Residual-current_device Wikipedia RCD entry]<br />
<br />
==Where are they used?==<br />
RCDs are mandated for protection of any circuit that your could reasonably expect to power portable equipment that could be used outside. So this would usually include at least the downstairs socket circuits, plus any circuits feeding outbuildings, garages etc. Forthcoming regulations (the 17th edition) will expand this requirement to basically cover all general purpose power circuits unless there is a specific reason not to protect them. <br />
<br />
It is not recommended that RCDs be used to protect lighting circuits (except TT installations - see below) since it is known that unexpected loss of lighting as a result of an electrical fault can pose more injury risk than the electrical fault in the first place. <br />
<br />
Note that the forthcoming changes to the wiring regulations will make an exception to this rule for bathrooms. <br />
<br />
===TT Installations===<br />
For properties that are not provided with a main earth connection by their electricity supplier (often those supplied via overhead wires), a local earth stake or grid is usually used to provide an earth connection. Since it is not usually possible to achieve a low enough resistance to earth with this technique to allow correct operation of circuit protective devices, RCD protection is mandated for '''all''' circuits. <br />
<br />
To maintain [[Electrical Glossary#discrimination|discrimination]] between different classes of circuit, and prevent the problems associated with having a [[Electrical Glossary#whole house RCD|"whole house RCD"]], typically several RCD devices are used. A device with a 30mA trip threshold will protect the relevant socket circuits, and a higher 100mA trip threshold device protects all the other circuits.<br />
<br />
See [http://www.diyfaq.org.uk/electrical/electrical.html#system Earthing Arrangements] for more information. <br />
<br />
==Types of RCD==<br />
There are a number of different types of RCD available with different form factors and technical ratings. Hence you need to select the right unit for the job.<br />
<br />
===Enclosure design===<br />
{| border="1" cellpadding="6" cellspacing="0" style="text-align:left"<br />
|-<br />
!Type<br />
!Description<br />
|-<br />
| Integrated plug adaptor RCD<br />
[[Image:PlugInRCD.jpg|Plug in RCD adpator]]<br />
<br />
Integrated Socket RCD<br />
[[Image:RCDSocket.jpg|Socket with built in RCD]]<br />
| There are a range of RCDs that are built into plugs and sockets. These are designed to offer enhanced shock protection to either an individual device, or small number of devices. Typically found on extension leads. <br />
<br />
There are also some fixed wiring sockets that include RCD protection, again designed to provide a safer connection point for certain categories of appliance. <br />
|-<br />
| Integrated RCD Spur <br />
[[Image:RCDSpur.jpg|Fused spur unit with built in RCD]]<br />
| A RCD integrated into a spur connection unit. Designed to provide individual RCD protection any fixed equipment that has a high electrical shock risk (e.g. a pool/bath hoist for disabled access).<br />
|-<br />
| Standard DIN rail mounting <br />
[[Image:DINMountRCD.jpg|DIN Rail mounting RCD]]<br />
| This is a modular device in a standard form factor that is designed to be used in electrical enclosures such as consumer units and other similar enclosures. These RCDs typically occupy two module widths (i.e. the space taken by two MCBs), and can be used to power one or more circuits. They also meet the isolation requirements for a main switch, so they can be used as a direct replacement for the double pole incomer switch on a standard consumer unit. <br />
|}<br />
<br />
<br />
===Electrical and Trip Characteristics===<br />
{| border="1" cellpadding="6" cellspacing="0" style="text-align:left"<br />
|-<br />
!Type<br />
!Description<br />
|-<br />
| Rated Current || This is the maximum current the device is rated to carry. Devices in DIN rail mounts are commonly available in 40A, 63A and 80A ratings. <br />
|-<br />
| Number of poles || RCDs are available for protecting both three phase and single phase circuits. (Three phase devices being typically twice the width of single phase ones)<br />
|-<br />
| Trip threshold or sensitivity || This is the maximum current imbalance that will be tolerated without the trip mechanism being activated. In reality the devices specifications are usually scoped such that the device will trip on 66% of the rated trip current (so as little as 20mA may be required to trip a 30mA device). <br />
<br />
Common trip thresholds include:<br />
* 10mA<br />
* 30mA<br />
* 100mA<br />
* 300mA<br />
|-<br />
| Trip time || General purpose RCDs (sometimes marked with a "G" suffix) are designed to trip as soon as possible after a trip condition is detected, and usually within two cycles of the mains (40mS for UK 50Hz supplies). <br />
<br />
There are also time delayed types that are designed to trip only after exposure to a trip fault condition that lasts longer than a pre-set delay (typically two seconds). The time delayed type (often denoted with a "S" suffix) are particularly useful where it is required to cascade RCDs. The time delay maintains [[Electrical Glossary#discrimination|discrimination]] between the cascaded devices so that the once closest to the fault trips first. <br />
|}<br />
<br />
===RCBOs===<br />
A Residual current Circuit Breaker with Overcurrent protection. These are effectively the combination of a Miniature Circuit Breaker and a RCD in a single unit. Hence they provide RCD functionality and also overcurrent protection. Unlike normal MCBs they include a separate connection to allow the neutral of the circuit to return first to the RCBO, and then be connected to the '''non''' RCD neutral busbar of the consumer unit. <br />
<br />
[[Image:DINMountRCBO.jpg|DIN rail mounting RCBO]]<br />
<br />
These are very handy devices since they ensure good [[Electrical_Glossary#discrimination|discrimination]] should they trip - only the affected circuit is taken out of action. The disadvantage of RCBOs is firstly they are expensive (especially if you need to protect a number of circuits), and secondly many of them are physically larger than a standard MCB. Hence they require the use of a consumer unit with more space. <br />
<br />
===ELCB===<br />
Earth Leakage Circuit Breakers were the forerunner of RCDs. There were two types: the most common was the Voltage Operated ELCB, which detected a large voltage rise on the main earth conductor (which was connected through it). The less common type; the current operated ELCB was in many respects similar to modern RCDs (although the detection method may have worked in a different way). <br />
<br />
So when you see ELCB, it could be an old RCD or an even older voltage operated ELCB:<br />
<br />
[[image:CrabtreeELCB.jpg|Picture of an old ELCB]]<br />
<br />
Old voltage operated circuit breaker connected in the meter tails before a consumer unit, with the main earth connection from the consumer unit fed back through the ELCB. <br />
<br />
==Nuisance trips==<br />
A Nuisance trip is an unexpected operation of a RCD that does not appear to be related to an immediately obvious fault. There can be many reasons that these trips occur, some indicate that there is a latent problem with the electrical installation, some may indicate the presence of a serious but as yet unobserved fault, and others may be the result of a minor fault that in itself poses little if any risk. <br />
<br />
Tracing the cause of nuisance tripping can prove to be very difficult and time consuming. This section will attempt to provide some guidelines to help. <br />
<br />
===What causes nuisance trips?===<br />
<br />
====Excess earth leakage====<br />
The RCDs operating principle is to measure the current imbalance between that flowing into and out of a circuit. In an ideal world this difference would be zero, however in the real world there are a various different types of equipment that will legitimately have a small amount of leakage to earth, even operating normally. If the RCD is protecting too many such devices then it is possible that the cumulative result of all these small leakages will be enough to either trip the RCD or to pre "sensitise" it. <br />
<br />
<br />
{| border="1" cellpadding="6" cellspacing="0" style="text-align:left"<br />
|+ '''Appliances that typically exhibit high leakage currents<br>'''<br />
|-<br />
!Item<br />
!Description<br />
|-<br />
| Electronic equipment with mains input filters || Much modern electronic equipment will include a mains input filter designed to stop electrical noise being passed in or out of the equipment via its mains lead. These typically include a pair of small [[Electrical Glossary#capacitor|capacitors]], one connected between the live and earth, and the other between the neutral and earth wires of the incoming mains lead. The capacitor values will be chosen such that they conduct well at the typical noise frequencies that are intended to be filtered. However a small amount of current flow will occur at mains frequency, and this results in leakage to earth. It is also worth noting that the filter circuit is designed to snub noise by coupling it to earth. Hence the noise itself can also contribute to the total leakage current seen by the RCD. <br />
<br />
|-<br />
| Heater elements || Many heater elements that are designed to heat water (kettles, immersion heaters in hot water cylinders, or washing machines, ovens, grills etc) use a mineral insulation that is hydroscopic. Hence when left unused for a time they can absorb a small quality of water into the insulation. Since water is electrically conductive this results in a small amount of leakage to the outer (earthed) metal case work of the heater element. Generally this type of leakage poses little if any risk. They way to clear the problem is to run the heater and drive off the moisture. However it is possible to enter a catch 22 situation here, where the RCD prevents the heater from being run. <br />
<br />
|-<br />
| Dampness || An device that handles water and electricity will be vulnerable to dampness getting into electrical connections or wiring harnesses. This can result in short term high levels of leakage that mysteriously vanish later (as the affected item dries out). Even condensation forming in equipment can cause this problem. <br />
<br />
|}<br />
<br />
<br />
====Sensitising RCDs====<br />
The effect of high natural leakage currents can be to consume most of the trip current "budget" of the RCD, leaving it very close to its tripping point. Once this situation has been reached, then even minor changes in circuit environment or use can result in trips. These include:<br />
<br />
<br />
{| border="1" cellpadding="6" cellspacing="0" style="text-align:left"<br />
|+ '''Events that can trip a sensitised RCD<br>'''<br />
|-<br />
!Event<br />
!Mechanism<br />
|-<br />
| Switch on surges || When devices with mains input filters are switched on, there will be a brief period where its filter capacitors are "charging up" and passing slightly more leakage than normal. This can be one cause of trips. Also some devices will absorb a large "inrush" of current when first turned on. This can itself generate lots of harmonic noise that is then dissipated to earth by the filter capacitors (same can happen on switch off).<br />
<br />
|-<br />
| Changes in humidity || A simple thing like a damp day can be enough to slightly lower the effectiveness of insulation used on cables and in equipment, resulting in more leakage. Electrical installations outside, or in outbuildings are particularly vulnerable to the effects of moisture. <br />
<br />
|-<br />
| More appliances in use than normal || Using more appliances than normal or an infrequently experienced combination of them may push the leakage over the limit. <br />
|}<br />
<br />
<br />
====Wiring faults====<br />
{| border="1" cellpadding="6" cellspacing="0" style="text-align:left"<br />
|-<br />
!Fault<br />
!Mechanism<br />
|-<br />
| Neutral to Earth shorts || A particularly problematic fault is a short between neutral and earth on a circuit. Since Neutral and earth are nominally going to be at a similar potential (especially in buildings with TN-C-S / PME earthing (see [http://www.diyfaq.org.uk/electrical/electrical.html#system Earthing Arrangements]). You can arrive at a situation where the current flow between neutral and earth is lower than the trip threshold of the RCD some of the time, however once the neutral current reaches a high enough level, its potential will be "pulled" away from that of the earth, and you get increased leakage current flow which may cause a trip. Needless to say this threshold will often be reached during transient current peaks caused by equipment being switched on or off. <br />
<br />
|-<br />
| Insulation breakdown or damage || As cables and wires age, their insulation can become less effective. This is especially true if you live in an old property that still has [[Cables#VIR|rubber insulated]] cables. Humidity will also reduce insulation effectiveness. <br />
<br />
|}<br />
<br />
<br />
====Faulty RCD====<br />
One obvious possibility (and often overlooked) is that the RCD itself is actually faulty and not tripping at the correct current. A RCD that refuses to reset even when all output connections are removed is an obvious candidate for landfill. Swapping the device with a known good one, or using a RCD test facility as described elsewhere on this page are other ways of finding faulty RCDs. <br />
<br />
Many RCDs include a "test" button that verifies the unit functions. Note however that this does not test if the trip threshold has drifted too low for example - only that the trip detection and basic mechanics still work. <br />
<br />
===How to locate the cause of nuisance trips===<br />
<br />
====Empirical tests====<br />
<br />
There are a number of empirical tests or experiments that you can try to narrow down the source of the problem. We cover some here. The first job is to identify which circuits the RCD is protecting. There is no need to concentrate efforts on examining circuits that are not connected and hence can not be affecting the outcome!<br />
<br />
{| border="1" cellpadding="6" cellspacing="0" style="text-align:left"<br />
|+ '''Techniques to try'''<br />
|-<br />
!Do what<br />
!Why<br />
|-<br />
| Turn off circuits in turn || You may be able to identify which circuit is causing the problem by isolating circuits in turn, and seeing which prevents the trip from reoccurring. <br />
<br />
|-<br />
| Remove appliances from suspect circuits || Disconnecting appliances from suspect circuits can let you identify if the fault is in an appliance (the most common situation) or the circuits fixed wiring. If you still get trips with everything disconnected then you may have a wiring fault. <br />
<br />
If it looks like appliances are to blame, you can apply the "binary chop" principle to narrow down the field quickly - i.e. unplug half of them and see what happens. If it still trips you know in which half the dodgy appliance probably is. The carry on in the same way - halving the list of remaining suspects, until you get close to the answer. <br />
<br />
|-<br />
| Check the likely culprits || Identifying which appliances you have from the "high risk" categories listed above can help to take you to the cause of the trouble faster. <br />
<br />
|-<br />
| Identify coincidental factors || Check for any patterns and relationships between trips and other events. Do they occur only in damp weather, or only at certain times of day, or only when the freezer switches on, or the central heating. Pay particular attention to automated systems (timers, thermostats etc) that can be controlling significant bits of electrical equipment in your home without your manual intervention.<br />
|-<br />
| Introduce extra leakage || To correctly test the function and trip threshold of a RCD you need a specialist test meter (see section later on testing). However there are various home built devices that can help you to perform some simple tests. One of these is a leakage plug, which can aid finding problem circuits by letting you introduce a known amount of leakage into a circuit. <br />
<br />
To make one you need a conventional 13A plug, fused with a 3A fuse, and and internal connection between earth and live made via a high value high power wire wound resistor. There are no other connections made to the plug externally, and the plug should be clearly labelled. Turning on each of the protected circuits one at a time, and using the leakage plug on it can help identify a circuit that leaks more than the others (since the combination of the plug and its leakage will trip the RCD on the high leakage circuit). <br />
<br />
A set of plugs wired for different leakages will help you get an approximate idea of the leakage level caused by the circuit (and its appliances) itself (note the better RCD testers have a current ramp facility to better conduct this test):<br />
<br />
{| border="1" cellpadding="6" cellspacing="0" style="text-align:center"<br />
|+Resistor Vs Leakage Table<br />
! Resistor Value (ohms)<br>(nearest prefered value)<br />
! Approx leakage caused (mA)<br />
! Power rating of<br>resistor required (W)<br />
|-<br />
| 47K || 5 || 2<br />
|-<br />
| 22K || 10 || 3<br />
|-<br />
| 15K || 15 || 4<br />
|-<br />
| 12K || 20 || 5<br />
|-<br />
| 10K || 25 || 6<br />
<br />
|}<br />
<br />
'''(Don't leave the plug connected for too long, or its resistor will get hot!)'''<br />
<br />
|}<br />
<br />
<br />
===Measurement Tests===<br />
<br />
This section deals with the particularly tricky problem of tracking down the causes of nuisance tripping that you have not been able to find by other methods. <br />
<br />
For detailed tests on RCDs a specialist test meter is required such as [http://www.tlc-direct.co.uk/Main_Index/Test_Meters_Index/Test_Meters_3/index.html this]. An insulation resistance tester such as [http://cpc.farnell.com/jsp/Test+Equipment/Electrical+Installation+Testers/MEGGER/BM221/displayProduct.jsp?sku=IN01094 this] may also be required to track down some of the more difficult to locate wiring faults. <br />
<br />
However it is possible to carry out a good number of tests using more basic equipment such as a multimeter.<br />
<br />
{| border="1" cellpadding="6" cellspacing="0" style="width:500px; text-align:center; background:yellow"<br />
|-<br />
| '''Warning'''<br />
<br />
There are procedures that are described here that require opening your consumer unit and making temporary wiring alterations within it. <br />
<br />
If you are not totally confident doing this, then please consult a technically skilled electrician.<br />
|}<br />
<br />
<br />
====DC Resistance tests====<br />
First ensure that power is switched off at the main switch. Ensure all appliances are disconnected from the circuit. These tests require that you disconnect the circuit under test from the consumer unit. In the case of a ring circuit remember to disconnect both legs of the ring. All tests are initially performed on the disconnected ends of the circuit. <br />
<br />
There are a number of basic tests that you can do that will identify a great many of the fixed wiring faults that can cause nuisance tripping. <br />
<br />
{| border="1" cellpadding="6" cellspacing="0" style="text-align:left"<br />
|+ '''Tests to perform'''<br />
|-<br />
!Test<br />
!Purpose<br />
|-<br />
| Live Neutral Resistance || The first test is a simple resistance test between live and neutral. This test should be done using the '''highest''' resistance range on your multimeter. Normally with all the appliances disconnected you would expect to see an open circuit between live and neutral. If this is not the case then you either have something still connected, or you have a serious insulation resistance problem. <br />
|-<br />
| Live Earth Resistance || This test should also indicate an open circuit with the meter on its highest resistance measuring range. Any non infinite reading here could be a direct indication of your problem. If you get a non infinite resistance reading, you may be able to track down the location of the fault by breaking the circuit up at strategic points (typically by disconnecting part of it at an accessory position). <br />
|-<br />
| Live Neutral Resistance || Again this test ought to indicate infinite resistance. However it is possible that a very low resistance measurement could exist and yet the circuit still work some of the time (especially on systems with TN-C-S earthing). Unlike a low resistance reading on a Live to Earth test, this fault would not immediately trip a MCB or blow a fuse. <br />
<br />
Tracing the location of the short or bridge can again be done using the segmenting procedure described above, and also by careful low resistance measurements made in conjunction with expected cable resistances as found in a [[Electrical_Circuit_faults#Wire resistance table|Wire resistance table]] (or see Table 9A in the IEE Wiring Regulations [http://tinyurl.com/32yb6h On Site Guide]). <br />
<br />
A typical cause of this type of fault, is where a concealed cable has been damaged by a fastening being driven through it. (so if any shelves or pictures have been hung recently, there is a good place to start looking).<br />
<br />
|}<br />
<br />
<br />
====Insulation resistance====<br />
If the DC resistance tests above fail to identify the cause of a circuit that is causing RCD tripping on its own (i.e. without the aid of the appliances usually connected to it. You may find that repeating the tests described using an insulation resistance tester will yield more information. Since the insulation resistance tester carries out the tests at much higher voltages than the multimeter (typically 500V) it will identify those few failures where the conduction path between a live conductor and earth is only visible at mains voltages. <br />
<br />
Take care when performing these tests, it is possible to get a nasty shock off an insulation test meter! <br />
<br />
====Series earth current measurements====<br />
A test technique that can be quite handy for testing individual appliances, is to measure the actual current flow in its earth wire connection. To do this safely one needs to make up a suitable teat lead to allow safe access to the earth connection. The best way to measure the current flowing in the earth wire is using a very high sensitivity clamp meter (see next section), since this leaves the earth wire connected directly to the appliance. <br />
<br />
If one of these is not available, then it is possible to make a measurement using and AC current measurement range on a multimeter. The meter will have to be placed in series with the earth wire and any leakage current will pass through the meter and can be measured. It is important to note however that this carries a certain amount of risk since should there be (or occur) a fault in the equipment, the full fault current may try to pass through the meter. Most decent quality meters will respond by blowing an internal fuse, but some might melt, catch fire, or explode! If the meter fuse does blow it will have in effect opened the connection between the appliance and earth. This will mean its exposed metalwork may now be sat at mains voltage with no protective measure to cause a fuse or MCB to operate. <br />
<br />
For these reasons it is not advisable to use this technique at the consumer unit for a whole circuit unless clamp meter is available. <br />
<br />
====High sensitivity clamp meters====<br />
Earth leakage clamp meters like [http://www.martindale-electric.co.uk/clamp.htm#cm67 this] have recently become a popular way to detect earth leakage faults. These can be safely connected around either an earth wire to directly measure leakage to the equipment earth, or around live and neutral to directly read current imbalance. Since they require no physical connection to the appliance or circuit under test they are a much safer way to measure either leakage to earth or imbalance in the supply to a circuit or and appliance. Measuring the imbalance will help detect where the leakage is not occurring through the circuit or appliances own [[Electrical_Glossary#CPC|CPC]] but instead is finding an alternate path. <br />
<br />
===Mitigating the effects of nuisance trips===<br />
<br />
While it is possible to eliminate most causes of nuisance trips with careful system design and testing, it is always wise to design the system to allow for the possibility of it happening:<br />
<br />
# Provide dedicated non RCD protected circuits for vulnerable equipment such as:<br />
::* Freezers<br />
::* Central Heating Systems<br />
::* Heated Aquariums <br />
::* Fire or smoke alarms<br />
::* Security systems and lighting<br />
::* Computer and IT equipment<br />
# Have as few circuits or devices as possible protected by the same RCD so that a trip impacts as few extraneous circuits as possible. The ultimate solution would use RCBOs for each circuit. Obviously expense has to be weighed against the implications of tripping. <br />
# Use [[Emergency_Lighting|emergency lighting]] to backup any important lighting circuits that need to be RCD protected (i.e. on TT earthing systems). In particular these should include lighting for:<br />
::* Stairs<br />
::* Fire escape routes<br />
::* Near trip hazards or other difficult to navigate areas<br />
::* Near the consumer unit<br />
# Consider using uninterruptible power supplies (UPS) to maintain running of critical equipment.<br />
# Power failure alarms might also be an appropriate measure in some circumstances.<br />
<br />
<br />
==System design using RCDs==<br />
Some of the system design aspects of using RCDs to good effect are covered in the mitigation section above. However the following basic principles should also applied:<br />
<br />
# Use split load consumer units, to allow circuits that do not benefit from RCD protection to be powered directly. <br />
# Don't place too many circuits on the same RCD. In particular identify circuits that are likely to have high leakage (e.g. those containing lots of IT other electronic equipment).<br />
# Where RCDs need to be cascaded, use time delayed types for the upstream device so that trips are contained close to the cause of the fault. <br />
# Don't place circuits to outside electrics and outbuildings on the same RCD as protects the house circuits.<br />
# Avoid placing high leakage devices on RCD protected circuits where possible.<br />
# Ensure accessories and wiring are not placed in excessively damp environments. <br />
# Don't use lower trip threshold devices that is appropriate for the level of risk present and protection sought. <br />
<br />
<br />
==See also==<br />
<br />
[[ELCB]]<br />
<br />
[http://en.wikipedia.org/wiki/Residual-current_device Wikipedia entry on RCDs]<br />
<br />
<br />
[[Category: Electrical]]<br />
[[Category: Fault finding]]</div>81.187.135.98