Talk:Earthing and Bonding
I took out the following since they should probably go in the article on types of earthing schemes. This article is about clarifying what is earthing and what is bonding
Some premises are not provided with an earth - these are typically farms with livestock (or stabling for horses), petrol stations, and temporary supplies.
In some cases it may not be possible for the REC to provide an earth as it may change the line characteristics (if overhead fed), your supply may not be capable of supporting an earth (TNS) where you have no suitable conductor, or where the network is otherwise unsuitable for various reasons, i.e. areas subject to tidal influence, tide comes in = good earth, tide goes out = bad earth.
Could go in the earthing types article... --John Rumm 15:23, 7 July 2008 (BST)
To-Do: incorporate changes suggested by Andy Wade
Too late - did em last night! --John Rumm 15:23, 7 July 2008 (BST)
On Mon, 07 Jul 2008 00:58:02 +0100, Andy Wade wrote: > YAPH wrote: > >> Earthing ensures that in the event of a fault a large fault current will >> flow causing rapid operation of a Circuit Protective Device > > The fault current doesn't necessarily have to be 'large'. In principle > 30 mA will do the trick if the device doing the automatic disconnection > is an RCD. > >> [...] (fuse or circuit breaker) promptly disconnecting the supply. > > Or RCD in some circumstances. (OK "circuit breaker" in its most general > sense includes RCCBs, but saying "fuse, MCB or RCD" might be clearer for > most readers.) > >> Earthing is also designed to limit the voltage rise of anything earthed >> that one can touch to a safe level (specified as being under 50V AC) >> during the fault. > > That's wrong. Touch voltage can be much higher during an earth fault: > half-mains or more, due to the voltage drop in the CPC. Shock > protection is achieved by limiting the fault duration, not the fault > voltage. Only in particular cases is it necessary to provide local > supplementary bonding to limit the voltage too. > >> The size of earthing conductors and characteristics of fuses and other >> protective devices are designed to ensure that a fault is cleared within 5 >> seconds for all faults, and within 0.4 seconds for circuits feeding socket >> outlets (to which our washing machines etc, which may be touched, are >> connected). > > This is out of date information now. Permissible disconnection times > have changed significantly in the 17th ed. and the old distinction > between socket circuits and fixed equipment has gone. For 230 V AC > supplies (incl. 230/400 V 3-ph) the following maxima now apply: > > System TN TT > ----- ----- > Final circuits <= 32 A 0.4 s 0.2 s > Final circuits > 32 A 5 s 1 s > Distribution circuits 5 s 1 s > > > Remember the mantra: earthing protects by reducing the duration of touch > voltages. Bonding protects by reducing their magnitude. >
Mine are uncoloured, but the current list only includes coloured ones NT 23:33, 19 October 2010 (BST)
BS 951 was ammended in 1999. It is possible that the colour coding came in then. The clamps in my house are not coloured and were installed in early 1999. The new clamps are coloured to allow for inspection.--ARWadsworth 09:17, 20 October 2010 (BST)
These are definitely post 99, I'll see if I can get a pic NT 09:41, 20 October 2010 (BST)
I have just given Legrand Tech a call. They say that there is no requirement in BS951 to colour code the clamps. They started their colour codes in 2000 to allow easy identification of the clamps. They also pointed out that some other firms use blue for the EC16. The clamps at my house have NO identification on them at all as to their type.--ARWadsworth 10:33, 20 October 2010 (BST)
It looks like BS951 has been updated again last year. I just did a quick search of it and can't find any reference to colour coding in htat version either. Checking my own supply of them, I seem to have a mixture of coloured and uncoloured - the main differentiator seems to be where they were bought (and hence probably the maker). --John Rumm 15:20, 20 October 2010 (BST)
A quick look at the different brands on the internat suggests that the majority do follow the colour scheme. I suggest the words "and are coloured" should change to "are often coloured" --ARWadsworth 15:58, 20 October 2010 (BST)
More on plastic pipes from elec FAQ
Earthing Plastic Pipes
There is an excellent article about earthing and plastic plumbing on the Hepworth Plumbing Products website, written by Paul Cook of the Institute of Electrical Engineers.
Quoting from the opening paragraphs:
"You do not have to earth plastic pipes. Plastic pipes make for a safer electrical installation and reduce the need for earthing. Festooning an installation that has been plumbed in plastic pipe with green and yellow earth wire is not necessary and is likely to reduce the level of electrical safety of the property, not increase it."