Difference between revisions of "Installing an electric shower"
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(→Choosing the components: removed details of cable selection and deferred to dedicated artucle on the subject.) |
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'''Step one: Find out the design current''' | '''Step one: Find out the design current''' | ||
| − | Most showers will include this in | + | Most showers will include this in their technical details. If not, take the input power and divide by 230. So a 9500W shower will draw 9500 / 230 = 41.3A (note many showers actually quote their full output power at 240V, and will deliver somewhat less at 230V, but this is the nominal value used for design purposes). |
'''Step two: Select a circuit breaker''' | '''Step two: Select a circuit breaker''' | ||
| − | The shower will need a circuit or fuse of the appropriate rating equal or grater than the design current. This will normally mean a 40, 45, or 50A breaker. (keep in mind that the more powerful showers will take a significant | + | The shower will need a circuit or fuse of the appropriate rating equal or grater than the design current. This will normally mean a 40, 45, or 50A breaker. (keep in mind that the more powerful showers will take a significant chunk of the available supply capacity to your house - especially of you only have a 60A supply. Some properties may have a supply even smaller than this. That can impose a practical limit on the size of shower to the very smallest. |
'''Step three: Select cable''' | '''Step three: Select cable''' | ||
| − | You will need to chose a cable of sufficient size to carry the design current | + | You will need to chose a cable of sufficient size to carry the design current. All but the lowest powered showers will require at least 6mm² T&E. 10mm² will commonly be required for the higher powered ones. See the article on [[Calculating_A_Cable_Size|calculating cables sizes]] for the full details of how to do this correctly. |
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| + | '''Step four: Select other parts''' | ||
| + | The only other component in a typical shower circuit is the isolation switch. This will typically be a ceiling mounted, pull cord operated, high current switch designed for the purpose. The switch needs to have a mechanical flag or some form to indicate when it in is the on position (most use a protruding tab, or colour patch to indicate the on state), and optionally, an illuminated indication. | ||
Revision as of 17:18, 3 January 2011
Work in progress....
Introduction
This article describes the electrical aspects of installing an instantaneous electric shower. This is the type of unit that takes a single mains cold water feed, and heats the water as it passes through the shower unit "on demand". For the sake of clarity, this does not include shower units that simply boost the pressure of existing hot and cold water supplies.
This is a deceptively complex task, and should not be attempted unless you fully understand the implications of the design decisions you will need to make, and are confident that you can produce a sufficiently high standard of workmanship.
Selecting the Power
The performance of an electric shower will be dictated by its power output, and since there is very little heat wasted in the shower itself, this is largely the same as the electrical power input. The advantage of the more powerful showers is they are able to deliver a greater volume of hot water in a given time. All showers ought to be able to provide a shower that is "hot enough" - however the less power you have available, the less water can be heated to an adequate temperature in a given time. Delivery rates are usually measured in Litres Per Minute (LPM. The table below gives you some idea of what to expect from the commonly available shower powers.
Note that even the most powerful shower will still only deliver a relatively modest flow of warm water - especially in the depths of winter when the incoming mains water is particularly cold.
Assuming a shower temperature of 40°C, you will get the following best case flow rates:
| Shower input Power (W) | Flow rate (LPM) at 5°C inlet temperature |
Flow rate (LPM) at 15°C inlet temperature |
|---|---|---|
| 7500 | 3.06 | 4.29 |
| 8000 | 3.27 | 4.57 |
| 8500 | 3.47 | 4.86 |
| 9000 | 3.67 | 5.14 |
| 9500 | 3.88 | 5.43 |
| 10000 | 4.08 | 5.71 |
| 10500 | 4.29 | 6.00 |
| 11000 | 4.49 | 6.29 |
| For comparison, a 24kW Gas fired Combi boiler |
9.80 | 13.71 |
Wiring it up
There are two stages to this exercise, the first needs a bit of design work to make sure that the electrical supply is up to the job. Electric showers are one of the highest power loads to be found in most domestic properties, and they may also be run for an extended time. This places a high demand on the electrical installation, and hence it must be designed and implemented correctly or there is a serious danger of undesirable consequences such as cables overheating and the danger of fires. That is before you add water to the mix!
Where to take the power from
Electric showers must be supplied from their own dedicated circuit. Under no circumstances can the power be taken from a normal socket circuit, or shared with any other device.
Choosing the components
Step one: Find out the design current Most showers will include this in their technical details. If not, take the input power and divide by 230. So a 9500W shower will draw 9500 / 230 = 41.3A (note many showers actually quote their full output power at 240V, and will deliver somewhat less at 230V, but this is the nominal value used for design purposes).
Step two: Select a circuit breaker The shower will need a circuit or fuse of the appropriate rating equal or grater than the design current. This will normally mean a 40, 45, or 50A breaker. (keep in mind that the more powerful showers will take a significant chunk of the available supply capacity to your house - especially of you only have a 60A supply. Some properties may have a supply even smaller than this. That can impose a practical limit on the size of shower to the very smallest.
Step three: Select cable You will need to chose a cable of sufficient size to carry the design current. All but the lowest powered showers will require at least 6mm² T&E. 10mm² will commonly be required for the higher powered ones. See the article on calculating cables sizes for the full details of how to do this correctly.
Step four: Select other parts The only other component in a typical shower circuit is the isolation switch. This will typically be a ceiling mounted, pull cord operated, high current switch designed for the purpose. The switch needs to have a mechanical flag or some form to indicate when it in is the on position (most use a protruding tab, or colour patch to indicate the on state), and optionally, an illuminated indication.
more anon...
--John Rumm 22:51, 27 December 2010 (UTC)