Monday, 16 June 2008

Upgrading Electric Showers

Many Londoners have a love hate relationship with electric showers. Landlords and property developers love them, because the allow an additional shower at relatively low cost. While tenants hate them, because of their mediocre performance (especially in Winter).

Electric showers are fed cold water directly from the mains. The shower then 'instantaneously' heats the the incoming water to the desired temperature set by the user. In fact what is happening is the shower slows the flow of water down to give it enough time to heat the cold water. That is why in winter, when the incoming mains water is very cold, all you get is a trickle from the shower head.

The more powerful the rating of the shower (7.5Kw, 8.5 Kw, 9.5Kw or 10.5 Kw) the quicker it can heat up the water and the less it has to slow the flow down.

A lot of people have picked up on this fact and have opted to upgrade their poorly performing 7.5KW showers with a more powerful 10.5KW shower. Unfortunately, DIYers don't always understand the electrical implications of changing the rating of an electrical appliance to the rest of their wiring and protective devices (fuses, miniature circuit breakers). Simply, the amount of current that a cable can carry without overheating is limited mainly by the cross sectional area of the cable. Fuses and MCB are in place to protect the cable from overheating and therefore are rated to blow or trip before the electrical current gets to the cables failure current.

A 7,5 KW shower will draw a maximum current of 30Amps - 32 Amps. An installer would thus get away with a using a 32amp MCB and a 6 mm2 cable. A 10.5Kw shower would draw a maximum of 40-43 Amps and therefore would require a cable thickness of at least 10 mm2 which should be protected by a 45amp MCB. So if a person wishes to install a 10.5KW shower in place of a 7.5KW shower they should be confident that the electrical supply is capable of coping with such a change.

With a bit of domestic electrical knowledge and plumbing knowledge, upgrading an electric shower is a straight forward job. But without knowing what one is doing it can lead to a dangerous situation, mainly a fire risk.

So my advice is if you are adamant on doing the work yourself, get a competent person to check your electrics for you. Otherwise hire a professional handyman to do the whole install for you.


Anonymous said...

Having checked the information, getting a handyman to do it would still require a part P qualified electrician to sign off on the work. Same as if i did the work, just with more cost, it must be cheaper to get an electrician to do it all. You should be more clear about that

Silver Saints said...

Part P of the building regulations has caused a lot of confusion! Replacing one electrical appliance with another electrical appliance falls under maintenance and not new works. So although you are upgrading the shower you will not be doing any new wiring works that would require a minor works certificate to be issued by a part p registered electrician. Having a competent person replace electrical fittings within a property does not require a minor works certificate. Adding wiring or circuits which go back to the consumer unit do.