DIY Doctor

A New Shower Question

Postby clarets » Thu Dec 16, 2010 10:23 am

I've just purchased a new Mira shower unit to replace the old one. The old shower was a 8.5kw, the new is 9.5kw. The wiring to the shower IS 10mm so am I ok to fit the shower myself or legally do I have to get a Part P registered electrician in?

Also, this is about curiosity more than anything......

I notice that on the new unit, the wiring block is only 10cm directly above the water inlet pipe with no barrier in between. My question is ( and i know water and electric dont mix well ), what would happen if for whatever reason, a leak sprung from the inlet pipe and sprayed upwards towards the wiring block. Would the unit shut off immediattely or give a lethal shock if a person was showering at the time? I only ask as i was amazed as to how close the wiring block was to the water inlet pipe. On the old unit, they were on opposite sides of the unit!

Thanks for any comments.
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Simply Build It

Postby ericmark » Thu Dec 16, 2010 6:34 pm

The legal question is not cut and dried as it says you can change like for like but it does not define what it means by that. I would consider since not the same power they are not like for like but it would be for the courts to decide.

Personally I would not want to be the person fighting a test case although I would expect neither would the LABC and it is unlikely they would make a test case from it.

Now to real world the 10mm cable is protected by a automatic disconnection device (MCB, RBCO or Fuse) and according to route could be protected with anywhere from a 32 to 64 amp device. Most likely 45A Reference Method 100# (above a plasterboard ceiling covered by thermal insulation not exceeding 100 mm in thickness). At 45A that = 10.35 kW so within the supply required. 32A = 7.35kW and 40A = 9.2kW and at first glance one would say these would be overloaded. However the MCB has a curve and even a 32A MCB will run for around 1000 seconds before it trips and most showers are completed within 15 mins.

As to shock risk there are a number of reasons why you should be safe. A B40 MCB will trip with the magnet part of the trip in about 0.1 seconds with an overload of 200A and with that in mind we check the earth loop impedance which must be below 1.15 ohm. To check if safe needs expensive meters and for this reason you are better not DIYing. This includes checking that the earth leakage trip (RCD) works at 30ma and at 150ma within 40ms on both half cycles. i.e not just pushing test button.

Both with legal and safety in mind better not to DIY. Last time I tried to hire meters they were £60 for min hire of a week and add the £100+ LABC fees to do an A1 job DIY will likely cost more then hiring an electrician.
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Postby FredStar » Mon Dec 20, 2010 11:53 am

Maybe Mira have Support Service...there you can ask your questions to the specialists. I know that Gainsborough Showers have the same Service. Thanks! p.s. When I bought two Stanza Black (it's electric showers 8.5 kw) for my parents and for myself the advices of Support service helped me to install this showers. :?:[/url]
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