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Electric Showers and plumbers

David Stone
I had a phone call from my son yesterday, the shower in his house had broken and not being a plumber/electrician got a couple of quotes. The old one was 6.5 kW with 6mm cable. The plumbers all seemed to think that the cable and MCB should be replaced as the current rating was inadequate for a replacement, the MCB is 40A. I had a quick check what could be fitted as there are many more powerful ones available and this weather the water is not wonderfully warm! I have not really thought about shower cables for a long time as they are almost always in good condition. Table 4D2 6mm clipped direct says 46A, continuous rating. A 10.5kW shower takes 45.65A on 230V so is quite satisfactory on the 6mm cable. In fact, the model I was looking at (Mira fancy thermostatic, expensive) would only take this power at full flow and temperature rise as it has electronic thermostatic proportional control and normal running current would be modulated and somewhat less. I consider this to be perfectly satisfactory, but the plumbers obviously haven't read the regulations. I often find the same with cookers, various sellers suggest 10mm cable, which may well not be the existing size. Should any change be made, and why do would you do this?
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    It seems odd that the traditional combination of a floor of boards and a ceiling of lath and plaster do not get a mention. I go with RM C. Cable lying on the ceiling seems pretty similar to cable on a floor. The cable could, of course, be clipped to the joists. And what about cables passing through a row of joists - most of the time they are in free air, but should one apply a grouping factor?


    Why is the space above the ceiling a "ceiling void" and not a "floor void"? Cable in a ceiling means a suspended ceiling to me. Building voids as in IM 40 onwards suggest routes in a building which have been set aside for the various services.


    Then we have the modern requirement in Part E for sound insulation betwixt a ceiling and a floor. Granted it does not fill the void, but can you guarantee to keep the cables well above it (assuming that it rests on the ceiling). I use IM 100 for that.
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    It seems odd that the traditional combination of a floor of boards and a ceiling of lath and plaster do not get a mention. I go with RM C. Cable lying on the ceiling seems pretty similar to cable on a floor. The cable could, of course, be clipped to the joists. And what about cables passing through a row of joists - most of the time they are in free air, but should one apply a grouping factor?


    Why is the space above the ceiling a "ceiling void" and not a "floor void"? Cable in a ceiling means a suspended ceiling to me. Building voids as in IM 40 onwards suggest routes in a building which have been set aside for the various services.


    Then we have the modern requirement in Part E for sound insulation betwixt a ceiling and a floor. Granted it does not fill the void, but can you guarantee to keep the cables well above it (assuming that it rests on the ceiling). I use IM 100 for that.
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