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?
Farmboy and Dave, you both mention RM A in your posts when i think you mean RM C. RM A refers to cables in conduit in an insulated walls (and architraves & windowframes). I agree it should be RM C in most ceiling voids.
I did remedials on an EICR recently and the cable type on the schedule of test results was given for all circuits as "A", as was the reference method. I was searching everywhere for cables in an insulated wall, especially near the CU since all circuits were classed as RM A, could't find any insulation. It was the same situation as Dave has, 6mm T&E, 8.5KW shower on a 40A MCB. The inspector C2ed it and recommended putting a 32A mcb in instead, "over-sized over current protective device".
I was referring to section 7.2 in regs appendix 4, page 384, which suggests RM A for 'cables installed in a ceiling', due to possible rise in temperature in JBs . So what I was trying to determine was should a cable in a ceiling void be considered as RM A even when no JBs are present, as the cables could still be subjected to the raised temperature?
Farmboy and Dave, you both mention RM A in your posts when i think you mean RM C. RM A refers to cables in conduit in an insulated walls (and architraves & windowframes). I agree it should be RM C in most ceiling voids.
I did remedials on an EICR recently and the cable type on the schedule of test results was given for all circuits as "A", as was the reference method. I was searching everywhere for cables in an insulated wall, especially near the CU since all circuits were classed as RM A, could't find any insulation. It was the same situation as Dave has, 6mm T&E, 8.5KW shower on a 40A MCB. The inspector C2ed it and recommended putting a 32A mcb in instead, "over-sized over current protective device".
I was referring to section 7.2 in regs appendix 4, page 384, which suggests RM A for 'cables installed in a ceiling', due to possible rise in temperature in JBs . So what I was trying to determine was should a cable in a ceiling void be considered as RM A even when no JBs are present, as the cables could still be subjected to the raised temperature?
