I was running a Triton Topaz T80i 8.5kW shower with a 63A fuse (RCD). The blue wire from the terminal block, connected to the thermal cut-out (inside the shower unit) got so hot (near the thermal cut-out) that caused the thermal cut-out to burn out. I was wondering whether the fuse rating was too high for the shower unit.

I want to install a new Creda 9.5kW shower to the same 63A fuse/circuit, but scared to, just in case the same as above happens to it. What’s your advice?

Norbert, July 2009

Had shower etc checked out... The fault was with the shower and not electric circuit.

Norbert, August 2009

Thanks again...

I thought I’d mention, I’ve had training and some experience at college on electrical installation and electronics (C&G qualifications), but no experience in the field.

When I first got the shower, I took details of it to an electrical wholesaler and they recommended what parts I should buy for the circuit. And I also did all my research on the internet before attempting the plumbing and installation of the electric circuit. The cable size is 10mm2. The 63A RCD (recommended by the electrical wholesaler) doesn’t power the whole house etc etc, only the shower; (I installed it myself). There’s also a 45A neon ceiling switch in the circuit. As mentioned, the shower has its own independent circuit connected to the blocks just after the electric meter.

Buy the way, it’s not 8 years as mentioned since the shower’s been in operation, it’s 5 years. Why didn’t the problem start long before 5 years? What’s the life time of an electric shower? I haven’t bought the new shower yet. I think I’ll just get a push-on mixer shower for the meantime; and as you suggested, get the shower circuit checked out and certificated (depending how much it’ll cost), or just uninstall the whole thing and have a power shower install – I understand they’re better than electric.

Norbert, July 2009

Your old shower at 8.5kW would take about 37A so a 40A MCB is just about right. The 9.5kW shower however will draw a little over 41A so your 40A breaker is under rated - a 45A will be needed - but you might just get away with your existing MCB.

The cable size required for 8.5 and 9.5kW showers is 10mm²

The 63A RCD very probably powers the whole house including the shower, cooker, lights, power sockets etc and the 30mA rating on it is normal - the Earth Leakage current it will trip at i.e. if there's a difference of 30mA between Live & Neutral the RCD will trip to stop the missing current passing through someone's body.

I did see this on a Creda site...

"in order to comply with the current building regulations you should have a competent certified installer carry out any electrical work to the IEE Wiring Regulations"

http://www.creda-showers.co.uk/creda-faqs

Peccavi, July 2009

Thank you...

I checked the connections on the terminal block and they are tight. When I first installed the shower, I double checked all the connections in the whole circuit to make sure they were tight. And an engineer from my electricity supplier came and checked everything out.

I forgot to mention, the shower circuit is independent with also a 40A MCB. On the fuse block where the 63A is written, also written is 30mA and an AC sign wave symbol. The shower has been in use for about 8 years before the Heater Can Assembly got scaled up, where I de-scaled it; and not very long after that the wire/thermal cut-out started overheating.

Norbert, July 2009

The burnt up blue wire in the terminal block will be due to a bad connection generating heat. The rating of the RCD will not have caused this but 63A is rather a lot - good enough for 14kW at 230V! The risk with an over rated fuse/RCD is that a fault in the system; shower and cable, may cause a fire before the fuse pops - which is not good and I doubt the cable feeding your shower is capable of carrying 63A.

As you're uprating the shower from 8.5 to 9.5kW you will do best (be wise) to consult a properly certified electrician to ensure the wiring and fusing meets the approved specifications and is safe. It will also make selling the property easier should you ever wish to.

Take care... Good luck...

Peccavi, July 2009