If there are any qualified sparkys on here, I need a simple bit of advice please. While I am stewing over my health issues, I have been trying to get some stuff around the house and one thing is getting round to replacing a basic electric shower and have noticed that the wiring may be wrong....in fact I am certain that it is wrong. The supply cable to the shower which seems to be 6mm2 (or it may be 10mm2 when I get round to inspecting it) has it's own RCD at one end and an isolator switch at the shower end. The tails from the meter go to a chocolate box from which similar size cables as the tails feed the consumer unit and circuit MCBs; but also directly to the shower RCD (rather than via the consumer unit). This means there is no MCB in the shower circuit and I am sure there should be. I would like to know if I can fit a single MCB in it's own enclosure between the RCD and the shower cable. I know it should be before the RCD and after the chocolate box, but as the supply to the chocolate box is bypassing the consumer unit, for safety I would need to pull the incoming electricity main cartridge which is not permissible. Any useful thoughts welcome..... Thanks AL.
Is it definitely just an RCD and not an RCBO with combined overcurrent protection? If it is just an RCD could you not replace it with an RCBO?
It's an RCD......but to replace it for an RCBO I would have to pull the main cartridge.....I have no other way of isolating the chocolate box to make it safe. The only way I can kill the power to the shower feed cable is to trip the RCD....I can't kill the power to the RCD without pulling the cartridge. I wonder if I could fit an RCBO between the RCD and the shower feed cable though.....that way the RCD would be an isolator??
Sounds like this has been lashed in, you should have a double pole isolator in the shower room. Who uses choc block on 6mm+ cable, if the consumer is fitted with RCD this should protect the whole house. For your own safety and peace of mind get a qualified electrician in to sort this, look on check a trade and read reviews. I had a complete kitchen wired in for £2k If the cable is ok it should not cost more than £300 to sort it. A lot cheaper than a funeral! Hope it goes well.
Al I think I understand your problem. Firstly it would help me for clarification, if when you say the tails go into a 'chocolate box' its' one of these? If it is , then to do the necessary disconnection from the supply, without pulling the service fuse, it is possible- if you know what you're doing- to carefully remove the lid of the connection block pictured above, and using an appropriate insulated screwdriver undo 2 of the large brass screws which are clamping the RCD's 'Live' tail, and withdraw it carefully by pulling the tail out of the brass terminal block. This has now rendered your shower RCD effectively safe to work on. Assuming the correct sized tails are fitted, the simplest way would be to replace your existing ( presumably 30mA RCD with an appropriate RCBO. You could as you say fit an MCB into the circuit but it would be far easier and cheaper to just swap the RCD for an RCBO. Of course extreme caution should be used when doing this. It's something I would do, and have done on numerous occassions when I needed to, but of course not something that should be done! Having said that, the most important thing is that the protective device ( the RCD or RCBO) operates quickly enough in the event of any fault conditions. To ensure the protective device operates quickly enough, a specialist piece of equipment is needed, something generally only an Electrician will have. There are numerous other things that need to be correct too, but I won't go into them.
There is no 6mm2 cable in the choc box. The RCD in the consumer box is bypassed. There is no connection to the consumer box. There is an isolator just outside the shower room. Please read wot I rit carefully. Thanks John, Yes it it is one of those....the closures are wired with seals but as they are on my side of the meter, I see no reason why I can't cut them. I have thought about what you suggest, but I was trying to avoid doing it even though I have the proper tools (courtesy of 24/7 before they changed). I think the tails you refer to are the same size as the ones from the mains cartridge to the meter, so they are fairly rigid and would hopefully go back into the choc box easily. Yes, you are quite correct, but cancer got in the way before I had a chance to progress anything; hence doing it now. By the way, I have had another closer look at the RCD and it is in fact an RCCB. All the pipework is bonded too. Thanks all.......AL
Al I think you know this but an RCCB doesn't provide overload protection so you still need to incorporate an RCBO or MCB into the circuit.
A basic diagram.......however, I have as yet to find out where the earth lead is on the sewage treatment unit is, unless the ground stake next to the treatment unit is sufficient. I also know that in addition to the PME connection there is also a ground stake outside the house from the earth bar in the consumer unit.
