Shower leaked and tripped RCD

[MARKF76]

Hi,

I recently had my house rewired. They did a very neet job and all seemed well until tonight. A seal in my electric shower failed and water poored everywhere, shorted the electrics and tripped the RCD. The thing is it did not trip the RCD for the shower. It triped the main RCD. Now I would say this is wrong in the first place but even more of a strange thing happened. Even though the main RCD tripped we still had power to the lights
I am no expert so forgive me if I am talking rubbish but I thought the idea of an RCD is to kill the power?

Any ideas?

Many thanks

 

[JohnD]

I expect you have a split-load consumer unit. This is a very common way of wiring a house today.

The RCD protects those circuits where injury is likely to be caused by a fault to earth. This is sockets which can be expected to be used with equipment used outside; electric showers, and possibly other sockets too.

It is safer not to put the lights on the RCD, because they are unlikely to cause a shock from an earth fault; and it is safer not to have them go out unexpectedly (for example, you might be running downstairs, carrying something heavy, or up a ladder when it goes dark).

 

[MARKF76]

Thanks John

That makes sense. Why has he installed an RCD for the shower if it is going to use the main RCD. purely convenience? So it can be isolated manually?

 

[MARKF76]

Sorry, I mean MCB not RCD

 

[Adam_151]

They are different things, an MCB works like a replacement for a fuse, if too much current flows it switches off, an RCD won't switch off if too much current flows, instead it monitors current in the live and neutral and if they don't match (and are out by 0.03A or so) it realises that current must be going astray to earth somehow (quite possibly through a person!) and so switches off.

RCDs are sensitive things, and a fault in an appliance that uses water will quite often trip it, if water allows currenet to flow to earth, then because water is a relativly poor conductor, no where near enough will flow to blow the fuse/trip the MCB, but the RCD will trip. Sometimes such a fault will go on for years before an RCD appears in the circuit and you find out about it (steam irons, etc), but where a shower is concerned nasty effects such as small shocks can sometimes be felt (electricity and wet bodies don't go too well together) which is why showers are recommended to be on the RCD side of the board

You can get a device which contains both RCD and MCB in one unit, called an RCBO, this means that when an RCD tripping fault occurs you only loose the one circuit, as opposed to half the board.... they are however expensive, costing the the range of £40 each, which is why split load boards are the de-facto way of doing things, and what you usually get unless you ask your sparky for something different

 

[MARKF76]

Thanks for the Info. Not faulty after all

Tell you what, I am glad we had it rewired. It was only a week ago we had it done. God know what would of happened if we still had the 40 year old fuses box

 

[Adam_151]

Thanks for the Info. Not faulty after all

Tell you what, I am glad we had it rewired. It was only a week ago we had it done. God know what would of happened if we still had the 40 year old fuses box

And its a good job your spark put the shower on the RCD side, some don't , its not actually a requirement of BS7671 (yet - that is very likely to change when the new version comes out in just over a year), other than equipment should be installed as per manufacters instructions, most shower instructions 'recommend' an RCD, but whether that counts the same as 'requireing' one?

Still I'd never eant one without RCD, and when a spark fitted ours, I made sure that it ended up on the RCD side of the board even though that was not the easiest option (I had to source an 80A RCD to swap out for the 60A)

Still remember this story that was told on the IEE forum

Well, while a single incident makes bad policy, I for one have replaced a shower whenere the symptoms were ' I get a tingle leaning on the tiles..' - the shower had developed a leak in top seal to the heater pot (about the size of a small beaker) and was spraying fine jet of water over the lugs carrying the incoming mains, this then trickled out of the plastic case and down the wall. The water down the wall was partly live, while the water under the main jet was earthed, but the leakage to earth was (not surprisingly) not enough to blow a 30A fuse (actually about a hundred mA or so seemed to go astray), and the fault had persisted 'for weeks' until the tingling sensation became worth asking me to take a look (as a visiting family friend) Otherwise it would probably be still leaking today.

Since that incident, I have become a great fan of showers being on RCD, even if not compulsory in the UK. I also note that bathroom cross bonding, had it been present, would in no way have increased the safety of the situation - actually it's very absence may even have helped current limit.

regards Mike.

PS 1 Whe I spoke to the guy at the plumbers merchants he was pretty nonchalent - yeah they all fail at that seal on that (triton 2) model - so it probably isn't an isolated incident.

PS 2 When I explained the significance of the tingling to the friend, I got the response 'ooh we could have had 3 dead bodies in the shower' - this being the number of us staying in the house at the time.
I don't know what it says for the IQ of the others, but I am positive that I would not have stepped in to take a shower if there was already a corpse in the shower tray ! - but then I prefer a bath anyway )