Boiler tripping RCD even when earth removed

[opps]

Yesterday a mate mentioned that his CU RCD was tripping. By flicking the MCBs off and on, he was eventually able to determine that it was something in the kitchen causing the fault. We unplugged everything and plugged them in one by one. The fault was eventually traced to the boiler.

As a further test, I did something which I now realise was incredibly dangerous and stupid. I decided to remove the earth from the boiler plug and flick the socket switch to see what would happen. Fortunately the RCD tripped immediately. I had forgotten that the water pipes were earth bonded, which is a good thing, because my stoopid move would(/might?) have made all of the rads and taps live.

My mate rang British Gas to ask them to send out an engineer to repair the boiler that they fitted last year. Initially he was told that the earliest slot was 6 days later. He aske another friend, a plumber to look at it. He said that he noticed a slight drip from the hot water diaphragm on to the micro switch below it.

 

[Deleted member 267285]

Leaks can cause the rcd to trip as can loose/poor wiring. Best leaving to a professional, albeit not sure if BG have many, let us know if they find anything.

 

[ericmark]

Birds on the power cables don't get fried, so it is a balance between earthing and not earthing, or as we call it IT (insulated from terrestrial) which is what we do with the bathroom shaver socket.

In 2008 the rules changes, and we stopped bonding to the same extent as long as we have RCD protection, but it has been pointed out since the problems with some RCD's being frozen if there is DC current on the AC supply, so it does get complex.

There was, likely still is RCD's which alert when getting near tripping current, and RCD's which auto test and reset once the fault has been removed, and type B which can handle DC, but these all as far as I know need to be double module thick, so not easy to fit in a reasonably sized consumer unit. So can't really be used with all RCBO (RCB and MCB combined) units.

I have worked on a tunnel boring machine which was IT, and the number of belts I got was silly, we walked around with volt pens and tested all metal before testing, so the TN and TT method is far better in the main.

Odd but until last month I have never been able to measure earth leakage, we should when converting from non RCD protected to RCD protected measure the back ground leakage first, we are told no more than a 1/3 of the RCD rating, so for a 30 mA no more than 9 mA, but since only just started to measure, no real idea how close to the wind I have been sailing, which is why I fitted all RCBO just to be on safe side.

 

[ericmark]

Leaks can cause the rcd to trip as can loose/poor wiring. Best leaving to a professional, albeit not sure if BG have many, let us know if they find anything.

The RCBO today can have an AFDD built in, which does detect sparking, but in the main a RCBO does not detect loose/poor wiring.