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[Bigron]

Yes, STEMO, that is why I asked my earlier question. In most (all?) installations, the neutral feed is connected to earth at its entry point to the property. As such, I couldn't see why an E-to-N short circuit would cause a problem.   

Ron.

[Kevin Wood]

To all intents and purposes, neutral is earth.

It might be at the same potential normally, but it's very different, and this also depends on the type of earth the incoming connection to the property is provided with.

I would disconnect both legs of the circuit at the consumer unit, and go round every socket separating the two legs and testing for the short. Fairly soon you'll find the faulty section of cable or (more likely) find a wiring fault behind a socket.

[Ever Ready]

What type of main switch do you have on your fuse board?

A neutral to earth fault won't trip an ordinary circuit breaker but the same fault will trip an RCD or an RCBO (RCBO is an RCD with overload protection combined)

Does the breaker that trips have a test button on it ?

Any chance of a picture of the board?

To all intents and purposes, neutral is earth.

Not to an R.C.D.

Neutral should be at earth potential but is not always the case

https://en.wikipedia.org/wiki/Residual-current_device

Hopefully this offers an explanation of how an R.C.D. works

[Ever Ready]

Yes, STEMO, that is why I asked my earlier question. In most (all?) installations, the neutral feed is connected to earth at its entry point to the property. As such, I couldn't see why an E-to-N short circuit would cause a problem.   

Ron.

In a TN-S system which provides separate earth and neutral at the consumers premises (the earth and neutral are joined together at the supply transformer, this is a very common type of supply in the U.K.

In a TN-C-S (aka PME) system the earth and neutral and earth are joined together at several points between the supply transformer and the consumers premises but are separated at the cable head where it comes into the premises.

TN-C & TT systems are also used by supply authorities.

[STEMO]

Yes, STEMO, that is why I asked my earlier question. In most (all?) installations, the neutral feed is connected to earth at its entry point to the property. As such, I couldn't see why an E-to-N short circuit would cause a problem.   

Ron.

Apparently, we're old school, Ron. 

[STEMO]

But......still don't see how an E/N short would cause the main circuit breaker to go, even though it might trip an RCD.

[Bigron]

You learn something new every day, "Ever Ready"!
Way back in my youth (ahem, a few years ago...) I learned that there could be a potential between earth and neutral some distance from the supply point, so I took great delight in getting "free" electricity by connecting a torch bulb between them in my bedroom - and it worked! 

Ron.

[STEMO]

You learn something new every day, "Ever Ready"!
Way back in my youth (ahem, a few years ago...) I learned that there could be a potential between earth and neutral some distance from the supply point, so I took great delight in getting "free" electricity by connecting a torch bulb between them in my bedroom - and it worked! 

Ron.

Good job the PD wasn't much, Ron, or you'd have made a loud 'POP!'

[TD]

But......still don't see how an E/N short would cause the main circuit breaker to go, even though it might trip an RCD.

main circuit breaker has the RCD built into it, in my case 

[Ever Ready]

Every day is a school day even for old dogs like me

Back when I started my apprenticeship in the seventies we never had circuit breakers never mind pesky RCD's

Everybody used to keep a card of fuse wire, usually from Woolies to rewire their fuses.

I was talking to a young pup (45) on site yesterday who can't remember a time before MCB's


Having an RCD as your main switch ( a requirement if your method of supply is aTT system) creates problems when one circuit causes a fault and puts the whole house in darkness.

One answer was split load boards with some circuits on the RCD and others not.

The best solution in my opinion is individual RCBO's which provide RCD protection and over current protection. Can be seen as too expensive

[TD]

To all intents and purposes, neutral is earth.

It might be at the same potential normally, but it's very different, and this also depends on the type of earth the incoming connection to the property is provided with.

I would disconnect both legs of the circuit at the consumer unit, and go round every socket separating the two legs and testing for the short. Fairly soon you'll find the faulty section of cable or (more likely) find a wiring fault behind a socket.

I think I'm going to have to do that.....

[Ever Ready]

Before you do that TD have you got any fused spurs connected to the circuits?

Burglar alarm panels etc are often spurred off the ring main.

Just a thought before you start dismantling your house

[TD]

Before you do that TD have you got any fused spurs connected to the circuits?

Burglar alarm panels etc are often spurred off the ring main.

Just a thought before you start dismantling your house

Good thinking 

But the only fused spur went to the boiler.....which I have ripped out the cable and shoved a plug on the end and plugged it into an extension lead running from the dining room....so I have heat and hot water 

Fridge/freezer is plugged into socket on the cooker panel and I have another extension lead for the other appliances in the kitchen....bit of a pain as I can only use one appliance at any time, so as not to overload the extension cable...but liveable with for the time being.

I haven't done anything on it this afternoon as I went over to my mums....I'm going to leave it until I can spend a day on it 

I'm still wondering if leaving a steam iron for 24hours could have caused the fault  as the socket in the bedroom where it was plugged in was where I found the original N/E short.....then got very confused as to what was going on.....

Hence I think Mr Woods suggestion is the way forward...

[TD]

Decided to have a go at the problem again this morning...

So did as Kev suggested.....disconnected L/N tails from the consumer unit and went round checking at the sockets (I had all the sockets disconnected too)

The N/E short (0.2 ohm) I was seeing yesterday had disappeared....I even checked at the consumer unit....no short. I also checked the sockets....

So reconnected all the sockets but left them hanging.....checked at the consumer unit....no short

Reconnected the tails at the consumer unit and turned the power back on......circuit working again, power at all the sockets.

Leaving the power on I reattached the sockets....half expecting the power to trip once the wires were pushed back in the back boxes.
But no, power stayed on.

So don't you just hate it when that happens. Fault has magically disappeared! Disturbing the wiring seems to have done something 

Gonna pop out to screwfix now and get one of these just to double check the sockets are ok....

http://www.screwfix.com/p/lap-ms6860d-socket-tester/91596?_requestid=136864

[TD]

Got the above tester and checked all the sockets.....all ok L/N/E present all the sockets  ....altho the tester carnt check a N/E reversal... but I'm not that much of an idiot to get that wrong.....been ok for about 8 hours now....

I'll give it a few days, to make sure the fault has disappeared......then reconnect the boiler to the fused spur...

Happy bunny at the moment.....

Thanks to all who suggested the way forward