Intermittent Fault

[Slumberland]

We have a problem with a possible fault on a ring main.
We think there is a live to earth fault somewhere under the floor. It has been difficult to trace as it is intermittent and we don't have full access only to the sockets. We did trace the fault to a cable with an insulatoin resistance tester at 500v and then it later dissapeared.
The system is TT and the earth stake was passing 20 amps under fault which would not blow the 32amp breaker......
The two Rcd are Protec and are now faulty after a recent electrical storm and wont trip under test. or under the fault condition.
There are two new rcd,s on order and talk of a surge protector to stop the rcds going down again. We hope to further track fault when it re -appears.
Any ideas regarding surge protection and this intermittent fault we think might be a stray conductor from mice/water intrusion?
Thanks chaps

Jason

 

[Spark123]

If you traced the fault to the cable, you'd be better off replacing it. The best place for Proteus is in the bin!! If you have been suffering surges then electronic RCDs are a no-no, especially on a TT system where you are relying on an RCD to disconnect the supply. I am thinking you are on overhead supply? Stick with the good old wire wound torroidal RCDs!!! (JohnD is gonna hate me for this )

 

[JohnD]

(JohnD is gonna hate me for this )

Not at all, I've always been happy with the old type RCDs, I have heard though, that if you don't connect the trace earth wire, the new RCDs work like old ones. Does anyone know if that's true?

 

[Slumberland]

Thanks

Yes it is an overhead supply in the fens.Theman a protec said a £145 surge protector on the input of consumer unit. Intersting comment on electronic rcds will look into manufacturers instructions.

Jason

 

[Spark123]

(JohnD is gonna hate me for this )

Not at all, I've always been happy with the old type RCDs, I have heard though, that if you don't connect the trace earth wire, the new RCDs work like old ones. Does anyone know if that's true?

Not a clue, I heard they don't like being IR tested and D-Loc doesn't work with them. I don't actually have a clue how the electronic ones do the biz, do you have by any chance a schematic JohnD?

 

[JohnD]

I think there might be a diagram on the side, I'll have a look later.

 

[Lectrician]

Overhead supplies DO NOT always mean a TT supply.

An undergroud service may not provide an earth terminal for many reasons, and an overhead (these days) can 99% of of the time provide a PME earth.

I would look to upgrade to PME, dump the proteus crap, and locate the fault and repair!

 

[securespark]

(JohnD is gonna hate me for this )

Not at all, I've always been happy with the old type RCDs, I have heard though, that if you don't connect the trace earth wire, the new RCDs work like old ones. Does anyone know if that's true?

Not a clue, I heard they don't like being IR tested and D-Loc doesn't work with them. I don't actually have a clue how the electronic ones do the biz, do you have by any chance a schematic JohnD?

You can IR test as long as you don't go P-N.

I've never had a problem with soft test tripping them.

What I do have problems with is testing RCD's from a socket outlet. This can introduce all sorts of false readings - you must test the RCD at source.

 

[securespark]

Overhead supplies DO NOT always mean a TT supply.

An undergroud service may not provide an earth terminal for many reasons, and an overhead (these days) can 99% of of the time provide a PME earth.

I would look to upgrade to PME, dump the proteus rubbish, and locate the fault and repair!

I've been working Staffs recently, and they have a lot of supplies that are underground that have no earth with them. Also, I've seen lots of supplies that some joker has labelled PME with a proper label, but it's TT....

I've even seen a suppy terminate as TNS on the outside of a property, and be TT inside...........

I will 2nd your advice. If you can PME a TT supply, then go for it. You can do away with the need for an S type RCD as well.

 

[Slumberland]

How do you pme a tt supply that must be something the board have to do?

 

[securespark]

Yeah. They charge round 100 sovs and ground the neutral at the pole end, then take an earth connection from the neutral at the cutout.