Locating discontiniuty in CPC - how? Help?!

[dennis]

A faulty bit of cable and the fault has always been there, not that that ever happens.

[ARWadsworth]

That is the most probable cause.

There are proper machines for that purpose that are a bit safer than using

230V. They are not cheap though.

[Dave Plowman (News)]

I got one off Ebay for about 30 quid. It's really meant for tracing signal cables - but I don't see why it wouldn't work on mains ones. Totally disconnected, obviously.

[Lobster]

Just thought I'd report back on the outcome of this thread...

I found an electrician willing and able to come in yesterday. First thing he looks at is my newly installed CU and with much sucking of teeth says "well this is a bit of a mess isn't it" - he was referring to the sequential numbers on the neutral terminals not matching up to those on the MCBs. Oh puh-leaze...

I explained how I'd tracked down the fault to one leg of the ring with

90% certainty using Mr Reagan's above method; however he didn't understand (or believe?) the technique and started his diagnostics from scratch; took him two hours with his Megger to reach the same conclusion I had. By this time I think he'd cottoned on that I wasn't a total muppet and aided with copious quantities of tea, relations had thawed somewhat.

In the end he decided to break into the wall at ceiling level to cut the affected cable for further testing (it was impossible to access it above the ceiling, which was where I'd come unstuck myself); that isolated the problem to a break between the ceiling and the socket below. Fortunately he was able to pull a new length of cable up through the capping, and then connect that with a jcb above the ceiling, so just leaving me a small hole to fill at ceiling level.

So - FYI here's the offending damage!:

caused by a picture hook or screw right into the cable. Because I'd had the room plaster skimmed last week, there was no evidence of this. The live wire is burned about 50% through but still intact.

After that all testing went OK and I got my periodic insoection report (which I was going to have done anyway, after installing the CU) without further ado. Interestingly the one (minor) issue he raised with the wiring was the lack of cross bonding of the CH system at the boiler; said he trusted me to install it today and wouldn't mention it on the report - I don't think that would have happened when he first arrived!

Thanks a lot for all the help from this ng

David

[ARWadsworth]

I cannot see the point in cross bonding the CH at the boiler. There is no requirement to do it.

[Dave Plowman (News)]

I did wonder. If that were deemed necessary, you'd have to cross bond every rad too?

[Bill]

In message , "Dave Plowman (News)" writes

I picked up one of these off Ebay a while back, mainly for use on twisted pair but I have used it on mains cabling. Most useful.

>

[ARWadsworth]

It used to be quite handy to cross bond a boiler if it was next to a bathroom and could be used for the bathrooms supplementary bonding. However in this case the 17th edition rules apply and there is no need for supplementary bonding.

[ARWadsworth]

What, you didn't ask me!

Hardly a major fault. I certainly would not have made a comment about it.

It should hve taken him 5 minutes if had listened

He did well on that bit.

Always do the electrical testing first.

[Ronald Raygun]

He would have, but you were busy with your neighbour's car.

[ARWadsworth]

It would have got me out of jump starting the neighbours car.

Mind you if David is 300 miles away from me I suppose he would not want to pay my petrol costs.

[A.Lee]

This came up on my 17th Ed. course, and the Instructor said it was more to do with the Gassafe regs - to make sure the boiler is earthed. I've seen it where there were 5 earth tags/cables on the pipes going into the boiler Though my gas fitting mate says it's bollocks, he just makes sure the gas and water pipes are properly earthed. alan.

[Lobster]

I think the last time I came across this issue (~5 years ago, pre-17th edn) it was the gasman who told me I needed to do this, so I duly installed 5 interconnected earth clamps. Then the sparky came round to do the PIR test, and told me it wasn't actually necessary (mind you, the same guy insisted on supplementary bonding in the kitchen, so go figure...)

On the current occasion when the new electrician raised it, I did query whether cross binding was definitely a requirement these days and he said yes, always has been and still is. Should I not bother?

David

[ARWadsworth]

You might as well do it now. After all you may one day want the bloke back to do other work.

And the bit about the neutral bar in the CU is here.

[Andrew Mawson]

wouldn't

happened

bonding.

pre-17th

bother?

bloke back

But that link does say that in single phase consumer units neutrals can be sequentially placed so not needing labelling, and implies it's only needed in some three phase boards. In the three phase boards I've installed here on the farm, all have labels adjacent to the neutral bar identifying breaker numbers, so again not needed.

AWEM

[ARWadsworth]

It is a long winded way of saying that the neutrals must be clearly marked or identifiable. Something that David must not have done, although with three circuits between two rcds it would only take about 3 seconds to work it out.