Insulation resistance

[martin43]

Hi guys

A quick querie if you'll indulge me, testing a ring final today and had a reading of 16M between N-CPC on a spur, everything else was well above 300M. Whilst I know this is ok for 7671, would you change the cable?

Regards
Martin

 

[Pensdown]

Is it a new installation or are you testing existing? Some more details would help us

 

[martin43]

Pensdown

It's part of a completely new ring in a kitchen, all new cables.

Martin

 

[securespark]

16 MOhm? Change cable? Nah.....

2 MOhm is pass.

Must be something in circuit.

 

[martin43]

Securespark

Nothing connected, it's purely the piece of cable, I've also done a continuity check to prove so.

Martin

 

[Pensdown]

If that's the case it sounds like the cable has been damaged.

Would I replace it? If the customer is paying for a new install then of course it should be replaced.

If it is damaged it will probably get worse over time and then the customer will be on here asking why their RCD has started tripping.

 

[JohnD]

Halve the circuit to find where the faulty bit is. There will never be a better time to do it.

 

[martin43]

Hi Pensdown Securespark & JohnD

Thanks for your thoughts, decided last night that I would have to investigate, it is a new install, my conscience wouldn't let it lie although it met the 7671 requirements. Anyway got the joiner to remove the facings and a lot of gyproc screws later discovered he'd pasloded the cable, see here http://i62.photobucket.com/albums/h113/martin43_2006/IMG_1089.jpg.

Thanks for the help, much appreciated, glad I bothered though.

Regards
Martin

 

[Pensdown]

Blimey, he was good shot, straight through the middle!

Well done Martin, you're no longer just a sparks you're a good sparks. You tested your work, you understood the results and you were prepare to do the hardest thing of all, admit you may have made a mistake and put it right at your own expense.

Now your customer will trust you and I hope “nail-gun man” buys you the biggest breakfast on the menu.

 

[martin43]

Thank you for the kind words Pensdown, for the record a test after replacement of the cable put the formerly faulty CPC-N reading now greater than 299MR, which seems to be the highest the Megger goes to.

The errant joiner also apologised for the poor aim and has been left to re-affix the gyproc and facings under warnings of a dire fate if he does it again. Along the lines of the nail gun and his dangly bits.

I realise this hasn't been strictly a DIY issue, but i'm sure anyone reading this thread will hopefully take on the implications of a hammer and nails at home. Thanks for all the help.

Regards
Martin

 

[Taylortwocities]

I too have suffered at the hands of nail-gun men.

Nail guns are the original labour-saving device, aren't they?

 

[dingbat]

Good story Martin and glad you resolved it.

In my experience it is good inter-trade PR to explain to the offenders what the problem was and how you tracked it down. Too many tradesmen have little or no idea what is involved in any trades other than their own.

Hopefully your chippy will now realise that we don't mess about with little yellow boxes just for fun.

 

[securespark]

That cable doesn't look like flat T&E?

 

[Softus]

I realise this hasn't been strictly a DIY issue, but i'm sure anyone reading this thread will hopefully take on the implications of a hammer and nails at home.

Martin - as per dingbat's comment, it's relevant to more people than you might think.

Lasy week, on a 2nd fix in a new extension, I made on the water connections from the old house, under the floor, with the electrician in attendance to do the bonding to my pipework. He wasn't keen on being the one to fix down the floor afterwards, so I took the time to mark the boards with exactly where the screws should be put and mark all areas where there were cables and pipes, for future reference.

However, there are plenty of times when I'm drilling into walls and cavities without any hope of being certain about what's behind, so your topic has given me a better an insight into what can happen and how it can be found.

How much is an insulation resistance tester, and what are the annual calibration costs?

 

[Taylortwocities]

From about £300 for a stand alone tester see http://www.megger.com/uk/products/ProductDetails.php?ID=719&Description=MIT220
but (as I'm sure you know) you must make a number of tests when installing electrical circuits so a multifunction tester like this will cover all of the required tests: http://www.megger.com/uk/story/Index.php?ID=170

TTC