Insulation resistance

Hi,

I've recently added five new sockets to a ring main and three ne lights to a lighting circuit. I have had a Periodic Inspection carrie out at the request of Building Control. The report states that there i a "Low Insulation Resistance reading". The inspector said that it coul be nothing (it could be a transformer somewhere on the circuit that i giving him misleading readings??), or that there may be a problem.

I am wondering what sort of things could cause a low insulatio resistance reading/ How serious is it? How likely could it be that thi is related to the new sockets/lights? When the electrician did th inspection, he told me that there was nothing that was a seriou problem but when I recieved the hard copy in the post, it raised thi issue. I appreciate that this is very little information to go on, bu I would just like to get a general understanding so I know a littl about it f I have to get an electrician to investigate. The rest of th installation is probably well over 20 years old

-- Jquinn

Reply to
Jquinn
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Is there fresh plaster around the boxes/fittings? Damp plaster working its way into boxes will/may give low insulation readings. This will dry out in due course, but it may be quicker to gouge out any plaster which may have oozed into the boxes/fittings.

Reply to
Frank Erskine

Presumably he said which circuit it was on. Which?

Reply to
Bob Eager

Who carried out the PIR, does he have C & G 2391, is he or his company a member of one the electrical trade organisations: NAPIT, ECA, NICEIC etc.? If so I would report him. "Low Insulation Resistance reading".means nothing unless the value is quantified, there is an acceptable level: - e.g. 2 Megohm for a domestic dwelling, but if less than 5, this requires further investigation. I suggest that you get the "inspector" to elucidate. Jaymack

Reply to
John McLean

As far as I am aware, the electrician who performed the test is from reputable company specialising in these tests, and he has all th relevant qualifications. There were mistakes on the report though. I said there was no earth bonding on the gas main when in fact there is It said that earth bonding was urgently needed in the bathroom, when i fact this is not necessary due to the use of plastic pipes -I pointe this out and he still said that it was neccessary, which to the best o my knowledge goes against the advice of the IEE!

The readings on the report for insulation resistance are:

Ring main: Phase/earth 1.12 Megohm Neutral/earth 0.35 Megohm No readings taken for Phase/phase These are obviously well below IEE recommended safe levels.

The lighting circuit just has ditto marks for the above readings? However, I know that there were low voltage transformers connected t the circuit, and at least two appliances and a lamp still plugged i

-is this the correct way to do the test? Could this interfere with th readings, or would they only affect readings on a phase/phase test? The plaster is pretty much dry I'd say. However, there has bben a lea that runs down a one of the wiring runs of about 2m length, and ther is a small amount of water exiting at the light switch at the end o this run -could this be the cause? As far as i can tell, all the switc contacts/terminals are dry though. We know where the leak is coming fro and it's now being fixed. What else can cause these readings? Is it more likely old deterioratin cable in the existing installation, or can it be due to workmanship i.e bad connections in a junction box or accessory.

Thanks for the help

-- Jquinn

Reply to
Jquinn

0.35M Ohm is typically what the meter would show if there was a neon indicator somewhere in the circuit.

It does look as if the inspector was not fully up to the job.

A common way to test the insulation is to test all the final circuits together (after disconnecting vulnerable circuits like the lighting). In this case the value obtained (usually >200M) can be entered into all the circuits that are have been tested simultaneously.

Reply to
Ed Sirett

find in a cooker switch for example -there is one of those in the rin main which I don't think was disconnected during the test although couldn't be 100% sure.

When you say it is common to "test all the circuits together" do yo mean that this explains the ditto marks for the lighting circuit?

Thanks

-- Jquinn

Reply to
Jquinn

It would then also depend on whether or not that fitting was in the on position or not.

Exactly, except in this case the next step would have been to find which circuit(s) were at fault.

Reply to
Ed Sirett

is a report; but the need to find out the cause of the low insulation level, does not seem to have stressed well enough. . Jaymack

Reply to
John McLean

Yes, I appreciate that it's not his job to fix it. He said it' possible that everything is absolutely fine and that he's gettin misleading readings for any number of reasons. So basically, I may hav a problem, or I may have no problem at all and if there is a problem then I am absolutely none the wiser as to what it is or where it ma be! Ha ha. £100 well spent! Clearly this is something which needs to be investigated further by a electrician. As for the the neon indicator, I suspect that it was actually switche off so that wouldn't have been a factor.

Thanks for the replies

-- Jquinn

Reply to
Jquinn

I wouldn't show this PIR to your insurance company; they would probably cancel your insurance until corrective action was taken. Likewise, if you are intending to sell the house and don't disclose the results, it could bounce back. I would be concerned that there is a fire hazard looming, as I said before, according to the BS7671, there is a minimum, acceptable insulation level of

2 Megohm in this case; but below 5 Megohm requires investigation. What is the wiring condition?, do you have RCD protection; and has he isolated the circuit/s involved? Jaymack
Reply to
John McLean

The wiring condition looks ok to me, although I am not an electrican No he hasn't isolated the circuits (which would basically involv cutting off the electricity as these two circuits supply all th lighting/sockets in the flat) and there is no RCD protection -This i going to be installed though. Anyway, I've got a qualified electrica to come down tomorrow and try to solve the problem. There is a pendan light fitting in one of the rooms which doesn't work -wonder if tha might have something to do with it.

Reply to
Jquinn

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