Insulation Testing Help needed!

[chrisgc]

Hi all

I am just practising testing on my own circuit at home and am getting a little confused with the Insulation Testing as there seems to be a few different ways to do it.

I have the on-site guide (which seems to be the easiest method) and the NICEIC - Inspection, Testinga and Certification books and finally the Megger poster sheets which I downloaded from this site - and they all appear to be different in the way they explain their Insulation Testing.

I am simply after the least confusing and the quickest and easiest method.

I have a few questions which I would really appreciate some help with:

By the way I am trying to do Insulation Test for my Socket ring using a megger 1553:

1 - Do I connect probes to earth and neutral bars as would have thought this would be testing the whole system OR do I disconnect the earth, neutral and line cables for the specific circuit I wish to test and put my croc clips on the cables as per test sequence (Socket ring)?

2 - NICEIC book states that the incoming neutral has to be disconnected yet cant find that method anywhere else? Whats that all about?

3 -The megger poster pics show a link between live and neutral on the main switch?

4 - Do I have to turn off ALL circuit breakers and RCD's and MAIN Switch off OR if working on an individual circuit is it just the main switch off and the specific circuit breaker off.

5 - Not even sure if insulation resistance is carried out on the whole system or the individual circuit which is being tested.

A simple walkthrough is really what I am after and would like to work to the on-site guide.

I think testing is one or if not the most important part of the electrical work so wish to become comfortable doing it so am using my house as practise.

Hope someone can be so kind as to help.

 

[Sparky Ninja]

Unfortunatley like many things in this industry, interpretation comes into play and everyone starts scratching their head.

 

[Jurasic Spark]

Pages 83-85 of OSG tell you all you need to know:
Test between Live conductors and between Live conductors and Earth so in your house thats L-N, L-E & N-E.
All circuits of a DB are usually tested together in parallel but if you only want to test your S/O circuit then do it by seperating the conductors from the other circuits....SIMPLES.

 

[malcolmsanford]

The method of a whole installation test as you described by "tail testing" is really designed for an "Initial Verification" . When you do a new installtion or a rewire it's easier to test this way as supply is isolated and you have full access to the installtion. I have to admit I though will test each individual circuit before connecting it and if all are 999 then that's what I put.

So this test is have your CU tails disconneted from the meter. Have your main earth condutor connected, croc clip the earth CU bar. then if possible connect the LINE/NEUTRAL together, as this is 25mm then it may not be possible. Before you test make sure your CU DP switch is closed(on) and all protection devices are closed(on). IR test L-E then N-E. Then remove croc from CU earth bar and IR L-N. If you have a result over 2 Mohm then your home and dry but I would expect much more on a new installation. OF course you must make sure before you test you have remove lamps, bypassed dimmers and PIR if you have them already in, Neon switches are open (off) etc.

The IR test is more complicated during a PIR. There is a chance you may not be able to isolate the whole installtion and do test as above. You then go down the road of setting limitations as you may not be able to disconnect equipment sensative to the test. You may decide to do just a L-E and N-E test on 250v DC rather than the 500V DC on a normal. You may get the chance to do isolate individual circuits and do a full test on them. If you can then you do as:

Disconnect the LIVE from the protection device and the NEUTRAL from the Bar, you can leave the earth on the bar, but me I always disconnect. As these will be smaller cables you may easily join the LIVE/NEUTRAL together.Then at 500v DC you test L/N-E then L-N. If you get a result over 2 Mohm then great move on. If you get under 2Mohm but over 1Mohm that is acceptable but you have to note that this needs further investigation and document it.

A PIR is a lot more involved and more involved than an Initial verification that is why the C&G created the 2392 course just for new work. A great book that will help you is this

Practical Guide to Inspection, Testing and Certification of Electrical Installations: Conforms to 17th Edition IEE Wiring Regulations BS 7671:2008 and Part P of Building Regulations: Amazon.co.uk: Christopher Kitcher: Books

Hope this as helped and answered some questions.

 

[WayneL]

Hi mate,

It does seem daunting at first, but all is easily explained

My Blue:

Hi all

I am just practising testing on my own circuit at home and am getting a little confused with the Insulation Testing as there seems to be a few different ways to do it.

I have the on-site guide (which seems to be the easiest method) and the NICEIC - Inspection, Testinga and Certification books and finally the Megger poster sheets which I downloaded from this site - and they all appear to be different in the way they explain their Insulation Testing.

I am simply after the least confusing and the quickest and easiest method.

I have a few questions which I would really appreciate some help with:

By the way I am trying to do Insulation Test for my Socket ring using a megger 1553:

1 - Do I connect probes to earth and neutral bars as would have thought this would be testing the whole system OR do I disconnect the earth, neutral and line cables for the specific circuit I wish to test and put my croc clips on the cables as per test sequence (Socket ring)?
You can just connect onto each bar - and yes, this tests between ALL earths and neutrals. Then test between the Line (of circuit you're testing) and earth bar and the Line and neutral bar

2 - NICEIC book states that the incoming neutral has to be disconnected yet cant find that method anywhere else? Whats that all about?
In TN systems the neutral conductor is connected to earth - either at the star-point of transformer, or (in case of TN-CS) at the cutout.
This is why they say the neutral has to be disconnected. You disconnect the neutral when you open the main switch.

3 -The megger poster pics show a link between live and neutral on the main switch?
This is because they are showing the method of testing between L & N connected together and Earth. You would then place your probes on either L or N and the earth bar.

4 - Do I have to turn off ALL circuit breakers and RCD's and MAIN Switch off OR if working on an individual circuit is it just the main switch off and the specific circuit breaker off.
Depends where you are testing.
If you are testing the whole installation at the main switch, then the main switch would be open (off) and all MCBs would be closed (on)

5 - Not even sure if insulation resistance is carried out on the whole system or the individual circuit which is being tested.
Depends what you are testing and why.

A simple walkthrough is really what I am after and would like to work to the on-site guide.

I think testing is one or if not the most important part of the electrical work so wish to become comfortable doing it so am using my house as practise.

Hope someone can be so kind as to help.

Hope that helps.

Wayne

 

[chrisgc]

Unfortunatley like many things in this industry, interpretation comes into play and everyone starts scratching their head.

Tell me about it lol.

Of course its confusing when the OSG is different to NICEIC book - especially when NICEIC are one of the bodies who judge you and make you competent.

Should have chosen plumbing lol.

 

[chrisgc]

Pages 83-85 of OSG tell you all you need to know:
Test between Live conductors and between Live conductors and Earth so in your house thats L-N, L-E & N-E.
All circuits of a DB are usually tested together in parallel but if you only want to test your S/O circuit then do it by seperating the conductors from the other circuits....SIMPLES.

Thanks Jurasic Spark - Nice and simple - like me ;-)

 

[chrisgc]

WayneL

Thanks for that - good description and appreciate the time spent.

Up the Reds

(Yanks out - Yanks In)

 

[chrisgc]

Malcolmsanford

Brilliant info - again thanks for all who have replied and took the time - this site is a god send.

 

[chrisgc]

Pages 83-85 of OSG tell you all you need to know:
Test between Live conductors and between Live conductors and Earth so in your house thats L-N, L-E & N-E.
All circuits of a DB are usually tested together in parallel but if you only want to test your S/O circuit then do it by seperating the conductors from the other circuits....SIMPLES.

Jurasic Spark

I have PM'd you.

Cheers