Insulation Resistance - help please

[Gazap]

Could anybody please give me any help understanding my reading of IR, just completed a 2392 and testing a few circuits. I have a megger 1552 and testing at 500v

circuit 1 sockets (radial) tested L/E >299 , L/N >299 , then N/E 2.95 , then disconnected both ends from bar and had a reading of N/E >299. Is the reading of 2.95 to do with continuity at source ?

circuit 2 sockets (ring final circuit) tested L/N >299, N/E >299 then L/N 0.4 ? there is continuity between L/N but could not find out where ? there are 2 switched fused spurs but these are switched off and nothing is plugged in to other sockets. I then did a test of (L & N together) and tested to E, reading was >99.9 (tested at 250V)

circuit 3 lights (radial) tested with 500V and again (L & N together) and tested to E as there are floresent tubes and dimmers. reading of 113 Mohms with all the bulbs removed. is this reading quite normal as was expecting >299. Also could i do this test with the bulbs left in if connecting both the L & N together and testing to E ?

I know there are a few questions but cant see anything in any books i have ?

 

[telectrix]

ok. your N/E of 2.95 is almost certainly due to the connections being left in the board. IR tests should be carried out with circuit totally dissed from any other circuits and supply.

your L/N of 0.4 could be the neons in the FCUs.

113 Mohm is a good reading. could be affected by the ballasts in fittings. always best to remove the loads completely before IR testing.

 

[Gazap]

I know you said best to remove the loads(bulbs) but would it be acceptable to do a test with the loads if difficult to reach eg very high ceiling ? appreciate your help, many thanks

 

[telectrix]

you can do a soft test . i.e. L/N shorted and 250v test to E. with lamps in.

 

[malcolmsanford]

Exactly as Tel above as highlighted.

As you have done the 2392 you will have concentrated on doing testing as an initial verification, what your doing now are tests to a PIR. I personally would advise you to do the very first IR test at 250v as if you miss something, say a booster in a loft or even a bell transformer or an alarm system CCTV system then by putting 500v through them could fry and you could be not just embaressed but facing a costly mistake.

By doing a 250v test you would pick up the problem as a low reading, and investigate further, finding what was on the circuit and isolating properly. Then if you got good reading you could give it a 500v blast then.

 

[SirKit Breaker]

I always test at 250 first as well.

 

[SPARTYKUS]

I always test at 250 first as well.

Me too

 

[Gazap]

cheers

 

[Gazap]

can the soft test (250) be recorded on the schedule of test results and if so where NICEIC?

 

[malcolmsanford]

It comes under section 612 of the regs, if you go to them you will see that it outlines the "soft" test.

On your schedule of results you will normally have 2 boxes if they are modeled exactly as the forms in the BS 7671-2008 for IR which is LIVE/LIVE and LIVES/EARTH, if your doing just the soft test as per 612 then you just fill in the one box LIVES/EARTH, which is often done on a PIR, where sometimes such as high bay lighting you can not isolate the loads.

On an initial verification though IIMO you should be well able to perform a full test.

 

[Gazap]

yes was thinking more of PIR, on the NICEIC 'Schedule of Test Results' it is Live/Live, Live/Neutral, Live/Earth, Neutral/ Earth, will have a good read of 612, Many thanks

 

[chrisc 77]

as an absolute amateur i would find it very helpful to revise the regs at home or whenever i get a spare minute , where can i pick up either a copy of them or a newly printed source ??

 

[Gazap]

i know someone who brought a digital copy off ebay for a few pounds , i believe there is a new regs book coming out soon.

 

[telectrix]

there is. there's a thread on currently, it's £60 pre-ordered.

 

[Gazap]

your L/N of 0.4 could be the neons in the FCUs.


no neons in the FCUs ?