pulling out the few hairs I have left! - INSULATION RESIST.

[JustCurious]

What on earth is happening?
doing an insulation resistance test at DB between live conductors. Phase on busbar & neutral terminal.

500 VDC setting (Fluke 1653)
- test reading 0.01 Mohm !!!
- test volt only coming up to 10 VAC

phase-earth 500VDC = 9.63 Mohm
neutral-earth 500VDC = 9.64 Mohm

then tried same test on other side of MCB, got
5.68 Mohm phase-neutral
9.66 Mohm phase-earth
9.57 Mohm neutral-earth

when tried again got similar readings as 1st time.

Then tried one of the light circuits
> 500Mohm phase-neutral
9.62 Mohm phase-earth
9.63 Mohm neutral-earth

Polarity correct, instrument has just been calibrated and is OK

Can you enlighten me !?!?!
Many thanks.
Getting bald

 

[breezer]

why would you test for insulation resistance between the same phase? i do not follow. your reading of 0.01 Mohm is ok, since if it is the same pahse/ cct you should be conducting a coninuity test. or perhaps its just the way i read what you have written

as for your other readings above 1M is fine, but also how about the batteries in your meter, how good are they?

 

[JustCurious]

why would you test for insulation resistance between the same phase? i do not follow. your reading of 0.01 Mohm is ok, since if it is the same pahse/ cct you should be conducting a coninuity test. or perhaps its just the way i read what you have written

as for your other readings above 1M is fine, but also how about the batteries in your meter, how good are they?

Many thanks breezer!
First couple of tests were done on SAME circuit ; on ring main circuit , with conflicting readings each time I tested.

As stated above:
- test reading 0.01 Mohm !!!
- test volt ONLY coming up to 10 VAC

last test on light circuit was fine and battery is ok indeed

what is CCT in Western Sahara or anywhere else for that matter?
Thank you.

 

[Lectrician]

CCT=circuit.

The meter will not be able to sustain the test voltage into a load of 0.01Mohm - the test voltage will drop.

 

[JustCurious]

CCT=circuit.

The meter will not be able to sustain the test voltage into a load of 0.01Mohm - the test voltage will drop.

Thank you for your reply Lectrician.

On alternative insulation test, voltage was fine , everything correct , except for weird readings on this circuit test.

System working fine, new circuits, OK

Don't reg-s state that lowest should be 0.5 Mohm , moreover H & S want minimum 2Mohm?
Eespite 0.01 Mohm system circuit working perfectly however , any ideas as to what's wrong really?
Could it be poor insulation
Pls. note Zs test, voltage both correct at socket outlets

 

[breezer]

i suspect either you connected it wrong (vaguley possible, and unlikley) or your meter is palying up, as you said 0.5 is acceptable, but at 0.1m i would expect mcb to trip

 

[JustCurious]

i suspect either you connected it wrong (vaguley possible, and unlikley) or your meter is palying up, as you said 0.5 is acceptable, but at 0.1m i would expect mcb to trip

Thanks mate but it's insulation resistance test, I only got 0.01Mohm NOT 0.1m ,plus test on light circuit afterwards was fine .
Here is the initial question :
doing an insulation resistance test at DB between live conductors. Phase on busbar & neutral terminal.

500 VDC setting (Fluke 1653)
- test reading ONLY 0.01 Mohm !!!
- test volt ONLY coming up to 10 VAC

phase-earth 500VDC = 9.63 Mohm
neutral-earth 500VDC = 9.64 Mohm

then tried same test on other side of MCB, got
5.68 Mohm phase-neutral
9.66 Mohm phase-earth
9.57 Mohm neutral-earth

when tried again got similar readings as 1st time.

Then tried one of the light circuits
> 500Mohm phase-neutral
9.62 Mohm phase-earth
9.63 Mohm neutral-earth

Polarity correct, instrument has just been calibrated and is OK

I must be very confused or it might be very hot where you are; Western Sahara
Many thanks.

 

[Lectrician]

Is the DB a submain??

Was the CU main switch OFF??

Is there an RCD or RCBO (mcb rcd combined) on the busbar - this will affect the reading, and you could have blown it

 

[JustCurious]

Thanks for your reply Lectrician.

Is the DB a submain??

- no, main board

Was the CU main switch OFF??

- yes

Is there an RCD or RCBO (mcb rcd combined) on the busbar - this will affect the reading

- no

I cannot figure it out at all

Regards.

 

[Lectrician]

You have one prong on the busbar, and one on the neutral bar?? MCB's off or on??

How many circuits/mc's?

 

[JustCurious]

Cheers Lectrician

You have one prong on the busbar, and one on the neutral bar??
- yes

MCB's off or on??

- on

How many circuits/mc's?

- I have 5

Thanks

 

[felix]

500 VDC setting (Fluke 1653)
- test reading ONLY 0.01 Mohm !!!
- test volt ONLY coming up to 10 VAC

phase-earth 500VDC = 9.63 Mohm
neutral-earth 500VDC = 9.64 Mohm

If all breakers are off then that 0.01 megohm between phase and neutral can only mean:

1) One of your breakers isn't really off.

2) There's a phase to neutral leak.

3) There's a load on the busbar you don't know about.

Have you got any MCBO's in there? Those things need some milli-amps to power their internal electronics.

Addendum: I've just read the posts that got in while I was writing this. Your MCB's are on. That load/leak could be anywhere!

 

[Lectrician]

Turn all MCB's off.

Seperate ALL neutrals from the neutral bar and each other.

Now test each circuit individually.

 

[JustCurious]

Many thanks to you both Felix and Lectrician !

I’ll do the circuits individually. If that fails , it looks like the CU could go to the scrap yard as it is that old.

Just the last one please , chaps :

How can you check CPC continuity which is incorporated inside steel trunking and conduit , since this will create a PARALLEL path ? - this is to do with a three phase installation which also has SWA and MICC cables

Thank you .

 

[Big_Spark]

I'll probably get slammed for this, but JustCurious..would I be correct in thinking you are not qualified?

If your not, as I suspect, then do you realise you are committing prosecutable offenses by working on a Commercial/Industrial installation.

To be honest I think it is a bit rich for someone who is not qualified to come on a DIY forum and ask PROFESSIONALS how to do THEIR job...

I just hope that you do not hurt yourself or someone else..