IR on lighting circuit very low

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Markiemarque

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Hi,

I am getting a very low reading on a lighting IR test (close to zero!).

The circuit is an existing domestic lighting installation that needs testing. Due to the high number of dimmers I am using the L&N to CPC test to avoid damaging any sensitive equipment.

The lighting circuit appears to work okay ie. it is not tripping the CB in normal use.

I cannot identify any equipment on the circuit that would give this type of reading .... any thoughts?

BTW - I would not expect to get a low reading doing L&N to CPC there is no potential difference across the Line and neutral .... am I missing something obvious?

All the other lighting circuits are fine + there are also emergency lights off each lighting circuit.

Thanks

Mark

 
Is it covered by an RCD in normal use? A meter reading "close to zero" on insulation range could still be looking at a resistance in the thousands of ohms - no real loading effect.............

Thoughts? If you can access any junctions on this cct., try disconnecting parts of the circuit, to determine where the fault lies. It could be old / damaged cable, dampness in a wall behind a switch, overheated cabling at a termination or within a luminaire.

Check around the whole circuit - fittings & switches. Don`t rely on the meter - use touch, sight & smell to see if you can spot any "dodgy" areas - then isolate them and test as a seperate part...

HTH

KME

 
Hi,

Thanks for the reply. The circuit is not on a RCD.

I was rather hoping I would not have to start breaking into the circuit ... hohum. I guess a good start would be to test from the load side of all switches to see if there is a fault on the load side of the cct - then work back.

Having said that I did think I had turned off all switches to prevent strange readings across lamps/dimmers.

Looks like a divide and conquer approach.

Are there any load devices that are renowned for giving bad readings on a Line+neutral to CPC IR test?

Cheers

Mark

 
How LOW is the low reading...

ie. have you tried reading with a low resistance continuity tester,

and/or digital multimeter..

As KME says 0Megohm...

could still be

90,000kOhm+ for example...

a "Steady" reading may imply a fixed contact between two parts..

a rising or falling value could imply some component charging or discharging..

(a capacitive effect), which may point you nearer to the cause?

Junction box with Damp across terminals?

Junction box buried in plaster in a wall? :_|

 
Hi,

I tried the low resistance setting on my megger and got nothing, which is what i would expect else = BANG :p

I am reading 0.01 Meg ohms, a bad reading on a circuit where I expect >200Mohms.

I am surprised at the reading and instinctively think there is a load causing the low resistance - I'll have to see on that one.

This piece of work is for a detailed PIR for a friend - if I was charging the real price they would have to give me bars of gold :eek:

Cheers everyone

 
Hi,I tried the low resistance setting on my megger and got nothing, which is what i would expect else = BANG :p

I am reading 0.01 Meg ohms, a bad reading on a circuit where I expect >200Mohms.

I am surprised at the reading and instinctively think there is a load causing the low resistance - I'll have to see on that one.

This piece of work is for a detailed PIR for a friend - if I was charging the real price they would have to give me bars of gold :eek:

Cheers everyone
Have you got a meter that can read in the 90,000Kohm down to 50ohm sort of range

e.g. GLS light bulbs can read 50ohm, 70ohm, 100ohms (100w, 60w & 40w)

 
Okay - it's a remove all lamps job, then the dimmers.

In terms of a general PIR ... this would be a code 3 .... still would not feel too good putting that; but the amount of work required to get to the bottom of these readings is big.

BTW - this house has about 130 s/o's over 4 floors, interested to see what people would quote for PIR (3 CU's, one of them is fed by a 10mm straight out of a henley block for 10m run.. no fuse)

Cheers

Mark

 
Yes - was surprised to see this. Looking to get EON to give me their view on powering down to add isolation/fuse/rcd + their take on existing earth bonding clamp x 2 on the incomer!

What a palava!!!

 
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