Strange IR readings on 3 phase board

[newfutile]

I am unable to take global IR readings on a 3 phase consumer unit, i have disconnected the neutral but when i try to measure the meter never settles and eventually times out.
i have tried 2 meter/s with same results

 

[Risteard]

Is the reading climbing? Extra characters.

 

[newfutile]

it seems almost random, put a clamp round the earth found 100mA leakage from lighting circuit,(14 double D fittings

 

[pc1966]

Sounds like some power is present even when isolated.

Have you looked to see what sort of volts L+N - E has when isolated? You might also need to put in a small load (1k resistor, or maybe a basic voltage tester in parallel to meter) so you are not seeing low current "phantom" voltages.

 

[pc1966]

it seems almost random, put a clamp round the earth found 100mA leakage from lighting circuit,(14 double D fittings

CPCs often have strange currents due to whatever route power from TN-C-S systems is finding back to the substation, etc.

Clamping L&N to get actual leakage is far more useful!

 

[newfutile]

Usually i would clamp the L-N but this is 3 phase so that’s quite tricky, the 100mA is only present when the lighting circuit is on ,when turned off it drops to 2 mA ,i have also clamped the cpc from the lighting circuit which confirms 99mA back down it!

 

[Rockingit]

Unless I'm missing something here or being slow (always an option!!) if you're wanting global IR then just gang the lines together? As for the leakage, 100mA on a large LED lighting circuit doesn't seem implausible, although if that IS the case then it's been poorly designed.

 

[pc1966]

Usually i would clamp the L-N but this is 3 phase so that’s quite tricky, the 100mA is only present when the lighting circuit is on ,when turned off it drops to 2 mA ,i have also clamped the cpc from the lighting circuit which confirms 99mA back down it!

OK, that is sounding like a N-E fault somewhere!

 

[pc1966]

As for the leakage, 100mA on a large LED lighting circuit doesn't seem implausible, although if that IS the case then it's been poorly designed.

Strewth! That would take about 1.38uF from L-E for filtering!

 

[newfutile]

Finally found the problem , this along with a loose cpc made for a rather dangerous situation on exposed class 1 head height light fittings.

thanks for all the suggestions