Strange IR readings on 3 phase board

newfutile · Feb 2, 2022

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 · Feb 2, 2022

Is the reading climbing? Extra characters.

newfutile · Feb 3, 2022

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

pc1966 · Feb 3, 2022

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 · Feb 3, 2022

newfutile said:
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 · Feb 3, 2022

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 · Feb 3, 2022

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 · Feb 3, 2022

newfutile said:
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 · Feb 3, 2022

Rockingit said:
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 · Feb 4, 2022

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