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Discuss Intermittent fault finding. in the Commercial Electrical Advice area at ElectriciansForums.net

GBDamo

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Was called to a commercial lighting issue on Friday where the circuit had tripped, RCBO protected.

On arrival reset the RCBO and all held, three lights weren't working, two were lamps and one had a black scorched ballast, replaced this and all works.

The circuit has eight lights, two PIRs a couple of fans on it from a quick look round and a handful of EM lights.

Only testing was a ramp and trip time on the RCBO, both fine.

Come today and its tripped again.

I'm thinking water ingress and a thorough all points visual inspection is required.

Finding and disconnecting all the points is a pain as some crettin has put a foot of isulation above the suspended ceiling. So IR testing is probably not time efficient plus, if the RCBO resets, the fault may not be there to find.

Are there any hints or tips for this kind of job or is it a case of doing the hard slog.

I'm working under the assumption the fault has cleared again so the normal route of splitting and IR is not going to cut it.

Cheers
 
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telectrix

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i would suspect ballasts tripping the O/L partof the RCBO, not RCD. you've found 1 scorched; there may be more damaged but not obviously from a visual inspection.
 

GBDamo

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i would suspect ballasts tripping the O/L partof the RCBO, not RCD. you've found 1 scorched; there may be more damaged but not obviously from a visual inspection.
If so then the circuit should energise with all switches off, which it did, but trip, which it didn't immediately.

Tomorrow, I'll clamp it, turn 'em on in sequence and look for high draw as its a reasonably quick 'look see'
 

Lucien Nunes

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#1 If the RCBO is tripping on leakage, there might be a neutral fault of quite low resistance that is easy to find by IR. If you tested the RCBO with the circuit disconnected you wouldn't know about this yet, although if you tested with the circuit connected such a fault would likely have affected the test results.

#2 There might be an intermittent or variable line conductor insulation fault that will not always cause a trip, but reveals itself through low IR. Remember that to trip a typical RCD at say 23mA the insulation needs to be as low as 10kΩ, 100 times lower than the lowest acceptable IR of one megohm. So you can have terrible insulation readings that lead you to a major burnout fault where everything is charred, without necessarily tripping the moment it's energised.

#3 Discharge lighting can have all sorts of leakage modes other than just plain faulty insulation, that may or may not show up with a 500V DC test.

#4 Occam's razor. If some lights are outside as your post seems to imply, water ingress, with or without follow-on failures such as ballast or ignitor burnout, is statistically the most likely.
 
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