Lighting intermittent issue

[sid1968]

Please forgive also posted on another site

i wonder if anyone can help with intermittent tripping problem

Distribution board 20amp MCB feeds a 20amp contactor to the outside sensor for external lights and bollards lights. Another small consumer unit wired in a way from the disi board and the contactor when the sensor turns the lights on the then gives power to the small consumer unit (hope this makes sense). Small consumer unit has 3 RCBOs for outside lights

the 20amp MCB in the the distribution board randomly trips ie about every hour.

the building is new about 3 years old and nothing changed. My understanding if a MCB trips its either a short or overload. Overload?? why as it just started happening. I dont think its weather related than the RCBOs would trip. Could it be the sensor or the contactor?

Any advice would be appreciated. Any further questions please ask

 

[Wilko]

Hi Sid - yes the theory is an mcb trip will be down to excessive current. Do the lights still work at all? It would be interesting to know if the trip is related to the contactor operating. Perhaps turn off the sub board and see if there are any further trips when the sensor triggers the contactor.

 

[Lucien Nunes]

How many amps of lighting load is it supplying?
Is the MCB hot when it trips?
Does it trip with the downstream RCBOs off?
What are the insulation resistances of the submain to the small CU and the final circuits to the lighting?

If there was always a borderline overload on the 20A MCB, once it has tripped the first time it may be more likely to trip again and again, but as it's only borderline it takes an hour to heat up.

 

[sid1968]

Yes Wilco the all the lights do come one but trips about hour. Will ckeck if mcb gets warm or the contactor

 

[plugsandsparks]

Clamp it to find out what current it is seeing

 

[sid1968]

Ok il put a clampmeter on it

 

[DT1991]

Have you checked the outside sensor for water ingress?

By the sounds of your description the sensor is supplied from the 20A submain

 

[sid1968]

Yes the sensor is supplied from a sub main. Would it still trip the MCB if ther is water ingress???

 

[DT1991]

It really is a process of inspecting and testing what the submain is supplying.

Previous posts highlight other things I would also be looking at.

 

[sid1968]

Update::
Put a clampmeter on it showing pullin 6amp on the 20amp breaker and tripped after 15mins

 

[telectrix]

if the 20A MCB is tripping at 6A it's bin time, unless you have an intermittent short circuit, and the trip occurs before it registers on the clamp meter.

 

[sid1968]

I have tried a different 20amp breaker and still trips
What would cause a intermittant short??
Would ingress cause 20amp breaker to trip??

 

[radiohead]

Have you carried out any IR tests on the wiring?

 

[sid1968]

This breaker is for all ouside lighting ,bollards, lamposts and wall lights all on 1 sensor. Some 2 bollards damaged ie cars reversed in to them etc
Trying to locate the orginal electrician so he he cn shed some light where the junction boxes and joints are
[automerge]1582739359[/automerge]
This breaker is for all ouside lighting ,bollards, lamposts and wall lights all on 1 sensor. Some 2 bollards damaged ie cars reversed in to them etc
Trying to locate the orginal electrician so he he cn shed some light where the junction boxes and joints are

 

[radiohead]

Have you carried out any IR tests on the wiring? (again)

 

[sid1968]

What i have noticed in the photocell sensor noticed littled burning sign on the the small circuit board
Going to bypass and chk