problems with lighting contactor

[dts71]

Hello guys. This is my first post on any forum so please go easy on me.
Thanks in advance for any help.

I'm a domestic electrician and so never have to deal with contactors but I'm doing a job for a friend of a friend and the lighting contactor ( Ac, 25A, 4 pole - L/N L/N ) goes: on off on off on off... quickly. It's one of those nightmare faults that 'only happens sometimes' . obviously never when I'm there.



First I checked voltages. No probs.
Checked wiring. No probs. ( apparently the polarity of a1 and a2 doesn't matter)
I changed the contactor for a new one but this morning I got a call saying that the new one was doing the same.

I've read online that fluctuating voltages can cause the Relay to let go but I haven't witnessed the issue so i'm not sure.
Apparently now the lights are off permenantly and the contactor is silent. (Presumably burnt out).
They did have a rodent problem a couple of months back but couldn't find any obvious damage on my checks.

Does anyone know what would cause this? Should I start ripping the place apart to find a chewed cable?
Also, is it possible for me to split the lighting loads to much lower levels and just whack them on their own circuits on a 3 or 4 gang switch?
Sorry if the answer is obvious and I sound stupid but I never have to deal with contactors.
Thank you for your time, the help is much appreciated.

 

[telectrix]

start with a thorough test of all associated cables. IR and continuity.

 

[Bobster]

What is it that's energising the contactor? Usually a volt free contact on something, PIR etc... this is where I would first look.

However if they have had rodent problems, testing the cables wouldn't be a bad start.

 

[dts71]

Thanks guys. Yes, I'm due there first thing tomorrow so I'll begin by testing both lighting circuits thoroughly. They were about to close when I was there the other day so I didn't have time to pull it apart.
Seems the best thing, think I'm just freaking out coz I'm not used to contactors.
The control circuit just goes through a 1 gang switch by the front door.
Thanks again.

 

[Plonker 3]

What test equipment do you own?

 

[dts71]

Hi dillb. Fluke 1652c so shouldn't be a problem to test just seemed strange to me that the contactor would behave like that but no tripping on mcbs.
Thanks.

 

[Farmelectrics]

what tests have you done

 

[ayjay]

check the coil circuit
if its switching on and off continuously there must be a fault there

 

[Richard Burns]

If the coil is switched by a standard light switch then I would be initially considering that the light switch was not closing properly and is sparking a bit and causing the coil to chatter. Either that of there is a loose connection on the coil supply somewhere.
Unless the coil is also fed from the lighting circuit, maybe as a latching method, then it is unlikely to be the lighting circuit at fault since the contactor would not care what was being fed through the contacts.

 

[Darkwood]

Loose switch wire or N somewhere would be my guess, check from origin to source and any switch points, if the old one was doing this it would make sense to confirm all is well before replacing, not replacing then finding you still have the same problem.

 

[Deleted member 72666]

If wired correctly and continuous then my money is on the switch.

 

[Guest111]

I'd say switch first followed by a neutral fault,if there is a bit of dust in the switch this will cause the problem.

 

[dts71]

Thanks for your help guys.
My test on the switch is fine, I tested the control circuit which is ok. But I just found a borrowed neutral from the toilet light upstairs on the load side. I was convinced that it must be the control but borrowed neutrals cause me all kinds of headaches so i'm guessing it's that. Would a borrowed neutral on the load side cause the Relay to engage and disengage? Just seems confusing as the contactor is essentially just a heavy duty switch so I wouldn't think it would affect the Relay. Sorry if I'm being stupid, as I say I have no experience of contactors.
Thanks again dudes.

 

[Richard Burns]

Think about what you have for your two circuits.
One circuit energising the coil via a manual switch.
One circuit energising your load by the closing of the contactor contacts.

These circuits are electrically different they are only mechanically linked by the contactor operation.
They do share a common supply at origin (or DB) but that is immaterial. Would you expect your house lights to flash on and off because of something you plugged into a socket (excluding common protective devices such as upfront RCDs)?

 

[dts71]

Hi. Sorry I haven't been on for a while. I've been ill this week and been run ragged at work. Thanks to everyone for your help, I found the problem last Friday.
While I was going around disconnecting the lights (they were wired straight in. No tails. ....aaaarrrrggg!!!) I found one of those lovely spaghetti junctions shoved down a wall. There were crossed neutrals and all sorts.
One of the worst connections I've ever seen. I still don't even know how it worked at all.
I rewired that, rewired the switches and tested everything. A week later and all good.
Invoice time!!!
Thanks again everyone for all your help.
Laters.