Intermittent mcb trip electric gate

[mickponte]

Hi, just registered, I qualified in 1973 and and not done much electical work for the past 30 odd years but I obviously have grasp of the theory.

I have an intermittent mcb tripping on my electric gate, which I installed. (All electric no hydraulics)
The mcb will trip in any weather conditions and can go days or weeks without tripping.
Sometimes it is the ocassional trip out, sometimes it is regular over a period of days then it might go a few days or a week before it happens again.
It happens when the gate is at rest and it has not happened when it is opening or closing but I think this is just coincidence and it could happen.
The gate was installed about 5 years ago and has worked ok up til now.

I have changed the mcb. There is no RCD. ( bad idea I know I will install one when Ive fixed this problem) The gate is 230v the breaker is 15amp. The safety circuits are 24vac I have changed the 230/24v transformer. The gate draws 0.03 amps at rest.
I have connected a temporary supply cable via an outside socket and this makes no difference.
I have tried disconnecting the earth and this makes no difference. But I wonder if it could still be an earth fault via the motor housing which is metal and is welded to a 20ft RSJ girder which is sunk in the ground, but then again how could it be, I have tried disconnecting the earth at both the motor end and the consumer unit. I do not have anything to test with except a multimeter.

Any advice gratefully recieved - thanks - mick

 

[Andy-1960]

Have you checked all of the cable entry points to make sure they are 100% sealed? I had a similar issue with slugs entering a gate controller panel and crawling over live connections. Slugs conduct quite well and end being blown to oblivion when they short things out. I fill all of the cable entries with silicon to prevent them getting in.

 

[mickponte]

thanks for that, Ill check, but I did have a 1amp fuse blow on the circuit board and I could see what was left of the slug, what baffles me is how the breaker will reset then go for days or weeks and then trip again

 

[mart spark]

Could it possibly be a spiders Web shorting between line and neutral? Just a thought, heard of it happening in sockets. May explain the intermittent tripping of mcb

 

[Wilko]

I have connected a temporary supply cable via an outside socket and this makes no difference.

Hi - does this mean the outside circuit’s MCB tripped when you did this?

 

[mickponte]

Hi, Matt Spark and Wilko, sorry for net gettin back to you computer kaput vista stopped working sorted now. Spiders web - good idea, Ill have a good look in the motor housing where all the cables and connections are. Do you think this could trip a 15am mcb before the web blew.
Regards the outside socket supply, it tripped the socket mcb not the gate mcb which I had disconnected from the gate circuit board.
Thanks

 

[plugsandsparks]

As it is happening at rest, i would suspect cable damage / water ingress to cable etc. The cable needs to be isolated both ends and IR tested, then you know where you stand.

 

[Bobster]

Agree with @plugsandsparks, likely water ingress somewhere, every time it clears it also clears the fault.

Likely if you had an RCD installed you wouldn't be able to reset the circuit.

 

[Toneyz]

and test for faults

Hi, just registered, I qualified in 1973 and and not done much electical work for the past 30 odd years but I obviously have grasp of the theory.

I have an intermittent mcb tripping on my electric gate, which I installed. (All electric no hydraulics)
The mcb will trip in any weather conditions and can go days or weeks without tripping.
Sometimes it is the ocassional trip out, sometimes it is regular over a period of days then it might go a few days or a week before it happens again.
It happens when the gate is at rest and it has not happened when it is opening or closing but I think this is just coincidence and it could happen.
The gate was installed about 5 years ago and has worked ok up til now.

I have changed the mcb. There is no RCD. ( bad idea I know I will install one when Ive fixed this problem) The gate is 230v the breaker is 15amp. The safety circuits are 24vac I have changed the 230/24v transformer. The gate draws 0.03 amps at rest.
I have connected a temporary supply cable via an outside socket and this makes no difference.
I have tried disconnecting the earth and this makes no difference. But I wonder if it could still be an earth fault via the motor housing which is metal and is welded to a 20ft RSJ girder which is sunk in the ground, but then again how could it be, I have tried disconnecting the earth at both the motor end and the consumer unit. I do not have anything to test with except a multimeter.

Any advice gratefully recieved - thanks - mick

Get hold of an installation resistance tester and test for low insulation readings disconnecting the earth is not a good idea.

 

[Lucien Nunes]

I have tried disconnecting the earth and this makes no difference.

Dangerous! You have an intermittent but substantial low-resistance fault possibly to the gate metalwork. If the MCB did not trip during a fault event, the motor housing and some of the surrounding metalwork and even the ground could become live.

Could it possibly be a spiders Web shorting between line and neutral?

No. It takes a piece of copper wire the thickness of a paperclip to repeatedly pop 15A OCPD without fusing itself. The resistance of a spider's web is probably billions or trillions of times too high to do that. Repeated heavy buildups of webs could possibly start a progressive carbonisation trail over damp insulation, but that would be a pretty extreme and spectacular situation. More likely a damaged cable or water ingress.

If the fault is bad enough to trip a 15A MCB you might will find evidence of it with just a multimeter, although an insulation tester is the proper tool.

 

[Toneyz]

My monies on the slug then

 

[Deleted member 105166]

Agree with @plugsandsparks, likely water ingress somewhere, every time it clears it also clears the fault.

Likely if you had an RCD installed you wouldn't be able to reset the circuit.

You could test this easily by going back to your outdoor socket supply with a plugtop RCD adaptor

 

[R-fur]

Has anyone thought of a faulty MCB? it does happen. Try swapping with another in the consumer unit.

 

[Lucien Nunes]

The OP says he tried changing it in post #1. This is likely a simple problem of a kind that is as old as electricity itself: Two bits of metal are touching together that shouldn't, or leakage through moisture has caused an insulation breakdown that has progressed to the point of not being insulation at all any more. It needs a thorough visual and an insulation test.