Fault finding query

[dav1980]

Any thoughts on this would be a great help.

I've got a 4pole 300mA rcd feeding a DB section through a contactor. The section in question feeds a load of 250/400w hit fittings through SP mcbs (4 per mcb x5 ). There are some other circuits on there but I've ruled them out.

The problem being that the front rcd trips when the lights are switched through the controller/cell. I've removed the controller from the equation, tried bringing them all on 1 circuit at a time. This only works when I do it slowly. I was thinking its to do with all the control gear coming on at once

Ramp tested the rcd 210mA. This seems low to me so I'm going to change it over but is it normal to have such a high fault current from these fittings? Or maybe the contactor could be giving me some problems also?

cheers

 

[Leesparkykent]

Is it a 4pole contactor?

 

[dav1980]

Yes it's a 4 pole contactor. It's only purpose is to allow staff to switch everything off from behind the counter. I can remove this if its possible that it's causing the tripping.

 

[UKMeterman]

Dependsing which contact hits first you can imbalance the RCD in such a way that it thinks it has an earth fault, if the N for instance opens first, closes late then the earth leakage through the emc filters of the discharge lamps can be enought to trip out the RCD. Split the RCD protection into smaller single phase sections.

 

[davesparks]

If the N is opening first and closing last then he has a very bad situation on his hands!

OP, is this a fault on a new install or an existing install? Is there any particular reason for the contactor being 4 pole?

 

[dav1980]

Aaargh sorry no, the contactor is NOT 4 pole. To clarify I am switching these mcbs on with the switch /contactor on.

cheers

 

[UKMeterman]

The problem can still occour with single phase, google the rcd handbook

 

[dav1980]

The problem can still occour with single phase, google the rcd handbook

Wouldnt that particular issue only happen when switching the contactor though? I've got the power through the coil and then switching the breakers on and the rcd is tripping when I do this quickly.
Also tripping with the contactor on and the lights being brought on All at once through the controller.

Apologies I am extremely bad at explaining things lol!

 

[UKMeterman]

With the contactor you are switching every single emc filter on at the same time, each emc filter has a capacitor live to neutral, if you hit the peak of the mains when switching on there is a high dv/dt and I = C DV/DT be that the RCD or contactor, again the problem is so many l to N capacitors being turned on at the same time. Have a read of the publication I mentioned.

 

[Richard Burns]

HID lamps cause earth leakage but this should be no more than 2mA per CG so unless you have one hundred fittings it should not be that, however if some of the control gear is failing then the leakage may increase to an unacceptable level.
It would be worth seeing if changing CG would help, however if this is a constant problem then fitting staged delay on timers after the MCBs may solve the problem.

 

[UKMeterman]

The problem can still occour with single phase, google the rcd handbook page 37 onwards

 

[dav1980]

Thanks guys, I was wondering what the leakage on the fittings would normally be. So if 2mA x 20 fittings = only 40mA so is well under the 210mA my rcd is tripping at on the ramp test.

So so probably a combination of old control gear and possible contactor issue. What about my rcd? I thought I should be changing it as its tripping well under 300mA?

 

[UKMeterman]

Again, HID lamps make a lot of noise and there may also be a faulty one which is breaking down when the ignitor goes off at turn on, spikes of several KV. Please read the notes I mentioned above, and split the load into several RCDs so one fault does not cause darkness.

 

[dav1980]

Again, HID lamps make a lot of noise and there may also be a faulty one which is breaking down when the ignitor goes off at turn on, spikes of several KV. Please read the notes I mentioned above, and split the load into several RCDs so one fault does not cause darkness.

I get what you are saying , the ideal setup would be individual rccbs.

To put you in the picture , this site is one which very shortly will no longer be maintained by my company and as such I have been instructed to keep the spend to a minimum. All I'm looking to do is get the lights switching normally through the controller.

Ill remove the switch and contactor and replace the rcd , also get up and replace any dodgy looking parts in the fittings.

cheers

 

[UKMeterman]

Check to see if there are any duff lamps and get your megger out, see if any fittings are leaky to earth if so get your ladder out!

 

[dav1980]

Got a mewp hire next week so I'll see what's up there then. Lights are on 24/7 for the moment . Thankfully this site will be gone shortly , nothing but hassle from it.

 

[Leesparkykent]

Thanks guys, I was wondering what the leakage on the fittings would normally be. So if 2mA x 20 fittings = only 40mA so is well under the 210mA my rcd is tripping at on the ramp test.

So so probably a combination of old control gear and possible contactor issue. What about my rcd? I thought I should be changing it as its tripping well under 300mA?

Was the load disconnected when ramp testing the RCD?

 

[dav1980]

Was the load disconnected when ramp testing the RCD?

Yes mate.

 

[Leesparkykent]

Yes mate.

The BS requirements for RCDs states that the RCD should operate between 50% and 100% of its rated tripping current.

 

[dav1980]

The BS requirements for RCDs states that the RCD should operate between 50% and 100% of its rated tripping current.

So mines is tripping at around 70%. Might change it over anyway and hope for the best.