Lights keep tripping

[mihobb]

Hi guys I am looking for help.
I have a problem with outdoor commercial lights. They are wired from DB on 63A CB. It goes to photocell through contactor (also override switch). Then it goes through 6A CB and to the lights (12 x 5foot twin + 4 downlighters). The problem I have is that when photocell activates the lights 6A CB trips. When I reset this CB lights stay on until morning when the photocell deactivates lights. Current is 4,3 when lights are on and there is no sign of overload. Even when I tested (by covering) photocell during the day amp meter did not detect overload on the circuit when CB tripped. What is strange for me is that CB doesn't trip every time. I've changed 6A CB but it keeps tripping. Resistance on the contactor contacts is good but I don't suppose this would cause tripping CB that is wired in before it. I don't think there is earth fault in the circuit as it would trip CB every time. I could not carry out insulation resistance test of the circuit yet due to H&S reasons on site ( it is a long process within company ). I would appreciate any ideas what might be causing tripping CB..

 

[Richard Burns]

If your running current is 4.3A then your initial starting inrush current could momentarily reach 200A which is enough to trip the breaker.
If it was working before then one of the ballasts current limiting may have failed.
If it never worked then see if the circuit can take a 6A type C or a 10A type C.
If it is only occasional tripping then this is the likely cause, the inrush current may be enough to trip.

 

[Engineer54]

I could not carry out insulation resistance test of the circuit yet due to H&S reasons on site ( it is a long process within company ).

Never heard of anything so ridiculous!! This system is for outdoor lighting right, so why have the H&S morons put restrictions on qualified electricians from carrying out insulation resistance testing??

RB ...good call!! lol!!

 

[Darkwood]

Agree ... .why in the world would H&S have any involvement with insulation testing final circuits never heard anything so ridiculous if its true... as a matter of interest why do you need permission to perform such a test as this will virtually restrict all electrical works from happening?

Answer Richards questions first but aa mentioned i assume its accumulative in rush.

 

[mihobb]

Engineer54 - H&S is more about acces to junction boxes in high level for further inspection, this instalation is too old. It is on the railway bridge.

Richard - It worked fine before, it only tripped every now and then. Now it keeps tripping quite often. I was wondering wether there might be fault on photcell or contactor. But it doesn't make sense asnthese two are wired before CB.

 

[mihobb]

Lights are on the railway bridge, high level with bad access.

 

[itselectric]

Nothing to do with fault here, but on first pic on post 1 there is only 1 neutral and 2 mcb's with a cable in each. Is there a borrowed neutral.

 

[mihobb]

I noticed that when I was rewieving pictures at home. I need to have look in to the board this week why it is wired like that.

 

[Richard Burns]

Richard - It worked fine before, it only tripped every now and then. Now it keeps tripping quite often. I was wondering wether there might be fault on photcell or contactor. But it doesn't make sense asnthese two are wired before CB.

So the situation has changed but it was tripping a bit before.

The circuit was probably right on the borderline and now something in one of the fittings (or possibly the cable, but not likely) has started to deteriorate and is drawing slightly more power on start up.

Unlikely to be the contactor as this would have to fail very badly to trip the lighting breaker.
If it were the photocell then the contactor would need to be on all the time and the photocell would be controlling the full load which would be pointless. However you can check this by switching on the lights with the override and seeing if they still trip.

Other than that try looking at the fluorescent fittings' control gear for signs of overheating or water damage that may be affecting the ballast.

You should have a situation like the picture below for the wiring, bit it is not possible to tell from your photos.

This should demonstrate which part of the circuit the fault is in as the breaker that trips will be either the contactor /photocell supply or the light supply.

 

[gumdrop]

If your running current is 4.3A then your initial starting inrush current could momentarily reach 200A which is enough to trip the breaker.
If it was working before then one of the ballasts current limiting may have failed.
If it never worked then see if the circuit can take a 6A type C or a 10A type C.
If it is only occasional tripping then this is the likely cause, the inrush current may be enough to trip.

I agree with rb on this one, i would start by isolating the ballasts one by one (use half split technique) to find offending one. Good luck.

 

[Lucien Nunes]

Also suspect failing PFC capacitors in the florry fittings, that flash over or arc when the contactor first closes. These often degrade with time, usually they blow themselves out completely but not always. If any wirewound ballast is bad enough to increase the current by much, you will see it in the tube failing rapidly. I agree that it was probably already borderline, something is just taking it over the edge but if you can't do an IR test on old and suspect wiring 'for safety reasons', surely that makes it much more difficult and dangerous to find the problem?!

 

[big-steve]

Can't you use/borrow an inrush ammeter? See what happens when it first starts up?

 

[DomCallear]

Nothing to do with fault here, but on first pic on post 1 there is only 1 neutral and 2 mcb's with a cable in each. Is there a borrowed neutral.

Great eyes :smart:

 

[Darkwood]

It looks like the contactor has the 2 Neutrals to account for the missing one although yes borrowed it is unlikely the cause of the tripping. I would agree though its a poor standard to do that and a danger to other contractors.