Rcd tripping in offices

[mgnelec09]

Hi there.

I have been investigating a job where I am struggling to find any thing wrong with the wiring/installation.

It is a dual CGD split board with the non rcd circuits on top and the rcd protected circuits below.

The constant problem is that when the lights are switched on at the switch, it sometimes takes out the rcd, and also sometimes happens when other lights are switched on.

I have tesed all three lighting circuits and all three socket circuits and all seems fine.

I have checked the klick ceiling roses and light fittings for loose connections.

I have also carried out earth loop tests, rcd test and continuity on the 3 ring mains.

All the readings are fine.

The rcd test also prove that the rcd unit is working correctly and the tripping times are good.

My theory is that when the light fittings are being switched on, the start up current is affecting the rcd as the are 600x 600 modular flourescent fittings throughout.

Any advice would be good. Many thanks

 

[telectrix]

RCds don't like florries at the best of times. can you not divert the lighting to the non-RCD side? ( assuming the buried in walls<50mm is not an issue)

 

[mgnelec09]

Hi,

Yes thats the problem, the lights are already on the non rcd side, although the neutrals are linked.

The main 25mm tails go into the top of the main isolater switch, then from the botom of the main switch there is two neutral link cables, one goes straight up to the non rcd circuit neutral bar then the other goes into the top of the rcd/rccd alond with a live tail to feed the rcd protected circuits.

Then out of the bottom of the rccd obviously you have the rcd protected busbar, then a neutral tail which goes to a separate neutral bar for the protected circuits.

I think the neutral is getting some feed back from the lighting circuits, then disrupting the rcd when both the rccd and the main switch are in the on position.

it doesnt seem to happen all the time, mainly in the morning when the lights are switched on from cold

 

[mgnelec09]

I guess we should have some more that is best.

EH??????????

 

[telectrix]

i thought that. to get back... have you tried ramp test on RCD. could have some leakage on it's own circuits.

 

[SimpleSimon]

How long has the problem occured and how long before the problem was the office in normal operation?

 

[mgnelec09]

yes I tried the rcd auto ramp test, results being around 32.0 x1, 12.0 at 5x,

did this on all three socket ring mains, but nothing out the ordinary.

could I maybe change the rccd for a 100 amp main switch and put the ring mains on their own rcbos?

Also with it being an commercial office block, is it essential for the ring mains to be rcd protected?although there is a small kitchenette and cleaners sockets in small corridor- these will need to wont they?

 

[SimpleSimon]

yes I tried the rcd auto ramp test, results being around 32.0 x1, 12.0 at 5x,

did this on all three socket ring mains, but nothing out the ordinary.

could I maybe change the rccd for a 100 amp main switch and put the ring mains on their own rcbos?

Also with it being an commercial office block, is it essential for the ring mains to be rcd protected?although there is a small kitchenette and cleaners sockets in small corridor- these will need to wont they?

The ring doesn't have to be on RCD as it can be classed as being supervised under a skilled person. But that would be your decision to make.
Putting them on their own RCBO's may not solve the problem as you may still get feed back. I'd be thinking why it's started now and not before? unless the light fittings have changed?

 

[mgnelec09]

No the light fittings are the same.

The whole installation was completed in 2008, so not very old.

after examining all the light fittings I have noticed that some of the tubes are looking like they are on their way out as they are starting to blacken a little near the end.

Maybe this could affect them starting?

 

[SimpleSimon]

Possibly. Maybe a lag in the start up current could be causing an inbalance.
Change the tubes first, see if that does anything.

 

[Engineer54]

Possibly. Maybe a lag in the start up current could be causing an inbalance.
Change the tubes first, see if that does anything.

Agree, tubes coming to the end of their useful life take more starting current, and if you have a large number of tubes on those lighting circuits starting up from cold, you could very well get a good enough inbalance. Especially if they are switch start fittings... Sometimes i wonder if the amount of RCD devices we have these days, are worth the hassel they can cause...lol!!

 

[jaresquire]

Its all work though, E54!

 

[mgnelec09]

Thanks for your help,

Would you leave the rcd as it is and replace all the tubes?

Or could I remove the rcd and install an isolator switch as it is a commercial job in case the problem re-occurs?

Its just that there are 2 sockts in the kitchenette and 2 in corridor for cleaners-surely these would have to be protected?

 

[SimpleSimon]

I would first look at the tubes.
See it this way, since 2008 what has changed in the installation to cause the tripping? Nothing you say. You've tested all circuits which are coming out fine so it would only point to accessories on those circuits. Aka the tubes. Think your best replacing these first, than if it don't work you can at least cross it off your list.

 

[malcolmsanford]

yes I tried the rcd auto ramp test, results being around 32.0 x1, 12.0 at 5x,

did this on all three socket ring mains, but nothing out the ordinary.

could I maybe change the rccd for a 100 amp main switch and put the ring mains on their own rcbos?

Also with it being an commercial office block, is it essential for the ring mains to be rcd protected?although there is a small kitchenette and cleaners sockets in small corridor- these will need to wont they?

That is not a ramp test that is the functional test for the RCD, you should do a ramp test, as that will tell you how many mA it takes to trip the RCD. If you have a 30mA RCD then I would want the unit to be tripping over 20mA, anything under and you may have a problem.

As for the sockets, you could just change the sockets in the kitchen and for the cleaners to actual RCD sockets and then put the rest on just MCB protection.