A local hall continues to have problems with fluorescent fittings tripping an up front 100mA RCD. The tails run from Meter to RCD and then to a TP&N MEM Metalclad Disribution Board (the supply is single phase, I guess the MEM was installed because of the number of ways required).

As the supply is TNS, is not a Domestic Install, and given that the all socket circuits are protected by 30mA RCBO's, my thoughts recently have been to do away with the up front RCD. It sounds like a cop out, and one that I would not normally consider, but its probably cheaper than replacing umpteen light fittings.
I have carried out tests on fixed wiring, and it is the lights causing the problem.
Your thoughts please

Regards

Julian

Can you not find the problematic fittings ?

-------------------------
Empty barrels make the most noise.

If the lights are leaking >50mA, your solution might need to include high integrity earthing for the lighting circuit....
- Andy.

sounds like dodgy capacitor!

Did your tests establish that disconnection times will be met without the RCD?

Yes, disconnection times not an issue, I wonder if the install was TT originally hence the 100mA RCD

I look after a few council installs and have noticed that all their installs (TNS) have an upfront 100ma RCD. Belt and braces I suppose!

I was just thinking maybe it's a left-over from a previous TT supply 74!

Dave.

The problem you have, is whether removal of the 100mA RCD would impair the safety of the installation.

I would say yes, (a danger) you would be removing a device for fire protection.
You would not be creating a danger if it were not there in the first place.
If you removed it, you would be using the power of the mains to blow hell out of whatever leakage was causing the RCD to trip in the first place.

6 - 10 - 30 mA (for direct-contact / life injury protection)

100 - 300 - 500 - 1000 mA (for fire protection)

Regards
jcm

Those poor old RCDs getting blamed for just doing their job. Can you smell burning coming from one of he fluorescent chokes yet?

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/

I know of at least one installational where the council electrician has come along to 'update' the install & removed a 60A switch fuse that was protecting a sub-main to an extension (with the feed to the switch fuse direct from the DNO meter) and replaced this by an 30mA RCD (I do mean an RCD ... not an RCBO or MCB/RCD combination). He has also replaced the board in the extension with a new board with a single 30mA RCD as the main switch!


So now, when the RCD's does trip ... the nursery nurses have to go to a locked switch room, find a set of steps to reach the feeding RCD which is 10 feet off the floor & re-set it. Meanwhile, 20 under 5's are running around in the dark....... mmmmmm thats much safer now!

Adrian

Sounds a bit overdramatic to me, an RCD not exceeding 300mA is a requirement for protection against insulation faults in section 422.3 headed 'Locations with risks of fire due to the nature of processed or stored materials' - I wouldn't normally expect a village hall to need this section implemented!

As the OP says the circuits meet disconnection times etc, I see there is no reason to suggest that the lighting circuits normal protective device would need back up from an RCD.

Ordinarily no - but in this case we already know there is at least 50mA of leakage present on the lighting installation - that would be enough to be very nasty in the wrong circumstances - the RCD is already telegraphing that problem.

Sort the leakage out and the 100mA RCD ceases to be a problem - and in reality, given fault currents gretar than 1 x Idn, would still be very effective at providing shock protection (although not compliant with BS 7671 fo additional protection)

Regards

OMS

-------------------------
Failure is always an option

I can see your point, but without the RCD, what is being refered to as 'leakage' probably caused by the gradual breakdown of insulation on a ballast, would simply become earth fault current in it's own due course and cause the lighting CPD to operate in the normal way.

For sure - it's just the period whilst it's becoming "earth fault current" that's dangerous - everyone will be dead long before there's enough current flowing to blow say a 6A Type B.

You wouldn't want to be touching any exposed parts and anything that might have escaped the bonding that's for sure. or any lighting circuit where the CPC may be a bit "iffy"

as i said, we alrady have 50mA flowing (at least) - we offer additional protection at 30mA - so we are already into dangerous territory as it stands

personally speaking, in a building type such as this, i wouldn't take it out - it's a retrograde safety action - sort out the leaky cap or ballast - or split up the circuits a bit more and install a few RCD's instead of the single unit currently

regards

OMS

-------------------------
Failure is always an option

How many fittings are there and how regular is the tripping? Could you disconnect one fitting and wait to see if the tripping stops? If tripping not stopped, re-connect and move on to disconnect the next fitting.....and so on....until problem fitting is identified.

The bill for your time is creeping up all the while mind you and it could be the last fititng that you try that is the problem.

John

At most non-RCD protected ballast failures I have attended there haven't been any dead bodies, or melted cpcs, usually just a popped CPD and a bit of a nasty smell from the offending item!




One would hope that the installation was properly installed in the first place and subsequently checked and maintained to prevent such issues!






I think the mA's here are irrelevant, there may already be sufficient current flowing to pop the 6A mcb, it's just that the RCD is operating first.

Of course the options to solve the issue are endless (money depending) but in my opinion the installation would not be necessarily be less safe from a BS7671 point of view with the removal of an RCD which was not required to be there in the first place.

I would tend to agree. The trip will be as a result of a developing earth fault from one or more of the fittings. It is far better to fix the fault(s) now, rather than removing the rcd and let the fault(s) develop into a possible fire.


Regards,

Alan.

regards

OMS

-------------------------
Failure is always an option