RCD Trip Query

[Aragorn84]

So our garage has finally been rewired by the landlord, and i decided today to hook up an extra pair of fluroescents to the new wiring.

The installation has a basic 17th dual RCD board in the house and then a "Garage CU" in the garage with another RCD and then two breakers, a B32 for the sockets and B6 for the lighting. I know the doubled RCD's isnt ideal, but i wasnt paying the bill, so i didnt get a say in the matter.

I turned the B6 off, and set about running some cable between the existing light fittings and my additional fittings. I tested for dead, and set to it, and as i was pulling the cable into the fitting i managed to touch the neutral and earth conductors together, which tripped both RCD's

Now in hindsight i should have turned the main switch off on the garage board, but i was using the ring for some backup lighting, and having tested for dead wasnt thinking anything would happen.

I've been thinking about it, and all i can come up with is that because the neutral isnt switched off by the lighting MCB, when i've touched them together i've created a path which has caused some of the current flowing thru the ring to flow to earth instead of back thru the RCD? The RCD has noticed this and done its job?

Obviously i'd have expected it to trip had it been live, but i wasnt expecting it because it was the neutral!

Is my assumption correct? Is that normal?

 

[holmslaw]

..

 

[rebuke]

Yes this is perfectly normal - neutral to earth linkage will trip RCDs for exactly the reason you stated...

It's one of the reasons why single RCD boards have essentially been banned by the regs, because a neutral-earth fault on any circuit breaks everything.

Incidentally though - does your landlord know you're altering his installation by adding light fittings?

 

[Aragorn84]

Thanks guys

 

[Taylortwocities]

Incidentally though - does your landlord know you're altering his installation by adding light fittings?

I think we know the answe to that one

 

[securespark]

Never mind adding the light fittings, does the LL know about the green pettikins that will be nurtured under the light fittings?

 

[Aragorn84]

ROFL!

I'd be needing a bit more than two 5ft fluros to be experimenting in horticulture!

The landlord wanted the bare minimum of lighting for his garage, and the two 4ft tubes werent particularly bright. I had already purchased a pair of 5ft fittings months ago while waiting for the rewire, and was until now running them from some flex and a 13A plug.

I'll just put it all back the way it was when i leave and there wont be a problem!