Strange smoke detector fault ADVICE NEEDED!

[CookyMan9999]

Hello People, wonder if you can help?

I have got a fault on a smoke detector circuit... wired 1.0 t+e from cu to 1st smoke then 3 core up to next smoke. IR tested and clear on every cable to N and to CPC and to eachother

When you put power on with no smoke heads up it holds.

When you put one smoke head on it trips one RCD

When you put the other head on it trips both RCD's

I tested where the cables go and they are definitely the right cables. There are no crossed Neutrals in the CU and i tried the smoke heads in different properties and they are fine.

So now im stumped any ideas? Thanks anyone who reads/replies...

 

[mikeyd]

You sure the neutral is in the correct terminal block in the consumer unit?

 

[flameport]

If both RCDs trip, there must be an interconnection between them. Probably a neutral in the wrong place.

As for one / both RCDs tripping - probably because the current drawn by a smoke alarm is tiny, so 1x alarm is just enough to trip the first RCD. The second RCD trips at a slightly higher current, so only trips with both alarms in place.

 

[ColJack]

smokes / fire alarms shouldn't be on RCD's anyway.. they are one of the few that should be on JUST and MCB..
the cabling needs to be installed to suit not being RCD protected also ( ie in conduit / earthed metalic sheath. etc.. )

 

[Chri5]

smokes / fire alarms shouldn't be on RCD's anyway.. they are one of the few that should be on JUST and MCB..
the cabling needs to be installed to suit not being RCD protected also ( ie in conduit / earthed metalic sheath. etc.. )

Or on an RCBO on the direct side of the board

 

[ColJack]

nope, won't put them on then either..
they are a safety device and won't under normal use be contacted by a person so the need to RCD is an invalid one in my opinion and will cause more problems than it cures..

 

[CookyMan9999]

thanks for replies, yea checked again the cables bell out and are on right side of CU....

Do you think by any weird and wonderful way like anything else could cause it?

maybe when cables installed they got pulled next to others and burned causing fault?

next thing is to run a wander lead and just see if it holds

cheers