Earthing In Smoke Detector Circuits

[jamieb100]

I have come across a mains operated battery backup smoke detector circuit where the earth has been used as the interlink cable. Where do I stand as to wether to connect it back into a new fuseboard in the near future?

 

[riveralt]

I have come across a mains operated battery backup smoke detector circuit where the earth has been used as the interlink cable. Where do I stand as to wether to connect it back into a new fuseboard in the near future?

What you are saying doesn't make sense. What has the smoke detector interlink got to do with connecting it back to the cu?
I take it we are talking about 1mm2 T&E where instead of using three core and earth the 'electrician?' has used the earth cable to link the first smoke detector to the second.
Is the earth cable sleeved in brown by chance?

 

[jamieb100]

Hi, yes it is 1mm t&e. The earth is still sleeved with earth sleeving. But as this is now used as the interlink there is no earthing on the circuit.

 

[Alarm]

Its a bodge.
Do NOT connect it back into the earth on the CU.

Time for a rewire, or go for the Aico radio link stuff and then earth correctly.

Seen this so many times now, fooking dire.

 

[jamieb100]

Thanks for the advice.

 

[riveralt]

Hi, yes it is 1mm t&e. The earth is still sleeved with earth sleeving. But as this is now used as the interlink there is no earthing on the circuit.

Most smoke detectors do not need an earth - however they normally provide a terminal block for the earth to run through the smoke detector circuit - this means you can conduct the appropriate tests at the end of the circuit.

Assuming it is a standalone circuit in broad termis it should run as follows:
1mm2 T&E from the consumer unit mcb to the first detector. L to L N to N and E to the Earth terminal block.
From the first to the second detector - 3 Core and Earth should be run with the L to L N to N and Interlink to interlink. Earth continuity would also be maintained.

So as a bodge replace the interlink earth with a brown sleeve - or replace the interlink cable with proper three core and earth.