gkenyon:

 

A supply to an alarm system or control system is definitely a power circuit. The function of the circuit is definitely not not "signalling and control".

 

I see what you are saying here in that the part of a circuit from the CU to the FCU has a solely power-supplying purpose, much like a distribution circuit. And that the part of the circuit past the FCU, which, because it has its own OCPD and can be considered to be a circuit in its own right, can have the reduced minimum CSA of 0.5 or 0.1mm2. But you mentioned in your earlier post that the fuse in the FCU would/could be redundant and if manufacturers' instructions do not specify an FCU, then it could be omitted, making the whole circuit from the CU a "signalling and control" circuit.

Also, the definition of a circuit in BS7671 states that more than one OCPD can be incorporated in a circuit, therefore irrespective of whether an FCU is used, the purpose of the whole circuit from the CU could be defined as a "signalling and control" circuit.

I am not nit picking, just pointing out apparent inconsistencies in BS7671, I agree with Andy in the thread I linked to earlier, it would make sense if BS7671 defined power circuits etc but it doesn't.

 

gkenyon:

 

A supply to an alarm system or control system is definitely a power circuit. The function of the circuit is definitely not not "signalling and control".

 

I see what you are saying here in that the part of a circuit from the CU to the FCU has a solely power-supplying purpose, much like a distribution circuit. And that the part of the circuit past the FCU, which, because it has its own OCPD and can be considered to be a circuit in its own right, can have the reduced minimum CSA of 0.5 or 0.1mm2. But you mentioned in your earlier post that the fuse in the FCU would/could be redundant and if manufacturers' instructions do not specify an FCU, then it could be omitted, making the whole circuit from the CU a "signalling and control" circuit.

Also, the definition of a circuit in BS7671 states that more than one OCPD can be incorporated in a circuit, therefore irrespective of whether an FCU is used, the purpose of the whole circuit from the CU could be defined as a "signalling and control" circuit.

I am not nit picking, just pointing out apparent inconsistencies in BS7671, I agree with Andy in the thread I linked to earlier, it would make sense if BS7671 defined power circuits etc but it doesn't.