The circuit that provides power for the smoke alarms or alarm panel must be a power circuit, as it provides power to that equipment.

Hence my point about any signalling or control circuit drawing some power in order to operate - where do we draw the line? If everything that draws power is a power circuit then there seems little room left for signalling or control circuits. Is the supply to a relay coil power or a signal? - or to an indicator lamp? or to a TTL input? All require a current flow.


In many ways it shouldn't matter - if power and lighting circuit are operating with similar protective devices in similar environments it doesn't really make sense for the c.s.a. requirements to be different.


I can perhaps see that there's perhaps an issue with energy let-though with MCBs which the UK has traditionally glossed over = but a 1.5mm min c.s.a. regardless of type of protective device or circuit arrangement isn't really a proper solution to that either. Likewise if it's a physical robustness concern 1.5mm² might be reasonable for pulling singles into conduit like the French do, but there doesn't seem to be a good reason for specifying anything higher than 1.0mm² for the sheathed cables that are normal UK practice.


   - Andy.

The circuit that provides power for the smoke alarms or alarm panel must be a power circuit, as it provides power to that equipment.

Hence my point about any signalling or control circuit drawing some power in order to operate - where do we draw the line? If everything that draws power is a power circuit then there seems little room left for signalling or control circuits. Is the supply to a relay coil power or a signal? - or to an indicator lamp? or to a TTL input? All require a current flow.


In many ways it shouldn't matter - if power and lighting circuit are operating with similar protective devices in similar environments it doesn't really make sense for the c.s.a. requirements to be different.


I can perhaps see that there's perhaps an issue with energy let-though with MCBs which the UK has traditionally glossed over = but a 1.5mm min c.s.a. regardless of type of protective device or circuit arrangement isn't really a proper solution to that either. Likewise if it's a physical robustness concern 1.5mm² might be reasonable for pulling singles into conduit like the French do, but there doesn't seem to be a good reason for specifying anything higher than 1.0mm² for the sheathed cables that are normal UK practice.


   - Andy.