IET announces new amendment to BS 7671 (IET Wiring Regulations)

I think it's simply not clear.

Agreed!

 

Is "additional protection" a form of ADS anyway

I'd suggest not. They're two different concepts. ADS (as described by 411) requires c.p.c., earthing and protective devices co-ordinated with Zs - additional protection doesn't demand any of that and can be applied to situations where there's no ADS at all - e.g. circuits protected completely by double or reinforced insulation (non-domestic of course) - e.g. called up the cables concealed in a wall regulations.

 

BUT then again it could be argued that a fuse "blowing" does not, strictly, provide isolation ...

Absolutely. I've seen some BS 3036 fuse carriers where the ceramic "shield" around the fusewire as been so "spattered" with condensed(?) copper after the fusewire blew I'd wondered if it wasn't conductive itself - likewise some ruptures are so gentle that you only get a tiny gap in the fusewire. Eitherway the achievement of a 3mm+ gap and associated creepage clearances don't seem to be reliably achievable. I'm not sure of the effect of sand (or similar) in cartridge fuses, but would suspect again that we don't necessarily end up with a clear 3mm gap equivalent. There's been no suggestion of outlawing fuses for ADS, so I have a fairly strong suspicion that only manual isolation is being asked for.


  - Andy.

I think it's simply not clear.

Agreed!

 

Is "additional protection" a form of ADS anyway

I'd suggest not. They're two different concepts. ADS (as described by 411) requires c.p.c., earthing and protective devices co-ordinated with Zs - additional protection doesn't demand any of that and can be applied to situations where there's no ADS at all - e.g. circuits protected completely by double or reinforced insulation (non-domestic of course) - e.g. called up the cables concealed in a wall regulations.

 

BUT then again it could be argued that a fuse "blowing" does not, strictly, provide isolation ...

Absolutely. I've seen some BS 3036 fuse carriers where the ceramic "shield" around the fusewire as been so "spattered" with condensed(?) copper after the fusewire blew I'd wondered if it wasn't conductive itself - likewise some ruptures are so gentle that you only get a tiny gap in the fusewire. Eitherway the achievement of a 3mm+ gap and associated creepage clearances don't seem to be reliably achievable. I'm not sure of the effect of sand (or similar) in cartridge fuses, but would suspect again that we don't necessarily end up with a clear 3mm gap equivalent. There's been no suggestion of outlawing fuses for ADS, so I have a fairly strong suspicion that only manual isolation is being asked for.


  - Andy.