I'm sure there are metal enclosure versions of "REC" switches out there.

But ones that can offer shock protection by means of double or reinforced insulation? I'm thinking of TT supplies and TN ones where Ze isn't necessarily below 0.38Ω (e.g. traditional TN-S in the generic case).


Then there's the whole issue of relying on the DNO's fuse for ADS. BS 7671 seems strangely silent on the issue (there's no equivalent of 434.3(iv) or 433.3.1(iii) in section 411). It does say we can use the DNO's fuse for protecting conductors under fault conditions - where the DNO gives their agreement - but some DNOs are declining to give that agreement these days, instead recommending that customers use BS 7671's rules to allow the omission of fault protection (<3m and installed to reduce the risks of faults and fire to a minimum). Presumably they don't want to he held responsible if network changes alter Ze or they change their protective device. Even the 0.35Ω figure for PME supplies isn't guaranteed - but just a figure the DNOs aim to meet most of the time.


So in the context of not even really being able to rely on the DNO's fuse to protect property from faults, how sensible is it to rely on it to protect life? even on TN-C-S systems?


  - Andy.

I'm sure there are metal enclosure versions of "REC" switches out there.

But ones that can offer shock protection by means of double or reinforced insulation? I'm thinking of TT supplies and TN ones where Ze isn't necessarily below 0.38Ω (e.g. traditional TN-S in the generic case).


Then there's the whole issue of relying on the DNO's fuse for ADS. BS 7671 seems strangely silent on the issue (there's no equivalent of 434.3(iv) or 433.3.1(iii) in section 411). It does say we can use the DNO's fuse for protecting conductors under fault conditions - where the DNO gives their agreement - but some DNOs are declining to give that agreement these days, instead recommending that customers use BS 7671's rules to allow the omission of fault protection (<3m and installed to reduce the risks of faults and fire to a minimum). Presumably they don't want to he held responsible if network changes alter Ze or they change their protective device. Even the 0.35Ω figure for PME supplies isn't guaranteed - but just a figure the DNOs aim to meet most of the time.


So in the context of not even really being able to rely on the DNO's fuse to protect property from faults, how sensible is it to rely on it to protect life? even on TN-C-S systems?


  - Andy.