AJJewsbury:

Andy thanks for the response.


BS7671:2018 states


"Voltage, nominal. Voltage by which an installation (or part of an installation) is designated. The following ranges

of nominal voltage (rms values for AC) are defined:"

– Extra-low. Not exceeding 50 V AC or 120 V ripple-free DC, whether between conductors or to Earth.

– Low. Exceeding extra-low voltage but not exceeding 1000 V AC or 1500 V DC between conductors, or

600 V AC or 900 V DC between conductors and Earth.

– High. Normally exceeding low voltage.


For the protective conductor not to be categorized into one of these groups it would mean that the protective conductor is not part of a system that has a designated nominated voltage. If that is the case then I agree however I am unable to find something to back this up in BS7671, perhaps this is further defined somewhere else ?

Sometimes you have to work things out from what isn't said.


Firstly protective conductors don't have a nominal voltage - in most systems (e.g. ADS) they carry the potential to which the system is nominally referenced (typically "Earth"). If you do want to consider the actual (rather than nominal) voltages that a protective conductor might carry (above true Earth say) then you'll find that it's not particularly related to the circuit's/system's nominal voltage either as potentials may be imported from other circuits, or other installations or even HV faults from the distribution system - so that doesn't help either.


Then consider why you'd want to allocate them to a voltage band - normal reasons would be for rating of functional insulation and acceptable approaches for shock protection - neither of which generally apply to protective conductors as they have no requirement to be insulated either for functional or safety reasons (the requirement for smaller protective conductors to sheathed with the equivalent of basic insulation is purely for mechanical and corrosion protection).


   - Andy,

 

AJJewsbury:

Andy thanks for the response.


BS7671:2018 states


"Voltage, nominal. Voltage by which an installation (or part of an installation) is designated. The following ranges

of nominal voltage (rms values for AC) are defined:"

– Extra-low. Not exceeding 50 V AC or 120 V ripple-free DC, whether between conductors or to Earth.

– Low. Exceeding extra-low voltage but not exceeding 1000 V AC or 1500 V DC between conductors, or

600 V AC or 900 V DC between conductors and Earth.

– High. Normally exceeding low voltage.


For the protective conductor not to be categorized into one of these groups it would mean that the protective conductor is not part of a system that has a designated nominated voltage. If that is the case then I agree however I am unable to find something to back this up in BS7671, perhaps this is further defined somewhere else ?

Sometimes you have to work things out from what isn't said.


Firstly protective conductors don't have a nominal voltage - in most systems (e.g. ADS) they carry the potential to which the system is nominally referenced (typically "Earth"). If you do want to consider the actual (rather than nominal) voltages that a protective conductor might carry (above true Earth say) then you'll find that it's not particularly related to the circuit's/system's nominal voltage either as potentials may be imported from other circuits, or other installations or even HV faults from the distribution system - so that doesn't help either.


Then consider why you'd want to allocate them to a voltage band - normal reasons would be for rating of functional insulation and acceptable approaches for shock protection - neither of which generally apply to protective conductors as they have no requirement to be insulated either for functional or safety reasons (the requirement for smaller protective conductors to sheathed with the equivalent of basic insulation is purely for mechanical and corrosion protection).


   - Andy,