RCD socket outlet.

AJJewsbury:

That is exactly the point I was making, you cannot connect a RCD to a circuit and installation that is not adequately earthed and bonded or else a fault elsewhere in the installation may raise the voltage of earthed equipment downstream of the RCD to dangerous levels, a RCD does not remove the requirements for basic and fault protection along with the requirement to mitigate touch voltages.

The point I was attempting to make was than even in a fully correctly earthed & bonded installation a fault elsewhere can raise the exposed-conductive-parts downstream of the RCD (as elsewhere) to dangerous levels - e.g. >115V for 5s in a TN system or 230V for 1s in a TT system -  the 'mixed disconnection time problem' isn't just something for inadequately earthed/bonded installations to worry about.


There is some advantage in having all your RCDs close to the MET (with the minimum of parallel paths on the c.p.c.s) - in that faults on your circuit are covered by the rapid disconnection time of your RCD and faults on other circuits shouldn't raise the potential on your c.p.c. relative to the MET (where both your c.p.c. and main bonding are connected) - but BS 7671 doesn't clearly advocate that approach (although perhaps hints at it in section 701).


   - Andy.

 

AJJewsbury:

That is exactly the point I was making, you cannot connect a RCD to a circuit and installation that is not adequately earthed and bonded or else a fault elsewhere in the installation may raise the voltage of earthed equipment downstream of the RCD to dangerous levels, a RCD does not remove the requirements for basic and fault protection along with the requirement to mitigate touch voltages.

The point I was attempting to make was than even in a fully correctly earthed & bonded installation a fault elsewhere can raise the exposed-conductive-parts downstream of the RCD (as elsewhere) to dangerous levels - e.g. >115V for 5s in a TN system or 230V for 1s in a TT system -  the 'mixed disconnection time problem' isn't just something for inadequately earthed/bonded installations to worry about.


There is some advantage in having all your RCDs close to the MET (with the minimum of parallel paths on the c.p.c.s) - in that faults on your circuit are covered by the rapid disconnection time of your RCD and faults on other circuits shouldn't raise the potential on your c.p.c. relative to the MET (where both your c.p.c. and main bonding are connected) - but BS 7671 doesn't clearly advocate that approach (although perhaps hints at it in section 701).


   - Andy.