In recent times, I have on several occasions had to qualify my comments about OPDs which were were rated too high to give adequate overload protection to the cable concerned with something like "... unless you argue that the (hard-wired) load in question is not able to result in an overload situation". The most recent example was 2.5mm² (and some 1mm² !) cable serving a dedicated immersion heater circuit but protected by a B32.
In such situations, if the circuit is such that the OPD can provide adequate fault protection (or if it's a TT installation in which fault protection is reliant on RCDs, anyway), if one argues that overload is not possible, one can seemingly have a compliant set-up even if the In of the OPD considerably exceeds the CCC of the cable.
I really am not very comfortable with that approach, and certainly would not want it taken in my home. The nearest to a rational electrical argument for my discomfort that I can come up with is that, in fairly exceptional circumstances, many fixed loads (e.g. those which include heating elements or motors) can theoretically result in 'overload' situations - i.e. drawing excessive currents, but not high enough to invoke 'fault protection' measures.
What do others think?
Kind Regards, John
In such situations, if the circuit is such that the OPD can provide adequate fault protection (or if it's a TT installation in which fault protection is reliant on RCDs, anyway), if one argues that overload is not possible, one can seemingly have a compliant set-up even if the In of the OPD considerably exceeds the CCC of the cable.
I really am not very comfortable with that approach, and certainly would not want it taken in my home. The nearest to a rational electrical argument for my discomfort that I can come up with is that, in fairly exceptional circumstances, many fixed loads (e.g. those which include heating elements or motors) can theoretically result in 'overload' situations - i.e. drawing excessive currents, but not high enough to invoke 'fault protection' measures.
What do others think?
Kind Regards, John