Derating Conductors due to bundling inside Low voltage switchgear

That might be slightly different - if you've derated the cable as it passes through some thermal insulation to keep the conductor temperature within limits, then almost by definition the cable must be running with lower conductor temperature before & after the insulation - the so some of the heat generated within the thermal insulation has somewhere to go along the length of the cable.


Inside a DB say, with an MCB or similar at one end, generating heat from it's thermal element, and perhaps a fully utilised bunch of cables wending their way to the rest of the building on the other end, the ability to loose heat along the length of the cable might not be anything like as favourable.


That said, inside switchgear you're normally dealing with single cores, rather than a cable of two or three current carrying cores - so provided there's a sensible gap between conductors their rating is likely to exceed that elsewhere on the circuit. I suspect the 'usual practice' in the UK is not to specifically calculate for inside the DB - just work with the ratings for the rest of the circuit - but at the same time lacing/bunching/cable-tying conductors together inside a DB is considered poor practice.

 

That might be slightly different - if you've derated the cable as it passes through some thermal insulation to keep the conductor temperature within limits, then almost by definition the cable must be running with lower conductor temperature before & after the insulation - the so some of the heat generated within the thermal insulation has somewhere to go along the length of the cable.


Inside a DB say, with an MCB or similar at one end, generating heat from it's thermal element, and perhaps a fully utilised bunch of cables wending their way to the rest of the building on the other end, the ability to loose heat along the length of the cable might not be anything like as favourable.


That said, inside switchgear you're normally dealing with single cores, rather than a cable of two or three current carrying cores - so provided there's a sensible gap between conductors their rating is likely to exceed that elsewhere on the circuit. I suspect the 'usual practice' in the UK is not to specifically calculate for inside the DB - just work with the ratings for the rest of the circuit - but at the same time lacing/bunching/cable-tying conductors together inside a DB is considered poor practice.