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I don't want to say any more with the thread [url=https://www.diynot.com/diy/threads/could-i-safely-replace-an-mcb-in-our-consumer-unit.557024/]Could I safely replace an MCB in our consumer unit? [/url]as it may cause problems for @Peter A so think better to start new thread.
In the main we rely on EEBADS (Earthed Equipotential Bonding and Automatic Disconnection of Supply) and the loop impedance needs to be below a figure it was 1.44 Ω now a little lower so the magnetic part of the MCB can operate with a short circuit. A 13 amp fuse was 2.42 Ω not sure if that has also changed, but in the main if the supply cord is crushed or otherwise damaged either the MCB will trip or the fuse will rupture.
However with a TT system we rely on the RCD, and with the heating system shown in that thread to trip in time again likely relying on the RCD. At the end of the heating run, some thing smashing into the skirting is unlikely to draw enough current to operated the MCB on the magnetic part.
With a dedicated RCD I see no problem, but with a shared RCD could other items cause the RCD not to trip? LED standard lamp for example, with 14 RCBO's even if type AC I think the chance of a fault causing DC and a fault needing the RCD to trip at the same time, when it is a TN-C-S supply so over load can also cause a rapid trip is very small.
But what when there are only 2 RCD's for whole house, should I have even mentioned it? I did as the ELI had already come up, and the resistance of cable dictating if a curve C MCB could be fitted. But was I right to mention it or not? I am not even convinced there is a real danger. [/SIZE]
In the main we rely on EEBADS (Earthed Equipotential Bonding and Automatic Disconnection of Supply) and the loop impedance needs to be below a figure it was 1.44 Ω now a little lower so the magnetic part of the MCB can operate with a short circuit. A 13 amp fuse was 2.42 Ω not sure if that has also changed, but in the main if the supply cord is crushed or otherwise damaged either the MCB will trip or the fuse will rupture.
However with a TT system we rely on the RCD, and with the heating system shown in that thread to trip in time again likely relying on the RCD. At the end of the heating run, some thing smashing into the skirting is unlikely to draw enough current to operated the MCB on the magnetic part.
With a dedicated RCD I see no problem, but with a shared RCD could other items cause the RCD not to trip? LED standard lamp for example, with 14 RCBO's even if type AC I think the chance of a fault causing DC and a fault needing the RCD to trip at the same time, when it is a TN-C-S supply so over load can also cause a rapid trip is very small.
But what when there are only 2 RCD's for whole house, should I have even mentioned it? I did as the ELI had already come up, and the resistance of cable dictating if a curve C MCB could be fitted. But was I right to mention it or not? I am not even convinced there is a real danger. [/SIZE]
