Hi,
Spent most of today fitting some new sockets in what will be a small kitchen and struggling to persuade at least some of the existing plaster to remain on the wall!
Adding a new circuit to an existing MK fuseboard which provides power to existing sockets, lights and doorbell and has AFAIK been working happily for some time.
After completing all my tests and connecting my circuit up for live testing one large pop and the 40A mcb supplying this CU (CU in another location) tripped. (No RCD fitted).
Further investigation showed that the existing lighting circuit has a very low resistance N > E (0.23Ohm). Checked my new cabling again and it passed all dead tests.
So for now my circuit is disconnected until I can go back to diagnose the problem properly (didn't have full access today).
My confusion is the following:
1. I would have expected one of the existing mcbs (2 * B6, B32) to trip before the B40A in the feed CU?
2. With a low N>E resistance like that, I would have expected the existing MCBs to trip? The cabling on the existing sockets is fairly short so presumably the Neutral resistance is lower. However, my new circuit is only 4m or so of cabling, so the Neutral resistance should be lower and hence no more likely to trip than the existing cabling.
Am I missing something really stupid? If so I blame the plaster dust for slowing my mental processes!
Spent most of today fitting some new sockets in what will be a small kitchen and struggling to persuade at least some of the existing plaster to remain on the wall!
Adding a new circuit to an existing MK fuseboard which provides power to existing sockets, lights and doorbell and has AFAIK been working happily for some time.
After completing all my tests and connecting my circuit up for live testing one large pop and the 40A mcb supplying this CU (CU in another location) tripped. (No RCD fitted).
Further investigation showed that the existing lighting circuit has a very low resistance N > E (0.23Ohm). Checked my new cabling again and it passed all dead tests.
So for now my circuit is disconnected until I can go back to diagnose the problem properly (didn't have full access today).
My confusion is the following:
1. I would have expected one of the existing mcbs (2 * B6, B32) to trip before the B40A in the feed CU?
2. With a low N>E resistance like that, I would have expected the existing MCBs to trip? The cabling on the existing sockets is fairly short so presumably the Neutral resistance is lower. However, my new circuit is only 4m or so of cabling, so the Neutral resistance should be lower and hence no more likely to trip than the existing cabling.
Am I missing something really stupid? If so I blame the plaster dust for slowing my mental processes!