final ring keeps tripping the mcb

[meady]

Hi, I have been asked to test a cabin in a friends garden which an electrician had wired up. The power is supplied by a 10mm swa cable to a b40 mcb within the cu. The cabin has 3 circuits, a lighting circuit which is fine, a ring circuit for 3 electric heaters which is fine and a ring for 10 double socket outlets. This last circuit is causing some problems. As soon as I switch the b32mcb on within the cabin distribution board the main mcb within the house trips. Could anyone suggest a possible fault for this. I have continuity in the circuit but the insulation is reading slightly lower than what I should be getting. Any suggestions on what it could be is most appreciated

 

[Andy™]

Hi, I have been asked to test a cabin in a friends garden which an electrician had wired up. The power is supplied by a 10mm swa cable to a b40 mcb within the cu. The cabin has 3 circuits, a lighting circuit which is fine, a ring circuit for 3 electric heaters which is fine and a ring for 10 double socket outlets. This last circuit is causing some problems. As soon as I switch the b32mcb on within the cabin distribution board the main mcb within the house trips. Could anyone suggest a possible fault for this. I have continuity in the circuit but the insulation is reading slightly lower than what I should be getting. Any suggestions on what it could be is most appreciated

how about telling us what the readings actually are

could be that other circuits are already taking up most of the current the house breaker can take, and turnin on the ring is too much

whats the rating of heaters etc, and any other equipment plugged in

 

[Doc Hudson]

Hello Meady, welcome to the forum. Although you have described some detail about the circuits, you haven't actually said what is connected on each circuit? Such as what power rating are the lights, heaters & what appliances are being plugged into the sockets? are there any high power consumption tools in use such as builders or welders type equipment etc? How old is the wiring? This sort of information, along with your test readings as requested by AndyC, will make it a bit easier to offer any probable causes or solutions.

Doc H.

 

[Evans Electric]

Does the ring have stuff plugged in, does the MCB stay in if all the plugs are out ? Is there a short on the ring ? Is there not an RCD in the cabin ? When you say "the main MCB in the house trips " do you mean the 40amp feeding the cabin via the 10mm cable ? Are you talking about an RCD ?

Deke

 

[binky]

If this problem has been there since installation then I would suspect crossed polarity on the circuit, if RCD trip, then damage to circuit, suggest disconnect circuit and check continuity and IR.

 

[dave b]

hi meady

i would test all basics, r1+r2 on ring for continuity etc and make sure readings are ok. insulation resistance and make sure you're within values allowed. if all ok i would distconnect all neutrals from the board in house and turn all other mcb's off, then try circuit again. could be picking fault up from other circuits in house?

is there a split load board in house? check that the swa 10mm feed neutral is not in the wrong neutral block on the split load. must be in the neutral block that isolates that mcb and neutral.

hope that helps

dave