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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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Wiring Ring mains to MCBs in consumer units
In my flat I've discovered that each end of the two socket ring mains
go back to separate MCBs. I've tested this by using a multimeter, turning off an MCB and still getting 240V on the live terminal (i.e I've got to switch off 2 MCBs to turn off the circuit). To clarify I have 2 32A MCBs per ring main, (4 in total). I would have thought that both ends of the ring main should go back to the same MCB (i.e. two wires into the MCB) The way it's been wired, each individual live wire goes back to an individual MCB. Have I got 2 MCBs too many in my fusebox. I think its wired incorrectly am I right Thanks. Jamie |
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Wiring Ring mains to MCBs in consumer units
Yes you are right!
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Wiring Ring mains to MCBs in consumer units
"jamie T" wrote
| In my flat I've discovered that each end of the two socket ring mains | go back to separate MCBs. I've tested this by using a multimeter, | turning off an MCB and still getting 240V on the live terminal (i.e | I've got to switch off 2 MCBs to turn off the circuit). To clarify I | have 2 32A MCBs per ring main, (4 in total). I would have thought | that both ends of the ring main should go back to the same MCB (i.e. | two wires into the MCB) The way it's been wired, each individual live | wire goes back to an individual MCB. | Have I got 2 MCBs too many in my fusebox. I think its wired | incorrectly am I right It is wired incorrectly. Each end of the ring should go back into the same MCB. Owain |
#4
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Wiring Ring mains to MCBs in consumer units
In my flat I've discovered that each end of the two socket ring mains
go back to separate MCBs. Yes. The current wiring is extremely dangerous and could easily lead to a fire. You should fix the problem immediately. I think the whole installation should be thoroughly tested. With one absolute shocker like that, there could be many other disturbing irregularities. Christian. |
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Wiring Ring mains to MCBs in consumer units
"Christian McArdle" wrote in message . net... In my flat I've discovered that each end of the two socket ring mains go back to separate MCBs. Yes. The current wiring is extremely dangerous and could easily lead to a fire. You should fix the problem immediately. I think the whole installation should be thoroughly tested. With one absolute shocker like that, there could be many other disturbing irregularities. does this mean that the circuits are effectively protected at (a chilling) 64A at the moment, or is the effect not quite that simple and liable to be indeterminate? -- Richard Sampson email me at richard at olifant d-ot co do-t uk |
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Wiring Ring mains to MCBs in consumer units
On Fri, 28 May 2004 14:48:24 UTC, "RichardS" noaccess@invalid wrote:
does this mean that the circuits are effectively protected at (a chilling) 64A at the moment, or is the effect not quite that simple and liable to be indeterminate? No, they're protected at 32A. Which is fine, as that is well within the rating of the ring as a whole. But, think what happens if ONE of those breakers trips. You are left with what is effectively a radial circuit, protected at 32A by the remaining breaker. But with a single cable feeding each outlet, the cable (if 2.5mmT+E) rated at as little as 20A. -- Bob Eager begin a new life...dump Windows! |
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Wiring Ring mains to MCBs in consumer units
does this mean that the circuits are effectively protected at (a chilling)
64A at the moment, or is the effect not quite that simple and liable to be indeterminate? It will be dependent on where the point loads are applied. It is protected at between 32A and 64A. I suspect it would be much closer to 64A on an average distribution of point loads. Christian. |
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Wiring Ring mains to MCBs in consumer units
On Fri, 28 May 2004 15:07:51 UTC, "Christian McArdle"
wrote: does this mean that the circuits are effectively protected at (a chilling) 64A at the moment, or is the effect not quite that simple and liable to be indeterminate? It will be dependent on where the point loads are applied. It is protected at between 32A and 64A. I suspect it would be much closer to 64A on an average distribution of point loads. (slaps head). Of course.... I was concentrating too much on the overload if one MCB tripped. Wther one is tripped or not, it'll still overload! -- Bob Eager begin a new life...dump Windows! |
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Wiring Ring mains to MCBs in consumer units
"RichardS" noaccess@invalid wrote in message .. . "Christian McArdle" wrote in message . net... In my flat I've discovered that each end of the two socket ring mains go back to separate MCBs. Yes. The current wiring is extremely dangerous and could easily lead to a fire. You should fix the problem immediately. I think the whole installation should be thoroughly tested. With one absolute shocker like that, there could be many other disturbing irregularities. does this mean that the circuits are effectively protected at (a chilling) 64A at the moment, or is the effect not quite that simple and liable to be indeterminate? I think that would only be correct if the load on the circuit was balenced e.g. at the mid point of the ring. If you put the 32A load within a few mm of one MCB I don't think you could draw much above 32A (at least not for long) before the 32A MCB trips but this is still above what the cables rated at since most of the current would be travelling down the shorter (lower resistance) leg. In summary your protecting the cable at 32A but the circuit between 32&64 A depending on where the load is. HTH Jim Jim -- Richard Sampson email me at richard at olifant d-ot co do-t uk |
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Wiring Ring mains to MCBs in consumer units
I think that would only be correct if the load on the circuit was balenced e.g. at the mid point of the ring. If you put the 32A load within a few mm of one MCB I don't think you could draw much above 32A (at least not for long) before the 32A MCB trips but this is still above what the cables rated at since most of the current would be travelling down the shorter (lower resistance) leg. In summary your protecting the cable at 32A but the circuit between 32&64 A depending on where the load is. The overload tripping current will be very close to 64 amps (probably over), the impedance for an overload current will have negligable difference anywhere on the ring main cabling - (Kirchov's current law if you want to look it up and work it out exactly) If it was a short circuit current then then the difference in the impedance would have a measurable effect but then the short circuit current would be only for a very short period of time and into the thousands of amps range. It is a very serious fire hazard in an overload situation as this could be applied for a long perion melting the cable. It is also a bad situation for anyone working on it. |
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Wiring Ring mains to MCBs in consumer units
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#12
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Wiring Ring mains to MCBs in consumer units
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#13
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Wiring Ring mains to MCBs in consumer units
"jamie T" wrote in message om... In my flat I've discovered that each end of the two socket ring mains go back to separate MCBs. I've tested this by using a multimeter, turning off an MCB and still getting 240V on the live terminal (i.e I've got to switch off 2 MCBs to turn off the circuit). Well spotted, but you should confirm ring continuity of live, neutral and earth conductors by checking impedance across the open ends of the cables you think are the ring. Then they both go to a single MCB. There are other tests as well. Think there may be guidance on the TLC website. Alan |
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