Extending Wiring behind Plug Socket

  • Thread starter Thread starter reepers
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Sen / Spin,
Can you clarify the current rating for the connectors?
thanks, fats (likes learning from the wise owls)
 
DIYDave. said:
As I said Sen, I'm just a dreaded diy'er but always thought that the cores should be gently bent back into the box, in a loose curve, not actually folded over to avoid stressing the copper - I may well be wrong of course :(
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That would be the case with the aluminium cables that were used for a while in the '70's but it's not a problem with copper Dave.
 
All fitted, used blocks and leccy taped em. Was fine in a 25mm box, works brill too. Thanks to everyone on this thread :)
 
seneca said:
16 amps is sufficient for a ring circuit, each leg only carries half the load.
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hi sen,
i had this back from wago some time ago when i asked them about their connectors on a ring which is why i questioned it mate:

The section in the installation requirements (BS 7671) that deals with ring final circuit in BS7671 is 433.1.103 where the relevant text says: "Such circuits are deemed to meet the requirements 433.1.1 if the current carrying capacity of the cable is not less than 20A and if under the intended conditions of use the load current in any part of the circuit is unlikely to exceed for long periods the current carrying capacity of the cable."
 
I've never really understood it either but I would prefere a good tight connection with a 15 block than a 30 a block. I don't think the rating of the block has a lot to do with anything anyway since the copper/brass used in the block looks to be much bigger csa than the cable.
 
Coloumb said:
I've never really understood it either but I would prefere a good tight connection with a 15 block than a 30 a block. I don't think the rating of the block has a lot to do with anything anyway since the copper/brass used in the block looks to be much bigger csa than the cable.
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Good point Col. i heard some sparks say not to use 20a dp isolators on rings for the same reason and know others who say its nonsense!
 
Agreed and also of course the cable will be quite a long length compared with the half an inch of brass in the connector!
 
seneca makes a good point, its all to do with length, look how thin a piece of 30A fuse wire is yet it sits there quite hapily because its only a couple of inches long, try to wire a ring with it and it would be a different story.
 
seneca said:
15/16 amps is sufficient for a ring circuit, each leg only carries half the load.
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Unfortunately such a situation where each leg carries half the load, only occurs when the load is connected at the mid point of the ring.
Where the load is connected at any other point on the ring the load on each leg is proportional according to where on the ring the load is connected.
A 20A load connected a quarter way round the ring would entail that the short leg carries 15A and the long leg 5A.
Remember, V = I x R.
The lower the resistance the greater the amperage.
The higher the resistance, the lower the amperage.
Generally, when constructing a ring, the equipment has a minimu current carrying capacity two thirds of that of the rating of the overcurrent protection.
 
Yes I agree with your theory explanation Spin but for all practical purposes we can assume that each leg will be carrying half the load current, in any case how many domestic rings will be running at full capacity. Text book theory is all very well but day to day in the real world we can't always do things quite "by the book"!
 
seneca said:
Yes FH, if it's a ring and fused at 30/32 amps each conductor will only be carrying half the current even at full load. Also, using connectors that are too big for the cable risks poor connections because the wire can end up down one side of the screw instead of underneath it!
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Technically however each leg must be capable of carrying 20A, as the load will not split evenly unless we had the load right at the midpoint of the ring without other loads present.
 
FatHands said:
Good point Col. i heard some sparks say not to use 20a dp isolators on rings for the same reason and know others who say its nonsense!
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The cable only has to be able to carry 20A, so no reason to hold a switch to a greater standard.
 
peter palmer said:
seneca makes a good point, its all to do with length, look how thin a piece of 30A fuse wire is yet it sits there quite hapily because its only a couple of inches long, try to wire a ring with it and it would be a different story.
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It sits there because it is not covered with insulation etc. so can dissipate heat to a much greater extent. It isn't the length of it which causes it to work as a fuse.
 
Risteard said:
It sits there because it is not covered with insulation etc. so can dissipate heat to a much greater extent. It isn't the length of it which causes it to work as a fuse.
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You could put 6" of 1mm in a ring main and it would run at the full capacity of 32A all day long without ever getting warm. However if you wired the whole ring main out of 1mm then you would have problems. A short length of something that is underrated will not be a problem, it may not say so in the precious regs book but in the real world its fine.
 
peter palmer said:
You could put 6" of 1mm in a ring main and it would run at the full capacity of 32A all day long without ever getting warm. However if you wired the whole ring main out of 1mm then you would have problems. A short length of something that is underrated will not be a problem, it may not say so in the precious regs book but in the real world its fine.
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No point in mentioning "the real world" Peter, some of them don't know it exists but others of us actually work in it!
 
peter palmer said:
You could put 6" of 1mm in a ring main and it would run at the full capacity of 32A all day long without ever getting warm. However if you wired the whole ring main out of 1mm then you would have problems. A short length of something that is underrated will not be a problem, it may not say so in the precious regs book but in the real world its fine.
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It would get warm actually. The difference is that a fuse can dissipate heat far more readily.

How do you claim that after a length of time 1mm^2 would not get hot with a constant 32A load regardless of its length?
 
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