Junction Box on Ring main

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I have discovered a junction box on my kitchen ring main when I pulled back the plasterboard to renew.

The MCB supplying the kitchen ring is 32 amp but the Junction Box is a 30amp one. I am not quite sure what purpose this junction box is serving (cable extension possibly???).

Obviously it was inaccessable behind the plasterboard but what are the consequences of having a 30 amp JB on a 32amp ring? Thanks
 
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Not good practice but as your 2.5mm (presumably) cable is rated at less than 30A anyway it's not going to be a problem.
 
Not good practice but as your 2.5mm (presumably) cable is rated at less than 30A anyway it's not going to be a problem.

How can it NOT be a problem if the cable is 30 amp and the MCB is 32 amp ?

I hope you are not suggesting the junction box will survive an overload for lonegr than the cable.
 
It is a ring main, just as the cable is rated at less than the breaker rating I don't see any reason why a junction box shouldn't be.
 
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I doubt there is any difference between a 30A JB and a 32A JB apart from the numbers printed on them.

if you have got the plasterboard off, now would be a good time to fit a new, accessible one anyway. Especially if the JB is a nasty round one.
 
Bernard,
How can the JB get more overloaded than the cable?

John,

What's wrong with round JBs?
 
round ones are often left draped about and hanging off their cables. And the cores inside are often a bit of a jumble.

I prefer the ones mounted in a square back-box with a 32A block inside, or the square white ones screwed to a wall.
 
Not good practice but as your 2.5mm (presumably) cable is rated at less than 30A anyway it's not going to be a problem.

How can it NOT be a problem if the cable is 30 amp and the MCB is 32 amp ?

I hope you are not suggesting the junction box will survive an overload for lonegr than the cable.

eh?? In that case are you suggesting the 2.5mm cable will survive an overload for longer than a 30A junction box?
By the way what is the current rating of the terminals on the back of a socket on a ring main?

EDIT: Ok seen your reply above now, had me going there :oops:
 
In a ring circuit, there are two cables running from the breaker carrying a total current of up to 32 Amps.

I suppose in a perfect circuit, with an evenly distributed load, the cables on each side of the ring would only carry a maximum of 16 amps each, and the current in conductors at a point on the opposite side of the ring would be zero.

This world is far from perfect, but it is unlikely that the current in one side of the ring will exceed 30 Amps, unless there is a fault on the circuit.

You can consider the ring circuit as two parallel networks of series resistors if you like. No matter where the load is applied, there will be a current in both sides of the ring.
 

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