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Commercial Radial circuit help

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Hi,
I went to look at job; it is a 2.5mm2 radial coming from the CU (from a 32A MCB) to two sockets and the sockets are using two appliances which are a 3.6 kW combi oven and a 2.5 kW 2 plate electric hob, what i've been told that it trips at the CU and sometimes it doesn't trip and the appliance doesn't work.

Any help plz.
 

SJD

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What trips - the 32A MCB, or an RCD?
Tripping using which appliance, or both? And using it/them exactly how?
Are these appliances on 13A plugs (incl. the 3.6kW oven), or something larger?
And with both appliances on, drawing over 25A, has the cable melted?
Have you done any tests on the circuit?
Or any tests on either appliance?
 

littlespark

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2.5mm from a 32A does not sound good.
I bet it was a 20 to start with and some clever clogs uprated the MCB cos it kept tripping.

Is there space in the board, and easy enough job to run a second radial and have each appliance on its own circuit?
 
Hello Ali are you a trainee because you originally posted this in the Trainee section which has restricted viewing access so it has been moved. Knowing this will help people with their replies.
 
  • Thread Starter Thread Starter
  • #5
What trips - the 32A MCB, or an RCD?
Tripping using which appliance, or both? And using it/them exactly how?
Are these appliances on 13A plugs (incl. the 3.6kW oven), or something larger?
And with both appliances on, drawing over 25A, has the cable melted?
Have you done any tests on the circuit?
Or any tests on either appliance?
Tbh I didn't go into it too much as it was just a quick check for someone and it didn't look safe to me; so I advised him not to use it and get it checked out by a competent person as I am a trainee
 
  • Thread Starter Thread Starter
  • #6
2.5mm from a 32A does not sound good.
I bet it was a 20 to start with and some clever clogs uprated the MCB cos it kept tripping.

Is there space in the board, and easy enough job to run a second radial and have each appliance on its own circuit?
Do you reckon it is better to have one socket each coming off the board (one radial circuit each) and thats exactly what I thought it should be a 20A MCB not 32A
 
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  • #7
Hello Ali are you a trainee because you originally posted this in the Trainee section which has restricted viewing access so it has been moved. Knowing this will help people with their replies.
Yes I am a trainee, I have 2 years experience; mainly domestic. I have done my level 3, but due to health issues I haven't been able to carry on properly
 

littlespark

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You are right, Ali. Its not safe.

Look at the current carrying capacity of 2.5mm, even without any installation method derating, and you'll find its under 32A (the highest i can see in the Big Blue Book is 30A, and that's laid on cable tray surrounded by "free air")

So, the cable is going to deteriorate before that 32A MCB will trip if the total load reaches 25A (both appliances on full)
 
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  • #9
You are right, Ali. Its not safe.

Look at the current carrying capacity of 2.5mm, even without any installation method derating, and you'll find its under 32A (the highest i can see in the Big Blue Book is 30A, and that's laid on cable tray surrounded by "free air")

So, the cable is going to deteriorate before that 32A MCB will trip if the total load reaches 25A (both appliances on full)
So you reckon one socket each on its own 20A circuit, using 2.5mm will do it?

And also what about if that existing radial was converted to a ring, would that work?
 
You need to resolve why it is currently tripping because those two appliances should not make a 32A device trip through overcurrent. If an appliance fault is causing it then altering the circuit configuration even though this is required may not resolve it.
 

Andy78

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Causes and solutions should not be guessed at. If you don't feel your training and experience are sufficient to enable you to fault find and rectify this job you probably should not be doing it.
 
Odd set up, but surely no worse than a double socket spurred from the MCB of a ring final? Incidentally does anyone know why the regs say an unfused spur on a ring final can feed 1 double socket, but not 2 singles?
 
... Incidentally does anyone know why the regs say an unfused spur on a ring final can feed 1 double socket, but not 2 singles?
I reckon because the two singles may be a long way apart, which might encourage the plugging-in of two high-current appliances on the same 2.5mm spur. No one sensible plugs two heavy appliances into one double socket. Except maybe whoever designed the OP's scenario, which is ridiculous.
 

Pete999

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Odd set up, but surely no worse than a double socket spurred from the MCB of a ring final? Incidentally does anyone know why the regs say an unfused spur on a ring final can feed 1 double socket, but not 2 singles?
Because a twin socket constitutes a spur as does a single see appendix 15 BS 7671
 

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