Radial Circuit MCB question

[LegionOfBrad]

Hi there,

Having looked over the CU in our house i have a quick question about a Radial circuit powering some sockets in our kitchen.

There is a 32amp MCB powering the circuit in the CU. The circuit is wired with a 4mm cable up until a junction box in the kitchen. Which then splits off powering sockets with 2.5mm cable. The entire cable length from the CU is < 4 metres.

Everything i have read suggests a 32amp MCB is ok for a 4mm cable. However because the previous home owner chopped into the cable and split off it using 2.5mm T&E the MCB should be rated down to 16amps? Is that correct? If so i will call a spark in.

 

[ban-all-sheds]

As long as each 2.5mm² branch serves no more than one socket it's fine.

If not a 20A or 25A MCB could be OK - it depends on how the cables are installed, so yes, if these branches are feeding more than one socket get an electrician to have a look.

 

[LegionOfBrad]

As long as each 2.5mm² branch serves no more than one socket it's fine.

If not a 20A or 25A MCB could be OK - it depends on how the cables are installed, so yes, if these branches are feeding more than one socket get an electrician to have a look.

Thanks

One branch terminates at a single socket however the other socket then branches to another socket. So i will call a spark in to change the MCB.

 

[JohnW2]

As long as each 2.5mm² branch serves no more than one socket it's fine. ... If not a 20A or 25A MCB could be OK - it depends on how the cables are installed, so yes, if these branches are feeding more than one socket get an electrician to have a look.

Thanks ... One branch terminates at a single socket however the other socket then branches to another socket. So i will call a spark in to change the MCB.

Changing the MCB will, of course, limit the total current available to all the sockets to 20A (or 25A if a 25A MCB is available for your CU). If that could be a problem, an alternative solution would be to get the electrician to reconfigure the circuit, such that the socket which currently is fed from another socket is fed directly from the JB (or, if logistically necessary, an additional JB).

Kind Regards, John

 

[LegionOfBrad]

Hi John, I've photoshopped (badly) a quick pic of the circuit. (1 is what is there atm) The cable between the two junction boxes looks to be the one that could be overloaded in the current config.

Are you suggesting doing something like 2?

Untitled

• LegionOfBrad
• 6 Dec 2014
• 1

Or could i perhaps get away with replacing the 2.5mm cable between the two JB's with a 4mm cable (which would be quite a simple option for me)

 

[ban-all-sheds]

If you replace the cable as you suggest then you can leave the 32A breaker in place.

 

[LegionOfBrad]

If you replace the cable as you suggest then you can leave the 32A breaker in place.

That is probably the best option then. The only issue maybe getting 2x4mm and 1x2.5mm in the junction box.

 

[JohnW2]

Hi John, I've photoshopped (badly) a quick pic of the circuit. (1 is what is there atm) The cable between the two junction boxes looks to be the one that could be overloaded in the current config.

Indeed.

Are you suggesting doing something like 2? ... Or could i perhaps get away with replacing the 2.5mm cable between the two JB's with a 4mm cable (which would be quite a simple option for me)

Either of those two options. The latter is not 'getting away with it' - it's satisfactory. As has been said, in both cases you could probably retain the 32A MCB.

Kind Regards, John

 

[LegionOfBrad]

Many thanks guys. 4mm Cable will go in on Monday.