Ring main not 32amp

[Jimmyb]

I’ve been asked by a family member who has just had some new wiring in his house if I could look over the job as they didn’t get why they had to have 2 rcd's now, I told them about the new regs but for their piece of mind I said ill pop over some time and have a look, everything look spot on apart from one thing the old downstairs ring being on a 20amp mcb when I look at test sheets it was tested as ring and all results was good so I decided to check it myself, all results the same as on sheet, so I thought ill ring him and ask,
the reply I got was the cable ref method was 102 due to the wiring being dropped down from upper floor and into the wall. I asked why not use 4mm then but he said it hard getting 2 x 4mm cables into the sockets

so my question is are 2.5mm rings with ref method 102 ok on 20mcb, I’ve only been in the trade for 2 years so wondered what you guys thought

 

[Notsosmart]

Jimmy

I don't think that you can berate the electrician but whilst the was right to put a 20A mcb on the circuit due to reg 523.7, he should have avoided that route in the first place (unless it is the only route down). As you said perhaps 4mm would have been a better choice.

The problem being, unless clearly marked, then in years to come who's to say that someone won't see a ring & decide change the breaker for a 32A.

 

[acvc]

Yep, agree with you notsosmart. Current carrying capacity for 2.5mm using ref method 102 is 21A, so 20A mcb ok.

This should be clearly stated on the schedule of circuits and test results. Anyone doing later work on the installation should check any documentation and certification before starting .

 

[AMST09]

Getting 2 4mm cables into a socket is not a difficult task...just undo the screw a little more
Just put 4mm in for a couple of ring mains due to the length of run and had no problems terminating

 

[andyb]

The current carrying capacity of the cable must not be less than 20amps,
So in this case it would be ok to protect the circuit with a 32amp mcb

 

[lister]

Im with andyb on this , surley as its a ring even in insulation then 32A mcb is ok ??
or am i missing something?

 

[acvc]

I'm assuming more than 500mm of insulation, but not taking for granted a prefectly balanced ring, so potential for more than 21A in the leg in the insulation.

I'd rather be over-safe than under-safe.

 

[madmaz]

I'd say its ok to put on 32A

What is the maximum current carrying capacity of a ring circuit ref method 102 is it 42A ????

Yep, agree with you notsosmart. Current carrying capacity for 2.5mm using ref method 102 is 21A, so 20A mcb ok.

This should be clearly stated on the schedule of circuits and test results. Anyone doing later work on the installation should check any documentation and certification before starting .

but the current carrying capacity of 2.5 installed method C is 27A therefore we shouldn't be protecting by 32A !