Radials?

[person]

Just realised the supply to my garage is actually 4mm instead of 6mm (not energised yet) and a 40amp mcb in main board in house.. I did have a lighting circuit and a ring of 6 sockets, Am I correct in saying that it would be better to change ring to a radial (if so what size 16 or 20) and my main mcb in the house to a 32? Also what is the maximum amount of sockets I could have on this radial?

 

[Aragorn84]

What type of 4mm cable?

I dont see why you'd need to change the ring to a radial even if the CU breaker is 32A?

 

[person]

The cable is 4mm swa. I've been told by 2 people now to change it to a radial and have my breaker a 32 at main cu. Thanks for response though.

 

[333rocky333]

The house mcb is to protect the swa so you may need to lower that.

The garage ring sockets are protected by the mcb in the garage if you have one, if 2.5 ring then possibly a 32a mcb.

There is nothing to prevent you fusing that ring at 16 or 20 if you want, to discriminate from the house mcb, but there is no need to change it to a radial, unless you want to.

 

[Aragorn84]

it will depend what insulation type is on the SWA...

If its XLPE it should be fine upto 49A
PVC can only handle 38A

I would leave the garage circuits alone regardless. You might well need more than a 16a or 20a supply down there at some point

 

[ericmark]

Just realised the supply to my garage is actually 4mm instead of 6mm (not energised yet) and a 40amp mcb in main board in house.. I did have a lighting circuit and a ring of 6 sockets, Am I correct in saying that it would be better to change ring to a radial (if so what size 16 or 20) and my main mcb in the house to a 32? Also what is the maximum amount of sockets I could have on this radial?

There is no reason why a ring main should not be supplied by a smaller MCB and to change from ring to radial could have an impact on volt drop so see no point in changing.

As to current rating of 4mm it can be anywhere between 17.5 and 45 amp depending on type of cable and it's run.

 

[ban-all-sheds]

If its XLPE it should be fine upto 49A
PVC can only handle 38A

XLPE can only handle 38A if it's connected to accessories only rated to 70°C...

 

[Aragorn84]

Well its easier to check some routing and possibly change an accesory or two than replace the entire cable?

Presumably if its a plastic CU at either end you will need to terminate in a metal box before the CU and use some heavier cable for the final connection?

 

[ban-all-sheds]

Well its easier to check some routing and possibly change an accesory or two than replace the entire cable?

If you can find suitable accessories.

Presumably if its a plastic CU at either end you will need to terminate in a metal box before the CU and use some heavier cable for the final connection?

You'd need long-ish pieces of heavier cable, because copper is an excellent conductor of heat.