1.5mm ring

[ban-all-sheds]

That's what I said above...

If you don't comply with (433.1.5) then you cannot have any higher rated protective device because it's a ring - you are limited to the Iz of the cable.

 

[ColJack]

sorry BAS, I hadn't gotten that far, I was repling to this..

You cannot have a ring final (I assume it was a socket circuit?) on anything less than a 30/32A OPD.

If the cable isn't rated at at least 20A then you have to increase the size of the cable, you may not reduce the rating of the OPD.

I didn't realise you'd contradicted yourself later on..

 

[ban-all-sheds]

OK - sorry - I meant you cannot have a 433.1.5 compliant ring final on less than 30/32A...

 

[Spark123]

Just to throw a spanner in the works,
What is the rated current carrying capacity of a piece of 2.5mm twin and earth clipped direct and protected by a BS3036 re-wirable fuse?

 

[ColJack]

still 27A.. the rating doesn't get changed.. the fuse rating does.. ( 433.1.3 )

ie 2.5mm cable clipped direct is rated at 27A, but you cannot have a BS3036 fuse protecting it that is rated higher then 19.575A.

or to put it another way, a radial protected with a 30A BS3036 needs a cable with a rating of 41.38A to satisfy 433.1.1

 

[Spark123]

still 27A.. the rating doesn't get changed.. the fuse rating does.. ( 433.1.3 )

ie 2.5mm cable clipped direct is rated at 27A, but you cannot have a BS3036 fuse protecting it that is rated higher then 19.575A.

Sorry if I wasn't clear, I meant the current carrying capacity of the a 2.5mm cable after applying the correction factor for a rewirable fuse. This is less than 20A hence there is a lot of RFCs up and down the country which do not comply with the fudge of a regulation 433.1.5 to the letter.

 

[ColJack]

again, the cable doesn't get downrated, it can still carry 27A..
the fuse protecting that cable however must not exceed 0.725 x the cable rating.. ( ie the 19.575A )

if you're installing a 30A BS3036 protected radial then you must use cable with a rating of not less than 41.38A..

the cable in the ring main STILL has a rating of 27A per leg, and as that satisfies the "must be rated over 20A" of the reg, and that the 30A BS3036 is specifcally mentioned in that reg with cable rated at over 20A, it complies.