Adding to garage via fused spurs

[AndyPRK]

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[JohnW2]

Ok John, so I'm taking that you have said no FCU would be needed if it was a ring circuit with a 20 amp breaker because 2.5mm can handle 20 amps?

Exactly.

But if I had a 32amp breaker (which I dont) then I would need an FCU to run the 3 double sockets?

If you had a 32A breaker, you would have to have an FCU (or, at least, a 20A breaker in an enclosure) to run anything through 2.5mm² cable, since that can't cope with 32A.

Sorry just trying to make sure I understand the idea rather than just doing what I'm told

You seem to be doing well at understanding.

Kind Regards, John

 

[JohnW2]

If, because the cable was run through insulation, its current-carrying capacity (CCC) were reduced to less than 20A, the dispensation in the regulations which allow ring circuits would not be applicable, so the MCB/fuse protecting the circuit would have to be reduced to no greater than the actual CCC of the cable (something less than 20A - so, in practice, probably 16A or 10A), whether it was wired as a ring or a radial. On the other hand, if the CCC were at least 20A, then it could be a 30/32A ring circuit.
So, as I said before, I really don't see what point there would ever be in having a 20A ring - but maybe I'm missing something!

Ah - well now - you are possibly missing the age of the installation. (Apologies if it's in the thread and I'm the one missing it... ) ... Prior to Amendment 1 2002 to the 16th edition, the old Regulation 433-02-04 required that the “minimum current carrying capacity Iz of the cable be not less than 0.67 x the rated current setting In of the protective device.” So it's possible that if installation method or other factors had reduced Iz to 14-16A there could have been a 20A RFC.

Possibly. Needless to say, I was talking about the current regulations. Whatever, as I've told the OP, if the circuit is protected by a 20A MCB, it matters not to him (in terms of the non-need for an FCU) whether it's a ring or radial circuit (unless he's found a way of getting CCC of 2.5mm² cable in a garage down below 20A).

Kind Regards, John
Edit: Typo corrected (RCD -> MCB)

 

[jim3010]

Thanks for the tip Andy.

Ban_all_sheds, I'm a newly qual plumber so no doubt I will be trying to learn all I can electric wise as it is all linked!

John, it's a b20 proteus MCB not RCD. The RCD covering that side of the CU is 63a rated. Not sure if you meant to type mcb or if this changes everything!

Many thanks to all a lot more input than I expected for 1 day

Cheers

 

[JohnW2]

John, it's a b20 proteus MCB not RCD. The RCD covering that side of the CU is 63a rated. Not sure if you meant to type mcb or if this changes everything!

Apologies - just a typo (now corrected). I did, indeed mean to type MCB

Kind Regards, John