2.5mm on 32A radial

[SUNRAY]

A quickie (hopefully).

A big extention on a house removed an upstairs ring final but 4 spurs (2xFCU & 2xSSSO) to the ground floor buried in decorated walls have been joined together onto the redundant shower cable.

Gut feeling says 25A mcb but FCU's are washing machine and tumble drier the 2 sockets are used for kettle and microwave so we'd like to leave it as 32A like it was on the ring.

Thoughts please.

 

[JohnW2]

Gut feeling says 25A mcb but FCU's are washing machine and tumble drier the 2 sockets are used for kettle and microwave so we'd like to leave it as 32A like it was on the ring.

All four of those 'spurs' (they are now really branches of a radial) are presumably protected by downstream 13A (max) fuses, so 2.5mm² cable is surely fine - as, I would have thought, is a 32A OPD, provided only that the Zs at the end of each branch is low enough for adequate fault protection.

Kind Regards, John

 

[EFLImpudence]

I would agree with that if 2.5mm² is only on the now branches.

You could, presumably, leave whatever rated MCB was used for the shower - subject to Zs limit

However, if they have been connected together with a length of 2.5mm²which has then been connected to the shower cable, then 25A would be the maximum.

 

[SUNRAY]

All four of those 'spurs' (they are now really branches of a radial) are presumably protected by downstream 13A (max) fuses, so 2.5mm² cable is surely fine - as, I would have thought, is a 32A OPD, provided only that the Zs at the end of each branch is low enough for adequate fault protection.

Kind Regards, John

Thanks John.
The test's are fine, well inside the limits and each outlet is a 13A device.

There were 3 of us on site:
One guy being very blase about it,
Second saying it has to be treated as a whole radial in 2.5mm (but it is 10mm to the joint) and
Me likening it to spurs off a ring final.

 

[SUNRAY]

I would agree with that if 2.5mm² is only on the now branches.

You could, presumably, leave whatever rated MCB was used for the shower - subject to Zs limit

However, if they have been connected together with a length of 2.5mm²which has then been connected to the shower cable, then 25A would be the maximum.

Thanks EFL.
It was a 50A but the builders did change it to B32, all 4 'spurs' are connected into one box directly on the end of the 10mm.

 

[JohnW2]

Thanks John. The test's are fine, well inside the limits and each outlet is a 13A device.

In that case, what I said still stands.

There were 3 of us on site: One guy being very blase about it, .... Second saying it has to be treated as a whole radial in 2.5mm (but it is 10mm to the joint) and ... Me likening it to spurs off a ring final.

As I implied, and as EFLI has said, provided each of the three 2.5mm² branches goes back to the 10mm² cable, then it's simply a 32A radial, with more-than-adequate initial cable (10mm²), with four 2.5mm² branches, each limited to 13A. That's even acceptable to the guidance in Appendix 15 (which shows initial 4mm² cable, but 10mm² is obviously even better). The second guy is therefore just plain wrong, both in terms of electrical common sense and regulations/guidances!

Kind Regards, John