Short Spurs

[Slumberland]

Hi Guys

Could you tell me if it is regulation to be able to reduce the cable size on a short spur from a ring final circuit. I am running a spur into an airing cupboard from the landing ring approx 500mm long to feed a single socket to plug in a 3 amp shower pump. I will use 2.5mm cable but i am sure 1.5mm will be ok.
Cant find in regs though. Can anyone settle a dispute please.

Thanks Jason

Son of an Electrician.

 

[Bright_Spark]

simply, No.

reasons: see your dad

 

[Job_n_knock]

Some here will correct me if Im wrong but I believe 2.5mm T&E has a rating of 27A which is why we use a ring circuit to split the load into 2 legs. But if you run 1.5 mm from one of those sockets to a spur then that cable is on its own radial and has a rating of only 18A but is protected by a 32A MCB....Potentially a fire in the making. So keep it as 2.5 to the spur and use a 5A fuse in the spur itself. Hope Im correct with the ratings......Im getting old and the memory aint what it used to be

 

[Slumberland]

I understand that now thankyou.
But there would never be more than 13amps pulled through the cable?
If is was a spur on a fused spur would that then be ok to reduce down to 1.5mm

Regards Jason

Son of an electrician (whos on holiday)

 

[Adam_151]

The spur cable is fused downstream by the plug fuse (or FCU fuse) so the 32A device back at the board only needs to provide earth fault protection and short circuit protection (same as with the 2.5, the cable is rated at 20A - 27A depending on installation method). The fusing factor of a BS1362 fuse is different from MCBs though, which would need to be taken into account of (as it needs to be with 3036 fuses). Also, consider if someone modifies it wrongly, daisy chained spurs on 2.5mm² seem to hold up quite well...

I suppose you could break out the adiabatic equation and check that 1.5mm² will withstand a phase->neutral fault and the 1mm² CPC a phase-> earth fault, and note it all on your cert, etc

... but it really, really isn't worth the effort, its far easier to use 2.5mm² then its a conventional arrangement and less fecking around calculation things, and better for the blood pressure of next person to work on it when the documentation has been lost

 

[Job_n_knock]

I suppose you could break out the adiabatic equation

You can get pills for that

 

[Slumberland]

Thanks Adam

Just passed 16th Edition exam.
I did quite well 100% on Definitions,Assesment,Protection,Selection and Erection and use of appendices but got 75% on Scope 87.5% on Inspection and Testing
For some reason got a dismall 57.1% on Special installations got to read carefully!

Regards Jason

Son of an electrician

 

[the_jinj]

Thanks Adam

Just passed 16th Edition exam.
I did quite well 100% on Definitions,Assesment,Protection,Selection and Erection and use of appendices but got 75% on Scope 87.5% on Inspection and Testing
For some reason got a dismall 57.1% on Special installations got to read carefully!

Regards Jason

Son of an electrician

Practice flipping through the reg index faster - that would improve your scores

On a similar note I have a human created index for the regs which is much more intuitave if anyone would like a copy?

 

[securespark]

a single socket to plug in a 3 amp shower pump.

Why bother with plug & socket??