SPUR and FCU

[peteelecs]

If I run a double socket spur off the ring main can i then run a FCU from that spur to a light fitting

 

[peteludman]

what size cable did you run the spur(double socket) in if 4 mm yep but 2.5 i wouldnt cos you can then draw the 32A if thats the mcb size and the cable can take about 27A

 

[Had8Lives]

Just a thought, but why not extend the ring to the double socket, then spur off the double socket to your FCU. Or extend the ring all the way out to your FCU, So, all in all the new double socket and FCU will be in the ring.

 

[Des 56]

If I run a double socket spur off the ring main can i then run a FCU from that spur to a light fitting

You can run the double socket off an unswitched spur off the ring
Then run the light off a switched spur off the double socket

 

[Risteard]

You can run the double socket off an unswitched spur off the ring
Then run the light off a switched spur off the double socket

I disagree.

You have an unfused spur to the double socket so you can't then spur off that.

 

[Deleted member 9648]

I disagree.

You have an unfused spur to the double socket so you can't then spur off that.

I suspect Des56 meant an unswitched fused spur which is how I would do it if it was not practical to extend the ring....you can then run as many points as you like off the spur with no fear of overloading the supply cable, obviously taking into consideration the load likely to be in use.

 

[Des 56]

I disagree.

You have an unfused spur to the double socket so you can't then spur off that.

I agree as well
Just read my reply and missed out that vital fused word,sorry

Use an unswitched FUSED spur and connect on until your hearts content

 

[Risteard]

I agree as well
Just read my reply and missed out that vital fused word,sorry

Use an unswitched FUSED spur and connect on until your hearts content

Sorry should have realised what you meant!

 

[Guest123]

what size cable did you run the spur(double socket) in if 4 mm yep but 2.5 i wouldnt cos you can then draw the 32A if thats the mcb size and the cable can take about 27A

Sorry but I must disagree with that Pete, it wouldn't matter if he wired the spur in 10mm T+E, as the reason you are only permitted to spur one point off any point on the ring without using a fused connection first is so as the ring circuit is not overloaded at any one point.

By spurring more than one you are in effect overloading the ring at the point of connection, and as you rightly state a 2.5mm will carry 27A but to spur more than one point could increase the current drawn to more than 27A.

The current in a ring circuit is assumed to be at 20A in any one leg with a possible further 12A evenly distributed, to spur more than one means an uneven current demand.

This is part of the reason why we can use a 32A MCB on a 2.5mm cable

 

[peteludman]

sorry but i must disagree with that pete, it wouldn't matter if he wired the spur in 10mm t+e, as the reason you are only permitted to spur one point off any point on the ring without using a fused connection first is so as the ring circuit is not overloaded at any one point.

By spurring more than one you are in effect overloading the ring at the point of connection, and as you rightly state a 2.5mm will carry 27a but to spur more than one point could increase the current drawn to more than 27a.

The current in a ring circuit is assumed to be at 20a in any one leg with a possible further 12a evenly distributed, to spur more than one means an uneven current demand.

This is part of the reason why we can use a 32a mcb on a 2.5mm cable

you are right but if you had the same equiptment pluged in on a ring would it not pull load in the same place in the ring.

You should evenly distrabu the heavy loads but not always easy and im sure lights on a spur with double socket wouldnt make a overload problem and lets face it ,its safe is it not.

I work with industrial electrical and that power is larger than a domesttic fridge or washing machine and never had a problem moving things around on ring there. Well not me moving them they like to put all -80 freezers on 1 end of large ring( not my designe )