new double socket spur plan

[dnel]

Hi, I'm intending to install a new double socket in my bedroom, the socket is located about 2ft away from my 32amp ring main running under the bedroom floor, my plan is to install a junction box on the main and spur off and run it to the double socket. I have 2 questions though before I start..

I am a little unsure whether 2.5mm would be sufficient for the maximum throughput of a double socket so I have 6mm cable to run to the spur, is this ok or is it best to keep 2.5mm across the whole circuit?

The maximum size junction box I could find was 30amps, is this safe to use on my 32amp ring main?

thanks in advance

 

[JohnW2]

I am a little unsure whether 2.5mm would be sufficient for the maximum throughput of a double socket so I have 6mm cable to run to the spur, is this ok or is it best to keep 2.5mm across the whole circuit?

2.5mm² would be usual for that situation - and 6mm² would be impractically large.

The maximum size junction box I could find was 30amps, is this safe to use on my 32amp ring main?

That's what everyone has to use - they never changed to making 32A ones!

You will probably get some more general comments about what you intend to do.

Kind Regards, John

 

[dnel]

2.5mm² would be usual for that situation - and 6mm² would be impractically large.

You're probably right, it is a bit beefy, I can use 2.5mm cable instead, is it possible that one double socket could overload 2.5mm cable though?

 

[JohnW2]

You're probably right, it is a bit beefy, I can use 2.5mm cable instead, is it possible that one double socket could overload 2.5mm cable though?

2.5mm² is totally standard in that situation, and compliant with the regulations - and won't get significantly overloaded. Don't forget that, contrary to common belief, a double socket cannot safely supply 2 x 13A loads - 20A is usual the maximum, and some would say 13A, either of which are within the capabilities of 2.5mm² cable.

Kind Regards, John

 

[ban-all-sheds]

my plan is to install a junction box on the main and spur off and run it to the double socket.

Why not extend the ring to the new socket?

 

[JohnW2]

You're probably right, it is a bit beefy, I can use 2.5mm cable instead, is it possible that one double socket could overload 2.5mm cable though?

I should have added that the current regulations require that the junction box should be 'accessible' for inspection and testing, unless you use something called a 'maintenance-free' one. Interpretations of 'accessible' vary, but most agree that under floorboards isn't!

Kind Regards, John

 

[JohnW2]

Why not extend the ring to the new socket?

That's obviously in some senses the 'ideal' but, as you know, the usual reason is that the cable position is such that two JBs (and a bit more work) would be required - and unfused spurs are fully 'accepted'.

Kind Regards, John

 

[ban-all-sheds]

Underfloor access - wherever the cable goes it can almost certainly be cut far enough away from where the new socket is to be to allow it to reach that position, then there's a cable from there to the cut and one JB - same as the spur.

And if the cables aren't plastered in, there should be the option of replacing some and not having any JBs.

 

[JohnW2]

Underfloor access - wherever the cable goes it can almost certainly be cut far enough away from where the new socket is to be to allow it to reach that position, then there's a cable from there to the cut and one JB - same as the spur.

Yes but, as you know, such an approach will often require more extensive lifting of floorboards.

And if the cables aren't plastered in, there should be the option of replacing some and not having any JBs.

Agreed, but probably even more work. As I said, the bottom line is that the concept of spurs is 'fully accepted' (without actually any suggestion in the regs or OSG that such is in any way less desirable than sockets on a ring, whatever we might think in engineering terms) - so, if it's more convenient to do ...

Kind Regards, John

 

[ban-all-sheds]

Yes but, as you know, such an approach will often require more extensive lifting of floorboards.

Yup.

Agreed, but probably even more work. As I said, the bottom line is that the concept of spurs is 'fully accepted' (without actually any suggestion in the regs or OSG that such is in any way less desirable than sockets on a ring, whatever we might think in engineering terms) - so, if it's more convenient to do ...

In my world I try very hard not to sacrifice elegance and excellence for convenience.

I accept that not everybody shares my standards.

 

[JohnW2]

In my world I try very hard not to sacrifice elegance and excellence for convenience. I accept that not everybody shares my standards.

I have to say that my 'heart' is with you in that, but the older in the tooth I get, the more do I see a place for pragmatism and expediency. I agree that spurs 'do not feel totally nice', but I'm fairly hard-pressed to come up with a rational basis for such a feeling - particularly given that, in some senses, ring final circuits, per se, 'do not feel totally nice', either'.

Looked at another way, most people have no problem (of 'elegance') with branching radial circuits, which is essentially no different from having spurs on a ring final. As for engineering/safety, even if someone did (inadvisedly) pull 26A through a double socket, I'm sure that would not actually harm 2.5mm² cable, even with the worst of installation methods - and with a 20A maximum load, there certainly would be no problem.

Kind Regards, John

 

[dnel]

There's not enough slack in the cable to reach the location of the socket, I need to feed it through a hold in one of the floor joists so adding cable is my only option.

It seems like I'll need a maintenance free junction box instead of the one I have though as access will not be possible after I carpet the room. Can you recommend any I can get hold of? I have a b&q and screwfix nearby but nothing stands out as "maintenance free" on their websites.

Alternatively, if I extend the cable and feed both to the socket, does the same accessability rules apply to simple straight-through joins to the cable?

 

[JohnW2]

There's not enough slack in the cable to reach the location of the socket, I need to feed it through a hold in one of the floor joists so adding cable is my only option.

That's what I suspected.

It seems like I'll need a maintenance free junction box instead of the one I have though as access will not be possible after I carpet the room. Can you recommend any I can get hold of? I have a b&q and screwfix nearby but nothing stands out as "maintenance free" on their websites.

There's only type of which I am aware - click here to see.

Alternatively, if I extend the cable and feed both to the socket, does the same accessability rules apply to simple straight-through joins to the cable?

Yes,they would still need to be 'maintenance-free' if not accessible.

Kind Regards, John