13A sockets on 50A RCBO

[Martin]

Can anyone see anything wrong with two double 13A sockets wired with 20m of 6mmsq SWA protected by a 50A RCBO. Normally I'd max radials at 32A, but the client has 4x 10A loads.

Since the 13A socket on a cooker supply is generally protected by around 40-50A I am guessing it's fine.

 

[AEC]

Not checked BRB.

But dont think 6mm SWA is rated for 50 Amp. And dont know installation method.

 

[scotsparky]

If the load is that heavy i would split it into 2 x 32A radials with a 6mm cable

 

[netblindpaul]

You should also check that "13A" socket outlets are rated at a continuous 20A combined load.
Paul

 

[scotsparky]

netblind they are there is a bit of back fusing in the "13A" fuse in the plugtop

 

[netblindpaul]

NO THEY ARE NOT, the fusing in the plug top could allow over 26A to be drawn from a single twin s.o.
Look up the characteristics of the standard 13A plug top fuse, see how muhc current it will pass without "blowing", then multiply that by two to see what you are expecting the s.o. to take.
As I understand the testing, standards etc. of a standard twin 13A s.o. from a professional standpoint this is an overload situation.
A SINGLE 13A load in a twin s.o. OK, 2 10A loads need to be checked.
The plug top fuses WILL NOT protect the s.o. how can they as they are downstream.
Paul

 

[Martin]

Thanks for resposes so far.

More info:
SWA will be clipped direct.
The tables give 62A for 6mmsq (volt drop 7.9v)
The MK double sockets are rated to 13A per socket.

As far as I can see this still should be okay.

 

[Johno]

Is this for arguments sake or are you going to do it?

 

[netblindpaul]

Martin,
You REALLY NEED to check directly with MK the per socket rating as the value you are quoting is higher than that required by BS1363 and that generally accepted.
Paul

 

[scotsparky]

Paul as the fuse limits th load that is able to be drawn by the cable to the appliance it also limits the load drawn from the downstream supply.
It is this reason that on larger installations 25mm cables can be taken from 300A busbars to 63A isolators as long as ther within 3 metres as th 63A protection is less than the maximum CCC of the 25mm cable.
have a look at Reg 434.2.1 .

 

[netblindpaul]

BS7671 is irrelevant here, you MUST refer to BS1363 for the allowable socket loads.
I am aware of the scenarios you suggest however, they have no relevance in the OP scenario.
Under the situation of small overloads of long duration what summated current could be drawn by 2 off 13A fuses without them "blowing"?
Paul

 

[Johno]

I once ( temporarily) put an immersion off a plug top thinking that 13A is ok, and it got very hot, so the moral of the story is don't take ratings in to account, common sense is more valuable.

 

[Guest123]

The only thing I would say is it's not recognised as a standard circuit in appendix 15 of BS7671 for ring and radial final circuit arrangements so you may have to note it as a departure.

 

[Deleted member 9648]

As Lenny says,..... or an alternative if feasible might be to run the 50a supply to a small DB and feed 4 single sockets or FCU's from 16a mcb's.

 

[netblindpaul]

As Lenny says,..... or an alternative if feasible might be to run the 50a supply to a small DB and feed 4 single sockets or FCU's from 16a mcb's.

Now that sounds like a plan!