Two single sockets on 16a MCB

thevdm · 12 Nov 2018

Hi all,

By our front door is a reasonable sized cupboard which has the consumer unit in it. We have the usual radial wiring for upstairs and downstairs plus a 16a (type B) MCB which goes directly to a single socket on the other side of the wall (next to the front door) via 2.5mm twin and earth.

I would like a single socket inside the cupboard so I can move a home server into the cupboard (I'm a computer science student).

Would it be considered within regulations if I was to add a spur from the single socket back through the wall to add a single socket inside the cupboard or would this be considered wrong as the socket isn't on a ring?

I understand that this setup wouldn't allow both sockets to draw the full 13a, but the home server setup will draw slightly under an amp at full load (around 200w, which it is never at), in reality the server setup draws around 70w. The socket in the hallway tends to be used for hoovering the stairs or using a strimmer in the front garden.

So my questions are more to do with safety & regulations.

Attached is an image of what I am proposing, if this wouldn't be within regulations I'll move the single socket to inside the cupboard and use a different socket for the hoover/strimmer.

Taylortwocities · 12 Nov 2018

Fron your description of the wiring, this is a radial circuit. You could put a hundered sockets on that, but - as you say - the total maximum current that can be drawn will be limited by the 16A MCB.
Its fine. Go ahead.

PS. This socket must be RCD-protected. Is it/will it be?

thevdm · 12 Nov 2018

Taylortwocities said:
Fron your description of the wiring, this is a radial circuit. You could put a hundered sockets on that, but - as you say - the total maximum current that can be drawn will be limited by the 16A MCB.
Its fine. Go ahead.

PS. This socket must be RCD-protected. Is it/will it be?

Just realised I have got my terminology wrong, the rest of the sockets are on a ring, with the hall socket being the only socket on a radial.

That makes perfect sense, no matter what I put on it the MCB will trip before the wire burns. The section of the consumer unit that the existing MCB is running off is covered by an 80A RCD with a 30mA trip, or do you mean using sockets with individual built in RCDs?

Thank you for your help.

securespark · 12 Nov 2018

You have a ring final protected by a 16A device? While by no means impossible, they're more usually protected by a 20, 30 or 32A device.

Taylortwocities · 12 Nov 2018

thevdm said:
The section of the consumer unit that the existing MCB is running off is covered by an 80A RCD with a 30mA trip, or do you mean using sockets with individual built in RCDs?

No. If the 16A circuit is protected by a 30mA RCD in the consumer unit then all is fine.
You do not need a socket with its own RCD.

OwainDIYer · 12 Nov 2018

1. You can take a new spur from the radial off the MCB and busbar terminals (assuming they're correctly sized for 2 x 2.5mm conductors, which they will be)

10. You can have a 2.5mm radial circuit on a 20A MCB.

Don't know why people use 16A MCBs. They're really only useful for old immersion heaters installations wired on 15A fuses on 1.5mm cable. Oh, and nasty continental ovens which specify them in the manufacturer's (usually abominably-translated) instructions.

JohnD · 12 Nov 2018

A single socket on a 16A radial?

50p says it used to be a night storage heater point.

thevdm · 12 Nov 2018

Ok, so it's sufficiently covered by the existing RCD.

From what I've read a 20A MCB is the norm for 2.5mm2 radials so this 16A one is a mystery (possibly because it only goes to a single socket). The 16A MCB for the radial is already in place, as I'm not an electrician I'll be leaving it in place. I can't see the 16A limitation being an issue for what I'll be using it for.

Not too sure about the storage heater point as the socket comes out right next to the front door (as in with a plug in the socket there's about 2 inches of clearance from the front door opening) so the heater would either block the door or the stairs. I think I'd put my money on a previous occupier wanting somewhere to plug a mower in for the front garden.

On a side note, it's an ex-council house, from what I gather they always opted for gas central heating (which I'm happy about after living in houses with storage heaters).

AndyPRK · 12 Nov 2018

Yeah the 20 and 25A MCBs are much nicer.

It must be history from the 15A round pin sockets!

ban-all-sheds · 12 Nov 2018

thevdm said:
I would like a single socket inside the cupboard so I can move a home server into the cupboard

Cooling?

Taylortwocities · 12 Nov 2018

16A is the sort of MCB that one has 'on the van' and is perfectly OK for the socket installed, and to add a second given the anticipated use.

20A and 25A MCBs need some thought by the every day installer, maybe a separate trip to Screwfix........

I know it would be the best solution for the MCB to be nearer to the CCC of 2.5mm² T&E but, really, it ain't worth even discussing.

@thevdm just get on with it mate. Anything else is just people who have nothing else better to do than to start an arguement.

thevdm · 12 Nov 2018

Quite possibly, when we moved in I found a round pin plug in the loft! The house is circa 1920s so will have gone through that iteration. The consumer unit is much newer though an the cabling going to the socket is blue/brown though.

Cooling isn't an issue at all, a single rack server in a cupboard with exterior air bricks will feel like it's on holiday. A full height rack stocked with servers may require some extra though (in cooling as well as the 16A MBC being an issue)

@Taylortwocities I'll source a new single socket and a couple of foot of 2.5mm t&e to get this sorted

AndyPRK · 12 Nov 2018

Splash out and get a double socket !

thevdm · 12 Nov 2018

AndyPRK said:
Splash out and get a double socket !

I'd have to check the bank balance to make sure I've got another 50p for that

monday · 13 Nov 2018

OwainDIYer said:
You can take a new spur from the radial off the MCB and busbar terminals (assuming they're correctly sized for 2 x 2.5mm conductors, which they will be)

Just curious. Is it in fact OK to take two radials off a single MCB? Absolutely OK or sort of OK? Assuming the MCB is correctly sized.

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Two single sockets on 16a MCB

thevdm

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