Can a ring main spur start at the consumer unit.

[Michael Chare]

Do the wiring regulations permit a 13amp ring main spur to start at the consumer unit. i.e. The two ring main cables, and the spur cable would connect together at the consumer unit.

[Doctor Drivel]

Why not put the spur on its own mcb for better protection, organisation and neatness, if you have a spare mcb slot of course.

[Andy Wade]

Yes, that is allowed. The spur can of course only feed one single or double socket, or one item of fixed equipment.

[Michael Chare]

Yes, - but I knew that I could do that! - I may have to if I can't get three wires into the fuse box terminal.

[Dave]

Stupid boy!

Why not answer the question?

Dave

[Stuart]

Does that also apply to taking a feed for a light in the cupboard the cons unit is fitted from one of the lighting circuits in n the cons unit ..

Stuart

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Shift THELEVER to reply.

[Andy Wade]

Yes - but bear in mind that it's a good idea to have such a light on a different circuit to the other surrounding lighting.

[Andy Hall]

If you were feeding a light from a ring circuit, then the connection would have to go via a fused spur unit with 3A fuse.

A better solution would be to connect the light to one of the lighting circuit MCBs - normally 6A

A better solution still would be to make the light a maintained emergency fitting and to have it switched on when you open the cupboard door. Little 8W ones are available for about £18.

[John Rumm]

Oh, the door switch is a nice wrinkle I had not thought of doing ;-) (works well in fridges I guess)

Out of interest where can you get maintained fittings for £18? (I know TLC do non maintained ones for that sort of money[1], but not seen a maintained one at that price)

[1] I needed a bog standard rectangular fluorescent bulkhead type fitting for a friends garage/workshop the other day, so I bought one of the newer cheaper non maintained ones they added to the catalogue recently. IIRC was about £14 instead of the normal £20 for the Legrand ones. It was actually a *much* better design from the POV of the installer. The base could be fixed in place and the the main module with tube and Tx etc fixed in place and then hinged down for wiring. Hence you did not need to play the game of dangle a 'kin heavy fitting from the supply wires).

[Mike Tomlinson]

In article , Andy Wade writes

Wouldn't that mean the spur would be fed from a 32A MCB (since the OP is talking about connecting the spur to the same MCB as a ring final circuit), and thus be incorrect? I'd have said that a spur wired using

2.5mm cable should have a 16A or 20A breaker.

[Trevor Smith]

I thought that all spurs on a ring main are fed from a 30A fuse/32A MCB or have I got it wrong all these years

[Dave Plowman (News)]

They tend to be the same size as those in sockets, so will take 3 x 2.5mm cables ok.

[Dave Plowman (News)]

In principle it's no different from any other spur on a ring. However, if the proposed new socket has easy wiring access to the CU (as is obvious) I'd say it would also be easy to incorporate it into the ring rather than making it a spur.

[Andy Wade]

No, you're quite correct. The 30 or 32 A device only provides s/c protection for the cable; overload protection is provided by the 13 A plug or FCU fuse(s) downstream. That's why there's a restriction to one load point (it being assumed that the load on a double 13 A socket won't exceed 20 A, and that only one side might be overloaded at any particular time).

[Christian McArdle]

No. A shortish length of 2.5mm may be short circuit protected by a 32A Type B MCB, provided that alternative means are found to protect against overload current. Such overload protection may be downstream in the form of BS1362 plug top fuses, provided that only one accessory (such as a double socket or fused connection unit) is attached.

Christian.

[John Rumm]

IME, they tend to be a good deal larger than that on modern CUs... the screw connection on the top of the MCBs tesds to be common across the range regardless of the actuall MCB rating. Hence are usually good for a

16mm^2 cable, and the neutral bus bar will usually have at least some locations that will take that size.

(much depends on the type/age of CU we are talking about here)

[Doctor Drivel]

If the spare slot is there use it, and do it professionally.

[Doctor Drivel]

I agree he is stupid.

And encourage people to do cowboy work? You would do that wouldn't you? You are lower than whale shit.

[Stuart]

I was intending taking it from the lighting circuit mcb but as someone else said a better idea would be to use a spare mcb so it's on it's own . Stuart

Shift THELEVER to reply.

[John Rumm]

Do stop talking crap.

A spur is a perfectly legal and acceptable way of extending a ring final circuit. There is no reason said extension can not be taken from the consumer unit if that is the most logical place to take it from.

The choice of how to feed the circuit should be decided by the intended use of the extension, and where it logically "fits" in the whole design. For example it may make far more sense if adding one extra socket to a "downstairs" power circuit to keep if fed from the same MCB as all the other sockets. Otherwise you create an additional safety risk when a future maintainer comes along and turns off the downstairs socket circuit without realising that one of them is fed from its own MCB that some plank forgot to label. If however you are adding a supply for a set of interlinked smoke detectors then that would be far better taken from a dedicated MCB.