Security Light

asuk73 · 31 Mar 2004

Hello,

I cannot connect to the indoor lighting circuit for an outdoor light supply so I'm thinking of teeing off the ring main with a junction box to supply a switched 3amp FCU to the (100w) light.

My (main) concern is that I might be teeing off an already dodgy spur supply rather than the ring main. I can't tell for sure because most of the wires are hidden in ceiling and wall cavities but it looks like there is only one cable supplying a double socket and one cable off that supplying another double. The sockets are currently only supplying electricity to a fridge freezer and are hidden behind new kitchen units.

Should I add a 13amp FCU and then worry about the JB and 3amp FCU? I've read here that as long as you put a 13amp FCU in a supply you can run a few spurs off it.

What other safety factors should I take into consideration? Will this work at all?

I'd appreciate any advice before I blow anything up or burn anything down.

Stod · 31 Mar 2004

asuk73 said:
one cable supplying a double socket and one cable off that supplying another double.

Does the "other double" have two cables to it? if so, it and the first double could both be on a ring.

Switch off at the consumer unit, remove both cables from the first double and check continuity from one cable to the other. If you have continuity, it's on a ring.

asuk73 · 1 Apr 2004

Turns out what I thought might be a dodgy spur is actually a Radial circuit for a dedicated Freezer supply. I've now fitted a 30amp JB and teed off to the 3amp switched FCU and everything works great.

Looks like my CU has a mixture of Radial and Ring circuits. Is this common?

sterose · 1 Apr 2004

asuk73 said:
Turns out what I thought might be a dodgy spur is actually a Radial circuit for a dedicated Freezer supply. I've now fitted a 30amp JB and teed off to the 3amp switched FCU and everything works great.

Looks like my CU has a mixture of Radial and Ring circuits. Is this common?

Yes, it is as common as white bread. Rings are generally only used for sockets, and everything else is radial. It wont hurt to have other circuits as rings though, if you do happen to have them.

securespark · 1 Apr 2004

sterose said:
It wont hurt to have other circuits as rings though, if you do happen to have them.

I think a little clarification would not go amiss here, sterose

kendor · 3 Apr 2004

Stod said:
asuk73 said:

one cable supplying a double socket and one cable off that supplying another double.

Click to expand...

Does the "other double" have two cables to it? if so, it and the first double could both be on a ring.

Switch off at the consumer unit, remove both cables from the first double and check continuity from one cable to the other. If you have continuity, it's on a ring.

just to add to stod's comment, if it is found out that the two double sockets are on a radial then this would not be permissable as you are only allowed three sockets on a radial and a double counts as two.

dingbat · 3 Apr 2004

kendor said:
just to add to stod's comment, if it is found out that the two double sockets are on a radial then this would not be permissable as you are only allowed three sockets on a radial and a double counts as two.

Sorry to butt in here but this statement is incorrect.

The On Site Guide, p.151, has this to say. "A ring or radial circuit, with spurs if any, feeds permanently connected equipment and an unlimited number of socket outlets and fused connection units."

Further, on p.153, "The total number of fused spurs is unlimited but the number of non-fused spurs should not exceed the total number of socket outlets and items of stationary equipment connected directly in the circuit." And finally, "A non-fused spur feeds only one single or one twin or multiple socket outlet. or one permanently connected equipment."

I think that's pretty clear. As many as you like on a radial but only one bit of kit (whether it be a single/multiple socket-outlet or permanent equipment) per non-fused spur. I would also add that you should apply a certain amount of common sense... if only it were more common. Hope that helps

Big_Spark · 3 Apr 2004

kendor said:
just to add to stod's comment, if it is found out that the two double sockets are on a radial then this would not be permissable as you are only allowed three sockets on a radial and a double counts as two.

Kendor, your comment is inaccurate. The number of sockets you can put on a radial is actually unlimited, it is goverened by floor area and protective device, please look it up if you don't believe me.

OSG, page 150, table 8A. I appreciate that common sense and the Regs may clash on this, and I agree there should be a limit, but unfortunately it is yet one more example of the Regs being out of touch.

Secondly, double sockets only count as a single outlet.

dingbat · 3 Apr 2004

Is it me, or is there an echo in here?

Big_Spark · 3 Apr 2004

Is it me, or is there an echo in here?

Don't know what your on about fella

Inspector · 4 Apr 2004

FWL
I agree with kendor that a double socket counts as 2. Please advise on where in the regs/OSG you are getting this info.

kendor · 5 Apr 2004

Unless things have changed drastically recently, I was always under the impression that the "unlimited" applied to ring circuits within 100m squared and that radials have always been limited to three socket outlets counting a double socket as two?
I'd be grateful if you could put me right on this by quoting the exact regulation index numbers that state otherwise

dingbat · 5 Apr 2004

kendor said:
Unless things have changed drastically recently, I was always under the impression that the "unlimited" applied to ring circuits within 100m squared and that radials have always been limited to three socket outlets counting a double socket as two?
I'd be grateful if you could put me right on this by quoting the exact regulation index numbers that state otherwise

See the On Site Guide pages 150 and 151, particularly Table 8A. The pertinent sentence is, "A ring or radial circuit, with spurs if any, feeds permanently connected equipment and an unlimited number of socket-outlets and fused connection units." In the table a 2.5 sq mm cable with a 20A overcurrent device could form a radial circuit serving 50 sq m floor area with an unlimited number of sockets. There is no specific mention of socket numbers or areas in the regs themselves, although regs 433-02-04, 131-03-01 and 553-01-07 are interprted by the OSG and Guidance Note 1 to come up with the accepted practice.

As for the number of socket-outlets per utilisation point issue, the same page in the OSG gives this advice, "...each socket-outlet of a twin or multiple socket-outlet being regarded as as one socket-outlet." So in this regard you are correct. The confusion arises because you can replace any single socket on a ring circuit with a twin or multiple socket-outlet without breaking the rules - you are increasing the number of outlets but not the floor area served. (This may be at odds with earlier editions of the regs.)

As FWL has said many times the regulations can be misleading and easily misread

kendor · 5 Apr 2004

Thanks for the info dingbat and to all that put me right on this (the mention of 50sq m jogged my memory on this, it was an old reg that mentioned max of 3), I have since read that there is a recommendation of a max of 10 outlets per circuit.
Regarding the ring circuit as you rightly said you can add unlimited sockets as long as the floor area(100 sq m) isn't increased is as i've always understood it.

dingbat · 5 Apr 2004

kendor said:
Thanks for the info dingbat, I have since read that there is a recommendation of a max of 10 outlets per circuit.

In any event, when designing a circuit the important thing is to bear in mind what it is for. Permanently connected equipment should either have its own circuit or be capable of being independently isolated/protected (fused spur being the norm). As for the number of sockets, a six-socket circuit serving the kitchen is likely to have a higher potential load than the same thing serving, say, a conservatory. The only bad outcome of having too many sockets on a circuit should be that your overload protection operates. Inconvenient maybe, but safe.

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Security Light

Stod

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