Wiring a ring and radial

[Multiplex]

Is it okay to wire a ring like this?

In my garage I'm putting in a radial circuit. Is it okay to run a cable round the beams and drop a single cable down the wall for each socket similar to the picture above? Does that affect the cable rating at all (using 2.5mm)?

Thanks,

Simon.

 

[sterose]

Is it okay to wire a ring like this?

In my garage I'm putting in a radial circuit. Is it okay to run a cable round the beams and drop a single cable down the wall for each socket similar to the picture above? Does that affect the cable rating at all (using 2.5mm)?

Thanks,

Simon.

Wiring the circuit as you suggest defeats, to a great extent, the point of having a ring.

The idea of a ring is that a low-rated cable can, using a ring, supply a much higher current, with half the current being drawn equally from both sides of the ring. So that the maximum (theoretical) rating of a 2.5sqmm ring would be about 50amps - more than enough to cope with someone operating every conceivable home electrical appliance at once.

However, since every outlet in your circuit will be on a spur, ultimately the ring serves no purpose, since the current is divided around both halfs of the ring, only to be recombined as it enters the spur cable. Therefore, assuming you are using 2.5sqmm, the maximum rating of the circuit, despite having a ring incorporated into it, is still only 25amps. And you would then have to use a breaker that is 25amp or less.

I suggest you either go the full whack and install a proper ring, with no spurs, or else simply daisy-chain the sockets on a single cable.

Also, what you need to consider is what will you be using these eight double sockets for? If you will have a number of high-load appliances on the circuit at once, you should consider opting for a proper ring.

 

[felix]

Sterose is correct. Last time I looked at any wiring regulations you couldn't have more spurs on a ring than sockets. I've always thought this a bit odd because if you want an extra spur you just put in a socket you don't need and might never use!

Your plan is a good example of how general purpose regulations can fail in specific cases. Replace those junction boxes with redundant sockets and, in theory, you'll have an acceptable circuit! Seriously though, bring the cables down to the sockets and create a proper ring. The cost of extra cable will be more than offset by the saving on those junction boxes (or redundant sockets). You'll also be able to add spurs to the sockets later.

 

[Multiplex]

Thanks for the replies. I think I've fully understood what you've said.

As I'm wiring my garage, which is off a 13a FCU, and the wiring inside the garage will be a radial sub-circuit, would that make any difference?

I.e. my question is, if the benefits of a ring are wasted when wired as in the picture above, does the same apply to a radial circuit in my garage?

Simon.

 

[andy]

Thanks for the replies. I think I've fully understood what you've said.

As I'm wiring my garage, which is off a 13a FCU, and the wiring inside the garage will be a radial sub-circuit, would that make any difference?

I.e. my question is, if the benefits of a ring are wasted when wired as in the picture above, does the same apply to a radial circuit in my garage?

Simon.

radials are wired completly differnt, and can have lower ratings or use bigger cable

 

[mapj1]

If the total current is limited to 16A by breaker (or 13A by fuse), you can do what you have drawn, and dont need the final loop to be closed. It is then a 16a /13A radial and any configuratrion is fine.
Or do it in 4mm cable, and call it a 32A radial.
In many cases like garages radials are easier to handle - and of course there is no way it can be mis-wired to break the ring.