Ring Main Wiring

[Mark Carver]

I have two ring mains, (downstairs and upstairs) both fed from 32A MCBs in the consumer unit. The 'downstairs' MCB has three live connections, so I assume there's a spur somewhere ?

I wish to add a small ring of 13A sockets (6 x 13A double sockets) in a new conservatory. As the downstairs ring is rather busy with kitchen appliances etc, I am planning to add this new ring to the 'upstairs' MCB.

A: Can I do this ?

B: Can I take a 6.0mm T&E from the consumer unit to the conservatory, and connect the other end to the new 2.5mm ring closer to the conservatory ?

TIA

[Lurch]

On Sat, 05 Mar 2005 21:03:17 +0000, Mark Carver strung together this:

Sounds like it.

Depends on the floor area. For a 32A ring circuit you should not be supplying more than 100m^2.

No. If you are going to add extra sockets to an existing ring then you need to extend the ring through the new sockets. You can either do this from an existing socket in the house or from the CU but you need to 'divert' one leg of the ring through the new sockets.

However, this is all covered by Part P as it's a reasonably major project so you should be NICEIC registered to carry out this, you don't sound very NICEIC like?

[Bob Eager]

Some might argue that he does...

[Lurch]

On 5 Mar 2005 22:33:43 GMT, "Bob Eager" strung together this:

I did think that as I was typing the response. ;-)

[John Rumm]

Or not, if he does it on a building notice...

(or ignores part P altogether ;-)

[Mark Carver]

That's OK then. The entire house is 120 m^2 (served by two 32A circuits), so upstairs will be 60ish. The conservatory is 14m^2.

So I need to 'break and loop' into the existing 'downstairs' ring, and take that through the conservatory ? Just to confirm, I can't run two rings from one 32A MCB ? (which was what I was getting at)

I'm not, and what's Part P? ;-)

[Doctor Evil]

A DIYer can replace parts of a ring, but not install a new one. I'm not sure where extending comes into it.

Do a Google with Part P in the subject line on this ng.

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[Mark Carver]

You didn't spot my winking smiley Doctor !

[bigcat]

kitchen

'upstairs' MCB.

you can do whatever you want. How you do it would determine whether its reg compliant. And I spose whether it would melt and catch fire or not. In principle its doable compliantly.

conservatory,

it wont be compliant though. If you do it that way, better to make it a radial circuit. And why 6mm?

NT

[Mark Carver]

Indeed, I'd just like it to be reg compliant (though of course doing the work anyway is against Part P)

The run to the conservatory is about 6 metres. If I make the conservatory a radial circuit in its own right both 2.5 mm tails will be taking the same route back to the CU. Rather than do this is there any reason why 6.0mm cannot be used for that run, connecting to two 2.5mm cables that run round the conservatory ?

I can easily break into the upstairs ring, and include the conservatory on this. From a common seance/Ohm's law perspective this is bad as it increases the loop resistance of that circuit. I return to the question posted at 08:50hrs, can I (regs wise) connect two radial circuits to one

32A MCB ? The load on that MCB will be exactly the same as if I were to break into the existing ring.

[Dave Plowman (News)]

Why not just change the CU for a suitable one with more ways? If it's reasonably recent, you should be able to re-use the existing MCBs and just add to them. A basic empty CU is pretty cheap.

[John Rumm]

No.

You can run a spur from a ring circuit, and it is legitimate to have the spur originate at the CU if required. Unless separately fused however you would only be able to supply a single outlet on that spur. Running two ring circuits from a single MCB would not be not common practice...

with a bit of luck someone will be along shortly to quote you the regs reference ;-)

Do you not have a spare way on the CU? Since that would be the preferable place to run either a new ring circuit for the conservatory, or a radial if that would be simpler.

[Mark Carver]

Interesting

There are no spare slots in the CU, see:-

(132k jpg)

It's as old as the house, (20 years). The 16A breaker feeds an (emergency only) immersion heater. Could I upgrade that breaker to 32A (assuming suitable MCBs still exist for my model of CU ?) and run the new ring main from there, making the immersion heater effectively a spur ?

[Dave Jones]

By rights you should upgrade the CU as all downstairs skts should be protected by a 32mA MCB

[Dave Stanton]

Bloody hell, he wont run much on that !!!

Dave

[Lurch]

On Sun, 06 Mar 2005 08:50:29 +0000, Mark Carver strung together this:

Yes.

No, one 32A MCB, one ring.

Amusing.

[Lurch]

On Sun, 6 Mar 2005 13:42:45 -0000, "Dave Jones" strung together this:

I assume you mean a 30mA RCD? If so, incorrect.

Being pedantic, socket outlets used to provide power to portable equipment used outdoors require RCD protection, this may or not be the downstairs ring circuit, and even then you may not need all the socket outlets to be protected.

[Andrew Chesters]

To deal with the Upstairs ring aspect. I wouldn't. If you, or one of yours, or a future owner were to have a fault, trip the breaker for downstairs and then fry, you would feel responsible?

In a conservatory, I would be especially keen to have an RCD on the circuit.

[Mark Carver]

I don't understand ? You mean switching off the downstairs breaker assuming it fed the conservatory, then electrocuting themselves ? If so I'd label the CU accordingly.

As you can see from my photo the entire house is protected by an RCD, although it's an 80mA device.

Anyway it looks as if I'm heading towards a complete CU replacement. It seems that my present breakers are BS 3871, doing some Googling these were withdrawn in 1994. I can't find any suppliers that do replacements ?

Of course replacing the CU, would require getting the lekky board to come and remove their main 100A fuse, what can of worms does that open ?

[Mike]

Might not be. When we tended to have smaller CUs it was quite common to run three wires from the CU through sockets in various directions and join them all together at some remote point so that all sockets had dual routing.

Not sure if this is still allowed in the latest wiring regs though.