Using a 6mm T&E to feed a Ring Main

[Ian B]

I'd appreciate peoples views on this, including compliance or otherwise with the regs.

I've come across a 1-bed flat where one ring main serves the small kitchen, and boiler & security alarm. The unusual thing is that the ends of the ring are then connected to a single 6mm T&E that runs back to the consumer unit.

6mm is run through ceiling/floor void, holes in joists (no insulation), and down a steel conduit to the consumer unit.
6mm Run length is 20m max and it's protected with a 32A MCB.

Kitchen is being refurbed, and the run back to the consumer unit is really difficult to access, so question 1 is, does the existing arrangement comply with regs?

Question 2. There is also a single 2.5mm radial from the consumer unit (16A MCB) to the Kitchen area (was an old storage heater I believe). Cable is run the same way as above.
Is this likely to be sufficient if they install a simple 600mm wide built-under oven and electric hob?
What about changing the MCB to 20A?
I guess the hob could be powered from the above "ring" if necessary.

Any thoughts?
Thanks.

 

[LlandrilloSpark]

Hi

In my opinion

The ring connected to the 6mm feed is a non standard final circuit but I wouldnt see an issue with it as long as the the Zs does not exceed the maximum stated for a 32A MCB and of course that your r1, rn and r2 values are good.

The single oven will be 13A Max and can be fed via a standard 13A Plug or fused spur from the 20A Supply under the cabinets

 

[i=p/u]

Re: Using a 6mm T&E to feed a Ring Main

Only you know by designing the circuits with the loads expected..

was at job last wek where the guy spur'd of ring in 4mm for 3 extra sockets, he said its covered by breaker do dead on.. Where I would of put spur in and then added 3 skts..

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Lollipop

 

[Octopus]

Its often referred to as a lollipop circuit, not that you would find it in a regs book.

Sometimes its the only way to work and thats to "adapt" a redundant cooker ciruit so if the dead readings are good and under the max for the MCB whats the issue - except how do you fill out the EIC?

 

[rattlehead85]

As far as point 1 is concerned, it is not a conventional circuit arrangement as set out by BS7671, However, this is what is commonly known as a Lollipop circuit and is safe. The 6mm2 is protected by the CPD you state. As long as the connection with the ring legs is accessible, the end to end readings of the ring portion are integral and the Zs values comply then electrically there is no adverse or unsafe conditions to note.

Point 2 You need to ascertain the characteristics of the oven you tend to install via this circuit. Generally if it is fan assisted you will find it comes with a plug top which means your circuit will be ok to use with a 20A MCB as these tend to be rated at around 2.4 kw.
If a conventional oven is to be placed you need to look into the possibility of a 32A 6mm2 circuit to cope with approx 5KW.

 

[trev]

Re: Using a 6mm T&E to feed a Ring Main

The RFC on the 6mm is as Llandrillo said, non standard BUT was commonly used once upon a time and is known as a lollipop ring. As long as all cables involved in this non standard arrangement have adequate ccc and as long as all disconnection times can be met then I see no problem with it. The changing of the 16A MCB on the radial to a 20A only you can answer that one mate as you're the one who knows the likely load on that cable.

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Edit, Beaten to it by just about everybody

 

[Ian B]

Thanks guys, that's confirmed what I was thinking, but couldn't identify anything specific in the regs.
Cheers.

 

[Guest55]

coffee for trev.
now hes woke up lol.
;-)

 

[singingfraggle]

Re: Using a 6mm T&E to feed a Ring Main

i have used 4mm t&e for the first and last legs on a large ring to help with volt drop if the sockets are a long way from the db
the joints are accessable as they are made in the socket outlets

 

[thomas-1981]

Is this likely to be sufficient if they install a simple 600mm wide built-under oven and electric hob?
What about changing the MCB to 20A?
I guess the hob could be powered from the above "ring" if necessary.

Don't think I would be supplying an electric hob from a ring circuit.

 

[Octopus]

Don't think I would be supplying an electric hob from a ring circuit.

What rating is it and what do the manufacturers instructions say?

 

[Heisenberg]

Isn't 433.2.1 going to have an impact on this setup?

 

[Octopus]

Isn't 433.2.1 going to have an impact on this setup?

But there isn't going to be a reduction in the current capacity is there? 1 x 6mm = 32A, 2 x 2.5mm = 32A

Just saying. lol

 

[Heisenberg]

But there isn't going to be a reduction in the current capacity is there? 1 x 6mm = 32A, 2 x 2.5mm = 32A

Just saying. lol

Doh, didn't think of it in that way, just in the reduction in cable size. 2nd time I've felt like a muppet this week :frown2:

 

[captainkev]

need to check if steel conduit is earthed also

 

[Octopus]

Doh, didn't think of it in that way, just in the reduction in cable size. 2nd time I've felt like a muppet this week :frown2:

Not a muppet mate, this is what the forum is for!

 

[kingeri]

Just to pick up on the point raised earlier, regarding spurring off a ring in 4mm to feed more than one socket outlet. I can kind of see the logic in that, and have seen it done a couple of times. Was debating this with another spark ages ago, my argument about not doing this would be that although the 4mm is protected, the potential exists to overload one point of the ring. Thoughts?

Personally, I don't see it as good practice. Regardless of the conductor size, I'd always fuse down when supplying more than one socket.

 

[TAZ]

I myself would use a spur as my interpretation of the regs was for a non fused spur direct of the ring was either one fixed 13A spur, 2 single sockets or one double socket. You can even use 1.5 T/E on the outlet connection of the fused spur to feed extra sockets BGB page425

 

[Guest55]

Just to pick up on the point raised earlier, regarding spurring off a ring in 4mm to feed more than one socket outlet. I can kind of see the logic in that, and have seen it done a couple of times. Was debating this with another spark ages ago, my argument about not doing this would be that although the 4mm is protected, the potential exists to overload one point of the ring. Thoughts?

Personally, I don't see it as good practice. Regardless of the conductor size, I'd always fuse down when supplying more than one socket.

its bad practice , frowned upon , and risks unbalancing 1 of the ring legs if not branched off at the ring mid-point.
but i've done it a couple times myself cos it solved a big headache lol.
i wont bother with the tin hat as im passed giving a crap.
;-)

 

[Richard]

Hi, this came up in professional electrician a few months back - they referred to it as a 'hybrid ring circuit'. The outcome was that it was perfectly acceptable. Useful it rings are to be controlled via contractors (I.e emergency stops ect)

 

[Engineer54]

Question 2. There is also a single 2.5mm radial from the consumer unit (16A MCB) to the Kitchen area (was an old storage heater I believe). Cable is run the same way as above.
Is this likely to be sufficient if they install a simple 600mm wide built-under oven and electric hob?
What about changing the MCB to 20A?
Any thoughts?
Thanks.

There is no-way a 16A or 20A radial circuit on 2.5mm T&E will cope with both an oven and a hob!! So you had best get a 6mm cable in while you can, to supply these two cooking appliances!!

 

[Engineer54]

Hi, this came up in professional electrician a few months back - they referred to it as a 'hybrid ring circuit'. The outcome was that it was perfectly acceptable. Useful it rings are to be controlled via contractors (I.e emergency stops ect)

Any circuit that isn't classed as a standard circuit, is classified as a ''Hybrid''.... Lollipop rings have been around for donkey's years!! lol!!

 

[GLENNSPARK]

Its often referred to as a lollipop circuit, not that you would find it in a regs book.

Sometimes its the only way to work and thats to "adapt" a redundant cooker ciruit so if the dead readings are good and under the max for the MCB whats the issue - except how do you fill out the EIC?

............

 

[Rampantchilli]

Hi, this came up in professional electrician a few months back - they referred to it as a 'hybrid ring circuit'. The outcome was that it was perfectly acceptable. Useful it rings are to be controlled via contractors (I.e emergency stops ect)

I was about to post this, glad I read the whole thing before I did