Ring main off a radial.

[Sparky_Chris]

Hello.

Just been looking at a job for a shop and noticed something that came to my attention. The ring main for the shop floor is run off a radial circuit from the CU. It runs in a single 2.5 t&e then into a 45amp cooker switch, so its easier to switch off at night (apparently), then into a ring. All protected by a rewireable wylex 30A fuse.

Would it be acceptable to either:

>Replace the 2.5mm cable from the CU to the switch with 4mm or 6mm?

>Or to down grade the fuse rating to a 20 or 16 amp?

I would prefer to rewire it to bypass the switch so the ring is straight into the CU but just wondering if any of the above options are a possibility.

Thanks.

 

[revjames]

The single cable is not sufficient size to remain on the 30A - should be downrated to 20A unless you convert the wiring to a ring.

 

[ADS]

Hi Chris,

I've debated this before and I personally don't have a problem with the set up - although half the sparks on here are going to disagree....guaranteed.

The problem is the 2.5mm - at the very least that needs upgrading to 4.0mm.

Other than that you'll have a 4.0mm feed into a double pole isolator, with a ring final run off that - not conventional, but I don't see a problem with it.

I assume there isn't a cooker running off the 'cooker switch' as well.

 

[ProDave]

Yes this was debated when I encountered one a while back.

In my case it was a 6mm feed, and the forum dubbed it a "lollipop" circuit.

Upgrade the 2.5 feed to ideally 6mm, or downgrade the MCB If you want to push it to the limit, you can sometimes get 25A MCB's.

 

[Doc Hudson]

Hi Chris,I've debated this before and I personally don't have a problem with the set up - although half the sparks on here are going to disagree....guaranteed.

The problem is the 2.5mm - at the very least that needs upgrading to 4.0mm.

Other than that you'll have a 4.0mm feed into a double pole isolator, with a ring final run off that - not conventional, but I don't see a problem with it.

I assume there isn't a cooker running off the 'cooker switch' as well.

Yes this was debated when I encountered one a while back.In my case it was a 6mm feed, and the forum dubbed it a "lollipop" circuit.

Upgrade the 2.5 feed to ideally 6mm, or downgrade the MCB If you want to push it to the limit, you can sometimes get 25A MCB's.

I have seen two common occurrences of this situation, one with kitchen sockets when an old electric cooker is replaced with gas and kitchen fitters use the cooker 6.0mm to supply a small sockets ring. Or during a loft conversion when an old electric shower feed becomes the supply for the loft sockets. Obviously in both of these situations the suppling radial cable was larger. I think the issue under concern previously was the CPC size. the 2x1.5mm CPC's of the 2.5mm T&E's against the single 2.5mm CPC of the 6.0mm T&E.

DOC H

 

[ianmacd]

That and its actually just a radial as it fails to comply with 433.1.5 so you should be complying directly with 433.1.1.

 

[gordy71]

The ring should go back to the board really otherwise it might get mistaken for a radial and continuity of the ring would not be confirmed when tested in future. Therefore even if you did upgrade the cable, the 2.5 part would be undersized if continuity was broken.

 

[Sparky_Chris]

Thanks for your replys.

Going back there tomorrow to sort it, just was interested to see what your views were.

Cheers.

 

[philbas]

It has been dicussed before, called a lolipop circuit, in my opinion (and that is not everyones), If the cables at any point meet the ratings its ok.

 

[PC Electrics]

Hello. Would it be acceptable to either:

>Replace the 2.5mm cable from the CU to the switch with 4mm NO or 6mm YES?

>Or to down grade the fuse rating to a 20 or 16 amp?

Thanks.

4mm won't comply on a 3036 - don't forget the 25% derating.

And put a label on the CU about the radial supplying a ring.

 

[NozSpark]

I should have Patented that "lolipop" idea

 

[philbas]

I should have Patented that "lolipop" idea

To late, strange though it may seem they have this setup at well known trainig centre for the 2391 exam, I got to test the board as part of my 2330 preparation.

 

[steptoe]

To late, strange though it may seem they have this setup at well known trainig centre for the 2391 exam, I got to test the board as part of my 2330 preparation.

Noz , you teaching now ?

 

[NozSpark]

Noz , you teaching now ?

Just learning mate,,, every day, something new!!

 

[Apache]

IF you want to do something about it you could always run another length of 2.5mm from CU to the isolator and take the rig back to the board, even if you still fed it through some kind of isolator.

 

[gordy71]

Think apaches suggestion is the best as it makes it clear what sort of circuit it is from the DB. Then add a 3 pole rotary isolator so that the legs of the ring are separated through the isolator, L,L AND N. No longer a sneaky ring in disguise:coat

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Oh but then the neutrals would be connected? :|

 

[Sidewinder]

4 pole rotary isolator, LNLN or LLNN appropriately marked ov course!