Cable size

[EFLImpudence]

The table in question is a nonsense.

There is nothing electrically wrong with what you have.

 

[Iggifer]

The table in question is a nonsense.

There is nothing electrically wrong with what you have.

I absolutely detest that table. Has anyone checked to see if its in the DPC of the 18th?

 

[JohnW2]

The difference is that the plug has a 13A fuse. That limits the maximum current and makes the use of 1mm cable acceptable.

I don't want to confuse Davey, but you will know what I mean if I say there is such a thing as (compliant) downstream overload current protection. However, that doesn't help one to get away from the fact that, for whatever reason, the regs don't allow a 1mm² cable on a non-'lighting' circuit'. Had it been 1.5mm², there is an electrical argument that it should be acceptable (supplying just one single socket).

Kind Regards, John

 

[ban-all-sheds]

Thanks for your replies gents.



Yes the arrangement would result in a single socket being fed via a 1.0mm spur from an existing twin socket on a 32amp ring. The fire would be plugged into this single socket and still protected by its 13amp plug fuse.

I understand this is not permitted by the Regs but, if I've understood you correctly, the only reason is because this is fixed wiring in a power circuit?

So presumably if I used a 1.0mm extension lead to plug directly into the double socket then it would comply with the Regs?

If so, then I suppose the question I'm asking is why as I can't see any difference electrically?

Thank you

The thing about the minimum size of cable for a "power circuit" is one of the lost-in-the-mists-of-a-Friday-afternoon kind, since clearly all circuits are power circuits, that's their point. The table mentioned above is pointless anyway, since all the other regulations conspire to stop a dangerously small cable being used.

The difference between the two scenarios you outline is that with the 1mm² spur is protected from a fault in it by the 32A breaker in the CU, the 1mm² flex is after a 13A fuse.

The different characteristics of those mean that they are closer in operation that you might at first think - I'm sure someone here who has some software to do it can churn the numbers. Fault currents can be large - easily several hundred amps, and all that energy is going to heat the cable up very fast. The way it works with fault protection is that the MCB or fuse protecting the cable does its thing so quickly that the current is stopped before the cable has got so hot that bad things start to happen.

 

[JohnW2]

I absolutely detest that table. Has anyone checked to see if its in the DPC of the 18th?

'Fraid so - but with an added footnote indicating that a 'lighting' circuit can also supply small non-lighting loads like extractor fans!!

Kind Regards, John

 

[ban-all-sheds]

I've had a gas fire removed and we want to replace it with a modern electric one.

Get one with a light in it, then you've got a lighting circuit.

 

[JohnW2]

The difference between the two scenarios you outline is that with the 1mm² spur is protected from a fault in it by the 32A breaker in the CU, the 1mm² flex is after a 13A fuse.

Indeed, but as I have just mentioned (by implication), it's quite (very?) possible that measurement and calculation would show that the 32A breaker provided adequate 'fault' (short-circuit) protection for the 1mm² cable and that it was adequately protected from overload by the downstream 13A fuse. If that were the case, then it would only be this nonsensical (and certainly not electrically-based) distinction between 'lighting' and 'power' circuits that would make it non-compliant.

Kind Regards, John

 

[JohnW2]

Get one with a light in it, then you've got a lighting circuit.

Indeed ... but that circuit would then not be allowed to have a fuse/MCB greater than 16A in the CU

Kind Regards, John

 

[ban-all-sheds]

Can't have everything.

 

[sparkwright]

Could the double socket supplying the 1.0mm2 be converted to a module system comprising of a 13 amp fuse and single socket module?

 

[JohnW2]

Could the double socket supplying the 1.0mm2 be converted to a module system comprising of a 13 amp fuse and single socket module?

That's obviously a possibility - but it still would not make the 1mm² cable on a 'non-lighting' circuit any more compliant, even though it would be protected by a 13A fuse! As I recently wrote to BAS, were it not for that silly 'rule', it's very possible that the downstream 13A plug fuse would be adequate, in which case there would be no need for the upstream fuse you mention.

Kind Regards, John

 

[sparkwright]

I sometimes run a 1.0mm2 t+e cable from a FCU fed by from a ring final circuit to a kitchen extractor fan.

As does the rest of the world.

So that wouldn't be compliant.

I'm not worried about it.

 

[JohnW2]

I sometimes run a 1.0mm2 t+e cable from a FCU fed by from a ring final circuit to a kitchen extractor fan. As does the rest of the world.

Indeed. I doubt that there are many of us who have not done something like that. Furthermore, even 'worse', I might even consider feeding that FCU with 1mm² cable, for reasons I have outlined above.

So that wouldn't be compliant.

Seemingly not.

I'm not worried about it.

Nor am I - but the likes of BAS may have something to say about our 'disregard for regulations we don't like'!

Kind Regards, John

 

[securespark]

There is also the unhelpful table about 'power' circuits having a minimum of 1.5mm and 'lighting' being the only valid use for 1.0mm

What's a lighting circuit?

[Dives behind sofa...again...]

 

[JohnW2]

What's a lighting circuit? [Dives behind sofa...again...]

I think the thing is that we all know essentially "what they mean", but what we don't understand as to why there should be a difference in minimum cable CSA between 'one of those' and any other type of circuit.

Kind Regards, John