Extending Ring - cable protection

[IJWS15]

I want to extend a ring circuit into a conservatory (Local BC say it is not notifiable).

As one of the cable runs crosses a doorway I was intending to use SWA for that run (not 50mm cover) and checking B&Q this morning the 1.5mm is rated at 28A (same as 1.5 t&E PVC which will be used on the other parts of the ring extension.

I was expecting to use 2.5mm SWA (same cross section as the 2.5 T&E)but looking at the rating am I OK with 1.5?

Circuit is protected by 32A MCB and 30ma/30MS RCD (Split load CU)

 

[jj4091]

Cable rated at 28A, MCB at 32A, do you think that seems ok? No go for the 2.5mm.

 

[Steve]

1.5mm² t+e is NOT rated at 28A! Think you were looking at the figure for 2.5mm².

I am unsure of the exact optimum rating - would think about 18 amps or so, but 1.5mm² is NOT to be used in ringmains! Not even as SWA!

It alters the current carrying characteristics of the ring to use different size cable, so stick to 2.5mm² all the way.

 

[JohnD]

OOI, are you enlarging the ring, or are you taking a spur off it?

 

[IJWS15]

Enlarging the ring! Want 3/4 twin sockets around the conservatory so it would be a couple of spurs, may as well join the ends and break the original ring.

The 1.5 SWA is definitely rated at 28 A - same as PVC 2.5 t&e> I looked twice. Ring cable so 28 * 2 = 56 with a 32A MCB.

See also
http://www.tlc-direct.co.uk/Products/SW1dot5slash2.html 27 Amps
and
http://www.tlc-direct.co.uk/Products/CA2dot5G.html 24 Amps

TLCs 1.5 SWA is rated higher than theri 2.5 PVC T&E! So if I can't use 1.5 SWA does that mean all the 2.5 T&E PVC is dangerous?

 

[Steve]

Those ratings quoted for cables are all "optimum"s and vary by manufacturer. The ACTUAL rating of a cable depends on the way in which it is installed and the distance of the run. So it is always best to stick to the norm.

The thing with a ring is it should be balanced as much as possible. Introducing different size cables immediately unbalances the current in the circuit, since part of the ring now has more resistance. Dont do it.

 

[IJWS15]

2.5 it is then.

 

[securespark]

Also, that higher rating is for XLPE SWA only. Ordinary PVC SWA is not rated that highly.

 

[Adam_151]

Also, that higher rating is for XLPE SWA only. Ordinary PVC SWA is not rated that highly.

Just to add to what simon has said for reference, even if you are using XLPE SWA, you should use the current carrying capacity tables for PVC SWA unless you have checked that whatever you are terminating it in can cope with conductors at 90 degrees C...

And yeah, 2.5mm² for a ring , don't be a daft git and do it in 1.5 , price of cable is falling again now you know...

 

[ricicle]

And yeah, 2.5mm² for a ring , don't be a daft git and do it in 1.5

Unless you're an MI fan

P.s 1.5mm² XLPE clipped direct is 27A not 28A as has been said above

 

[Adam_151]

Unless you're an MI fan

Not really, my MI work seems to have more kinks than any girl I know...

 

[ricicle]

Unless you're an MI fan

Not really, my MI work seems to have more kinks than any girl I know...

It needs more caressing with your fingers