SY Cabling - Current Carrying Capacity

SY is not recommended if the braid is the only earth, but if you use it where it is not critical, where you could have used arctic flex or something its not really an issue 4D2a is probably a good place to start for similar situations.

Mike

In my view, the braid of SY cable should be earthed under all common conditions, but should not be relied upon as the sole means of earthing. One core should be used as the earth IN ADDITION to the braid.

The braid needs earthing as it could become live in cases of damage. The braid should not be relied upon as the sole means of earthing as the conductivity is too low.

Returning to current carrying capacity, I would expect that SY would have a greater current carrying capacity than a similar sized PVC insulated and sheathed flexible cord, due to the greater diameter and surface area from which heat can be dissipated. However in the absence of any PROOF of this higher rating, I would adopt a cautious approach and assume the same rating as PVC flex. 

Manufacturers' data?

centralcables.co.uk/.../YY-CY-or-SY-style-current-ratings.pdf

Was not aware of that. It would in my view be reasonable to use the current ratings supplied by the maker. De rate if required for grouping or high ambients.

broadgage said:

It would in my view be reasonable to use the current ratings supplied by the maker.

But it would have to be the specific manufacturer and product, because there is no constructional standard.

Which is OK ... but there's a lot of the stuff out there with no apparent markings for us to check ...

That's not really true, The copper core areas and insulation thicknesses are set by various DIN standards and the copper CSA is to the same standard as any  similarly stranded flex without the outer braid.

The great unknown is the sometimes rather whispy steel braid, which when earthed is very good at blowing RCDs if the cable gets damaged, but tends to lose if pitted against a hot wire fuse of more than perhaps 10A, burning back from the nail or what-ever faster than the fuse blows (a self clearing fault..). Braid coverage also varies between brands from about 85% of the outer area to something like the wire braid equivalent of fishnet tights from the shallowest  end of the market.

The second unknown is the degree of UV resistance, but that varies among ordinary cables too, and if in doubt avoid the most exposed locations or insist it be inspected regularly.

We use a lot of it at work for things that need screening from an EMP and to be flexible, but do not use it as an armour,

Hence my earlier comment that it is fine as  slightly  tougher than arctic flex for similar locations, but it is nothing like an  SWA. And I agree with Broadgage - earth braid tails at both ends please, but use a CPC core as well.

Mike