- Reaction score
- 2,441
From a quick look most places seem to use the same table in their literature, even the cable makers - though the one in the OSG seems to suggest it's more for Twin and Earth, not singles (with the 2 cables reference), Though if they are run cable tied together that probably has no effect anyway.interesting. so if the fuse is, as you say, to protect the DNO's cable etc., then the tails are not, themselved protected. only downstream in the CU, and indirectly by the actual max. load that may be relevant at any one time. therefore, using 25mm tails just because the DNO fuse is 100A is not justifiable. tin hat on by a guy who regularly fits 16mm tails.
you say 92A for 16mm, but according to table F4(i) in osg ( green 17th ed), no figures are given for 16mm single cables in free air (ref. method F). 25mm CCC has a 45% highr rating method F as opposed to methoc C, which woulf extrapolate for 16mm as 114A.
Cable tails do often need to be clipped to secure them so the actual rating is likely somewhere between Free Air and Clipped Direct
Prysmian give 87 for 16mm and 114 for 25mm (clipped direct) but don't give a "Free Air" rating.
You could probably up that a bit in many locations because of ambient temperature being lower than 30C.
And I imagine a majority of houses with gas heating and without multiple electric showers never come close to that load for any length of time in any case.
So it's likely an issue of theoretical 'risk' rather than a practical one. I've seen youtube videos of 63A RCDs that have clearly been melted/damaged by overload where they are protecting multiple high load circuits, but not seen any equivalent damage to the tails.
Personally now that Toolstation have the Doncaster 19 strand easi fit tails I tend to get them automatically because they are so much easier to wrangle into place. It also means one less thing I have to worry about when deciding what is needed.