DIYbanter - View Single Post - Cable Capacities

Andy Wade

wrote:
I have only just found the self build wiki[...]

In the electrics section, regarding cable capacities it says:
The current carrying capacity of typical cables a
6242Y T&E : 1.0mm2 14A
6181Y Single: 1.0mm2 11A

Why is the capacity of the single significantly less than the T&E?

Incorrect, out-of-date or inadequately specified cable ratings abound on
the Web, so be careful. In fact it is rare, IME, to see correct
figures. BS 7671:2001 + Amd 2:2004 and the On-Site Guide are your friends.

In this case it looks as if comparison is not being made between similar
installation methods.

The up-to-date clipped direct rating for 1 mm^2 T&E (6242YH) in a single
phase circuit is 16 amps, or 11.5 amps if enclosed in conduit in an
insulated wall (with the conduit against studwork or masonry. [BS 7671
Table 4D5A]

For singles we use Table 4D1A which gives 15.5 amps clipped direct
(which would apply for 6181Y sheathed singles) or 11 amps in conduit in
an insulated wall as above (& would normally be 6491X insulated singles
as in an all-conduit/trunking installation).

When properly compared the ratings are very similar.

I would have thought it would be the other way round as there is
potentially twice the current flowing in the T&E cable and hence a
higher heating effect.

No, the ratings are always for a _circuit_, either single phase (2 wires
or cables) or 3-phase (3 or 4 wires or cables). (For a ring circuit
interpret this as the rating per 'leg' of the circuit.)

HTH
--
Andy