For the purposes of this posting ...
(a) ... keep the current carrying capacity of a three-core mains flex constant.
(b) ... ignore any specialist mains flex such flex designed for permanent outdoor use.
(c) ... do not ignore the possibility that there may be a greater or lesser number of filaments (depending on what is permitted) in the multi-stranded cores.
-- (Q1) Is there a defined range of dimensions which the insulation protecting each of the three cores must adhere to?
Tim
-- Sent from Birmingham, UK timdunne at blueyonder.co.uk 'God's electrician sparked up the heavens once again, heading northbound
Hi Tim, that's the nicest thing anyone has said to me all day!
-- I think you will find that the specs governing cables and similar items are not freely available on the Net.
Ain`t no totally defined current carrying standards either, got a reel sitting here thats going back mainly because its the wrong colour, its catalogue page said 13A 3 core flex, conductor area is 1.25mm, usually wouldn`t pull 13A along much thinner than 1.5mm or 2.5mm at any distance. Current handling and length are related.
PVC, toughened rubber, silicone etc. Best bet would guess would be taking an average of O.D.s of appropriate cables from somewhere like R.S
Adam
The PAT test guidelines are good for this. For a 13A extension cable:
1.25mm² max length 12m 1.5mm² max length 15m 2.5mm² max length 25m (but won't fit nicely into 13A plugs). (spot the pattern -- these are easy to remember:-)These max lengths are to ensure earth fault loop impedance is still acceptable at the far end of the cable. Other alternatives are to use an RCD at the start of the cable, or to reduce the fuse value below 13A, in inverse proportion to the excess length above the maximum values above.
-- Andrew Gabriel
snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote in news:4589bbb8$0$762$ snipped-for-privacy@news.aaisp.net.uk:
Nice guide. I question that bit about the fuse though, mains voltage is usually constant enough that it can't drive extra current to overcome the extra resistance. Even if it did, the heat dissipated per unit length is the same along the whole length, so there's no danger unless the cable is coiled up tightly enough to allow enough heat buildup to melt the insulation.
It makes sense to choose the fuse value to suit the appliance's maximum draw (which will be partly based on knowing what the cable can supply), but it doesn't make sense to base the fuse value on the cable directly except where the current can rise, unless you take into account the effect of heat buildup, maybe.
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