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MG TD TF 1500 - Thinwall Cables Scare Me

I'm presently making up a new wiring loom for my TF to include heavy duty wires for the charging circuit (alternator fitted) and relays for the head lamps, auxiliary lamps and electric fan. I've sourced all the cables, in the correct colours from Vehicle Wiring Products and am using single core PVC thinwall cable. The wires to the relay coils from the switches are rated at 16.5amps but are only 2m/m external dia. Original type wire rated at 8.75amps is 2.5m/m dia. The power feed to the relay contacts and then on to the headlamps is rated at 25amps (60watts x 2bulbs divided by 12vots = 10amps so plenty of safety) and is 2.8m/m dia. I've checked our year old Toyota and sure enough the cables are thinwall. Even so it is scary to see small diameter cables replacing the bulky old ones. I've also found that AutoSparks will cotton braid my new loom in original materials.

Jan T
J Targosz


Iím going to use the CSA standards for calculating load by wire size, as I canít quickly find the Eurocodes.

Temperature ambient notwithstanding, a copper wire of 2 mm dia is a equivalent to AWG 12 which is rated 41 amps in free air. Enclosed (like in a plastic sheath), its rated at 23 amps.

Similarly, a 3 mm dia copper wire is rated between AWG 8 and AWG 10 and can carry
≈64 amps in free air and ≈40 amps enclosed.

In either case, thatís a lot of current and I donít know what devices you are connecting but, except for the horn, no device I know on a T-Series, including a heater, approaches these kinds of loads. So I donít think you have anything to worry about.

As for the PVC wire jacket, you and I will not live to see its deterioration!

Sounds like a very professional installation.

Gord Clark
Rockburn, Quť.
Gordon A Clark

Hi Gordon,

Go to (UK is lower case but my iPad changes it to upper) and you will find details of the number of strands, diameters and current capacity for all sorts of cable.

Have a good weekend

Jan T

J Targosz

This thread was discussed on 08/08/2014

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