On Tuesday, 21 November 2017 09:00:48 UTC, GB wrote:
Wiring immersion heater - how important is it to use special heat
resistant flex?

Also, will 1.5mm2 do for a length of just over 1m in open air, or is
2.5mm2 required?

PVC's temp limit is only a bit above DHW temp. Ordinary 1.5 would be fine if the terminals were cold, but they're above DHW temp, so you need heat resistant pvc plus thicker flex to minimise the temp rise in the flex due to the current it carries.

As Brian points out PVC can be run above its temp limit, but doing so is not really safe. It goes very soft, conductor migration occurs easily and only a little contact resistance sends it over the edge.


NT