Question for electricians

[graduate_owner]

Hi all, I wonder if any electricins can answer this for me. I have a 6mm cable feeding an instant heat shower (6.5kW). There is a short section of cable (about 25cm) that runs in an uninsulated space and that space now needs insulating. Would there be an issue with local overheating of the cable if I fill the area with expanding foam? If so, would it be sensible to cut out that section of 6mm and replace with 10mm? The same applies to a different area where there is a 2.5mm ring main cable. If necessary, should I upgrade to 4mm?

Many thanks,

K

 

[Spectric]

A bigger problem is not overheating of the cable but chemical reaction between the PVC cable and the foam. The plasticers in the cable insulation can react with the foam and make it harden. You need to put the cable into a length of conduit where it passes through this cavity and assuming you have taken the loop impedances then you will know if the total length of the circuit is suitable for 6mm but you do not need to increase to 10mm through that cavity. Depending upon the loop impedance which is dependant upon several factors of which cable length has a large bearing you will also know the volt drop and confirm 6mm is the right cable, providing the lengths are not excessive a 6mm cable can take a 9 kW resistive load.