I think it would depend on the circuit or circuits & what equipment the RCD is protecting. I guess changing it will cover further additions or changes of equipment that would need DC protection.
As James posted. It would seem that upgrading to a 2.5mm cable reduces volt drop, but the 13amp connections at either end may warm up with long periods of welding even if you manage to wire them. What is the max load of the welder?
Unfortunately, that is why a skilled or a Competent person with Electrical knowledge is required & especially in the workplace a senior member of staff is no substitute to being Skilled. Makes me wonder if you have heard of the Electricity at Work Act & various HSE requirements in the workplace.
Public Liability when I was doing Domestic work was for £2Million, now mainly commercial I have increased liability to £5million.
I use part-time labour & have Employers Liability for £10Million.
It is not possible to earth the casing with only 2 wires. If the element leaks current to the casing & is not protected then it may become live to the touch. Proof that the element is double insulated or purchase another unit may be a 12v with a 230v/12v transformer.
So your thermostat has a 13 A UK socket where you want to plug in your element? How do you earth the element then as it only has 2 wires ? Which I do not think is double insulated, Are there any labels with a square within a square symbol? Is the incubator casing metal at all?
Sorry , just seen...
This situation within kitchens I think has never been successfully discussed with a sound solution., leaving the installation of a dual cooker plate & everything connected to it regardless of individual appliance circuit protection.
Do not put a plug on it.! Post pictures of the element & its intended use. As it is aluminum cased it will need to be Earthed. Also on its own it will be constantly heating without a thermostat
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