[Drramore]

If I want to weld a patch on to my very thin (1 mm) metal shed, and so use electrode negative so as not to blow through the sheets and to get a good weld, is there a risk that clamping the positive electrode to the shed, which is likely to be earthed simply due to contact with moist soil / deep metal pins, etc., will cause an electrical short.. at best tripping a switch, at worst causing an accident / fire?

Would someone opening the door to the shed be at risk of an electrical injury?

Thanks people

[cwby]

NO. You will be good to go.

[Oscar]

Agreed. In short, No, you will be fine, regardless of what polarity the clamp is. The electricity from the welder will not short to the actual earth ground.