Electronic – How far apart should PCB traces be for mains isolation

high voltagepcbpower

As a hobby project I'm building a power line monitor to detect when a load is switched on and turns on some additional loads. I have 120 V 220 V running through my board and was curious what the standard board spacing is for high voltages.

I'm sure there's some specs by UL or other agencies for this, but I'm cheap.


Correction, the voltage I'm working with is 220 V, powers a cabinet saw. In any case, is there a general formula, possibly even for higher voltages (e.g. flyback for fluorescent lights)

Best Answer

Minimum 2.5mm for standard insulation (across mains), 5mm for reinforced ("double") insulation (mains to low-voltage)