02-10-2015, 07:54 AM
(01-10-2015, 12:53 PM)ppppenguin Wrote: I wouldn't like to connect this sort of thing to anywhere other than a safety earth. Even in normal operation when it absorbs a surge it will dump energy into the earth so that earth had better be reliable and solid.
Ah! Interesting!
Yes I agree, that the earth should be reliable and solid else the surge won't be dumped. However, I'm inclined to the opposite view!
Leakage to earth must be limited to 5mA typically (hence the restriction on the maximum size of Y capacitors) - this is because the safety earth may NOT turn out to be reliable and solid, and we don't want metal casing etc floating up to a semi-live situation. Even worse, we don't want leakage to the earth lead in one piece of equipment to make all other pieces of equipment float up, due to a bad earth connection.
A separate 'earth' for RFI purposes (not connected to metal casework etc) may also not be solid, but in that case the surge won't be dumped. It won't make touchable metalwork live, or cause a dangerous situation. However, this is going OT because the original question - which came as a reequest frmo a customer - IS to connect the varistors between live and safety earth.
