On Wed, 23 Apr 1997 [email protected] wrote: > I have another question regarding class II equipment. My power supply > intends to use a printed wiring spark-gap for transient/lightning > protection. It's inherent design requirements are such that the air-gap > spacing are less than those specified for double insulated (4mm). If the > gap is increased to 4mm then this spark-gap will not work except at > voltages too high to provide protection.
> Is anyone familiar with exceptions to the clearance rules when using > spark-gaps? I have heard that some European countries don't like using MOVs > (an alternative to a spark-gap) but a spark-gap cannot fail in a short > circuit like a MOV could. It is a dangerous assumption to make that spark gaps do not go short circuit. With sufficient energy in the arc generated, the printed circuit base material can carbonise and leave a conductive path. Additionally we have used spark gaps in low voltage circuits and to be effective any conformal coating or screen must be left off in this area. This can cause leakage due to dust and moisture build up. If the spark gap may bypass other protective insulation, then I believe this is just as dangerous as an MOV in the performing the same function. My views only, Bruce Hunter
