Hi Eric:
You pose some good questions about functional grounding versus safety grounding. The products I am working with are double/reinforced insulated, but are provided with a ground for EMC and ESD purposes, not for safety purposes. (We do this because we KNOW that the product will be used in sites where there is no ground -- we are willing to sacrifice EMC and ESD performance, but not safety.) Nevertheless, the ground wire and its connections must comply with all of the applicable safety requirements. This is because, without a detailed knowledge of the product, one cannot tell whether the ground is functional or for safety purposes. Therefore, it must be assumed to be for safety purposes. The ground wire is brought into your product and fastened to some metal part which you require to be grounded. In one of our products, this was the core of the transformer. Or, if you don't have any metal, then the wire goes to a terminal. Note that up to the point where the ground wire terminates is the extent of your "safety" ground. At this "terminal," you transition to functional grounding. With regard to hi-pot testing, yes, you do need to perform the hi-pot test from mains to ground. This test will also simultaneously test the insulation from mains to your 12 volts. (You will need to decide whether to test at double insulation levels or grounded levels. I recommend you test at double insulation levels.) The transient protection from 12 volts to functional ground will not be activated because there is insufficient current through the mains-to-12-volt insulation system. However, during the hi-pot test, due to the circuit and device capacitances, the transient protection circuit will tend to hold the 12 volts near ground potential. There is no need to perform a hi-pot test between signal and functional ground as the 12 volts is considered safe to touch. Regards, Rich ------------------------------------------------------------- Richard Nute Quality Department Hewlett-Packard Company Product Regulations Group San Diego Division (SDD) Tel : 619 655 3329 16399 West Bernardo Drive FAX : 619 655 4979 San Diego, California 92127 e-mail: [email protected] -------------------------------------------------------------
