UL compliance leakage testing, GFCI

[tiberinus]

Hello,

A general question on UL compliance testing on safety, this is for vending machine. UL 751 to be exact.

1) The GFCI can it be a class C? The equipment is 250V rated and grounded. Class A trips at 4-6mA Class C 20mA

2) paragraph 59.7 allows removal of EMC filter capacitors (DC path) for hi-pot, the filter capacitors also provide a path during leakage current testing. Can the capacitors be removed prior to leakage current testing?

Thanks for looking

 

[Sunnysky]

If using AC HIPOT , filter caps must. be removed as filter leakage current to ground is proportional to Vcm-gnd HIPOT test.

This is why DC HIPOT is better with 1.41* AC voltage. with a slow ramp.
I recall 10% higher voltage permits a 1 second test vs long test.
Then no caps need to be removed as they must be rated for 3kV min.

HOwever, HIPOT cable should be modified to insert many 100K series R's to withstand the voltage and limit the current when an arc occurs, yet still trip the tester and thus protect the DUT. Otherwise failures will also catastrophically damage the DUT from capacitance discharge of a DC HIPOT tester

The DC filters have nothing to do with the AC leakage test. HOwever if DC output is grounded and not floating, then and the transformer isolation has more stress with a DC HIPOT test, damage can occur on the DC side without the above modification to HIPOT cable or tester.