Hello John:
> I've never measured the 'frequency response' (trip current vs.
> frequency) of a GFCI (they don't occur in UK, we have RCCBs) but I
> suspect that the trip current is higher than the design value
> at higher
> frequencies.
As far as I know, there is no frequency compensation in
the GFCI. The frequency response is determined by the
core characteristics and the IC amplifier characteristics.
Virtually all US/Canada GFCIs use the National Semiconductor
LM1851 IC. The data sheet includes some good information on
GFCI circuits and circuit performance. There are no frequency
response specs that I could find. Here is the URL for the
LM1851 and data sheet:
http://www.national.com/mpf/LM/LM1851.html
Here is another web site for GFCI information:
http://www.codecheck.com/gfci_principal.htm
The original question pointed out that the leakage current
was in spec, but the load nevertheless tripped the GFCI.
The only conclusion is that the leakage current meter and
the GFCI do not have the same measuring circuits -- which
they don't. We do know that the leakage current measuring
network accounts for the response of the body to frequency,
while the GFCI has no such metering circuit network.
Best regards,
Rich
Richard Nute
Product Safety Consultant
San Diego
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