I spoke with UL and they told me that those GFCIs have to comply with a new
immunity standard since January 1st, 2003.
Basically it is the immunity to injected HF (like IEC61000-4-6).
I think that's why some "old" models trip with kHz common mode currents and
the new ones don't.
Maybe the GFCI doesn't trip because of the quantity of HF current through
its current or voltage sensor, but it may trip because its sensor circuit
has some lack of immunity to HF.
Maybe...
Günter J. Maass
[email protected]
om To:
[email protected]
Sent by: cc: [email protected]
[email protected] Subject: Re: GFCI and High
frequency (kHz) applications
29/05/2006 15:21
I had not seen a response on this subject, so I will do the best that I
can. First, let me state that I am not an expert on GFCIs. I do have some
familiarity with the devices and I have done some testing on them in the
past.
The GFCI will react to the 50 or 60 Hz earth leakage current through
Y-capacitors. However, there is not enough energy at the higher
frequencies to generate significant current. The current must be sustained
for a few milliseconds in order to trip the GFCI and this will not happen
at the higher frequencies. Conducted high frequency noise due to
switch-mode supplies should not cause a GFCI to trip.
It is worth noting that IEC 60950 allows a typical Type A plug connected
ITE device to have up to 3.5 mA earth leakage current. There is a risk of
unintended operation once you connect more than one ITE device to the same
GFCI protected circuit. The risk increases with every ITE load connected.
GFCIs should be used for outdoors and potentially wet locations, but not
for Information Technology Equipment.
I would also like to mention a new type of device that is now required for
certain installations in the United States. There is a device called an
Arc Fault Circuit Interrupter, AFCI. An AFCI is only require in a few
locations, including circuits for bed rooms. The purpose of the AFCI is to
detect faults in wiring that are resulting in arcing. It is intended to
detect arcing both phase to neutral and phase to ground. The AFCI devices
incorporate a microprocessor that is looking at the current on the phase to
detect sudden changes that could be arcing. However, the current measured
>from arcing can look a lot like the current resulting from dimmer switches
and switch-mode power supplies. Most AFCI manufacturers have proprietary
firmware and will not give information on the precise algorithm for their
devices. However, it is clear that switch-mode power supplies are very
likely to trip AFCI devices. Unlike a GFCI, the AFCI will trip when
detecting very short current transients.
Ted Eckert
American Power Conversion Corporation
The items contained in this e-mail reflect the personal opinions of the
writer and are only provided for the assistance of the reader. The writer
is not speaking in an official capacity for APC nor representing APC's
official position on any matter.
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