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.
Gunter_J_Maass@em
braco.com.br
Sent by: To
[email protected] [email protected]
cc
05/22/2006 12:28 Subject
PM GFCI and High frequency (kHz)
applications
Dear Group
Question about GFCIs (ground fault circuit interrupter devices):
GFCIs are very common in the USA for safety.
It basically measures the differential current between PHASE and NEUTRAL.
If more than the threshold current, it trips and protects the user that is
causing the ground fault.
It is not a new component, I think it has been used for several years.
As far as I know, the basic requirement for any GFCI is a tripping fault
current of 5mA/60Hz.
Question: Household appliances are using more electronic circuits with
switching frequencies of several kHz, and an attached EMI filter (Y2 caps
to the ground). Is there any special requirement for the GFCIs regarding
the frequency of the ground current ?
The fact is that GFCIs are tested and UL approved for 60Hz only.
It does not avoid unwanted trippings caused by the high frequency
components produced by switching frequencies.
Something that I know is : For the same product (with some kHz circuit),
there are GFCIs that trip (unwanted trips) and there are the ones that
ignores the high frequency currents.
Thanks in advance !
Günter J. Maass
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Instructions: http://listserv.ieee.org/request/user-guide.html
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