Rich Lanz wrote
> From: rlanz
> To: [email protected]
> Subject: RF choke in protective earth
> Date: Friday, February 27, 1998 9:55AM
>
> Good Morning.
>
> Seeking opinions on use of RF choke in protective earth. Due to invertor
> circuitry, rf noise is tripping GFCI. Series coil in P.E. appears to
> solve
> problem. RF coil will not effect 10-25 A PE safety test done at 60 Hz.
> Also
> coil shall be equivalent to AWG of PE conductor to pass equivalent
> ground
> fault circuitry.
>
> Nevertheless, it is disconcerting to place a series component in the
> Protective earth conductor. Comments are appreciated. Thank You
>
> Rich Lanzillotto
> [email protected]
Hi Rich
I do not think you'll be happy with the earth choke. In my opinion, earth chokes
can
reduce the 50Hz/60Hz current in ground loops by increasing the impedance of the
loop.
If you place them in components inside your equipment they are useless since
they
are shorted:
The outer end is connected to your cabinet and the inner end is connected to the
(metal) case of
the component (e.g. inverter) which is also connected (I hope) to the cabinet.
The point you addressed is the use of GFCIs RCDs in combination with inverters,
drive controls
and their power line filters.
You'll have five phenomena, all causing the GFCI to trip:
1. The inverter in the equipment causes common mode current noise (spikes). They
can trip the GFCI.
2. If voltages of L1, L2, L3 are not symmetrically arranged around earth
potential
or Y capacitances in your
power line filters are not identical you'll have a leakage current ( 50/60Hz)
which may or WILL trip the GFCI.
3. If the voltages in the power line system have a high harmonics component, the
harmonics currents trough
Y capacitors would trip the GFCI. Do not forget that currents of the
harmonics
3, 6 and 9 are in phase.
4.When connecting the equipment you have to load the Y capacitors in the power
line
filters (e.g. 15uF ).
5. If there is a voltage spike / or drop in the power line system you would
have a
common mode current spike
between the power line system and the filter in your equipment flowing
through
the GFCI. The GFCI would
trip.
We made a lot of experiments with chokes and with different GFCIs. We even
tried to
modify a GFCI so that it would not trip to short spikes. (Than it did not comply
with some
other standards for GFCIs).
The result was:
DO NOT USE GFCIs.
There are other methods to make an equipment safe. But there is a problem if
your
customer
wants to have a GFCI.
Greetings
George
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