[R-390] GFCI trips!

[Paul Galpin]

 Hi gentlemen, and R390 owners!
(From a R390 wannabe owner)

>From my experience, and many similar dead-horse communications several years
ago on this list, here FWIW, are some facts!

1. US GFCIs (Earth Leakage Trips to us in RSA) are set to go off at about 5
mA. This means that they are only used in (apparently) dangerous places,
like bathrooms - or so I was told by US R39x owners.

2. The R39x filters have capacitors from Line to Earth, and Neutral to
Earth, so they pass a "leakage" current and trip the GFCI. This is not a
component fault, but a 50's design anomaly which we have to take into
account.

3. In RSA, our ELTs trip at around 30 mA, and must, by law, be active in
circuit with every power socket in the house. In Gauteng, it is normal to
have the entire house on the ELT, but down here in Eastern Cape it's usually
only the wall sockets, not lights, geyser, or stove. I know, from experience
with an R390A, that the filter will pass _almost_ enough current to trip the
breaker, which means that just a couple of mA on any other circuit will do
the job! Very frustrating to find!

4. One cure for this is to open the filter, and lift the capacitors off
ground,, so that they are only across the mains power supply, OR as 5 below.

5. Using an isolation transformer to supply power, one has the choice (if
local regulations allow) of earthing one side of the secondary, or balancing
it about earth to give max 110V (or 55V in 110 countries) to earth. If you
then put a separate ELT (GFCI) on the isolated balanced circuit, you have
the best of all worlds!

5. AFAIK, modern equipment with built-in mains filters does not connect to
Earth. It relies on series chokes, and parallel capacitors across the power
supply. Presumably, this is because of the problems caused to ELTs (GFCIs).

Rave on!!

Paul Galpin
ZS2PG