[R-390] Need help fixing R390A not to trip GFI breaker

[Roy Morgan]

At 10:13 AM 8/21/2007, Barry wrote:
> >I am looking for some suggestions in repairing my R390A so that it does not
> >trip the GRI breaker (outlet) here in the garage/radio room. ...
>As was mentioned, the problem is in the leaky line filter capacitors.

I promised my family and therapists I would not get on this soap box again but:

<Soap box mode ON>

The caps in the line filter may not be LEAKY.

They are simply acting like capacitors.  They are connected from each side 
of the line to the chassis. If the chassis is not grounded, this creates a 
capacitive voltage divider and you get about half the line voltage on the 
chassis.  If the chassis is grounded, the capacitive current through the 
caps from line to chassis unbalance the currents in the line and neutral 
enough to trip the GFI device.

The possible courses of action include:

1) Remove the offending original line filter and replace it with a modern 
one that does not create such ac currents in the chassis (as Barry did).

2) Ensure you have a good electrical ground system in your outlets and 
avoid Ground Fault Interrupter (GFI) type outlets or circuit breakers.

3) Remove and dissect the line filter.  Replace the caps with much smaller 
ones, preferably from LINE to NEUTRAL and from NEUTRAL TO 
CHASSIS.  Reassemble and reinstall the line filter.

4) Use an isolation transformer.

5) Remove the line filter and discard it altogether. Use a three wire 
grounded line cord. If you need to, use line filter caps as in 3 above, 
line to neutral and neutral to chassis.

<Soap box mode OFF>


Some closing notes:

- The filter in the R-390/URR is not the same inside as the filter in the 
R-390A/URR.  The R-390/URR line filter (and the ones in the R-389 and 
R-391) have more capacitors.

- The capacitors may, in fact, be leaking. That is, have a leakage 
resistance from terminal to terminal.  They do seem to be paper-foil 
capacitors and were in fact made a long time ago.  However, purely 
capacitive currents are enough to account for tripping GFI devices.

- Faulty or incorrectly wired household outlets have been reported and can 
lead to big trouble. An outlet tester can be bought for under $10.  No shop 
should be without one.
   Amazon's price is $7.75:
<http://www.amazon.com/AEMC-Outlet-Tester-100-125V-Receptacles/dp/B0000WS7M6>
Grainger seems to want $19.83 for the same thing:
http://www.grainger.com/Grainger/items/3T885
But does offer a cheaper one at $5.64:
http://www.grainger.com/Grainger/items/4YE77

- Normal "variacs" are NOT isolation devices.  (There ARE some, however. 
See http://www.elect-spec.com/isovar.htm  It's not clear if these are 
variable transformers with a separate isolation transformer.)

Happy leaking to all.

Roy



- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing
13033 Downey Mill Road, Lovettsville, VA 20180
Phone 540-822-5911   Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-975-6097
roy.morgan at nist.gov --