[GreenKeys] Ground Fault Circuit Interrupters

[Jeffrey D Angus]

Ground Fault Circuit Interrupters.

 From the Underwriters Labs:
<http://www.ul.com/global/documents/offerings/perspectives/regulators/technical/ul_GroundFaultProtectiveDevices.pdf>

 From 4 to 6 mA current imbalance to trip.

At 60 Hz and 120 VAC, this is equal to  2000 to 3000 ohms.
For capacitive reactance in that range it is 1.326  to 0.884 uF

However, even a 0.47 uF capacitor with wax paper dielectric that
has aged badly over the years may have an equivalent parallel
resistive leakage current as  high as 4 to 6 mA.

Almost ALL equipment up through the 70's tended to have both
sides of the AC line bypassed to the chassis.

A side effect of this, is that with a faulty or non-existent ground
this acts like a voltage divider and puts roughly 60 vac between
the chassis and ground. (Or with a good ground, causes leakage
current to unbalance the GFCI equipment.)

Newer equipment has a single capacitor across the line, THEN a
common mode choke in series with the line, and then two bypass
capacitors to ground. Current UL rules require the use of type X
and type Y capacitors in this configuration to keep from either a,
shorting out or b, setting fire to themselves in the event of a
failure.

Jeff-1.0
wa6fwi