[HBR] That General Coverage HBR Project -- 2

[N2EY at aol.com]

In a message dated 10/8/06 9:48:53 AM Eastern Daylight Time, 
Hopperdhh at aol.com writes:


> Maybe just the capacitance is tripping the GFI. 

Hmmm....let's do the math...

IIRC, a 120 volt GFI is supposed to trip at 20 mA or less. Say Walt's got one 
that trips at 10 mA.

120 volts divided by .010 amp is 12,000 ohms. So a capacitance of 12,000 ohms 
at 60 Hz is needed.

Xc = 1/(6.28 x f x C)

Rearrange to 

C = 1/(6.28 x f x Xc)

For 60 Hz and 12,000 ohms

C = 1/(6.28 x 60 x 12,000)

C = .00000022 F or 0.22 uF

If there's a dozen or more bypass caps of .01 each, plus some other leakage - 
SNAP!!


Of course there's also the C of all the wiring and any other sources of 
leakage to ground. 


73 de Jim, N2EY