Was having problems this morning. The GFCI protected circuit my tv and DirectTV sat receiver is on, started faulting. TV goes off, reset the outlet, everything starts up, about 30 mins later the the circuit faults again. Repeat...

Then I notice, before the fault happens, the Dtv receiver is acting strange. Playing fine one moment, the next, I'm hearing audio from another channel, and sometimes seeing the other channel too. Then the fault happens again.

So now I'm thinking there has to be a connection between the observed symptoms. On this circuit, there is a power inserter (PI-28) which provides power over coax to the DTV SWM module.

That module switches the receiver between different outputs from the dish. So if it is working poorly, you could see the channel mysteriously change.

So after unplugging the PI, bypassing the SWM & loosing the ability to watch one record one, the GFCI isn't tripping any more.

Seems like it's time for a new power inserter.

And time to give thanks to the GFCI for keeping the defective power inserter from frying some of the more expensive equipment down-line from it!

tanstaafl.

Mmmm.. Gotta think about this.

A GFCI simply checks for equal current on the two main prongs (hot and neutral). If they ever differ, it trips.

So what happens with a power injector, which is sending current one-way down a coax, and using earth as the return path?

Sounds like a potential current imbalance at the outlet, though I suppose that would depend upon exactly how the injector is converting the mains-AC to DC-for-the-injector.

If it uses an old-school transformer, no problem. If it used something akin to a diode and lots of serial resistance (or waveform chopping), then perhaps that would result in a one-way flow from hot to earth (and trip the GFCI) ?

I'm sure the injector uses a chopper. What's likely is some ground loop current is tripping the gfci. My tv stuff always seems to have ground loops as they are grounded at multiple places around the house.

The GFCI doesn't care a whit about the ground (earth) connection. It just looks for an unequal current flow between hot and neutral.

But if current is escaping to ground (earth) somewhere, that will trip a GFCI when the flow is high enough. Not because of the ground connection, but because the current flow on hot will be different than that on neutral.