Calling all Professional Electricians.

OK, this one would be for the pro's.

I need to know if I can pass AC power back through a 20 amp 120 VAC GFCI electrical receptacle???

I think you can as the current is AC, but need to check with the pro's.

Using this in a location that needs an externally mounted standby generator, no way to run the power from it directly back inside the building, (main power is inside the building) all there is, is one external GFCI power receptacle at the location where the generator will be mounted, the building in question is a historical landmark, and in no way can we drill through a 168 year old stone wall without going through many many many requests, wait a long time, and beg for permits.

The generator will be under a fake rock like what is used for propane tanks, and also at the back of the building, the GFCI was put in many years ago, and took almost a year to get the permission and permit to do so.

So this said, if the GFCI will pass power backward (I know stupid to ask) then we are set, this circuit will be put on an auto switch over, and only the one circuit is needed.

Every-time the wind blows over 10 MPH here in California they shut the power off to us in the mountains, we are getting very tired of it.

I am not a pro but I have done lots of electrical work and worked with electricians. The GFCI has a load and a line side. I know that you cannot backfeed a GFCI.

(If you change the GFCI receptacle to a normal one then you are in business).

Also, I don't know about California code but where I live when you energize a panel from a generator you are required to interrupt the neutral as well as the mains. If you are planning to install a transfer switch at the receptacle it will not de-energize the mains or neutral. Your transfer switch must interrupt the mains or you will be energizing the line beyond your house.

The transfer switch is setup for a generator, it has a 6 circuit setup, (3 per phase) you remove the circuit you need to power up with the generator from the main panel breaker assigned for that circuit and route it to the transfer switch, then back to the main panel breaker for that circuit.

The transfer switch is a double pole double throw relay (6 circuit DPDT) on each circuit, the internal relay in the switch is energized for the circuit to be connected to the main power and to the load,(normally closed when energized) when the main power drops out the circuit is then connected to the generator output to the load,( normally open when energized) the main is isolated from the generator, the generator has a few seconds delay before applying power to it's output.

The computer that will be on this will have a UPS system, with standby power for about 15 minutes, the UPS will also regulate the voltage and frequency for the computer.

I've done this before, but was unsure about the GFCI, as can it take a reverse power feed, if needed I could tap in on the incoming line before the GFCI.

Yes, that setup will work but I'm quite sure you will need to tap in before the GFCI.

If you aren't using an inverter generator I hope your UPS will be OK. I once connected an online type Liebert UPS to a non-inverter generator and after the loud bang I discovered the input filter of the UPS blew up. I think the generator output was too "dirty".