# Alternative uses for GFCI receptacles

#### mperedithe

Aug 4, 2014
3
Hello All!

I'm needing a little help. I'm trying to design a circuit that, when switched, trips a gfci receptacle. The basic concept is to have the circuit built with a plug in that will be plugged into the gfci receptacle in question.

Here's what I know: I understand that the circuit will be connected to the hot wire and ground. Between these two points will be the switch and one or more resistors. The resistors create an imbalance that the gfci detects and reacts to.

What I don't know: What resistors are needed to get the desired results.

Thanks in advance! You guys are great.

mperedithe

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,506
First find the current required to trip the device.

Then calculate the appropriate resistor using your mains voltage, the current from the step above, and Ohms law.

Then calculate the required power (v * I would give it to you)

Then buy a resistor of the calculated value an rated at higher than the calculated power.

Lastly, connect the resistor (without electrocuting yourself) between live and earth. The breaker should trip almost immediately.

Note that you can get plug in testers for these breakers that require no calculations and which are safe to use.

#### mperedithe

Aug 4, 2014
3
Thanks *steve*. I'm not actually building a tester, though they both do the same thing. This piece of my project will actually be attached to a water leak detector. I need to create an outlet that shuts off when water is present (and not come back on without human intervention). I'll simply replace the switch with a relay.

I did find a company that makes exactly what I'm needing however they have discontinued the product. The upgraded version is far more than I need (lots more outlets) and way too expensive.

#### Tha fios agaibh

Aug 11, 2014
2,242
How about using the relay in the homes junction box,instead of using the GFCI outlet for other than its UL listing . Not a good idea to intentionally divert household current to ground regardless of the curent. Better to use low a switching circuit like a switching transistor to fire the relay and use the relay in the building wiring to disconnect the receptacle outlet.

(BTW, GFCI trip around 3 to 6 milliamps)

#### mperedithe

Aug 4, 2014
3
Thanks for the reply fios. Um, no, it's not an outlet in a home... I would never do that. It's a separate gadget that will have it's own housing. Imagine a big bulky surge protector with a distinct function.

Sending the current to ground won't even work, as I understand it (& depending on brand of gfci). Remember these things are built to detect an imbalance in current moving through the receptacle. When this happens it means that the current not returning is looking for ground elsewhere (usually), which is very dangerous, and therefore kills power to the outlet.

***disclaimer*** please excuse the ridiculously crude description of gfci operation.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,506
Maybe you should tell us *exactly* what it's for.

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