Will a GFCI 20 Amp 120 Volt receptacle act like a circuit breaker if it is supplied by a 50 Amp breaker?

You first need to figure out what size the circuit is supposed to be!!! Does it need to be on a 20A, 50A, or none of the above?

Second of all, a GFCI is not a circuit breaker!!! There are so many misconceptions about GFCIs. THEY ARE NOT OVER CURRENT DEVICES. THEY ARE DESIGNED TO TRIP WHEN THERE IS A DIFFERENCE IN CURRENT FROM HOT TO NEUTRAL, AND NOT NECCESSARILY DESIGNED TO TRIP WHEN THERE IS A GROUND FAULT. A 20A GFCI is a rating of the size of the circuit it can go on, not an overcurrent rating because a GFCI is not an overcurrent device. GFCI PROTECTS PEOPLE, NOT EQUIPMENT.

I know why they supplied this circuit with a 50A breaker. It's because they're stupid.

Figure out how much amperage the pool pump is rated to draw, and then ask another question of how you should go about wiring it when you have that information. We'll help you get this pump wired correctly.

What size wire is coming from the 50amp breaker, and is the motor sharing a circuit with anything else??

PER NEC a pool pump must have a dedicated GFCI power source supplied to it. Check the plate on the pump for amperage. 12awg is good for 20amps. If more that 100' from power source you have voltage drop and wire need number 10awg wire(if it is 15-18 amps).

Is there a subpanel out at the pool area that might have breakers for pump lights,etc. If not and number 12 wire is feeding that 50 amp indeed REPLACE with 20 amp.

Also, the pool frame and pump should be bonded with #8 bare copper wire, not 12/2... G

Actually it is not a problem. The GFCI does act as a circuit breaker. The 12/2 wire is fine for the 20 amps you are using. It may be that at some other time another circuit was run off that same breaker. It would not hurt to change it to a 20 but you don't have to.

Yes you can put the 20 amp GFCI in place of the 15 amp receptacle. The circuit will react to the breaker in the panel as to what current level is will accept before it trips. So, the receptacle does not affect the braker. The 20 amp receptacle is a better built device than the 15. The GFCI trips differently than a standard breaker. The 20 and the 15 amp GFCI will both trip at 4 - 6 milli amps. (.004 amps) not 15 or twenty. The trip current in not the load current, but the fault (to ground) current or leakage current.

A gfci is a ground fault circuit interrupter, not an overcurrent device, it won't trip based on amps. That receptacle being used on a 50 amp circuit is not legal.

BUT, no answer here is complete.

Motors have different requirements for wire size and breakers than lights and receptacles do. Wire and breaker size is either manufacturers instructions or 125% of motor nameplate rating (NEC 430.24 http://freenec.com/T281.html) and the circuit breaker is allowed to be 250%-400% of nameplate (NEC 430.52 430.54)

So for instance the motor could be rated at 20 amps, 125% is 25 amps, requiring #12 (using 310.16 http://freenec.com/T125.html, 90 or 75 degree column which is allowed as starting point for derating purposes) and 400% could be as high as 50 amps, or as high as 80 amps if startup causes tripping.

Your concern is justified! That is definitely not a safe situation.

The Ground Fault Circuit Interrupter (GFCI), will protect what is plugged into it, but will not protect the wiring coming from the panel to the outlet. Since 12 gage wire is only rated for 20 amps, if you had a short in the wire, it could melt and start a fire without activating the breaker. To make sure everything operates correctly you should have an electrician check the pump for it's amperage draw and wiring requirements. If it's not wired properly there could be a possibility of causing damage to the pump.

I hope this helps,

Good luck

What ELSE is supplied by the 50 amp breaker? It's certainly conceivable that there are other circuits supplied by the 50 amp breaker. The 20 amp GFCI receptacle is there to trip in the event you plug a faulty appliance into the receptacle, especially in a damp/wet user environment. Damp/wet environments are a much greater hazard than having dry (hands, feet) environment. The 50 amp breaker at the house supply panel is to trip in case the sum of all circuits supplied by the breaker top out over 50 amps (at one time). 50 amps, in 120 volt circuit would imply abt 6000 watt energy draw.

The maximum allowable breaker serving a #12 wire is 20 amps. Dont really know of any special circumstances regarding the use of higher rater breakers for lower rated wires. While the GFCI may trip if there were excessive voltage, this seems fishy to me. I would definately call an electrician to make sure this is a correct application asap.

if the 50 amp breaker is in the fuse box and the GFCI is 20 amps

is will then trip if 20amps or more cause it to trip. the 50amp is only the supply power the 20 amp is the protector and the users end.

a GFCI NOT IN A LOAD CENTER OR BREAKER PANEL IS NOT A CIRCUIT BREAKER. IT IS AS ITS NAME IMPLIES - A GROUND FAULT CIRCUIT INTERRUPTER..... NOT A OVER CURRENT INTERRUPTER. THE 12/2 CAN AT THE MOST BE PROTECTED BY A 20 AMP CB. CHECK YOUR MOTOR AND SEE IF IT CALLS FOR A FUSE, IF SO PUT ONE IN A SUB PANEL AT THE MOTOR DON'T USE A CB AT THAT POINT. AND REMOVE THE 50 AMP CB.