Another Spa Panel Question

[smoothlarryhughes]

Does the GFCI in a spa panel require 4 wires in from the main panel to work? My situation is I have a Robobrew 65L that takes hot hot ground, but I want to GFCI protect it with a spa panel. Can i wire up a spa panel to plug into a 3 prong dryer outlet, or do I need to run a dedicated line with the 4 wire configuration (hot hot neutral ground) into the spa panel and then wire 3 out to my Robobrew?

 

[doug293cz]

You can wire a spa panel that feeds a 240V only (no 120V components) device with three wire supply. The white pigtail wire from the GFCI breaker should connect to ground in the spa panel enclosure. Make sure the "Test" button works after everything is wired and powered.

Brew on

 

[smoothlarryhughes]

I keep reading that a neutral is required from the main panel to the disconnect for the GFCI to work. Do you any more info on how wiring the pigtail to ground will work? Is it because the ground and neutral are bonded in the main panel, so it's basically the same thing?

 

[doug293cz]

I keep reading that a neutral is required from the main panel to the disconnect for the GFCI to work. Do you any more info on how wiring the pigtail to ground will work? Is it because the ground and neutral are bonded in the main panel, so it's basically the same thing?

Pretty much. The pigtail is just there so that the "Test" function will work. The Test button creates a connection between one of the hots and ground/neutral thru a resistor that limits current to ~6mA. That test current bypasses the current sensing loop in the GFCI, thereby creating an imbalanced current thru the coil, which causes the breaker to trip. The test current mimics what would happen if any current leaked (a "ground fault") from one of the hots or neutral (if present). The sensing coil doesn't care how many wires go thru the coil, it just determines whether the current flowing in one direction is the same as the current flowing in the other direction (which should always be the case in normal operation.)

It's possible to wire a spa panel with three wire (H-H-G) input to provide four wire output (H-H-N-G) but it does not meet code, since you will have current flowing in the ground line under normal operation. In a four wire system with 240V & 120V loads current should flow only thru the hots and neutral - the ground is just there for safety. In a 240V only system, all current flows thru the two hots, so a neutral is not needed, but a safety ground is.

If a system has four wire input, then the GFCI pigtail should be connected to the neutral bus, and ground and neutral buses in the spa panel should be kept isolated from each other. With three wire input there is no neutral, so the pigtail gets connected to the ground bus in the enclosure. Ground and neutral should only be bonded at the main service panel.

Brew on