**I'm not an electrician** You should only believe the first line after this:
Install the GFCI.
In the above link, regarding 220v GFCI function, it says:
"GFCIs for 220 VAC applications need to monitor both Hots as well as the Neutral. The principles are basically the same: the sum of the currents in Hot1 + Hot2 + Neutral should be zero unless a fault exists.
To detect a grounded neutral fault, a separate drive coil is continuously energized and injects a small 120 Hz signal into the current carrying conductors. If a low resistance path exists between N and G downstream of the GFCI, this completes a loop (in conjunction with the normal connection between N and G at the service panel) and enough current flows to again trip the GFCI's internal circuit breaker."
You can also reference the WIKI Here:
From my research:
On a 3 wire 240v circuit, the GFCI measures H1 + H2, and compares it to Neutral. That's why it won't trip when you have 15 amps on one leg and 20 amps on the other.
If you touch H1 and Neutral, you'll add to that load. H1 + H2 - Neutral still = 0, and the GFCI May not
trip. This is bad
THIS is the important part:
If your body is the short between H1 OR
H2 to GROUND
(This is Earth! Or you touch anything - grounded metal/conduit/shelf/anything else near your rig), you cause a ground fault. Even on a 3-wire 240 circuit. The GFCI trips. This could save your life, and for that alone it's worth installing one.
Just do it.
I can see the eulogy... "He spent $2187 on the brew rig, and $7 on the breaker"