yeah but last I looked on my panel both common and ground connect to same bar.
so what's the difference?
if you take a l14-30 plug
put the green wire to the l prong
and the white and black to the hots won't this work?
The Procedure for Wiring a NEMA L14-30 Plug
The cable to which you attach a 30-amp twist lock plug has to be a minimum of 10 AWG, which is one size larger than standard 120-volt residential cable. You need three conductors plus a ground. Two of the conductors, which are red and black, are hot wires, and one – the white one – is neutral. The ground wire, which may be bare or coated with green insulation, is required but it isn't considered a conductor. All 240-volt, 30-amp appliance cords conform to these specifications...
the 2 hots form the c19-c20 cable and the ground/common
In my home my breaker box has 2 120volt hots and a common/ground bar
when I wire 120 I do black to one hot 120 then both the white and bare ground to the common/ground bar.
when I do 220
I do 1 to hot 120
I do 1 to other hot 120
I do 1 to common/ground bar
I don't do 4 wire 220 wiring
which would be
1 to hot 120 A
1 to hot 120 B
1 to common /ground bar
2 to common /ground bar.
since his gear will use a 3 prong receptacle and the c19 to c20 is 3 wire
you wire to the 4 prong
1 to the hot
1 to the other hot
1 to the L shape prong which I called a ground.
0 to the 4th spot.
both the L shaped prong and the 4th spot will go to the common/ground bar.
so whether you call it a common or a ground in either case they lead to the same spot.