[Sunking]

I've forgotten the designation, but it is a four prong plug.

That would be a NEMA 14-30 which is the wrong plug type for the application, unless you needed 120 volt along with 240.

A NEMA 14-30 is a 4 Wire with an EGC. One of the 4 lines is the grounded circuit conductor (neutral conductor) which derives 120 volts. Only place you see them occasionally is something like a close dryer, where the motor and controls operate at 120 volts and the heating elements work on 240 volts.

For a 240 volt charger all you need is L1, L2, and G. Neutral serves no purpose.

 

[Sunking]

So if I wanted a twist-locking style connector for a 5kw, 220v/110v Elcon charger where either 220v or 110v would operate the charger and 120v would operate a charge-interlock relay at all times... could I use a NEMA L14-30?

I would think so because it is 4-wire (L1, L2, N, + G) You have to have neutral to derive 120 VAC.

I am curious about the charger being either 240 or 120. At 120 the power would have to be half right? No way to get 5 Kw at 120 volt with 30 amps. Technically to be code and UL compliant the maximum continuous load current you can run on a connector is 80 % of the rating. So with that said I would think the max power at 120 volts would be 2660 watts.