[LazyPup]

The welder specs.are as follows:Input: 230V, 60Hz, single phase, Welding current range; 30-120 amps; Duty cycle: 15%@115 amps; Draws 15 amps @ 230V; Max. open circuit voltage: 36V.

Nothing at all confusing about those specs: It is a straight 230V machine that draws 15amps.

The existing 230v 40amp circuit should be more than adequate to handle the load, however The present 40 amp breaker could handle nearly 3 times the demand load without tripping, not much of a safety factor there, I would want to either reduce the ampacity of the main breaker or install a small sub-panel breaker near the machine and drop the breaker size to not more than 20amps. .