Hi EddieHello and welcome to the Forum.
I've found a photo ( on an Australian website ) - it is a very large SIP power source, with a separate wirefeed unit. The control PCB in the WFU looks the same as in the smaller SIP compacts, such as the Ideal 180 or 240.
Are you looking to use it, or repair it? If the latter, what is the fault?
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Thanks EddieYour theory sounds correct. Probably someone only did half of the voltage conversion process, on the main welding transformer. The single-phase transformer for the auxiliary power supply is still set to run off the phase-to-phase 440 volts, so it is not providing enough output to hold the contactor.