I bought a mill wired so one VFD could drive two motors with a switch select. By the time it arrived it was pulling the RCD and soon after the mill died completely. I replaced one VFD with two and dumped an amazing quantity of transformers, contactors, connectors, complicated switches and stuff. How they could wire that lot in just to save on the cost of one extra VFD is beyond me. Anyway, the VFD pulling the RCD was symptomatic of a being on its' last knockings :)