[Al Skierkiewicz]

philso,
There is no current limit that I am aware of other than the fuse/breaker. It is just two SPDT relays between input and output with the drive circuitry connecting to the coils. The input is opto coupled from the DSC lines. The Spike does not have the internal protection from dirt and other crud so it is possible that both of your Spikes have a serious amount of contaminant. If you have a fuse in place, they sometimes look good but actually have a small crack that opens with current. Try changing with a new one to be sure.