Abstract: A current source circuit includes a variable impedance circuit coupling the returns of dual-floating power sources, and is configured to limit maximum current output in the event of fault and facilitate detection thereof. The first power source powers the current loop using its source, with the current loop returning through the second power source's return. Control circuitry detects an increase in current beyond the predetermined maximum and appropriately increases the impedance between the first and second power sources returns to limit current provided to the current output to the predetermined maximum. This amount of current is detected by, for example, analog to digital conversion and the fault can thereby be appropriately signaled.