I see no mention of this in the installation manual, but... The two wires from the shunt, being essentially connected to the power bus / battery, should each have some form of circuit protection installed at the shunt end, to either break the circuit or limit the current should one of the wires becomes shorted to ground.
The common forms of circuit protection, fuses or circuit breakers, would do the trick. But they are big and bulky, and are more than should be needed in this application, because the current through those wires in normal operation should be miniscule. I'm thinking that a simple/cheap/elegant solution in this case would be to put a simple resistor in series with each wire at the shunt end, to serve as a current limiter, and should have no adverse effect on the normal functioning of the current measurement circuit.
Since under normal conditions there is very little current flowing in those wires (Likely nanoAmps, and certainly no more than microAmps, I presume. How much, actually?), a series resistor of reasonable value (say, 1K Ohm) should have very little effect on the voltage seen at the EFIS (No more than millivolts). And if the resistors on the two wires are well-matched, and the leakage current of the two EFIS input pins is reasonably well-matched, then the voltage drop associated with the resistors should also have no effect on the current measurement. This is because it only introduces a common-mode voltage shift, i.e. same voltage shift on both wires, and the current measurement is a differential measurement between the voltages of the two wires.
Rob, can you please comment on the above? Can you tell me what is the approximate worst case leakage current of those inputs? Can I go ahead and use a matched pair of resistors for circuit protection as I outlined above, or do you see any problem with this?
Thanks,
-Roee