Inexpensive field deployable non-invasive current sensor
simulate this circuit &ndash; Schematic created using CircuitLab



Your Sparkfun probe with suitable burden resistor and recording interface is the ideal cheap Ammeter probe for 30A suitable for 1cm wire including insulation.

I hope it is obvious why your 1.5" bundle does not work, because the currents cancel when sensing both wires together from the loop current in both wires.

To make this work, each output must be "invaded" to bring out an insulated wire for clamping the probe. Where and how you do this may not be feasible.

To avoid the "trade-show" blues, it may be more sensible to measure the current at the distribution panel where the wires are accessible at the fuse panel.  Then measure voltage drop at the end-points. Normally drop in a well designed distribution network is 0 to 5% and another 5% at source.  Variations > 10% voltage may indicate excess ratio of Amps to Ampacity or load for the cable length and gauge. 


  If you network measurements of end-point voltages and current at breaker for each end point, you will have better luck determining who is drawing too much power if you have a power layout schematic or wiring table.


Details on deployment depend on access points, qty, and cost of not managing power outages to prevent "trade-show blues".