Ross, I don't know your machine but at a guess, there is a poor connection or signals are affected by noise.
The E cable seems a suspect based on the manual.
Does the machine use ohmic sensing? I am aware of one new HF machine where the ohmic probe signal as being triggered spuriously by noise (the Ohmic wire is a very effective antenna). On that system, it was an error if the probe was triggered while cutting so the machine halted intermittently. It was under warranty but we thought a $15 decoupling capacitor where that wire entered the control panel would have fixed the issue. Of course manufacturers don't want to listen to advice like that from apparent amateurs!When the ProLine 2150 is ordered with the integrated Inova torch height controlsystem, connect the Inova C cable between P8 on the rear of the power supply and P3 on the Inova control panel. The C cable is used to interface the plasma start, plasma hold, and machine motion signals between the Inova and the ProLine 2150. Next,connect the Inova D cable between P7 on the rear of the power supply and P2 on the Inova control panel. The Inova D cable is used to interface the cutting arc voltage and plate sensing circuit between the Inova and the ProLine 2150. Next, connect the Inova E cable between the Work terminal on the ProLine power supply and theGround lug on the Inova control panel. Note that the E cable is not a safety ground. It is part of the voltage feedback circuit used for arc voltage control. See the Inova manual for details on x/y machine, operator’s remote, and positioner interface.