There are two contactless methods of which I'm aware. Both have been used in locomotives for measurement of current up to 2000 amps dc at voltages of 1200 VDC.

The first is called a transductor. It requires an ac source to excite a pair of windings and resistor in series. The current carrying conductor passes through the center of the two toroidal windings. Potential across the resistor indicates current linearly. Contact Spang, Inc. in the US.

The second is a split core with a Hall effect sensor in the air gap to sense the magnetic field. The current carrying conductor passes through the center of the core. This device only requires 12 to 15 VDC to operate. Contact LEM in Switzerland.

Good Luck,

Bruce Bailey