how can measuring current transformers work when the concerned cables are shielded?

Question

And the shields tied to ground. I assume the magnetic field from the cables cannot escape an earthed shield?

Answer 1

The shielding reduces the electrical noise generated by the cable. If the cable wasn't shielded, there would be a large 60 Hz signal generated by a cable carrying that much current. However, the shielding doesn't do anything to stop the magnetic fields; they strictly work on the electrical part. So measuring shielded cables works exactly the same way as measuring unshielded ones.

Answer 2

Yopu can measure them at the hookup point or measure them in a series circuit.The wires should be exposed at the point of contact.