A detachable current sensor provides an isolated and convenient device to measure current passing through a cable such as an AC power cable or non-metallic (NM) sheathed cable. Information about the magnitude and or phases of the currents passing through and/or voltages on the conductors is obtained by measuring the magnetic field at multiple circumferential positions around the cable using multiple semiconductor magnetic field sensors. A processing subsystem coupled to the multiple semiconductor magnetic field sensors determines information about the currents flowing in the conductors of the cable, including the current magnitude(s), and/or the phases and number of phases present in the cable, which can form part of a power measurement system that is used for energy monitoring, and/or for control purposes.