NCC, Non-Contact AC current detection :
1) when AC current flows > 1-5A approx
2) to identify the connection between consumer unit and electrical socket as well as AC current comparison
3) defect even through concrete walls when AC current flows > 1-5A approx. with or without transmitter
4) to locate the wire in concrete walls, shielded / armored cable when AC current flows > 1-5A approx.
NCV, Non-Contact AC voltage detection / trace wire or cable