Overcurrent protection constitutes the basic protection of a network. It must be both responding and quick, as to limit (electrodynamic and heat) constraints applied to the electrical devices during a fault condition.
Further, it must be selective, i.e. capable to isolate only the faulty element, and to keep the safe elements electrically supplied.

Below the list of products dedicated to the protection of transformer and line feeders.

	Device	Series	ANSI	Description
	NP BC915	NP 900	60, 74TC, 25, 79	Bay Control IED with IEC 61850 protocol
	NP F910	NP 900	50/51, 50N/51N, 50H/51H/68H, 46R/46L/46, 49L, 87N, 50BF/52BF, 74TC, 79, 68, 86	Feeder protection IED with IEC 61850 protocol
	NP F915	NP 900	50/51, 50N/51N, 67, 67N, 50H/51H/68H, 46R/46L/46, 49L, 87N, 59, 27, 59N, 59P/27P/47, 81O/81U, 81R, 78, 32/37/32R, 50BF/52BF, 21FL, 60, 74TC, 25, 79, 68, 86	Enhanced feeder protection IED with IEC 61850 protocol
	NP T916	NP 900	87T, 87N, 49T, 50/51, 50N/51N, 50H/51H/68H, 46R/46L/46, 50BF/52BF, 49L, 74TC, 86	Differential protection IED with IEC 61850 protocol
	NP TA915	NP 900	87N, 49T, 50/51, 50N/51N, 50H/51H/68H, 46R/46L/46, 59, 27, 59N, 59P/27P/47, 24, 49L, 50BF/52BF, 60, 74TC, 90	Voltage Regulating and back-up protection IED with IEC 61850 protocol
	NPI800	NP.800	46, 46BC, 49, 50, 50N, 50BF, 51, 51N, 86, 74TC	Phase and Earth Overcurrent Protection
	NPI800R	NP.800 R	46, 46BC, 49, 50, 50N, 50BF, 51, 51N, 86, 74TC	Phase and Earth Overcurrent Protection
	NPID800	NP.800	46, 46BC, 49, 50, 50N, 50BF, 51, 51N, 67, 67N, 86, 74TC	Phase and Earth Overcurrent Protection with directional criteria
	NPID800R	NP.800 R	46, 46BC, 49, 50, 50N, 50BF, 51, 51N, 67, 67N, 86, 74TC	Phase and Earth Overcurrent Protection with directional criteria
	NPIH800	NP.800	50N, 50NBF, 51N, 86, 74TC	Earth Overcurrent Relay
	NPIH800R	NP.800 R	50N, 50NBF, 51N, 86, 74TC	Earth Overcurrent Relay
	NPIHD800	NP.800	50N, 50NBF, 51N, 67N, 86, 74TC	Earth Overcurrent Relay with directional criteria
	NPIHD800R	NP.800 R	50N, 50NBF, 51N, 67N, 86, 74TC	Earth Overcurrent Relay with directional criteria
	DMS 7002	PROCOM	87T	Transformer differential protection
	RMS 700	PROCOM	50, 50N, 51, 51N	Phase and Earth Overcurrent Protection
	RMS 7992 RMST 7992	PROCOM	50, 50N, 51, 51N, 49 (only RMST 7992)	Phase and Earth Overcurrent Protection with advanced functionalities
	RMSD 7000	PROCOM	67, 67N	Digital multicurve directional overcurrent relay
	RMSR 7000	PROCOM	50, 50N, 51, 51N, 67N, 79 (7991), Logical Selectivity (7992)	Phase and Earth Overcurrent Protection with recloser (7991) and logical selectivity (7992) facilities
	DTT 7031	STATIC	87T	Transformer differential protection
	IAG 7014	STATIC	87T	One phase high impedance differential protection
	ITD 7000	STATIC	67, 67N	Phase and earth directional overcurrent relay
	ITG 7100	STATIC	50, 51, 50N, 51N, 37 (solo ITG7118)	Phase and Earth Overcurrent and Undercurrent relays
	ITH 7111 ITG 7011 ITG 7111	STATIC	64	Sensitive zero sequence relays supplied from ring CT
	STEP 7000	STATIC	26	Temperature supervision relay