What is difference between type 1, type 2 and type 3 surge protective devices?

Type 1
Type 1 Surge Protective Device (SPD)s are intended for installation between the secondary of the service transformer and the line side of the service equipment overcurrent device, as well as the load side, including watt-hour meter socket enclosures, and are intended to be installed without an external overcurrent protective device. Type 1 devices are dual-rated for Type 2 applications as well, providing the highest ratings available for installation at the service entrance.

Type 1 SPD can dis­charge light­ning cur­rent with wave­form 10/​350μs. This, if re­quired, will be in­stalled in the primary dis­tri­bu­tion board at the ori­gin of the elec­trical in­stall­a­tion. A Type 1 SPD does not in it­self of­fer the re­quired pro­tec­tion level and must be used in con­junc­tion with co­ordin­ated type 2 devices. An in­stall­a­tion with a light­ning pro­tec­tion sys­tem will re­quire a Type 1 SPD.

Type 2
Type 2 Surge Protective Device—Type 2 SPDs are intended for installation on the load side of the service equipment overcurrent device, including SPDs located at the branch panel.

Type 2 SPD can discharge  8/​20μs current wave , they can pre­vent the damage of transient over­voltage in the elec­trical in­stall­a­tions and pro­tects equip­ment con­nec­ted to it. It usu­ally em­ploys metal ox­ide varis­tor (MOV) tech­no­logy. The device would nor­mally be installed in sub-dis­tri­bu­tion boards and in the primary dis­tri­bu­tion board if there was no re­quire­ment for a type 1 device

Type 3
These SPDs have a low dis­charge ca­pa­city. They must there­fore only be in­stalled as a sup­ple­ment to Type 2 SPD and in the vi­cin­ity of sens­it­ive loads. Type 3 SP­D’s are characterized by a com­bin­a­tion of voltage waves (1.2/​50 μs) and cur­rent waves (8/​20 μs).

Type 3 SPDs are normally installed right before the protected equipment.


Iimp – Im­pulse cur­rent of Type 1 SP­Ds with 10/​350 μs wave­form

In –  Norminal discharge current of Type 2 SPDs with 8/​20 μs wave­form

Imax- Maximum discharge current of Type 2 SPDs with 8/​20 μs wave­form
Up – The re­sid­ual voltage that is meas­ured across the ter­minal of the SPD when In is ap­plied
Uc – The max­imum voltage which may be con­tinu­ously ap­plied to the SPD without damage the SPD

Britec Electric offers full range of surge protective devices including Type 1, Type 1+2, Type 2 and Type 3 SPDs.


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