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How to choose Surge protection devices?

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How to choose Surge protection devices?
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Choosing Surge Protectors


Britec’s line of AC power surge protectors is designed to cover all possible configurations in low voltage installations. They are available in many versions, which differ in:
- Type or test class (1, 2 or 3)
- Operating voltage (Uc)
- AC network configuration (Single/three-Phase)
- Discharge currents (Iimp, In, Imax, Uoc)
- Protection level (Up)
- Protection technology (varistors, spark gap, filter)
- Features (differential mode, plug-in, remote signaling, compact).


The surge protection selection must be done following the local electrical code requirements (e.g.: minimum rating for In) and specific conditions (e.g.: high lightning density).


Choosing the Type of surge protectors


The type of surge protector is based on its location and the constraints of the installation to be protected.


Configuration SPD Location BRITEC
Installation equipped with LPS or could be hit by lightning

Type 1+2

Type 1+2+3

Origin of the installation origin (Panel or main switchboard)





Installation without LPS

Type 2

Type 2+3

main switchboard



Secondary protection (downstream primary SPD)

Type 2

(or Type 3)

close to protected equipment




Choosing the operating voltages Uc and UT


The SPD Uc voltage (maximum continuous operating voltage) depends on:
- Nominal voltage of the AC network (Uo)
- Type of AC system (TN, TT, IT).

The level of resistance to temporary overvoltage (UT) is related to the Uc voltage. In addition, withstanding the “high voltage” TOV (1200 Vac, 300A, 200ms) between Neutral and PE is needed in TT AC system.


Operating voltage Uc (Line/Ground)


AC Network 230/400V 120/208V
AC system TT TN IT TN
Voltage Uc mini 255V 255V 440V 135V
Voltage UT 335/440 V 335/440 V --- 230/175 V
TOV N/PE 1200 V      


Choosing Iimp


The impulse current Iimp is defined for Type 1 SPD. The minimum rating for Iimp is 12.5 kA by pole, following IEC 60364-5-534. This level is adapted to the real phenomenon. This value can, however, be increased according to the risk (calculation according to EN 62305-1). BRITEC proposes, in its Type 1 SPD range, 3 levels of Iimp current by pole: 12.5kA, 25kA and 50 kA.


Configuration Iimp/pole BRITEC
Maximum risk 50kA BR-50GR
Very high lightning density Bad earthing 25kA



High, medium or low lightning density 12.5kA BR-12.5M


Choosing In current


The relevant nominal discharge current In for the SPD is in relation with the lightning risk in the installation area.
The minimum rating of In for a SPD connected at the installation entrance is 5 kA (8/20 μs waveform), required by standard.
Nevertheless higher ratings are advised in case of high lightning density.
Moreover higher values of In current will increase the SPD lifetime.
Imax (max. discharge current) rating is linked to In.


Conditions In BRITEC
Very high lightning density > 20 kA



High or medium lightning density 10-20 kA



Low lightning density or secondary SPD 5 kA BR-15DP


Choosing the protection level Up


The user must select a surge protector with a protection level Up adapted to the withstand level of terminal equipment. In every case, the lower the protection level Up, the better the protection.
IEC 60364 standard calls for the minimum protection level of 2.5 kV for a SPD connected at the entrance of a 230/400 V network: this level is in compliance with the withstand of robust devices (electromechanical type).
Electronic-based terminals have lower impulse withstand and require a better protection: so, surge protectors with 1.5 kV protection are necessary to provide efficient protection.


Conditions Recommended Up

230/400 V

AC network

120/208 V

AC network

SPD at the installation entrance 2.5 kV max. 1.5 kV max.
Electromechanical protected equipment 2.5 kV 1.5 kV
Electronic-based protected equipment 1.5 kV 0.8 kV


Pub Time : 2021-08-13 16:20:44 >> News list
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