How to Size Surge Protection Device

How to Properly Size Surge Protective Devices

Created by: Glen Zhu | Updated Date: October 22nd, 2024

How to Choose Surge Protection Device

How to Size Surge Protection Device

Selecting the appropriate surge protection device (SPD), the specification of the main circuit breaker is crucial. The size of the main circuit breaker directly determines the size of the surge protection device. The size of the main circuit breaker reflects the power consumption needs of the user’s electrical system, so understanding the actual power usage of user equipment is a fundamental step.
First, users need to evaluate the rated power and operating current of all devices to ensure they can cover peak loads and starting currents. In addition, users should also consider factors such as equipment operating modes (continuous operation or intermittent use) and potential future expansion needs.
The rated current of the main circuit breaker should generally be higher than the total power requirement of devices to provide sufficient protection margin. Reasonably selecting the specification for a main circuit breaker helps determine the required capacity for an SPD.
When there is a larger rated current for a main circuit breaker, choosing an SPD with corresponding specifications will ensure that in case of surge events, devices can withstand them effectively and respond quickly, thereby avoiding equipment damage or system downtime.
Coordination between the surge protective device and its associated disconnect circuit breaker or fuse (Based on IEC/EN 61643-11)
Main Switch (ACB / MCCB / MCB)Dedicated MCCB / MCB or FuseSurge Protective Device (SPD)
 MCCB / MCBFuseTN-S NetworkTN-C NetworkTT Network
Single Phase3 PhaseSingle Phase3 PhaseSingle Phase3 Phase
ACB ≥ 630A
MCCB: 630A ~ 315A
200A315A ~ 250A

Type 1 SPD FLP25-275/1(S), FLP25-275/2(S), FLP25-275/1(S)+1Type 1 SPD FLP25-275/4(S), FLP25-275/3(S)+1Type 1 SPD FLP25-275/1(S)Type 1 SPD FLP25-275/3(S)Type 1 SPD FLP25-275/1(S), FLP25-275/1(S)+1Type 1 SPD FLP25-275/3(S)+1
MCCB: 400A ~ 200A

125A ~ 100A125AType 1+2 SPD FLP12,5-275/1(S), FLP12,5-275/2(S), FLP12,5-275/1(S)+1Type 1+2 SPD FLP12,5-275/4(S), FLP12,5-275/3(S)+1Type 1+2 SPD FLP12,5-275/1(S)Type 1+2 SPD FLP12,5-275/3(S)Type 1+2 SPD FLP12,5-275/1(S), FLP12,5-275/1(S)+1Type 1+2 SPD FLP12,5-275/3(S)+1
MCCB: 200A80A ~ 50A80AType 1+2 SPD FLP7-275/1(S), FLP7-275/2(S), FLP7-275/1(S)+1Type 1+2 SPD FLP7-275/4(S), FLP7-275/3(S)+1Type 1+2 SPD FLP7-275/1(S)Type 1+2 SPD FLP7-275/3(S)Type 1+2 SPD FLP7-275/1(S), FLP7-275/1(S)+1Type 1+2 SPD FLP7-275/3(S)+1
MCCB: 100A ~ 63A40A ~ 32A40A ~ 32AType 2 SPD SLP40-275/1(S), SLP40-275/2(S), SLP40-275/1(S)+1Type 2 SPD SLP40-275/4(S), SLP40-275/3(S)+1Type 2 SPD SLP40-275/1(S)Type 2 SPD SLP40-275/3(S)Type 2 SPD SLP40-275/1(S), SLP40-275/1(S)+1Type 2 SPD SLP40-275/3(S)+1
MCB: 32A20A20AType 2+3 SPD SLP20-275/1(S), SLP20-275/2(S), SLP20-275/1(S)+1Type 2+3 SPD SLP20-275/4(S), SLP20-275/3(S)+1Type 2+3 SPD SLP20-275/1(S)Type 2+3 SPD SLP20-275/3(S)Type 2+3 SPD SLP20-275/1(S), SLP20-275/1(S)+1Type 2+3 SPD SLP20-275/3(S)+1
/16A ~ 10A16A ~ 10AType 3 SPD TLP-275/2(S) Type 3 SPD TLP-275/2(S) Type 3 SPD TLP-275/2(S) 

According to the above table, We can quickly select the appropriate surge protection device through the main circuit breaker, making it very simple to choose a surge protection device.

1. At the incoming distribution box, if the main air circuit breaker is greater than 630 A or MCCB is between 315 A and 630 A, the upstream dedicated disconnector of SPD should use a 200 A circuit breaker or a 250~315 A fuse. SPD can be selected Type 1 SPD FLP25 series.

2. At the outgoing distribution box, if main circuit breaker is between  200 A and 400 A, the upstream dedicated disconnector of SPD should use a 100~125 A circuit breaker or a 125 A fuse. SPD can be selected Type 1+2 SPD FLP12,5 series.

3. At the main distribution box, if main circuit breaker rated at 200 A, the upstream dedicated disconnector of SPD should use a 50~80 A circuit breaker or an 80 A fuse. SPD can be selected Type 1+2 SPD FLP7 series.

4. At the sub-distribution box, if main circuit breaker rated at 63~100 A, the upstream dedicated disconnector of SPD should use a 32~40 A circuit breaker or fuse. SPD can be selected Type 2 SPD SLP40 series.

5. At the sub-distribution box, if the main circuit breaker is 32 A, the upstream dedicated disconnector of SPD should use a 20 A circuit breaker or fuse. SPD can be selected Type 2+3 SPD SLP20 series.

6. At the sub-distribution box, for surge protection of industrial control equipment, the upstream dedicated disconnector of SPD should use a 10~16 A circuit breaker or fuse. SPD can be selected Type 3 SPD series.

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