Surge protective devices (SPDs) should be installed as close as possible to the power supply entry point in the distribution box, typically on the supply side of the main circuit breaker, with proper grounding.

Placement in the Distribution Box

Type 1 SPDs are designed to handle high-energy surges from external sources such as lightning strikes or utility grid switching. They should be installed at the main distribution board where electricity enters the building, usually on the line side of the main circuit breaker. This ensures that high-energy surges are diverted to ground before reaching downstream equipment, protecting the entire electrical system . Type 2 SPDs are intended for the load side of the main service disconnect or at sub-distribution boards. They protect against residual surges that pass through Type 1 devices and internally generated surges from motors or variable frequency drives. Installing Type 2 SPDs at intermediate panels helps clamp voltage spikes and safeguard branch circuits . Type 3 SPDs are point-of-use devices installed as close as possible to sensitive equipment, typically within 10 meters. They handle low-level residual transients to protect electronics such as computers, PLCs, or medical devices .

Installation Guidelines

• The SPD should be installed immediately where cables enter the distribution box to prevent surge propagation into the system .
• Short, thick grounding wires must connect the SPD to the building's equipotential bonding system. Each centimeter of line length increases residual voltage, so the connection should be ≤ 0.5 meters .
• In a three-phase five-wire system, the SPD can be installed in front of or behind the main air switch, depending on whether it is on the supply or load side .
• A cascading protection strategy is recommended: Type 1 at the service entrance, Type 2 at distribution boards, and Type 3 near sensitive loads, ensuring progressive voltage reduction and comprehensive protection .

Summary

To maximize protection against lightning and transient surges:

1. Type 1 SPD: Supply side of the main breaker at the building entry.
2. Type 2 SPD: Load side of the main breaker or sub-panels.
3. Type 3 SPD: Directly upstream of sensitive devices.
4. Ensure short, properly sized grounding connections.
5. Follow a tiered, cascading installation for full system protection. This configuration ensures that surges are progressively mitigated, protecting both the distribution system and sensitive downstream equipment.