If an SPD and a lightning arrester are both installed at a service entrance switchboard and a surge occurs, which device will do all the work to handle the surge current?

If an SPD and a lightning arrester are both installed at a service entrance switchboard and a surge occurs, which device will do all the work to handle the surge current?

• A. Lightning arrester
• B. SPD
• C. Neither
• D. Both

Answer: (B)

Surges are most effectively handled by devices that limit the voltage seen by the protected circuit and provide a low-impedance path for the transient energy. An SPD is designed for this role: it detects the surge and quickly conducts excess current away from the equipment, clamping the voltage to a safe level and sending the surge current to ground or neutral. This makes SPDs the primary line of defense against non-extreme and extreme surges alike. Lightning arresters, on the other hand, are intended to protect against very high-energy impulses from direct or near-direct lightning. They provide a discharge path when the voltage spikes dramatically, but they aren’t sized or intended to continuously manage surge current in the same controlled way as an SPD. They respond to extreme events and help limit peak voltage, but the everyday surge current is managed mainly by the SPD. So, when both are installed, the SPD handles the bulk of the surge current, keeping voltages within safe limits for the equipment. The lightning arrester acts as an additional safeguard for extreme impulses, not the primary current-handling device.

Surges are most effectively handled by devices that limit the voltage seen by the protected circuit and provide a low-impedance path for the transient energy. An SPD is designed for this role: it detects the surge and quickly conducts excess current away from the equipment, clamping the voltage to a safe level and sending the surge current to ground or neutral. This makes SPDs the primary line of defense against non-extreme and extreme surges alike.

Lightning arresters, on the other hand, are intended to protect against very high-energy impulses from direct or near-direct lightning. They provide a discharge path when the voltage spikes dramatically, but they aren’t sized or intended to continuously manage surge current in the same controlled way as an SPD. They respond to extreme events and help limit peak voltage, but the everyday surge current is managed mainly by the SPD.

So, when both are installed, the SPD handles the bulk of the surge current, keeping voltages within safe limits for the equipment. The lightning arrester acts as an additional safeguard for extreme impulses, not the primary current-handling device.