Surge Protection Device

A Surge Protection Device (SPD) is an electrical protective device installed on a power system to limit transient overvoltages and divert surge current away from equipment, reducing damage from lightning, switching events, and other voltage spikes. In Canadian code practice, the relevant product standard is CSA C22.2 No. 269.1 for permanently connected applications.

On a manufacturing or shop floor, an SPD is typically installed at the main service entrance, distribution panel, motor control center, control cabinet, or near sensitive equipment such as PLCs, drives, HMI panels, instrumentation loops, and networked automation hardware. It is wired in parallel with the protected circuit, and during a transient it drops to a low-impedance path to divert excess energy to earth or back toward the source. This reduces nuisance downtime, protects process control electronics, and preserves safety-related systems where surge-induced failure could create operational or safety consequences.

• ⚠️Wrong SPD type or wrong installation location: using a point-of-use strip where a permanently connected Type 1 or Type 2 device is required, or placing the device too far from the equipment it is meant to protect, reduces effectiveness and can leave control panels exposed.
• ⚠️Ignoring grounding and bonding quality: an SPD depends on a low-impedance path to earth; poor grounding, loose terminations, long conductor runs, or bad bonding can prevent proper diversion of surge energy and can create misleading 'protected' installations that still fail in real events.
• ⚠️Assuming the SPD is permanent: many SPDs degrade after repeated surge events and can fail quietly, so not checking status indicators, end-of-life alarms, or replacement intervals can result in a nonfunctional device that still appears installed.