A surge protection device (SPD) is an electrical protection component installed in a power or signal circuit to limit transient overvoltage (surges) and divert surge energy safely to earth (ground). SPDs protect EV chargers and site electrical infrastructure from voltage spikes caused by lightning-induced events, utility switching, and fault disturbances.
In EV charging deployments, SPDs are commonly installed in main LV panels, sub-distribution boards (SDBs), feeder pillars, street cabinets, and sometimes within charger enclosures depending on system design.
Why SPDs Matter in EV Charging Installations
EV chargers include sensitive power electronics, metering, and communications hardware that can be damaged or destabilized by surges. Proper SPD selection and installation helps:
– Reduce charger downtime and electronics failures
– Improve reliability at exposed outdoor sites (kerbside, depots, car parks)
– Protect supporting equipment such as routers, gateways, and LTE modems
– Lower maintenance cost and warranty claims
– Reduce nuisance resets and intermittent faults after grid disturbances
What an SPD Protects Against
SPDs are designed to address short-duration transient events such as:
– Lightning-induced surges (nearby strikes and induced voltages)
– Switching surges from network operations (breaker switching, capacitor banks)
– Fault clearing events and voltage spikes on distribution feeders
– Inductive load switching within the site (motors, HVAC, lifts)
SPDs do not protect against long-duration overvoltage, undervoltage, or sustained poor power quality on their own.
How an SPD Works
An SPD remains inactive during normal voltage conditions. When a surge occurs:
– The SPD “clamps” the overvoltage to a safer level
– It provides a low-impedance path for surge current to flow to earth
– After the event, it returns to its normal high-impedance state
Common internal technologies include MOVs (metal-oxide varistors), gas discharge tubes (GDTs), and TVS devices, often combined depending on SPD class and application.
SPD Types and Where They Are Used
SPDs are typically selected by type/class depending on installation location and expected surge energy:
– Type 1 SPD: higher-energy protection, often used at service entrances where lightning currents can enter the building installation
– Type 2 SPD: most common for distribution boards feeding charger groups and building loads
– Type 3 SPD: point-of-use protection close to sensitive devices when needed
Many EV charging sites use a coordinated Type 1 + Type 2 approach (site entrance + local distribution), depending on lightning exposure and network characteristics.
Key Selection Parameters
Important SPD selection factors include:
– System voltage and earthing arrangement (TN, TT, IT, etc.)
– Maximum continuous operating voltage (Uc)
– Discharge current ratings and impulse current capability
– Voltage protection level (Up) and coordination with downstream equipment
– Number of poles and protection modes (L–N, L–PE, N–PE)
– Environmental requirements (IP rating, temperature, mounting method)
Correct coordination ensures the SPD limits voltage without failing prematurely.
Installation Considerations and Common Pitfalls
SPD performance depends heavily on installation quality:
– Keep SPD connection leads short to reduce voltage let-through
– Ensure low-impedance bonding to the protective earth (PE)
– Place SPDs at the right points in the distribution chain (main + local)
– Protect communication lines where they enter outdoor cabinets (Ethernet, antennas)
– Monitor SPD status indicators and replace units after end-of-life or major events
A common failure mode is installing SPDs correctly on paper but with poor lead routing or weak earthing, which reduces real protection.
Benefits for Operators and Site Owners
– Higher charger uptime and fewer storm-related failures
– Reduced replacement of PCBs, meters, and communication modules
– More stable operation for public sites with long feeder runs
– Lower lifecycle cost and stronger network reputation
Related Glossary Terms
Surge Protection
Surge Arrestor
Surge Immunity Test
Earthing / Grounding
Protective Earth (PE)
Equipotential Bonding
Main LV Panels
Sub-distribution Boards
Power Quality