An SPD in an EV charger is a surge protective device: a component that clamps brief voltage spikes, for example from nearby lightning or grid switching, and diverts the surge current to earth before it damages electronics. SPDs are classified by type (Type 1, 2 or 3 in IEC terms) and described by a few ratings: continuous operating voltage, discharge current and voltage protection level. Some chargers contain small surge components; a full SPD is usually a separate device in the panel.
Key Takeaways
- An SPD clamps voltage spikes and diverts surge current to earth.
- Type 1, 2 and 3 devices are tested for different surge levels and locations.
- Check Uc, In, Imax and Up on the datasheet.
- Internal varistors do not replace a correctly rated SPD fitted by an electrician.
What an SPD Is Made Of
IEC 61643-11 describes SPDs as devices with at least one nonlinear component that limit surge voltages and divert surge currents. The common building blocks are:
- Metal oxide varistors (MOVs): resistance drops sharply above a threshold voltage, so the spike is shunted away. They wear with each large surge.
- Gas discharge tubes (GDTs) and spark gaps: ionize and conduct during very high surges, often used in Type 1 devices or combined with MOVs.
- Thermal disconnectors and status indicators: isolate a worn or overheated device and show when it needs replacing.
Inside a charger’s power supply you may find small varistors on the circuit board. They protect that board against modest transients but are not a replacement for a properly rated SPD in the installation.
SPD Types and Where They Go
| IEC class | Tested for | Typical location |
|---|---|---|
| Type 1 | Very high impulse currents, such as partial lightning current entering the building | Origin of the installation, where a lightning protection system or overhead supply is present |
| Type 2 | Induced and switching surges | Main panel or sub-panel, the most common choice for homes and businesses |
| Type 3 | Lower-energy surges close to sensitive equipment | Near the equipment, always in addition to an upstream Type 2 |
North American products are listed to UL standards with their own Type numbering. Whether an SPD is required, and where, depends on local codes; our article on whether EV chargers should have surge protection covers the US NEC requirement for dwelling services.
Reading SPD Ratings on a Datasheet
| Rating | Meaning | Practical check |
|---|---|---|
| Uc (max continuous operating voltage) | Highest voltage the SPD can sit at permanently | Must suit the supply, including normal voltage swings |
| In (nominal discharge current) | Surge current it handles repeatedly in tests | Higher means more endurance |
| Imax or Iimp | Maximum single surge (Type 2) or impulse current (Type 1) | Match to exposure: overhead lines, rural sites, lightning risk |
| Up (voltage protection level) | Residual voltage let through while clamping | Lower is better; must be below what the protected equipment withstands |
| Modes of protection | Which conductor pairs are protected (live-neutral, live-earth, neutral-earth) | Should suit the earthing system |
Reading the rest of a charger specification is covered in our guide on how to read an EV charger datasheet.
What Buyers and Installers Should Ask
- Does the charger include internal surge components, and to what level is it tested?
- Does the installation manual recommend or require an external SPD?
- Is the site exposed (overhead supply, long outdoor cable runs, lightning-prone area)?
- Will the SPD have a status indicator so worn units are replaced?
Choosing and fitting an SPD in a panel is work for a qualified electrician. Good earthing is part of the picture; see whether you need an earth rod.
EVDANCE chargers such as the EV-ACT5006T 48A Level 2 wall charger and the EV-AC03201T dual-connector AC station include over-voltage protection, and our team can advise installers on external SPD requirements through our commercial charging solutions.
Frequently Asked Questions
Does an SPD wear out?
Yes. Varistors degrade with large surges. Many SPDs have an indicator window or remote contact that shows when replacement is needed.
Is an SPD the same as an RCD?
No. An RCD disconnects on earth leakage to protect people. An SPD limits voltage spikes to protect equipment.
Can one SPD protect several chargers?
A panel SPD protects circuits fed from that panel. Long cable runs may justify additional protection near the chargers, as an electrician decides.
Related Reading
- Why Is My EV Charger Flashing Red?
- Common EV Charger Faults and How Suppliers Should Handle Them
- Do I Need an Earth Rod for My EV Charger?
