Choose a surge protective device (SPD): Type 1 vs Type 2 vs Type 3, voltage protection level Up, In/Imax ratings and coordination with upstream breaker.
A surge protective device (SPD) is the component most panels leave out and is often blamed on lightning. In reality most surges are internal — contactor switching, motor starts, capacitor banks — and an SPD sized for the wrong location does nothing useful. This guide covers what changes the part number: type, voltage protection level, current ratings, and coordination with the upstream breaker.
An SPD clamps transient over-voltages to a safe level by diverting the surge current to earth (or between lines) for the few microseconds the transient lasts. It does not switch the circuit off and it is not a substitute for the insulation or the earthing system. Its job is to keep the voltage across your equipment below the level that equipment can survive. The single number that expresses this is the voltage protection level, Up.
The Type states where the device is installed and what surge it absorbs.
| Type | Installed at | Surge source | Typical rating |
|---|---|---|---|
| Type 1 | Service entrance, exposed to direct lightning | Direct strike, partial lightning current | Imax 12.5-25 kA per pole |
| Type 2 | Main or sub-distribution boards | Indirect surges, switching | In 20 kA, Imax 40 kA common |
| Type 3 | Outlet / equipment end, fine protection | Residual local surges | Low energy, always behind Type 2 |
Type 3 is never used alone: it is the last stage behind a Type 2 device, protecting sensitive equipment at the point of use, with Type 3 added at critical outlets.
At the main incomer, a Type 1 or Type 1+2 device protects the whole installation from the incoming surge. At each sub-distribution board feeding long runs or outdoor circuits, add a Type 2 device so the surge is clamped near the load. For IT, security and process equipment, a Type 3 device at the outlet is the final clamp. Rule of thumb: clamp as close to the load as practical, in stages.
An SPD must be backed by a short-circuit protective device — usually a gG fuse or an MCB — so that if the SPD fails short-circuit, the backup clears it safely. The SPD manufacturer publishes a coordination table stating which breaker or fuse is acceptable. Use it. A Type 2 SPD on a 100 A board with a 63 A backup that cannot clear the fault is a hazard, not a protection. Also confirm the backup device is selective with the board's main breaker so a failed SPD does not black out the installation.
For a TN-C-S or TN-S system a 1P+N or 3P+N device clamping line to neutral is adequate. For a TT system, or where the neutral is not reliably connected, a 3P or 4P device that also clamps between lines and to earth is safer. A device that only protects line-to-neutral leaves the line-to-line path open, so confirm the pole count matches the supply.
ELEHPD supplies Type 1, Type 1+2 and Type 2 surge arresters from 10 kA to 40 kA Imax, including DC surge arresters for PV strings, with matching backup fuses and coordination data for a complete scheme.
Send the ratings, dimensions and quantities you are working to and we will confirm the closest match from the ELEHPD catalogue, the compliance documents available for it and the lead time. OEM branding, private model numbering and buyer-specific cartons are available on qualified volumes.