How to choose an SPD / surge arrester: Class I, II and III, where each goes in a panel, and why it needs a backup fuse.
A surge protective device (SPD) is cheap insurance against the one event that can take out an entire panel at once — a lightning-induced or switching surge riding the supply. The trick is putting the right class in the right place and protecting it with a fuse, or it becomes a hazard itself.
| Class | Installed at | Role |
|---|---|---|
| Type 1 (I) | Main incomer, exposed sites | Diverts direct/near lightning current |
| Type 2 (II) | Distribution / sub-boards | Protects equipment from residual surge |
| Type 3 (III) | Outlet / equipment side | Finishes off residual micro-surges |
A typical installation cascades Type 1 at the incoming board and Type 2 at each distribution board; Type 3 is only added at sensitive equipment. Never fit Type 1 without the earthing and bonding to carry the diverted current away.
An SPD that fails short-circuit must be disconnected by a coordinated backup fuse — usually a gG fuse or a dedicated SPD disconnector — sized from the manufacturer's coordination table. Without it, an end-of-life SPD can weld and feed a fault into the board. Specifying the SPD and its backup as a matched pair is non-negotiable.
ELEHPD surge arresters, surge-protected boards, MCBs and busbar let panel builders assemble a coordinated, fuse-backed protection stage.
Cascade them: Type 1 at the main incomer of an exposed site to divert direct lightning current, Type 2 at distribution boards for residual surges, and Type 3 only at sensitive equipment. Without proper earthing and bonding, Type 1 does nothing.
Yes — a coordinated gG fuse or dedicated SPD disconnector sized from the manufacturer's table. Without it, an SPD that fails short-circuit can weld and keep feeding a fault into the board.
Up is the residual voltage let through to equipment — keep it below the equipment's withstand, typically ≤ 1.5 kV for Type 2. Imax/In is the surge current the device survives, matched to the site's lightning exposure.
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.