Surge Protective Device – Basic Q&A

1. What exterior types of surge protectors (SPDs) are currently available?

There are mainly two types:
- A square-shaped SPD, which is installed inside our company’s street lighting distribution box.
- A cylindrical SPD, which is installed inside the light pole outside the distribution box.

The reason for this difference is that most distribution boxes from other manufacturers in the market are outdated and have limited internal space, making it impossible to install an SPD inside. Therefore, the SPD has to be placed inside the pole. Our company’s distribution box is currently the only one on the market that can accommodate an SPD internally!

2. When an SPD is damaged, will the street light still illuminate?

- If using a parallel SPD, the street light will continue to operate normally as long as the LED light source is not damaged, even if the SPD has failed. However, once the SPD is damaged, it can no longer protect the LED source from lightning strikes. In the event of another strike, the LED source is likely to be damaged.
- If using a series SPD, the street light will not illuminate even if the LED source is still good, because the failed SPD interrupts the circuit. The LED source itself remains intact.

3. Are the company’s SPD samples parallel or series type?

All SPD samples currently provided by the company are parallel type. However, we can manufacture series-type SPDs upon request.

4. Can both square and cylindrical SPDs be made into series versions?

Yes. Both square-shaped and cylindrical-shaped SPDs can be manufactured as either parallel or series versions.

5. Under what circumstances should a series SPD be used?

In general, when street lights are installed in remote areas where maintenance personnel cannot perform frequent inspections, series SPDs are recommended.

With a parallel SPD, the street light continues to illuminate even after the SPD fails, leaving the LED source unprotected and highly vulnerable during the next lightning strike.
With a series SPD, a failed SPD causes the street light to stop illuminating even though the LED source is still good—allowing maintenance personnel to easily identify the failure. Series SPDs typically do not include indicator lights to reduce cost.

6. When a street light is powered by 220V mains, what type of cable is used, and what SPD specification is required?

A 220V mains cable typically has three conductors:

- Red: Live (L)
- Yellow: Earth (E)
- Blue: Neutral (N)

Correspondingly, the SPD must also include three wires—one red, one yellow, one blue—with a Uc rating of 277V.

7. When a street light is powered by 380V mains, what type of cable is used, and what SPD specification is required?

(1) A 380V mains cable is generally a 3‑phase, 4‑wire system with three red live wires and one blue neutral wire.
- If powering two LED drivers, the SPD must include two red live wires and one blue neutral wire (three wires total), with a Uc rating of 380V.

(2) If powering one LED driver, the wiring is the same as for 220V systems: one red live wire, one yellow earth wire, and one blue neutral wire, with a Uc rating of 277V.

8. Can a Class III SPD replace a Class II SPD? Are their protection performances the same?

(1) A Class II SPD typically has a Voc of 10 kV and can reach up to 20 kV. A Class III SPD generally has a Voc of 5–6 kV and can reach up to 10 kV at most. Therefore, a Class III SPD can partially replace a Class II SPD but cannot completely match its protection capability.

(2) A Class II SPD can also be used together with a Class III SPD to provide dual-layer protection and increase product value.

(3) Class III SPDs are usually pre-installed inside LED light sources by manufacturers, while Class II SPDs are installed in distribution boxes or poles by contractors.