Incorrectly installed surge protection poses a liability risk for planners and installers of switching devices. Connecting cables that are too long often lead to problems. Find out about correct installation and how to comply with the required cable lengths.

Location for Installation of Primary SPD

SPDs are located where the main electrical supply originates or at the main switchboard.
SPDs are installed at remote switchboards and must be coordinated with a primary SPD, in a manner specified by the manufacturers.
In some situations, such as sensitive electronic equipment at hand, supplemental localized protection may be needed, which applies to the equipment itself.
Specialized sites such as telecommunications hubs, remote telemetry stations, and industrial process control facilities require special consideration.

In large electrical systems, a separate transformer is often used for feed-in. A main power distribution with a miniature circuit breaker up to 7,000 A is installed on the low-voltage side. Surge protection must also be provided in these distributions in accordance with DIN VDE 0100-443.

In power distributions with feed-in from below and a busbar system at the top or in the middle, the surge protection is usually installed above the miniature circuit breaker. There is a lot of room here in the incoming panel for the surge protective device and the necessary backup fuse.

Tools and Materials Needed:

SPD (appropriate for the application and voltage level)

Screwdriver and pliers

Multimeter for voltage and continuity checks

Circuit breakers or fuses (if needed)

Insulated gloves and other personal protective equipment (PPE)

Installation:

SPDs shall be installed in accordance with the following:

- Installation: Installed after the main switch but before any Residual Current Device (RCD).
- Protection: Protected by a separate fuse or circuit breaker.
- Connection at Main Switchboard: Between phase and neutral at the main switchboard.
- Connection at Remote Switchboards: For switchboards without MEN connections, connect from each phase to neutral and from neutral to earth.
- Labelling: SPDs shall be marked clearly and indelibly in accordance with Clause 2.10.5.1.
- Status Indication: If SPDs are alarmed to provide status indication, they shall fail safely.

Figure F1 shows the connection of a primary SPD for a single-phase system.

Figure F2 shows an example of a secondary SPD installation for a single-phase system.

Step-by-Step Installation:

1. Turn Off Power

Safety first: Disconnect the power at the main breaker before performing any electrical work.

Use a multimeter to ensure that the power is completely off at the installation site.

2. Identify the Connection Points

Identify the phases (L1, L2, L3), neutral (N), and ground (PE) terminals in the distribution panel.

3. Install Circuit Protection (Optional)

Install a circuit breaker in front of the 3 phase surge protection device device for additional protection. Ensure that the breaker rating corresponds with the current handling capacity of the 3 phase surge protection device.

4. Mount the Surge Protection Device

Install the Surge protection device near the main distribution board to minimize the lead length between the surge protection device and the connection points.

Shorter lead lengths improve the effectiveness of the surge protection device by reducing response time to surges.

Keep all connecting wires as short and direct as possible to reduce impedance and improve protection.

5. Test the Installation

Verify connections with a multimeter to ensure there are no loose wires or shorts.

Turn on the power and check that the surge portection device is functioning correctly. Many SPDs have an indicator light to show if the protection is active.

6. Label the Installation

Clearly mark the SPD’s location on the panel for future reference. This is important for maintenance and safety purposes.

Overcurrent Protective Devices for SPDs

Protection Requirements
SPDs shall be protected against short circuits by proper overcurrent protective devices. The short-circuit withstand capability of the SPD and its protective device shall be at least as great as the prospective short-circuit current at the installation point.

Current Rating Guidelines
The current rating of the overcurrent protective device should:

Follow Manufacturer Recommendations: It must not exceed the SPD’s maximum backup fuse rating as specified by the manufacturer.
Be Less Than the Upstream Device Rating: The protective device rating should always be lower than the immediate upstream device.

RCD Considerations

An SPD, connected downstream of an RCD (Residual Current Device), shall have the RCD’s breaking capacity be at least 3 kA.
S-type RCDs compliant with AS/NZS 61008.1 and AS/NZS 61009.1 are acceptable.

Conductor to Connect SPD
Minimum Cross-Sectional Area for the Connecting Conductor
The connecting conductor needs to be sized to correspond with the backup fuse rating or circuit breaker.

Length
Conductors should be as short and direct as possible and not contain loops. Total length of both the active and earth/neutral must not exceed 1 m but, where practical, should be between 300 mm and 600 mm.

Neutral Conductor Connection
Connect to the neutral conductor as near as possible to the MEN link (Main Earthing Neutral link).

Basic principles: Cable lengths and voltage protection level in detail

The connection of surge protective devices, especially the cable length, has a significant influence on the effective voltage protection level in the switching device.
DIN VDE 0100-534 therefore stipulates a maximum cable length of 0.5 m between the phase and PE.

Voltage protection level in a switching device.