When Does an SPD Need Replacing?
Surge Protection Devices (SPDs) do not necessarily last for the lifetime of the electrical installation.
Each time an SPD deals with a significant transient overvoltage, its protective components can experience stress. Over time, or following a sufficiently severe surge event, the SPD may reach the end of its service life and require replacement.
How Do I Know If an SPD Has Failed?
The easiest way to check many SPDs is the status indicator on the front of the device.
A common arrangement is:
Green – SPD operational
Red – SPD requires attention or replacement
The exact meaning of the indicator varies between manufacturers, so the instructions for the specific SPD should always be checked.
If an SPD that previously displayed green is now showing red, this can indicate that the protection module is no longer providing its intended surge protection.
Why Do SPDs Wear Out?
An SPD works by limiting transient overvoltages and diverting surge current away from the protected installation.
The internal components are designed to withstand surge events, but their capacity is not unlimited.
The service life of an SPD can therefore depend on factors including:
- Number of surge events experienced
- Severity of those surge events
- Electrical supply conditions
- SPD specification
- Installation conditions
- Manufacturer and device design
For this reason, there is not necessarily a fixed replacement interval that applies to every SPD.
Does an SPD Need Replacing After Every Surge?
No.
SPDs are designed to deal with transient overvoltages, and a correctly selected device can withstand multiple surge events within its rated capabilities.
A surge occurring does not automatically mean the SPD needs replacing.
The device's status should be checked following a significant event or where there is reason to suspect the SPD has operated.
If the status indicator shows that the protection module has failed, replacement may be required.
Do SPDs Have an Expiry Date?
SPDs generally aren't replaced according to a simple expiry date in the same way as some other safety products.
Their condition depends primarily on the SPD design and the electrical stresses it has experienced.
The status indicator and manufacturer's instructions should therefore be used when determining whether the device remains operational.
Do I Need to Replace the Whole SPD?
Not always.
Many SPDs consist of two main components:
SPD base – the fixed section connected to the electrical installation.
Replaceable cartridge – the removable protection module containing the surge protection components.
If the cartridge reaches the end of its service life, some manufacturers allow the cartridge to be replaced while leaving the existing base and wiring in place.
Other SPDs are supplied as complete devices and require the entire unit to be replaced.
Can I Replace a Red SPD Cartridge Myself?
Work inside a consumer unit or distribution board can expose you to dangerous voltages.
SPD replacement should be carried out by a competent person with the appropriate electrical knowledge and equipment, with the installation safely isolated and the manufacturer's instructions followed.
Do not remove an SPD cartridge or cover solely because the indicator has changed colour without first establishing the correct replacement procedure for that device.
What If the Correct SPD Is Discontinued?
Consumer unit and distribution board ranges change over time, meaning the original SPD or replacement cartridge may eventually become difficult to source.
Before substituting another device, identify:
- Manufacturer
- Original SPD part number
- Cartridge part number, if applicable
- SPD type
- Electrical ratings
- Pole configuration
- Consumer unit or distribution board range
A newer SPD should not automatically be considered a direct replacement for an older model simply because it is produced by the same manufacturer.
Finding a Replacement SPD
If your existing SPD is displaying a failed status, start by taking a clear photograph of the front of the device.
Make sure the manufacturer, model number and electrical ratings are visible.
If the SPD contains a removable cartridge, check whether the cartridge also has a separate part number.
ReCircuit Resale stocks a range of new, surplus and discontinued SPDs and replacement components from major electrical manufacturers.
For older or discontinued devices, searching by the exact part number is usually the best place to start.
Next Guide: Can You Replace Just the SPD Cartridge?