What is surge protection?
Surge protection devices (SPDs), also called transient voltage suppressors (TVS), protect electrical systems and electronics from abnormal voltage spikes caused by lightning or switching events. They divert surge current to earth and limit the voltage reaching equipment.
Why it matters
- Lightning-induced surges are a leading cause of failures in instruments, PLC/DCS cards and communication equipment
- Downtime and replacement costs far exceed the cost of protection
- Hazardous areas need certified SPDs that do not compromise intrinsic safety
Types of SPD
- Type 1 – at the service entrance, for direct lightning current (10/350 µs)
- Type 2 – in distribution boards, for induced surges (8/20 µs)
- Type 3 – close to sensitive equipment
- Signal and data SPDs – for 4–20 mA loops, fieldbus, RS485 and Ethernet (e.g. Eaton MTL SD, TP48)
Good practice
- Coordinate power and signal protection in zones (IEC 62305-4)
- Keep earth connections short and bonded
- Install protection at both ends of long field cables
- Test SPDs periodically (e.g. with an MLDT tester)
VTL designs and supplies complete surge protection schemes with Eaton MTL and Weidmüller VARITECTOR.
