Published March 2026 • Installation Practices • 4 min read

Surge Protection in Hazardous Locations

Lightning and switching surges can damage equipment and, in rare cases, compromise explosion protection. Surge protective devices (SPDs) in classified areas must be explosion-protected themselves and compatible with the rest of the circuit. This note outlines the essentials.

Use Certified SPDs

General-purpose SPDs belong outside the hazardous area unless the unit carries a valid Ex certificate and marking for your zone, gas group, and temperature class. The certificate defines mounting location, enclosure type, and connection rules.

Coordination With Intrinsic Safety

Check before you add

  • Confirm the SPD is approved in series or parallel with your Ex i barrier and field device.
  • Re-run entity or system parameters if capacitance or inductance changes.
  • Follow the manufacturer’s grounding diagram for the barrier and the SPD.

Installation

Keep lead lengths short; long leads reduce SPD effectiveness. Bond the SPD ground to the same reference used for equipment grounding. Document the SPD in the equipment register with certificate number and revision.

Site standard: Many owner specifications require coordinated lightning protection, grounding, and SPD selection at the building entry and at the field panel. Align Ex SPD rules with that standard so nothing is double-counted or omitted.

HazloLabs can review surge and grounding schemes for hazardous locations so protection devices match your classification and wiring method.