Electrical equipment lives in two seismic worlds. Inside a building — switchgear, ATSs, UPSs, panelboards — ASCE 7-22 Chapter 13 and AC156 govern. Outside on a substation pad — transformers, circuit breakers, disconnects — IEEE 693 governs. The two standards have different philosophies, different qualification methods, and different deliverables. Choosing the wrong one delays both jurisdictional and utility approval.

IEEE 693 — Recommended Practice for Seismic Design of Substations

IEEE 693 is published by the IEEE Power & Energy Society and adopted by major US utilities. It applies to high-voltage substation equipment: transformers ≥ 35 kV, circuit breakers, disconnects, surge arresters, instrument transformers, capacitor banks, and the support structures that carry them. IEEE 693 defines three performance levels:

  • High — qualified to a Required Response Spectrum (RRS) of 1.0 g ZPA. Used in seismically active regions (California, Pacific NW).
  • Moderate — RRS of 0.5 g ZPA. Used in moderately seismic regions (Midwest, parts of the Southeast).
  • Low — analytical qualification only. Used in low-seismicity regions.

ASCE 7-22 + AC156 — building-mounted electrical equipment

Inside the building envelope, ASCE 7-22 §13.6 and the Ipprovisions of §13.1.3 govern. Active electrical equipment with Ip = 1.5 (life-safety, hospital) requires special seismic certification per §13.2.2 — typically by AC156 shake-table testing. See our AC156 guide.

The fundamental difference

  • IEEE 693 assumes the equipment is at grade on a substation pad. The RRS is fixed by performance level; it does not depend on a building's SDS or z/h.
  • ASCE 7-22 / AC156 derives the RRS from the project's SDS, the component's Ip, and the elevation z/h. The same generator gets a different RRS on the ground floor vs the roof.

Dual-jurisdiction projects

Hospital campuses with a separate utility-owned substation are common in California. The substation transformer is qualified to IEEE 693 High; the in-building switchgear served from that transformer is qualified to AC156 with an OSHPD OSP. Coordination items:

  • Verify the IEEE 693 qualification level on the utility's submittal.
  • Verify the in-building equipment OSP and the AC156 RRS used.
  • Anchor design for both follows the local building code (IBC + ASCE 7-22 + ACI 318-19) regardless of qualification standard.

Anchorage requirements compared

  • IEEE 693: anchorage qualification is part of the equipment test program; the equipment is shipped with a qualified anchor pattern.
  • ASCE 7-22: anchorage is project-specific and designed by the SEOR or specialty engineer per ACI 318-19 Chapter 17 with §17.10 seismic provisions and Ω0p per §13.4.2 — see Ω0 overstrength.

When does IEEE 693 reach inside a building?

Some utilities require IEEE 693 qualification for medium-voltage switchgear that serves their distribution side, even when installed in a building. Read the project's electrical specification carefully — look for "qualified per IEEE 693 Moderate" or similar language. When present, the equipment must satisfy both IEEE 693 (utility) and ASCE 7-22 / AC156 (jurisdictional) — the more stringent governs each component.

Qualification deliverables side by side

  • IEEE 693: Test plan, RRS comparison, test report, IEEE 693 qualification statement signed by a qualified test engineer.
  • ASCE 7-22 / AC156: AC156 test report, Certificate of Compliance with the Special Seismic Certification Label, project-specific anchorage calculation per ACI 318-19. For California hospitals, an HCAI OSP. See OSHPD OSP guide.

Common mistakes

  • Submitting an IEEE 693 certification for in-building switchgear in lieu of the AC156 / OSP. The Authority Having Jurisdiction will reject it.
  • Submitting an AC156 certification for a substation transformer when the utility specification calls for IEEE 693.
  • Using an IEEE 693 qualified equipment anchor pattern as if it were an OPM/OSP — it is not a project-side anchorage design.
  • Confusing IEEE 344 (nuclear) with IEEE 693 (substation) — they are different standards with different acceptance criteria.

Decision checklist

  1. Where is the equipment installed? Substation pad → IEEE 693. Inside a building → ASCE 7-22 / AC156.
  2. Who owns it? Utility-side often → IEEE 693. Customer-side → AC156 / OSP.
  3. What does the project spec say? Defer to the spec and confirm with the AHJ in writing.
  4. Anchorage to the supporting structure is always project-side and follows the local code.

How PANACHE ENGINEERING helps

We coordinate IEEE 693 qualification reports with ASCE 7-22 anchorage calculations on dual-jurisdiction projects. Contact us with your equipment list and we will map each item to the right standard and the right deliverable.