California Portable Engine Registration (PERP): When Registration Is Triggered

Why this matters

A contractor who rolls a portable diesel generator from job to job in California can be operating an engine that needs an air-quality registration, and many do not know it until an inspector asks for the PERP sticker. California's Portable Equipment Registration Program (PERP), run by the California Air Resources Board (CARB) under 13 CCR sections 2450 through 2465, lets the owner of a portable engine register statewide instead of getting a separate permit from every local air district the equipment travels through. Knowing when registration is triggered, and when a unit instead needs a local district permit, keeps a fleet legal and avoids the unit being red-tagged on site. This article lays out the rule and the field flow to determine which path a portable generator falls under.

The rule

PERP is a voluntary statewide registration program for portable engines and equipment that move from location to location. The core trigger is engine size and portability:

• The program applies to portable internal combustion engines, with the registration framework generally written around compression-ignition (diesel) and spark-ignition engines rated at or above 50 brake horsepower (bhp). Engines below that threshold and certain equipment are handled differently; confirm the current threshold and applicability in 13 CCR 2451 definitions before relying on a number.
• "Portable" means the engine and equipment are designed and capable of being moved (on wheels, skids, or otherwise) and are not permanently fixed at a single location. An engine that stays at one site beyond the program's residence-time limits is treated as stationary and falls under local air-district permitting instead of PERP.
• Registration is statewide and recognized across local air districts, which is the whole point: a registered portable unit can operate in multiple districts without separate local permits, subject to the program's operating conditions.

The practical decision is almost always: is this engine portable and within PERP's scope (register with CARB), or is it effectively stationary at one location (get a local air-district permit)?

When it applies

PERP registration is the right path when:

• The generator is a genuinely portable unit at or above the program's horsepower threshold that moves between job sites (construction, events, rental fleets, agricultural operations that relocate equipment).
• The owner wants one statewide registration instead of chasing permits in each district the equipment enters.
• The unit will not remain at any one location long enough to be reclassified as stationary under the program's residence-time provisions.

A LOCAL air-district permit (not PERP) is required when:

• The engine is installed and operated at a single fixed location (a building's permanent standby generator). Permanent standby gensets are stationary sources and are permitted by the local air district, not registered under PERP.
• A nominally portable unit stays at one site beyond the residence-time limit and is therefore deemed stationary.

Field compliance flow

1. Determine the engine rating. Read the engine data tag for brake horsepower. Compare against the program's applicability threshold in 13 CCR 2451. Below-threshold and exempt categories follow their own rules.
2. Determine portability and use. Is the unit on wheels or skids and genuinely moved between locations, or is it bolted down at one address as the building's standby power? Permanent standby equals stationary equals local-district permit.
3. If portable and in scope, confirm or obtain the PERP registration. Registered units carry the CARB registration and identification; verify the unit displays its registration and that it is current.
4. If the unit is staying put at one site, check the residence-time provisions. A portable engine that overstays the program's location limits at a single site loses portable status and needs a local-district permit for that location.
5. For a permanent standby install, route the customer to the local air-quality management district (for example a regional AQMD/APCD) for the stationary-source permit. PERP does not cover the fixed-install standby generator.
6. Keep the paperwork on or near the unit. An inspector will ask for the PERP registration (portable) or the district permit (stationary); a unit with neither, where one is required, can be shut down on site.

Confirming the right path

• Portable, in-scope, moving between districts: PERP registration with CARB is the compliant path; the unit carries its statewide registration.
• Fixed permanent standby generator at a building: local air-district stationary-source permit; PERP does not apply.
• Borderline (portable unit parked long-term at one site): the residence-time rule decides; once it overstays, treat it as stationary and get the local permit.

References

• California Air Resources Board, Portable Equipment Registration Program (PERP), 13 CCR sections 2450 through 2465.
• 13 CCR 2451, Definitions, for the portable-engine and horsepower applicability threshold and "portable" definition.
• 13 CCR 2452 through 2456, registration, operating conditions, and residence-time provisions distinguishing portable from stationary equipment.
• Local air quality management district / air pollution control district rules for stationary-source (permanent standby generator) permitting.