Class Code 3724
Millwright Work; Electrical Machinery/Auxiliary Apparatus
Class code 3724 covers millwright work on electrical machinery and auxiliary apparatus — the mechanical installation, alignment, maintenance and relocation of motors, generators, pumps, compressors, and their support equipment. The approved pure premium rate for California (effective Sept 1, 2026) is $4.235 per $100 of payroll. Understanding this classification helps employers assign payroll correctly, manage exposure, and control workers' comp costs.
What Class Code 3724 Covers
This class applies to millwrights and machine mechanics who perform mechanical assembly, dismantling, rigging, setting, aligning and testing of electrical rotating machinery and associated auxiliary apparatus. Typical operations include installing and aligning electric motors and generators, mounting pumps, fans and compressors, setting foundations and baseplates, coupling shafts and installing bearing assemblies, and performing preventive mechanical maintenance on electrically driven equipment. Millwrights under this code generally handle the mechanical and structural work around electrical machinery but do not perform live electrical wiring or high-voltage circuit terminations unless separately classified as electrical work. The class covers work in industrial plants, power generation, manufacturing, pulp and paper, food processing, and facilities with large mechanical-electrical systems.
Who It Applies To
- Industrial millwrights and machine mechanics who install and maintain electric motors, pumps, compressors, and gearboxes
- Turnaround and maintenance crews in refineries, power plants, and chemical plants performing machinery changeouts
- Facility maintenance teams that relocate or realign electrically driven production equipment
- Contract rigging and machinery moving firms hired to remove and set heavy electrical rotating equipment
- Millwrights working in manufacturing, food processing, pulp & paper, and utilities
Common Job Duties
- Unloading, rigging and setting heavy electric motors, generators, pumps and compressors
- Leveling and aligning shafts, couplings and gearboxes using lasers and dial indicators
- Installing baseplates, grouting foundations and securing vibration isolation mounts
- Disassembling and reassembling rotors, bearings and housings for mechanical repair
- Installing belts, pulleys and auxiliary drive components and checking clearances
- Coordinating with electricians for lockout/tagout, final wiring, and testing of energized systems
- Performing preventive maintenance: lubrication, belt/chain replacement, and vibration checks
Common Injury Risks
Understanding the $4.235 Rate
The pure premium rate of $4.235 per $100 of payroll represents the portion of the workers' compensation cost that covers expected claim frequency and severity for this occupational classification. Insurers multiply this rate by your payroll in hundreds to calculate the pure premium; the final premium can then be adjusted by experience modification, policy schedules, minimum premiums, deductible programs, and carrier filing factors. Employer-specific factors that affect the actual premium include past loss history, safety programs, payroll mix, and whether operations are split across multiple classifications.
Cal/OSHA Compliance Requirements
Millwrights working on electrical machinery must follow Cal/OSHA requirements for control of hazardous energy (lockout/tagout), machine guarding, crane and rigging safety, and fall protection when working at heights. Employers should also implement confined space entry procedures, hearing conservation where noise exposures exist, and coordinate with qualified electricians for de-energized work or when exposed to live parts; NFPA 70E guidance is commonly used for electrical safety practices. Regular written procedures, training records, and documented permits (LOTO, crane lifts, confined space) will help demonstrate compliance.
How Key HR Helps Employers Under Class Code 3724
A PEO like Key HR helps California employers with class code 3724 by auditing payroll classifications to prevent misclassification, implementing targeted loss-control programs (rigging training, LOTO training, fall protection), and providing claims management and nurse case triage to control medical costs. Key HR can also support return-to-work programs, coordinate safety training on site or virtually, and negotiate with insurers through consolidated purchasing to reduce overall workers' comp spend.
Get a QuoteFrequently Asked Questions
If my mechanic wires motor connections, should they still be in class 3724?
If the worker's primary duty is mechanical millwright work—installing, aligning and maintaining electrical machinery—they typically fall under 3724. However, substantial electrical installation, conduit running, or high-voltage wiring should be separately classified as electrical work and handled by licensed electricians; insurers will reclassify payroll if wiring is a primary job function.
What are the most effective ways to reduce workers' comp costs for millwright crews?
Documented rigging and crane lift procedures, strict lockout/tagout enforcement, routine preventive maintenance to reduce emergency repairs, formal return-to-work/light-duty programs, and targeted training (rigging, LOTO, confined space, fall protection) reduce claim frequency and severity. Accurate payroll allocation and proactive claims management through a PEO can also lower premiums over time.
When should I require a qualified electrician on the job?
Require a qualified electrician whenever workers will make final electrical terminations, work on live circuits, perform high-voltage testing, or access energized switchgear. Even for mechanical millwright tasks, electricians should be involved to de-energize equipment and verify zero energy per lockout/tagout procedures.
Quick Facts
- Class Code
- 3724
- Classification
- Millwright Work; Electrical Machinery/Auxiliary Apparatus
- Pure Premium Rate
- $4.235 / $100 payroll
- Effective Date
- September 1, 2026
- Source
- WCIRB Approved Filing
Manage Workers' Comp Through a PEO
Key HR provides pay-as-you-go workers' comp for California employers — no large deposits, no audits, better rates.
Get a Quoteor call (800) 922-4133Ready to Simplify Workers' Comp for Class Code 3724?
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