Why does the application label matter?
Caterpillar explains that rating selection depends on load pattern, required power, operating hours and utility-parallel or isolated operation. Its guide distinguishes several manufacturer rating categories and notes that its terminology does not align identically with every industry-standard category.
Critical Power Drafting is independent and is not affiliated with Caterpillar. Use the selected product documentation and approved project basis. This article does not reproduce a rating standard, choose a duty class or apply a universal prime-to-standby conversion factor.
Sources: Caterpillar: Caterpillar: Understanding Generator Set Ratings, checked 20 October 2026
What belongs beside the power value on a drawing?
Reconcile the generator tag and exact submittal revision before copying any number. Keep the original manufacturer label even when an office schedule uses a shorter field name.
| Drawing field | Evidence | Mismatch to flag |
|---|---|---|
| Generator identity | Approved tag, model and revision | Rating copied from another variant |
| Power quantity | Explicit kW or kVA heading | Different quantities merged |
| Application rating | Exact manufacturer designation | Generic capacity field only |
| Duty conditions | Approved load and operating basis | Assumed unlimited application |
| Site basis | Accepted environmental conditions | Unverified reference conditions |
| Approval | Engineer and supplier disposition | Largest figure selected without review |
How can the wrong number reach the one-line?
Illustrative example. A fictional supplier sheet gives 500 kW under a standby heading and 450 kW under a prime heading. The approved schedule calls for review against prime duty, but a drawing records 500 kW because it is the larger number. The difference is 50 kW; it is not spare capacity established for that approved duty.
The drafter preserves both original headings, flags the copied value and requests the actual design decision. These fictional figures do not describe a product, establish a 90 percent conversion rule or show that either rating is adequate. No operating-hours or overload permission follows from this example.
How should changes to duty be controlled?
If the operating plan changes, keep the revised duty request separate from an ordinary drawing transcription correction. The supplier and responsible engineer must assess the actual rating and constraints; a drawing edit cannot create a new equipment capability.
Trace the accepted decision through the equipment schedule and one-line so later documents do not restore the superseded number. Engineering sign-off is performed only by the registered engineer on the job.
Common questions
What else should the bid team know?
Are two kW figures interchangeable if the units match?
No. Their application ratings and conditions must also match.
Is prime always a fixed percentage of standby?
Do not use a universal percentage. Obtain the actual product data.
Does this worksheet select the generator rating?
No. It reconciles the approved inputs for technical review.