Cummins Onan Serial & Model Number Guide

Every Cummins Onan generator carries a model/serial label. Here is where to find it, what each part of the number means, and how to use it for parts, service and age.

Where to find it: the Onan nameplate on the generator set housing — look for the MODEL and SPEC NO. line. The electrical characteristics (voltage, phase, Hz, amps) are printed on the lower portion of the same nameplate.

Break down your Cummins Onan number

Paste your model / spec number (e.g. 15.0 JC-3CR / 9597T) and we'll label each part. Best-effort — always confirm against your data plate.

What the number means

Worked example — 15.0 JC-3CR / 9597T:

Part	Meaning	Detail
`15.0`	Kilowatt rating	The set's rated output in kW.
`JC`	Series identification	Onan factory code for the engine/alternator series.
`3CR`	Voltage & feature code	The numeral is a voltage / phase code (e.g. 3 = 120/240 V 1-phase); a C denotes a reconnectible winding and an R denotes remote electric start.
`9597`	Optional-equipment code	Factory option code designating optional equipment.
`T`	Specification letter	The spec letter advances A → B → C… each time the factory makes a production modification. It tells you the revision level of your exact unit.

Using the serial number

The MODEL/SPEC number gives the specification (and the spec letter the revision level); the SERIAL number gives the build date. Onan serials encode the manufacture date: 1968–Oct 1974 they read MMYYnnnnnn (e.g. 03 72… = March 1972); from Nov 1974 it is an alpha-month + 2-digit year + serial + plant code, and modern Cummins-Onan portables use alpha-month (A=Jan…L=Dec) + 2-digit year (e.g. J20… = Oct 2020). On modern large commercial gensets, confirm the serial format before decoding a date.

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Decode rules verified against: Onan operator manual, “MODEL IDENTIFICATION” page. Figures are for reference; confirm against the official documentation for your exact unit.