Most wrong orders for industrial parts start with a part number that was almost right. A missing suffix, a confused series letter or a serial number sent instead of the catalog number can lead to a unit that does not fit, does not power up, or does not talk to the rest of the system. This guide explains the fields you will find on a typical nameplate and how to use them when you ask for a replacement.
Catalog number versus serial number
Two numbers on a label look alike but do very different jobs:
- Catalog number (also called part number, order number, type or model): identifies the product and its options. This is the number a supplier needs.
- Serial number: identifies one individual unit. It is useful for the manufacturer's records and sometimes to work out the production date, but it does not tell a supplier what product to send.
Some labels also show an internal article or material number, a barcode, or a reference used for spare parts. When in doubt, send all of them, clearly separated.
How catalog numbers are built
Manufacturers usually build catalog numbers from blocks, each block coding one characteristic. The exact meaning differs by maker and family, but the pattern is similar:
- Family or bulletin: the product line.
- Size or rating: frame size, current rating, number of I/O points.
- Options: number of poles, auxiliary contacts, enclosure, communication port.
- Voltage code: often a letter or letter-number pair at the end that selects the coil or supply voltage.
Because the voltage and options are often coded in the last characters, cutting a number short is one of the most common mistakes. Two catalog numbers that differ by one character may be two different products.
A typical catalog-number structure (fictitious example).
Series and revision letters
Over a product's life, manufacturers make design changes without changing the base catalog number. They mark the change with a series or revision field. On many Allen-Bradley labels, for example, it appears as "Ser." or "Series" followed by a letter. Other makers use "Rev.", "Version", "Product version" or a similar field.
A later series is often a direct replacement for an earlier one, but not always. Changes can affect firmware, connector type, power consumption or mounting. If your system documentation names a specific series, or if the unit works with other modules in a rack, give the series when you ask for a quote. Programmable devices may also show a firmware revision on the label (Allen-Bradley uses "FRN" on many products); note it too.
Voltage and frequency fields
Look for separate markings for:
- Coil or control voltage: the voltage that operates the device, for example the coil of a contactor or the supply of a sensor. Check whether it is AC, DC or both.
- Frequency: 50 Hz, 60 Hz or 50/60 Hz. Some AC coils are wound for one frequency only.
- Rated operational voltage: the voltage of the main circuit the device switches or protects, which is often different from the coil voltage.
- Supply voltage range on electronics, such as 24 V DC or 100-240 V AC.
The coil voltage is sometimes printed on the coil itself rather than on the main label, especially on contactors whose coil can be changed.
Ratings
Ratings tell you what the device is allowed to do. Depending on the product, you may see:
- Rated current, and current by load type (for example AC-1 for resistive loads and AC-3 for motors; see IEC utilization categories).
- Motor ratings in horsepower or kW at several voltages.
- Short-circuit ratings and breaking capacity; see our article on short-circuit current ratings (SCCR).
- Contact ratings for auxiliary contacts and relay outputs.
- Enclosure or protection rating (IP code or NEMA type).
A replacement should meet or exceed the ratings of the original for your application, unless the design has been reviewed by a qualified person.
Approval and conformity marks
Marks show which standards a product was evaluated against or which rules the manufacturer declares it meets. Common ones in North America are listing and recognition marks from UL and CSA, often combined for the United States and Canada. A component mark (UL Recognized) is not the same as a full listing. The CE mark is a manufacturer's declaration for the European market, not a North American approval. Our article on North American standards and certifications goes into more detail. If your inspector or customer requires a specific mark, confirm that the replacement carries it.
Date codes
Many labels carry a date code showing when the unit was built. Formats vary: some are a plain year and week, others are letter codes that only the manufacturer's documentation explains. A date code can help match a replacement to the rest of an installation, but it is not a quality indication on its own.
Take a clear photo of the label
A good photo answers most questions before they are asked:
- Shoot straight on, with enough light and no flash glare.
- Include the whole label, then a close-up of the catalog number and series.
- Photograph the coil marking, the side labels and any option module.
- If the device is still installed, de-energize and lock out the equipment before opening a panel; work must be done by qualified personnel following the applicable electrical code and the manufacturer's instructions.
Nameplate fields at a glance
| Field | Why it matters |
|---|---|
| Catalog number | Identifies the product and its options: send it in full |
| Serial number | Identifies one unit; useful for history, not for ordering |
| Series / revision | Design changes that can affect fit and firmware |
| Firmware revision | Compatibility with software and other modules |
| Coil / supply voltage | Wrong value means the device will not operate or will fail |
| Frequency | Some AC coils work at only one frequency |
| Ratings | Current, power and short-circuit limits for the application |
| Approval marks | Acceptance by inspectors and customers |
| Date code | Production period; helps match an installation |
Where to find each field on a nameplate (fictitious example).
Key takeaways
- Order by catalog number, never by serial number alone.
- Send the full number: options and voltage codes are often in the last characters.
- Give the series or revision letter and firmware level for programmable or rack-mounted products.
- A sharp photo of the whole label is the fastest way to get the right part.
Related parts at 3JIndustry
Browse used Allen-Bradley / Rockwell and Siemens parts, or read our checklist for buying used and legacy parts.
Looking for a discontinued part? Send the full part number to sales@3jindustry.com or use our contact page.
