When a breaker or a drive fails, the label is usually the fastest route to a replacement. It tells you what the part is, what it is rated for and, often, which hardware revision it is. It may also tell you when the part was made – though every manufacturer writes that date differently.
Key takeaways
- Order by the full catalog number; record the style number, series and serial number too when the label shows them.
- On a breaker, read the frame, trip rating, interrupting rating at your voltage, voltage rating, poles and listing.
- On a VFD, read the input and output ratings, the normal-duty and heavy-duty power and current, the frame and the series or firmware.
- Date codes are not standardized: a printed date, a week-and-year code or a code inside the serial number. Use the maker's documentation to decode them.
- A date code tells you when a part was made, not how it was stored or used.
Safety first: many labels are inside panels or behind drive covers. Open equipment only as a qualified person, with the circuit de-energized under your lockout/tagout procedure; drive DC bus capacitors stay charged after power is removed, so wait the time on the drive's warning label and verify zero voltage with a properly rated meter.
Reading a breaker nameplate
Catalog number and style number
The catalog number is what you order by. It usually encodes the frame, the number of poles and the amp rating, sometimes with letters for the interrupting level, terminals or accessories. Some labels also carry a style number or another internal reference that identifies the exact build. Copy both, exactly, but search by the catalog number first.
Frame and trip rating
The frame is the breaker family and its maximum current; the trip rating (ampere rating) is the continuous current this breaker protects at, which can be lower than the frame size. On breakers with interchangeable trip units or rating plugs, the trip rating may be on the trip unit or the plug rather than on the main label. A breaker rated to carry 100% of its rating continuously says so on the label.
Interrupting rating (kA or AIC)
The label lists the highest fault current the breaker can interrupt, in kiloamps at each rated voltage – for example one value at 240 V and a lower one at 480 V. Read the value for your system voltage; it must be at least the available fault current where the breaker is installed. IEC-rated breakers show two values: Icu (ultimate breaking capacity) and Ics (service breaking capacity).
Voltage, frequency and poles
A straight voltage rating such as 480 V applies on any 480 V system; a slash rating such as 480Y/277 V only on a solidly grounded wye system. Check for a DC rating if the breaker will be used on DC – an AC-only breaker is not suitable. Count the poles, and look for LINE and LOAD markings: a breaker marked this way is not meant to be fed from the load end.
Trip unit type
Thermal-magnetic breakers may show an adjustable instantaneous setting. Electronic trip units show their functions, often abbreviated LSI or LSIG (long-time, short-time, instantaneous, ground fault), and their sensor rating. Magnetic-only motor circuit protectors are marked as such.
Listing and standards marks
In North America, look for a listing mark and the standard: UL 489 for molded case breakers, UL 1066 for low-voltage power circuit breakers. Devices listed to UL 1077 are supplementary protectors, not branch-circuit breakers, even when they look the same. IEC breakers are marked to IEC 60947-2 with Ue (rated operational voltage) and In (rated current). A CE mark alone does not make a breaker suitable for a North American panel. Our molded case breaker ratings guide covers what has to match for a replacement.
Reading a VFD nameplate
Model or catalog number
Drive catalog numbers usually encode the family, voltage class, rating, enclosure and options such as a built-in filter or braking transistor. Copy the whole string: one character can change the options. For Allen-Bradley drives, our catalog number guide explains the fields and the series letter.
Input ratings
The input block gives the supply voltage or range (for example 380–480 V), the phases, the frequency (50/60 Hz) and the input current, sometimes for each duty rating.
Output ratings
The output block gives the output voltage (up to the input voltage), the output frequency range and the continuous output current – the number that has to cover the motor's full-load amps.
Power: normal duty and heavy duty
Many drives carry two ratings. Normal duty (sometimes light or variable-torque duty) suits fans and centrifugal pumps; heavy duty (constant torque) suits conveyors, mixers and other hard-starting loads, with more overload capacity and a lower continuous current. The nameplate may show HP, kW or both for each duty. Size by current: our motor and VFD sizing guide walks through it.
Frame, series and firmware
The frame or size – a letter or number, depending on the maker – sets the dimensions and mounting. The series or hardware revision is often printed on the label; the firmware revision may be on a separate sticker or only readable from the drive's keypad or software. Match both when the drive talks to a network, a PLC program or saved parameters.
Enclosure and listing
Look for the enclosure rating, such as IP20 or NEMA/UL Type 1, the rated ambient temperature, and the listing. Current drives are commonly listed to UL 61800-5-1; older drives to UL 508C.
Finding the date code
There is no industry-wide standard for date codes. Depending on the maker and the product line, the date of manufacture may be:
- printed plainly – a month and year, or a full date, on the label;
- a week-and-year or year-and-week code – a four-digit code can be read either way, so don't guess the order;
- a letter or letter-number code for the year and month;
- built into the serial number, where some characters stand for the plant, year and week;
- stamped or inked on the case, separate from the main label.
Look on the side and front labels, near the serial number, under a drive's cover and on the packaging. Treat other dates with care: a box label may show when the part was packed, circuit boards and components carry their own dates, and a firmware date is not a manufacture date.
Decode it with the manufacturer's documentation – product literature, a published date-code guide or the maker's support line with the serial number. Tables found online may cover another product line or an older scheme.
Why the date matters
The date helps you match the era of the equipment around it, spot mixed lots and judge storage. Drives and power supplies stored unpowered for years may need their DC bus capacitors reformed before full power – follow the manufacturer's guidance. An older date alone does not mean a bad part; condition and storage matter more. See surplus part conditions explained.
From nameplate to replacement
Photograph the whole label square-on, plus any trip unit, rating plug, option cards and the serial number. Every item we stock is photographed, so you can read the label before you buy – browse molded case breakers and AC drives and VFDs, or search by the catalog number. Send your photos through the breaker and switchgear quote page or the VFD and drive quote page: a single part is quoted within 1 hour during business hours (Mon–Fri 9–3:30 CT), and a list gets an official written quote in under 24 hours on business days.
Frequently asked questions
Where is the date code on a circuit breaker or drive?
It depends on the manufacturer and the product line. Look on the side and front labels, near the serial number, under a drive's cover or stamped on the case. Some parts show a printed date, others a week-and-year code or a code inside the serial number; the maker's documentation explains its format.
Is the catalog number the same as the style number?
Not always. The catalog number describes the product and is what you order by. Some labels also carry a style number or another internal reference for the exact build. Record both, and search by the catalog number first.
What is the difference between normal-duty and heavy-duty ratings on a VFD?
They are two ratings for the same drive. Normal duty suits fans and centrifugal pumps and allows a higher continuous current with less overload; heavy duty suits conveyors, mixers and hard-starting loads, with more overload capacity and a lower continuous current.
Does an old date code mean a part is bad?
No. A date code tells you when a part was made, not how it was stored or used. Drives and power supplies stored unpowered for years may need their capacitors reformed – follow the manufacturer's guidance – and condition, photos and the return policy matter more than age.