Industrial parts come with their own vocabulary: condition grades, rating abbreviations and purchasing shorthand. This glossary collects the terms our buyers and technicians use every day. Each definition is short; where a guide or a shop category covers the term, it is linked.
Key takeaways
- Condition words (new surplus, open box, used, refurbished, for parts) describe a unit's history, not its series or firmware.
- Ratings such as FLA, SCCR and kAIC decide whether a replacement is safe where it is installed.
- ISO lists, RFQs and BOMs are all ways to ask for a quote – send whichever your system produces.
Safety first: definitions here are general. Before working on equipment, follow your site's lockout/tagout procedure and the manufacturer's instructions, and verify the absence of voltage with a properly rated meter.
A
- AIC / kAIC
- Ampere interrupting capacity: the highest fault current a breaker or fuse can safely interrupt, in kiloamps (kA) at a stated voltage. Breaker ratings →
- Auxiliary contact
- A small extra contact on a contactor or breaker that signals its state to the control circuit. Auxiliary contacts →
B
- BOM (bill of materials)
- A list of every part, with quantities, in a machine, panel or project. Send a BOM →
C
- Catalog number
- The manufacturer's number for one exact product, including option letters. Siemens calls it the order or article number. Reading catalog numbers →
- CE marking
- The manufacturer's declaration that a product meets the European Union requirements that apply to it. Marks guide →
- Contactor
- An electrically operated switch for motors and other heavy loads, switched by a control coil. Contactors →
- Control relay
- A relay that switches control signals rather than power loads. Control relays →
D
- Date code
- A code on the label showing when a unit was made; useful for judging shelf age. Shelf age →
- Derating
- Using a device below its nameplate rating because of heat, altitude, single-phase input or similar conditions. VFD derating →
- DIN rail
- The standard 35 mm metal rail that relays, terminal blocks, breakers and power supplies clip onto. Terminal blocks →
- Discontinued
- No longer sold new by the manufacturer, though repair or support may continue for a time. Lifecycle terms →
E
- Encoder
- A feedback device that reports shaft position and speed. Incremental encoders count pulses; absolute encoders report the position itself. Encoders →
- End of life (EOL)
- A manufacturer's notice that a product will be discontinued, often with a last-time-buy date. SLC 500 example →
F
- Firmware
- The software inside a module, drive or controller, identified by a version such as FRN 20 or V3.3. Firmware →
- FLA (full-load amps)
- The current a motor draws at rated load, voltage and frequency, from its nameplate. Drives are sized by it. Motor nameplates →
- For parts or not working
- Sold as-is for repair or components; not expected to work. Condition grades →
- Frame size
- For motors, standard mounting dimensions (NEMA 254T, IEC 132); for breakers, the physical family and its maximum current. Motor frames →
- Fuse
- A one-time overcurrent device whose element melts to open the circuit. Fuses →
H
- Heavy duty / normal duty
- Two current ratings on many drives: heavy duty for hard-starting, constant-torque loads; normal duty for fans and pumps. VFD sizing →
- HMI (human-machine interface)
- The operator screen or panel used to run and monitor a machine. HMIs →
I
- I/O (inputs and outputs)
- The points or modules that connect a PLC to sensors, valves, starters and lights. Analog I/O carries ranges such as 4–20 mA. PLC I/O modules →
- IEC
- The International Electrotechnical Commission, whose standards set ratings and sizes used for much of the world's electrical equipment.
- IP rating
- Ingress protection code, such as IP65: the first digit rates protection against solids, the second against water. Servo nameplates →
- ISO list
- An in-search-of list: the part numbers and quantities you need a supplier to find. Send an ISO list →
L
- Lead time
- The time between ordering and receiving a part. Parts sourcing →
- Lockout/tagout (LOTO)
- The procedure for isolating energy sources, then locking and tagging them so equipment can't be energized during work.
M
- MCB (miniature circuit breaker)
- A small breaker, usually DIN-rail mounted, for control and branch circuits. Miniature breakers →
- MCCB (molded case circuit breaker)
- A breaker in an insulated molded housing, rated by frame, trip current, voltage and interrupting rating. MCCB guide →
- MLFB
- Siemens' term for its order or article number, such as 6ES7 315-2AG10-0AB0. Siemens numbers →
- Motor starter
- A contactor and an overload relay combined to start, stop and protect a motor. Motor starters →
- MRO
- Maintenance, repair and operations: the spares and supplies that keep a plant running.
N
- Nameplate
- The label with a product's identification and ratings: catalog number, series, voltage, current and more. Reading nameplates →
- NEMA size
- A US starter or contactor size (00, 0, 1, 2 and up) tied to a horsepower rating. IEC devices are rated by utilization category, such as AC-3, instead. Motor starters →
- New
- Factory-new stock from the manufacturer's authorized channel, normally with the manufacturer's warranty. Our conditions →
- New surplus
- Unused stock from outside the manufacturer's authorized channel, with no manufacturer warranty. Condition grades →
O
- Obsolete
- No longer made or supported by the manufacturer; spares come from surplus, repair or exchange. Obsolete parts →
- OEM (original equipment manufacturer)
- The company that made a part or machine. An OEM part comes from the original maker.
- Open box
- Unused, but the packaging has been opened or damaged, or is missing. Condition grades →
- Overload relay
- Protects a motor from sustained overcurrent by opening the starter's control circuit. Overload relays →
P
- PLC (programmable logic controller)
- An industrial computer that reads inputs, runs a program and controls outputs. PLC processors →
- PO (purchase order)
- A buyer's formal document authorizing a purchase on agreed terms. Business buyers →
- Power supply
- Converts line voltage to control voltage, most often 24 V DC. Power supplies →
R
- Refurbished
- Restored to working order by a seller or repair shop. Ask what was done. Condition grades →
- Resolver
- A rugged analog rotary feedback device used on some servo motors instead of an encoder. Servo feedback →
- Revision (REV)
- A smaller hardware change within a series, printed on some labels. Series vs revision →
- RFQ (request for quote)
- A request for a supplier to price specific parts, quantities and conditions. Send an RFQ →
S
- Safe Torque Off (STO)
- A drive safety function that removes the power that makes torque in the motor. STO example →
- SCCR (short-circuit current rating)
- The fault current a component or control panel can withstand when protected by the specified overcurrent device. Breaker ratings →
- Series
- A letter marking a hardware revision of the same catalog number, such as Ser B. What Ser B means →
- Service factor (SF)
- The continuous overload a motor tolerates on sine-wave power under stated conditions, such as 1.15. Motor nameplates →
- Servo drive (amplifier)
- Controls a servo motor's torque, speed and position using feedback from the motor. Servo drives →
- Servo motor
- A motor, usually permanent-magnet, with built-in feedback for precise motion. Servo nameplates →
- Soft starter
- Ramps motor voltage to limit starting current and torque; unlike a VFD, it does not control running speed. Soft starters →
- Surplus
- Stock a plant, distributor or OEM no longer needs, resold new or used. Selling surplus →
T
- Trip unit
- The part of a breaker that senses overcurrent and trips it: thermal-magnetic or electronic. MCCB guide →
U
- UL Listed / UL Recognized
- UL marks for complete products (Listed) and for components used inside listed equipment (Recognized). Marks guide →
- Used
- Previously installed or used, with normal wear; often removed from working equipment. Condition grades →
V
- VFD (variable frequency drive)
- An AC drive that controls motor speed by varying output frequency and voltage. VFD basics →
- Voltage class
- The supply range a drive or motor is built for, such as the 240 V or 480 V class. Input voltage →
Can't find a term?
Labels often use abbreviations specific to one manufacturer. Our guides to Allen-Bradley catalog numbers and Siemens order numbers decode two of the most common, or send us the part number and we'll tell you what it is.
Frequently asked questions
What does MRO stand for?
Maintenance, repair and operations (sometimes maintenance, repair and overhaul). MRO parts are the spares and supplies a plant uses to keep its equipment running, as opposed to the materials that go into its products.
What is the difference between an ISO list, an RFQ and a BOM?
An ISO (in search of) list names parts you need someone to find. An RFQ (request for quote) asks suppliers to price specific parts, quantities and conditions. A BOM (bill of materials) lists every part in a machine or project. Any of them can be sent to a supplier for a quote.
What is the difference between SCCR and an interrupting rating?
An interrupting rating (AIC or kAIC) is the highest fault current a breaker or fuse can safely interrupt. SCCR is the fault current a component or a whole control panel can withstand while its protection clears the fault. Both must be at least the available fault current where the equipment is installed.