The nameplate tells you almost everything you need to know before ordering a replacement. Here's what each field means:
The nameplate is the single most important piece of documentation on any motor. It is the manufacturer's declaration of what the motor is and what it can do. If you can read it correctly, you can replace the motor correctly. Here is what each field means and why it matters.
HP: Horsepower output at rated load.
Horsepower is the mechanical output rating at the shaft, not the electrical input. A 5 HP motor delivers 5 HP of usable work at the shaft when running at full load, but it draws more than 5 HP worth of electricity to do it. The difference is efficiency losses.
Small motors are often rated in fractional horsepower: 1/4, 1/3, 1/2, 3/4. Integral horsepower starts at 1 HP and climbs in standard steps: 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20. These steps are not arbitrary. They are NEMA standard ratings, and each one pairs with specific frame sizes.
Some WEG motors are dual rated, showing something like 5/2.5 HP. This indicates a two-speed motor, with the horsepower corresponding to each speed.
RPM: Full load speed. The RPM shown is full-load speed, not synchronous speed.
The nameplate RPM tells you the pole count:
- Approximately 3450 to 3550 RPM means 2-pole (3600 synchronous)
- Approximately 1725 to 1770 RPM means 4-pole (1800 synchronous)
- Approximately 1140 to 1175 RPM means 6-pole (1200 synchronous)
- Approximately 850 to 880 RPM means 8-pole (900 synchronous)
Speed is not optional to match. On a pump or fan, power demand varies with the cube of speed. Dropping in an 1800 RPM motor where a 1200 RPM motor was will more than triple the power the load demands, and you will burn up the new motor immediately.
Frame: The physical dimensions. Frame 56 is not interchangeable with 56C unless you match the mounting.
The NEMA frame designation. This single field controls almost all the physical dimensions: shaft height, shaft diameter, keyway size, mounting bolt pattern, and overall envelope.
The number is not arbitrary. For frames 143 and above, take the first two digits and divide by 4 to get shaft height in inches from the mounting base to the shaft centerline. A 145T has a 3.5 inch shaft height. A 184T has 4.5 inches. For frames 48 through 56, divide the whole number by 16 instead: a 56 frame is also 3.5 inches.
The third digit encodes the distance between mounting bolt holes along the base. This is why 143T and 145T share a shaft height but will not bolt into the same holes.
Suffix letters matter as much as the number:
- T: the current standard frame series, in use since 1964
- U: the older, physically larger standard with different shaft diameters
- C: C-face, a machined flange with a bolt circle for direct mounting to a gearbox or pump
- D: D-flange mounting
- JM / JP: close-coupled pump shafts with extended shaft profiles
- Z: nonstandard shaft, meaning the dimensions were customized
A 56C and a 56 have the same base dimensions but only the 56C has the face mount. If your gearbox bolts to the motor face, you need the C.
Volts: Often shows dual voltage like 208-230/460. Wiring configuration inside the peckerhead determines which one you're on.
The voltage the motor is designed to operate at. Single voltage motors list one number. Dual voltage motors list two, separated by a slash.
A common dual voltage listing is 208-230/460. This means the motor can be wired for the low range or the high range. Inside the conduit box, nine leads let you configure the windings in either series (high voltage) or parallel (low voltage). WEG includes a connection diagram on the nameplate or inside the box lid.
The 208-230 range matters. A motor rated 230V will run on 208V, but with reduced torque and higher current. If your supply is nominally 208V, verify the motor is rated for it. Running a 230V-only motor on 208V is a common cause of overheating.
Voltage tolerance is typically plus or minus 10 percent of nameplate. Beyond that, expect problems.
FLA: Full load amps. Use this to size overloads and wire.
Full load amps: the current the motor draws at nameplate horsepower and nameplate voltage. On a dual voltage motor, you'll see two values, and the higher current always corresponds to the lower voltage. Same power, half the volts, double the amps.
FLA is what you use to size overload protection, conductors, and starters. It is not what the motor draws at startup. Inrush current is typically 6 to 8 times FLA for a fraction of a second, which is why breakers and fuses for motor circuits are sized differently than for resistive loads.
Measuring actual running amps against nameplate FLA is the fastest field check for whether a motor is overloaded.
Service Factor: 1.15 means the motor can handle 15 percent above rated HP continuously under normal conditions.
A multiplier on nameplate horsepower. A 5 HP motor with 1.15 SF can produce 5.75 HP.
This is margin, not capacity. Service factor exists to absorb occasional overloads, momentary load spikes, ambient temperature slightly above 40 degrees C, or supply voltage a little off nominal. At service factor load, the motor runs hotter, efficiency drops, power factor shifts, and speed sags slightly.
Common values are 1.00 and 1.15. A 1.00 SF motor has no margin at all, which is typical on many inverter duty and some TEFC designs.
Overload relays must be sized to the motor's actual service factor. Setting overloads for 1.15 SF on a 1.00 SF motor removes the protection you thought you had.
Enclosure: ODP, TEFC, TENV, or explosion proof.
How the motor is sealed against its environment.
ODP (Open Drip Proof) allows outside air to pass directly through the motor and over the windings. The vent openings are angled so that liquid falling from up to 15 degrees off vertical cannot get in. ODP motors cool efficiently and cost less, but they belong only in clean, dry, indoor locations.
TEFC (Totally Enclosed Fan Cooled) seals the windings from ambient air completely. A shaft-mounted external fan under a shroud blows air across the frame's cooling fins. Nothing from the environment touches the windings. Use TEFC outdoors, in dust, in agricultural settings, or anywhere debris and moisture exist.
TENV (Totally Enclosed Non-Ventilated) has no fan and relies on frame surface area alone. Common on small motors and on motors that run at variable speed, where a shaft-mounted fan would lose effectiveness at low RPM.
Washdown duty adds epoxy paint, stainless hardware, and sealed shafts for food processing and sanitary environments.
Explosion proof motors are built and certified for classified hazardous locations. They are not interchangeable with TEFC. If the location is classified, the motor must carry the matching Class, Division, and Group markings.
TEFC motors also carry a drain plug. Orientation matters. The plug must sit at the low point of the motor as installed, or condensate collects on the windings instead of draining out.
Insulation Class: B, F, or H. Indicates temperature tolerance.
The maximum temperature the winding insulation system can withstand. This is a total temperature limit, combining ambient temperature, allowable temperature rise, and hot spot allowance.
- Class B: 130 degrees C
- Class F: 155 degrees C, the most common on modern general purpose motors
- Class H: 180 degrees C
Class F insulation with a Class B temperature rise is a common WEG spec. That combination means the motor is built to Class F limits but designed to run at Class B temperatures, giving you roughly 25 degrees C of thermal margin. That margin translates directly into insulation life.
The rule of thumb is that every 10 degrees C above the insulation rating cuts winding life roughly in half. This is why heat is the enemy and why a motor that runs hot is telling you something before it fails.
If the nameplate is unreadable, frame dimensions and shaft measurements are usually enough to cross reference a replacement. Contact us & we'd be happy to help!