Castair 7-213-3 Electric Motor — 7.5 HP, Three Phase, 1725 RPM, Frame 213T
The Castair 7-213-3 is a 7.5 horsepower three-phase electric motor built for Cast Air industrial air compressors. It runs at 1725 RPM on a 213T NEMA frame, accepts 208/230/460V three-phase power, and is rated Open Drip Proof (ODP), UL and CSA listed. Service factor is 1.15. Weight is 130 lbs. If your facility has three-phase power available, this is the motor to put on a 7.5HP Cast Air compressor — three-phase motors run cleaner, start more smoothly, and cost less to operate over time than equivalent single-phase units.
The 7-213-3 is the three-phase counterpart to the single-phase 7-215-1 (1725 RPM, 215T frame, single phase). Both run at the same 1725 RPM slow-speed configuration that Cast Air designed their industrial cast iron pumps around. The difference is the power source and the frame size — the 7-213-3 is slightly lighter and uses a 213T frame versus the 215T on the single-phase model.
Full Motor Specifications
- Part Number: 7-213-3
- Horsepower: 7.5 HP
- Phase: Three phase
- Voltage: 208/230/460V (three-phase)
- Amperage: 23A at 208V / 22A at 230V / 11A at 460V
- RPM: 1725 (synchronous: 1800, slip-rated: 1725)
- NEMA Frame: 213T
- Shaft Diameter: 1-3/8"
- Service Factor: 1.15
- Enclosure: Open Drip Proof (ODP)
- Certifications: UL listed, CSA listed
- Weight: 130 lbs
- Price: $840.34
Why Three-Phase Matters for a 7.5HP Compressor
If your shop has three-phase power, using it for your compressor motor is always the right call. Here is why:
- Lower inrush current: Three-phase motors start with significantly lower inrush than single-phase motors of the same horsepower. The 7-213-3 at 460V draws 11 amps running and a fraction of the inrush that a single-phase 7.5HP motor demands. This means a smaller breaker, smaller wiring, and less strain on the panel at every startup.
- Smoother starting: Three-phase current creates a rotating magnetic field naturally — no capacitor start, no centrifugal switch, no start winding to burn out. The motor starts smoothly under load every time.
- Lower operating temperature: Balanced three-phase loads run cooler than single-phase motors. Cooler windings mean longer motor life — particularly important in a compressor application where the motor cycles on and off repeatedly throughout the day.
- No capacitor maintenance: Single-phase motors use start and run capacitors that fail over time. Three-phase motors have no capacitors. One fewer failure point.
- 460V option cuts wire size: At 460V three-phase, this motor draws only 11 amps running. That means significantly smaller conductors from panel to motor compared to a 230V single-phase installation drawing 31–38 amps for the same horsepower.
The 1725 RPM Speed — Why It Matters
Cast Air designs their industrial cast iron pumps to run at slow speed — typically 600–900 RPM at the pump for the larger models. At 1725 motor RPM, the belt-drive reduction ratio needed to hit pump speed is moderate and achievable with standard sheave sizes. Compare this to the 7-184-1H (3450 RPM single-phase high-speed motor), which requires a much larger reduction ratio to achieve the same pump speed. The 1725 RPM configuration is also gentler on the belt and bearings — lower speed at the motor sheave means less centrifugal stress on the belt and longer belt life.
The 1725 RPM designation on three-phase motors reflects real-world slip from the synchronous 1800 RPM of a 4-pole, 60Hz motor. At full load, this motor will run between 1,700 and 1,725 RPM — consistent and predictable for calculating pump speed from your pulley ratio.
Frame 213T — What It Tells You
NEMA frame 213T specifies the motor's physical mounting dimensions:
- Shaft height: Standardized for 213T — ensures the motor shaft aligns with the existing motor mount height on compressors designed for this frame.
- Bolt pattern: 213T bolt pattern is standardized — replacement is a bolt-on swap on a compressor designed for this frame.
- Shaft diameter: 1-3/8" — confirm your existing sheave is bored for 1-3/8" before ordering.
- T designation: NEMA T-frame motors have a shorter overall length and higher efficiency than older U-frame motors. If you are replacing an older motor, verify the mounting dimensions against T-frame specs.
Voltage Configuration — 208/230/460V Three-Phase
This motor accepts all three common three-phase voltages used in North American industrial facilities:
- 208V three-phase: 23 amps full load — common in older facilities and light commercial buildings.
- 230V three-phase: 22 amps full load — standard industrial voltage in many shops.
- 460V three-phase: 11 amps full load — the preferred voltage for large motors. Half the current means half the conductor size, lower voltage drop, and a smaller contactor in the control panel.
The motor is internally reconnectable between 208/230V and 460V via the terminal box. The wiring diagram inside the terminal cover shows the correct lead connections for each voltage. If you are unsure which voltage your facility runs, check the panel nameplate or ask your electrician before ordering — the motor needs to be set to the correct voltage before the first start.
Placing the 7-213-3 in the Castair Motor Lineup
The full 7.5HP Castair motor lineup covers three configurations:
- 7-184-1H: 7.5HP, 1Ph, 208/230V, 3450 RPM, 184T frame, 7/8" shaft, 95 lbs — high-speed single-phase
- 7-215-1: 7.5HP, 1Ph, 208/230V, 1725 RPM, 215T frame, 1-3/8" shaft, 145 lbs — slow-speed single-phase
- 7-213-3 (this motor): 7.5HP, 3Ph, 208/230/460V, 1725 RPM, 213T frame, 1-3/8" shaft, 130 lbs — slow-speed three-phase
The 7-213-3 and 7-215-1 run at the same RPM and carry the same shaft diameter. The difference is phase: if you have three-phase power, use the 7-213-3. If you only have single-phase, use the 7-215-1. Do not substitute the 7-184-1H (3450 RPM) unless your compressor''s pulley configuration is specifically designed for a 3450 RPM drive motor.
Stepping up within the three-phase lineup, the next motor up is the 10-215-3 (10HP, 3Ph, 208/230/460V, 1725 RPM, 215T frame, 1-3/8" shaft, 135 lbs). Stepping down, the 5-184-3 (5HP, 3Ph, 208/230/460V, 1725 RPM, 184T frame, 1-1/8" shaft, 65 lbs) covers the 5HP range.
Replacement and Compatibility Checklist
Before ordering, confirm the following:
- Shaft diameter: 1-3/8" — your existing sheave must be bored for 1-3/8". If you are replacing a 7-215-1 (also 1-3/8" shaft), the sheave transfers directly.
- Frame: 213T — verify your motor mount and base are drilled for 213T bolt pattern. Note: 213T and 215T have different bolt patterns despite similar frame numbers.
- Phase and voltage: Confirm three-phase power is available and confirm the voltage (208/230 or 460) so you can set the motor correctly.
- Rotation direction: Three-phase motors can be reversed by swapping any two leads. Confirm the required rotation and verify after first start before connecting the belt.
- RPM match: Confirm your pulley ratio is designed for a 1725 RPM motor, not a 3450 RPM motor.
Why Buy From Air Compressor Factory Direct?
- Cast Air specialists: We know the motor lineup and which motor belongs on which compressor. Give us your compressor model number and we will confirm the 7-213-3 is the correct replacement before you order.
- Free shipping on qualifying orders.
- Free technical support: Call 866-217-0063. Questions about voltage wiring, rotation setup, sheave compatibility, or breaker sizing — we can help you get the installation right the first time.
- Genuine Cast Air motors: OEM motors built for Cast Air compressors. UL and CSA listed, correct frame, correct shaft dimensions.
- Straightforward pricing: $840.34. No hidden fees. What you see is what you pay.
- Honest guidance: If the 7-213-3 is not the right motor for your application, we will tell you and point you to the one that is.
Call 866-217-0063 for quick answers and help!
