🔧 NEMA Motor Frame Reference

Frame Dimensions, Shaft Sizes & Mounting Patterns for Motor Replacement

Overview

Frame Lookup

Dimension Tables

Frame Suffixes

Mounting Types

Field Tips

📐 What is a NEMA Frame Size?

NEMA (National Electrical Manufacturers Association) frame sizes are standardized motor dimensions that ensure interchangeability between manufacturers. When you need to replace a motor, matching the frame size guarantees the new motor will have the same shaft height, bolt pattern, shaft diameter, and mounting footprint as the original - regardless of who made it.

✓ Why Frame Size Matters

Ensures physical fit on existing base
Shaft aligns with driven equipment
Bolt holes match existing pattern
Coupling/pulley fits shaft

⚠️ What Frame Doesn't Tell You

Horsepower rating
Voltage or phase
Enclosure type (TEFC, ODP)
Efficiency class

📋 Key Dimensions Defined

D: Shaft centerline height
2E: Bolt hole spacing (width)
2F: Bolt hole spacing (length)
U: Shaft diameter

🔢 Decoding Frame Numbers

The frame number itself tells you the shaft centerline height:

💡 Quick Formula

Shaft Height (D) = First 2 digits ÷ 4

Examples: 143T → 14÷4 = 3.5" | 256T → 25÷4 = 6.25" | 326T → 32÷4 = 8"

📏 Critical Dimensions Explained

📊 Common Frame Sizes by HP Range

42-48

Fractional HP

1/4 - 1/2 HP
Small fans, pumps

56

1/3 - 3 HP

HVAC, small machines

143T-145T

1 - 3 HP

Conveyors, mixers

182T-184T

3 - 7.5 HP

Pumps, fans, compressors

213T-215T

7.5 - 15 HP

Industrial equipment

254T-256T

15 - 30 HP

Large pumps, blowers

284T-286T

25 - 50 HP

Heavy industrial

324T-365T

40 - 100+ HP

Large equipment

🔍 Frame Size Lookup Tool

Enter a frame size to get all dimensions, or search by dimensions to find matching frames.

📏 Measure to Find Frame

If nameplate is missing, measure these dimensions:

🔧 Shaft Key Sizes

Standard keyway dimensions by shaft diameter:

Shaft Dia (U)	Key Width	Key Height
7/16"	3/32"	3/32"
1/2"	1/8"	1/8"
5/8"	3/16"	3/16"
7/8"	3/16"	3/16"
1"	1/4"	1/4"
1-1/8"	1/4"	1/4"
1-3/8"	5/16"	5/16"
1-5/8"	3/8"	3/8"
1-7/8"	1/2"	1/2"
2-1/8"	1/2"	1/2"
2-3/8"	5/8"	5/8"

📋 Complete NEMA T-Frame Dimensions

All dimensions in inches. T-Frame is the current standard (since 1964).

Frame	D (Shaft Ht)	2E (Width)	2F (Length)	U (Shaft Ø)	N-W (Shaft Len)	BA (Base Len)	Typical HP
42	2.625	2.06	1.69	3/8	0.75	2.50	1/20-1/6
48	3.00	2.75	2.12	1/2	1.50	3.00	1/6-1/2
56	3.50	3.00	2.44	5/8	1.88	3.40	1/3-3
56H	3.50	3.00	2.44	5/8	1.88	3.40	1/2-2
143T	3.50	4.00	4.00	7/8	2.25	5.50	1-2
145T	3.50	4.00	5.00	7/8	2.25	5.50	2-3
182T	4.50	4.50	4.50	1-1/8	2.75	6.50	3-5
184T	4.50	4.50	5.50	1-1/8	2.75	6.50	5-7.5
213T	5.25	5.50	5.50	1-3/8	3.38	7.50	7.5-10
215T	5.25	5.50	7.00	1-3/8	3.38	7.50	10-15
254T	6.25	5.25	8.25	1-5/8	4.00	10.50	15-20
256T	6.25	5.25	10.00	1-5/8	4.00	10.50	20-30
284T	7.00	5.50	9.50	1-7/8	4.62	11.00	25-40
286T	7.00	5.50	11.00	1-7/8	4.62	11.00	40-50
324T	8.00	6.25	10.50	2-1/8	5.25	12.50	40-60
326T	8.00	6.25	12.00	2-1/8	5.25	12.50	60-75
364T	9.00	7.00	11.25	2-3/8	5.88	14.00	60-100
365T	9.00	7.00	12.25	2-3/8	5.88	14.00	75-125
404T	10.00	8.00	12.25	2-7/8	7.25	16.00	100-150
405T	10.00	8.00	13.75	2-7/8	7.25	16.00	125-200
444T	11.00	9.00	14.50	3-3/8	8.50	18.00	150-250
445T	11.00	9.00	16.50	3-3/8	8.50	18.00	200-300

🔤 Understanding Frame Suffixes

The letter(s) after the frame number indicate special features, mounting configurations, or design standards. Getting the suffix wrong means the motor won't fit!

📐 Common Suffixes

Suffix	Meaning	Key Feature
T	T-Frame (Standard)	Current NEMA standard since 1964
TS	T-Frame Short Shaft	For direct coupling, shorter N-W
TC	T-Frame C-Face	Flange mount on drive end
JM	Jet Pump - Close Coupled	Special shaft for pump mounting
JP	Jet Pump - Extended	Extended shaft for pump impeller
U	U-Frame (Old Standard)	Pre-1964, larger dimensions
H	Larger shaft diameter	Same frame, bigger shaft
Z	Special mounting or shaft	Non-standard, check specs

🔧 T vs TC vs TS Comparison

⚠️ C-Face Flange Sizes

TC frames have standardized bolt circle diameters:

Frame	Flange OD	Bolt Circle	Pilot Dia	Bolts
143TC	7.50"	6.00"	4.50"	4 x 5/16"
145TC	7.50"	6.00"	4.50"	4 x 5/16"
182TC	9.00"	7.25"	5.50"	4 x 3/8"
184TC	9.00"	7.25"	5.50"	4 x 3/8"
213TC	10.00"	8.25"	6.50"	4 x 3/8"
215TC	10.00"	8.25"	6.50"	4 x 3/8"
254TC	12.00"	10.00"	7.50"	4 x 1/2"
256TC	12.00"	10.00"	7.50"	4 x 1/2"
284TC	14.00"	11.50"	9.00"	4 x 1/2"
286TC	14.00"	11.50"	9.00"	4 x 1/2"

💧 JM vs JP Pump Frames

⚠️ Critical Note

JM and JP motors are NOT interchangeable with standard T-frames. They have different shaft diameters and configurations specifically for jet pump applications.

🔩 Motor Mounting Configurations

Motors can be mounted in various positions. Lubrication and ventilation may be affected by mounting position.

📐 Foot Mount (F1, F2)

📐 C-Face Mount (FC)

C-Face Advantages

No need for separate coupling
Self-aligning via pilot diameter
Compact installation
Common for gearboxes and pumps

📐 Vertical Mounting

⚠️ Vertical Mount Considerations

Must be specified when ordering - affects bearings
Thrust bearing required for shaft-up loads
Check lubrication requirements
Different bearing preload than horizontal

🔧 Mounting Position Codes

Code	Description	Shaft Position
F1	Foot mount, horizontal	Horizontal
F2	Foot mount, wall (feet on side)	Horizontal
C1	C-Face, no feet	Horizontal
C2	C-Face with feet	Horizontal
V1	Vertical, shaft down	Down
V2	Vertical, shaft up	Up
V3	Vertical, shaft down, flange top	Down
V4	Vertical, shaft up, flange bottom	Up
V5	Vertical, shaft down, flange bottom	Down
V6	Vertical, shaft up, flange top	Up

📏 Measuring in the Field

When the nameplate is missing or illegible, measure these dimensions:

Shaft Height (D) - Base to shaft centerline
Shaft Diameter (U) - Use calipers or micrometer
Shaft Length (N-W) - End of shaft to shoulder
Bolt Pattern (2E × 2F) - Center to center of mounting holes
Bolt Hole Size - Diameter of mounting holes
Key Size - Width and height of keyway

💡 Pro Tip

Take photos of the old motor before removal, including any visible nameplate data, conduit box location, and mounting arrangement.

⚠️ Common Mistakes

✗ Don't Do This

Ignoring suffix: 256T ≠ 256TC ≠ 256TS
Mixing U-frame with T-frame: Pre-1964 motors are different
Wrong rotation: Check CW vs CCW from shaft end
Overlooking NEMA vs IEC: Metric frames are different
Ignoring mounting position: Vertical requires special bearings

✓ Always Verify

Voltage and phase matches supply
HP meets or exceeds application
RPM is compatible with driven equipment
Enclosure suits the environment
Service factor for overload capability

🔄 T-Frame vs U-Frame

If replacing a motor on old equipment (pre-1964), it may be U-Frame:

Feature	U-Frame (Pre-1964)	T-Frame (Current)
Dimensions	Larger	Smaller
Efficiency	Lower	Higher
Direct replacement	Not interchangeable!

⚠️ U to T Conversion

When replacing U-Frame with T-Frame, you'll need adapter bases or new mounting arrangements. T-Frame motors are physically smaller for the same HP.

🌍 NEMA vs IEC Frames

IEC (metric) motors use different frame designations:

NEMA Frame	IEC Frame	Shaft Height
143T	D90	90mm / 3.54"
182T	D112	112mm / 4.41"
213T	D132	132mm / 5.20"
254T	D160	160mm / 6.30"
284T	D180	180mm / 7.09"
324T	D200	200mm / 7.87"
364T	D225	225mm / 8.86"

⚠️ NEMA and IEC are NOT directly interchangeable. Mounting patterns and shaft sizes differ.

📋 Quick Reference Card

Shaft Height Formula

D (inches) = First 2 digits ÷ 4

143T → 14 ÷ 4 = 3.50"
256T → 25 ÷ 4 = 6.25"
364T → 36 ÷ 4 = 9.00"

Must Match for Replacement

✓ Frame size (including suffix)
✓ Shaft diameter and length
✓ Mounting bolt pattern
✓ Rotation direction
✓ Voltage/phase/frequency
○ HP can be equal or greater

Common Suffix Meanings

T Standard T-Frame
TC C-Face flange mount
TS Short shaft
JM Jet pump close-coupled
JP Jet pump extended shaft