Complete Wiring Guide for Leeson Electric Motors Step-by-Step Diagrams
Begin by verifying terminal markings on the nameplate–LEESON units typically follow a dual-voltage layout with T1-T3 and T4-T6 groupings for three-phase models. Single-phase variants use L1-L2 plus an auxiliary winding marked A1-A2. Cross-reference these labels against the lead configuration in the technical manual or embossed connection block; mismatched labels risk overheating or reversed rotation.
For three-phase 230/460V setups, wire Series Delta (230V) by joining T4-T7, T5-T8, T6-T9 and connecting incoming lines to T1, T2, T3. Switching to Parallel Wye (460V) requires linking T4-T5-T6 and attaching input to T1, T2, T3. Confirm amp draw against the rated values: 230V applications pull roughly double the current compared to 460V.
Single-phase 115/230V arrangements demand careful start capacitor placement. Link L1 to A1, L2 to A2, and bridge the auxiliary winding to the run capacitor (typically 10-30µF). Omit the capacitor on permanent split-capacitor designs–these rely solely on the main winding. Measure resistance across A1-A2; infinitesimal values signal shorted windings.
Ground connections must terminate at the designated chassis stud, never the conduit fitting. Use THHN wire sized per NEC Table 430.250: 14 AWG for 1 hp 115V, 12 AWG for 5 hp 230V, and 8 AWG for 20 hp 460V. Torque terminal screws to LEESON’s specification: 10 lb-in for steel lugs, 7 lb-in for brass. Loose connections induce voltage drop and localized heating.
Direction reversal involves swapping any two line leads on three-phase units or L1-L2 on single-phase variants. Avoid partial-phase swaps–these create dangerous circulating currents. Validate rotation with a non-contact tachometer or phase sequence indicator before load engagement. Uncontrolled startups against an incorrect rotational field can shear motor shafts.
Connecting Schematics for Leeson Motor Assemblies
Begin by identifying the terminal box on the motor housing–typically located on the side or rear–where the labeled connectors (U1, V1, W1 for three-phase or L1, L2 for single-phase) are exposed. For dual-voltage 230/460V units, ensure the jumpers between T1-T3 and T4-T7 are configured per the voltage rating: parallel for 230V (short T1-T2, T3-T4, T5-T6) or series for 460V (short T1-T12, T2-T3, T4-T5). Use 12-gauge THHN copper conductors for circuits under 20A; upgrade to 10-gauge for 25-30A loads. Ground the frame via the dedicated lug adjacent to the main terminals using a green-insulated wire, bonding it to the building’s grounding system with a minimum #10 AWG conductor.
For reversing rotation on three-phase models, swap any two leads at the terminal block–U1 with V1 or W1–or at the source disconnect if remote control is required via a reversing starter. Single-phase capacitor-start motors demand a start capacitor connected between T5 and T8; confirm capacitance (µF) matches the nameplate rating–typically 145-310µF for 1HP units–using an ESR meter to verify health before energizing. Apply a megohmmeter at 500VDC across windings and frame to confirm insulation resistance exceeds 1MΩ before first startup.
Determining Terminal Hookups on Schematics for Leeson Power Units
Locate the nameplate on the unit housing. Leeson’s standard terminal designations follow NEMA conventions: T1 through T12 for three-phase configurations, with last digits pairing for opposite polarity. Single-phase units use L1, L2 for line inputs and T1-T8 for auxiliary or start/running connections, depending on voltage rating (115V, 208-230V, or 460V). Cross-reference these markings with color-coding – brown/white (L1), orange/black (L2), yellow/red (T1/T2), and so on – to confirm hookup points on schematics before making any physical attachments. Ignore generic labels; always verify against the specific series (e.g., 19XXX, 13XXX) for minor variations.
| Terminal | NEMA Code | Common Purpose | Typical Wire Hue |
|---|---|---|---|
| T1 | U1 | Main lead (Δ/Y) | Yellow |
| T2 | V1 | Start/aux winding | Red |
| T3 | W1 | Ground/common | Black |
Trace the schematic’s bridge symbols. For dual-voltage single-phase units, capacitors align vertically between auxiliary windings and T-terminals; note whether the schematic shows a solid or dashed line–solid indicates 230V configuration, dashed for 115V. In three-phase reversible models, check for jumper paths between T2-T5, T3-T6, T4-T7; these configurations allow clockwise or counterclockwise rotation by swapping any two leads. Confirm each connection with a multimeter reading continuity between corresponding terminals to avoid miswiring. Leeson’s schematics often embed thermal overload cutouts as small triangles, typically between T3/T6 for single-phase and T5/T10 for three-phase–ensure these bypass paths are clear before energizing.
Connecting Single-Phase Leeson Drives: A Practical Walkthrough
Locate the schematic bundled with the motor’s data plate–typically a 9-lead arrangement labeled U1, U2 (main coil) and Z1, Z2 (auxiliary coil). Verify supply voltage matches the plate rating; for 115V connections, join L1 to U1 and L2 to both U2 and Z2, then bridge Z1 to a capacitor rated at 370VAC or higher. Missteps here risk coil burnout; always dead-check leads with a multimeter before energizing.
Capacitor and Switch Integration
For reversing rotation, swap Z1 and Z2 connections at the starting switch–most centrifugal types require manual toggling before power-up. Use a dual-capacitor setup (run + start) if the motor stalls under load; select values from the nameplate (e.g., 150 µF run + 45 µF start). Solid-state relays can automate reversal but demand snubber circuits to suppress transient spikes.
Secure all splices with insulated butt connectors and strain-relieve cords near the terminal box; vibration loosens wire nuts within hours. Ground the frame via the green screw to the supply’s earth bus–omitting this exposes rotating shafts to 70VAC leakage. Test phase continuity at full RPM; a 10% voltage drop across U1-U2 indicates internal shorting requiring re-winding.
Key Connection Schemes for Dual-Voltage Three-Phase Leeson Power Units
Always prioritize verifying the nameplate voltage rating before connecting leads. A 230/460V unit requires distinct terminal arrangements depending on the supply: for 230V, link all winding sets in parallel (T1-T4, T2-T5, T3-T6), while 460V demands a series delta configuration (T4-T7 bridged, T5-T8, T6-T9). Misalignment risks winding overheating or catastrophic failure within minutes–use a multimeter to confirm continuity between bridged terminals before energizing. Leeson’s standard labeling assumes L1/L2/L3 correspond to T1/T2/T3 for high-voltage setups, but some industrial setups reverse polarity; double-check phase sequencing with a rotation tester if directional operation is critical.
Delta vs. Wye Switching for Optimal Torque and Current Draw
For 230V applications, a Wye (star) starting scheme reduces inrush current by ~33%, but sacrifices peak torque–ideal for centrifugal loads like pumps or fans where gradual acceleration prevents mechanical stress. Conversely, delta direct-on-line delivers maximum torque at the cost of higher starting currents (~600% of FLA); this suits high-inertia loads like conveyors or crushers where brief surges are tolerable. Transition between schemes by relocating jumpers: Wye shifts T9 to neutral, while delta connects T9 to T4. Always size overload relays based on the actual running current, not nameplate FLA, as delta configurations exhibit ~73% of line current through each winding.
Low-voltage (230V) setups demand 12 AWG copper conductors for runs under 50 ft; beyond that, upsize to 10 AWG to limit voltage drop below 3%. High-voltage (460V) circuits can use 14 AWG for identical distances, but ensure conduit fill ratios comply with NEC 310.15(B)(7) for derating–Leeson’s Class F insulation tolerates 155°C, but thermal margins shrink rapidly if ambient exceeds 40°C or altitude surpasses 1000m. Grounding requires a minimum #10 copper conductor to the frame; omit this for static-sensitive applications like medical centrifuges where stray currents corrupt measurements–use an insulated grounding kit instead. Never rely on conduit alone for grounding in dual-voltage setups, as corrosion or loose connections can create hazardous floating neutral conditions under load shifts.
Resolving Connection Problems in Leeson Machinery with Schematic Analysis
Start by verifying the power supply matches the motor’s voltage rating. A mismatch often triggers overheating or erratic operation. Check the nameplate for required voltage–many models tolerate ±10% variance, but exceeding this risks damage. Use a multimeter to confirm live voltage at the terminals before proceeding.
Inspect terminal leads for oxidation or loose connections. Corroded contacts disrupt current flow, causing intermittent failures. Clean terminals with a wire brush or contact cleaner if corrosion is visible. Tighten all screws to specification–torque values typically range between 8-12 inch-pounds for most Leeson units.
- Measure winding resistance between phases using an ohmmeter. Healthy windings show balanced readings (e.g., 1-5 ohms for smaller models). A zero reading indicates a short; infinite resistance signals an open circuit.
- Compare readings across all phase pairs–deviation over 2% suggests insulation breakdown or internal faults.
- Test ground continuity by probing from the housing to each lead–unbroken conductors should show near-zero ohms.
Examine capacitor circuits if the motor uses single-phase power. Swollen or leaking electrolytics fail silently, leading to poor startup or humming. Replace with identical microfarad/voltage ratings–most Leeson models specify 20-440 µF capacitors. Never substitute with lower voltage ratings.
Trace the circuit layout against factory schematics to identify misrouted conductors. Reversed polarity on dual-voltage models causes rotation reversal or locked rotor conditions. Mark leads during disassembly–standard color codes (L1=black, L2=red, T1=blue, T2=white) simplify reassembly.
Test thermal overload protectors if the motor trips repeatedly. Bypass the protector briefly (with caution) to confirm whether the failure lies in the motor or external conditions. Replace defective protectors with identical ratings–most Leeson models use bimetal disk types rated for 1.0-1.5x full-load amperage.
- Check centrifugal switches on single-phase machines. Worn contacts prevent winding engagement during startup. Manually spin the shaft while monitoring continuity–a properly functioning switch should click near 75% of rated RPM.
- Lubricate bearings if rotation feels stiff, but avoid over-greasing–Leeson bearings typically require only 20-30% fill capacity.
- Listen for unusual noise during operation. Grinding sounds suggest bearing wear; electrical arcing often produces a faint buzzing.
Log all measurements and replacements. Pattern analysis over time reveals recurring failure points–Leeson motors often exhibit capacitor fatigue at 5,000-8,000 hours, while bearings degrade around 12,000 hours of continuous duty.