Chart
Motor starting current and torque curve comparison
Compare across-the-line, reduced-voltage, soft starter, and VFD motor starting current and torque behavior.
Chart boundary
Does not select a starter, size conductors or protection, guarantee starting torque, or replace manufacturer application review.
multi curve comparison
Starting current and torque tradeoff
The chart compares methods by shape, not by one universal current value.
Scopemotors and vfdsX-axistime / motor speedY-axiscurrent and torque shapeReviewAnnualNextMotor starting method selection guide
Across-the-linehigh current / high torque
Simple but high dip and mechanical stress.
Wye-deltareduced voltage transition
Torque reduction must fit the load.
Soft startercontrolled ramp
Settings and bypass duty matter.
VFDdrive-controlled profile
Application, cable, and harmonics questions follow.
Decision table
Show how starting method changes inrush, torque, and voltage-dip risk before motor-start calculations.
Scroll sideways to keep row labels aligned with hidden columns.
| Method | Best fit | Watch point | Handoff |
|---|---|---|---|
| Across-the-line | Simple robust starting where supply can tolerate inrush | Voltage dip and mechanical stress | Motor LRA calculator |
| Wye-delta or autotransformer | Reduced-voltage starting for suitable loads | Torque reduction | Starter manufacturer data |
| Soft starter | Controlled acceleration without full drive control | Bypass and heat limits | Motor starting dip calculator |
| VFD | Speed control and controlled acceleration | Cable length, filters, harmonics | VFD cable chart |
Notes
- Treat this chart as a planning and conversation aid only.
- Confirm current utility requirements, product markings, manufacturer instructions, and local authority requirements before field work.
- Use the linked calculator or table when the task needs project-specific arithmetic.
Source links
Open the underlying public sources before treating the chart as project guidance.