Motor control panel feeder equations
The preliminary feeder basis combines 125% of the largest motor with remaining motor and non-motor load.
Ibase = 1.25Ilargest + Iother × Fdemand + 1000Snonmotor/(√3V)Idesign = Ibase × (1+Fspare)where:
- Ilargest
- Largest motor full-load current[A]
- Iother
- Sum of remaining motor currents[A]
- Snonmotor
- Balanced non-motor load[kVA]
Verify the adopted motor-feeder rule and complete assembly SCCR.
How to use the Motor Control Panel Load Calculator
Estimate an MCC or motor-control-panel feeder ampacity from the largest motor, remaining motors, non-motor load, demand, and spare capacity. Start by choosing the operating mode, then enter values from nameplates, measurements, or project documents in the units shown. The result updates immediately and keeps intermediate quantities visible for review.
- Confirm the system and calculation mode.
- Enter measured or manufacturer-rated values.
- Review the primary result and intermediate metrics.
- Continue with the related protection or equipment-selection checks.
Calculation method and validation
The equations and symbol definitions above show the complete calculation basis. Inputs are checked before calculation so zero, negative, incompatible, or physically impossible combinations are flagged instead of silently producing a misleading result.
How to interpret the result
Use the main result as a starting value and read every supporting metric. Balanced three-phase non-motor load Motor currents are nameplate or adopted table FLC values Largest-motor 125% feeder screen A passing or recommended result means the entered mathematical conditions are satisfied; it does not certify the complete installation or a particular product combination.
- Balanced three-phase non-motor load
- Motor currents are nameplate or adopted table FLC values
- Largest-motor 125% feeder screen
Selection limits and next checks
Preliminary engineering estimate only. Verify the final design against the current applicable standard, local rules, manufacturer data, and project conditions. Adopted code rules may not permit demand on motor feeder conductors as entered. Final MCC design requires SCCR, busbar, main device, starter coordination, neutral, heat, enclosure, and assembly verification. Compare the output with the current applicable standard, local rules, exact VIOX product datasheet, environmental conditions, protection coordination, and the engineer's project requirements before procurement or installation.
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Assumptions
- Balanced three-phase non-motor load
- Motor currents are nameplate or adopted table FLC values
- Largest-motor 125% feeder screen
Important Warnings
- Preliminary engineering estimate only. Verify the final design against the current applicable standard, local rules, manufacturer data, and project conditions.
- Adopted code rules may not permit demand on motor feeder conductors as entered.
- Final MCC design requires SCCR, busbar, main device, starter coordination, neutral, heat, enclosure, and assembly verification.