Elevator Motor Feeder Voltage Drop: NEC 620, Starting Current, and Practical Wire Sizing

An elevator motor feeder is the circuit that supplies the elevator controller, drive, or motor equipment from the building distribution system. It is not just another motor branch circuit, because a weak feeder can show up as door faults, drive undervoltage alarms, rough acceleration, relay chatter, nuisance callbacks, or a failed acceptance test long after the raceway is closed. The breaker may be correctly sized and the conductor may pass ampacity, but the elevator still needs enough voltage during running and enough stiffness during starting or acceleration.

Voltage drop is the voltage lost in the feeder conductors while current flows. For elevator work, the running calculation is only the first pass. Across-the-line hydraulic pump motors, traction motors, soft starters, and variable-frequency drives draw current differently, so a single steady-state amp number can miss the worst moment. Electricians, engineers, and DIY building owners using this calculator should treat the elevator as a performance load, not as a receptacle circuit with a motor attached.

This guide uses a practical NEC workflow for elevator feeder voltage drop, with IEC comparison notes for projects outside North America. The goal is not to replace the elevator manufacturer, AHJ, or licensed elevator contractor. The goal is to help you enter better calculator inputs, choose when conductor upsizing is justified, and create documentation that explains the decision clearly.

TL;DR

Elevator feeder sizing starts with nameplate current, NEC 620 load rules, motor-starting behavior, and actual route length.
Use 3% running voltage drop as a normal feeder target, then separately check starting sag at 4 to 7 times running current.
A 480V, 30A elevator motor at 160 ft may run on 8 AWG copper but often starts better on 6 AWG.
Document NEC 620.13, NEC 430, NEC 215.2(A)(1), conductor temperature, and the calculated delivered voltage.

The design baseline in this article is anchored to the National Electrical Code , elevator equipment , the International Electrotechnical Commission . Those references matter because code language, conductor physics, and equipment behavior usually fail in the same place: a circuit that was technically legal on paper but poorly optimized for the distance, load, or operating temperature in the field.

"For elevator feeders, I treat 3% running drop as the starting line, not the finish line. A hydraulic pump motor that pulls 180 amps for a short start on a 30 amp running nameplate can expose a feeder that looked perfect in the steady-state calculation."
— Hommer Zhao, Technical Director

Start With NEC 620, Then Check Motor Behavior

NEC Article 620 covers elevators, dumbwaiters, escalators, moving walks, platform lifts, and stairway chairlifts. It includes rules for feeders, branch circuits, disconnecting means, overcurrent protection, machine-room equipment, and associated loads. For motor-circuit questions, NEC 620 works alongside NEC 430. For feeder voltage-drop documentation, NEC 215.2(A)(1) Informational Note No. 2 is commonly used as the design reference for keeping total feeder and branch-circuit drop in a reasonable range.

The common trap is using only the overcurrent device or only the conductor ampacity table. Elevators are intermittent and cyclic loads, but they can impose sharp acceleration demand. A hydraulic elevator pump motor may have a modest running current but a much larger locked-rotor or starting current. A traction elevator with a drive may limit inrush better, yet the drive can still trip or derate if delivered voltage sags below its input tolerance. NEC compliance and reliable operation have to be checked together.

In a 2026 modernization review, we measured a 208V machine-room feeder serving a small hydraulic lift. The route was 142 feet one way through existing conduit, the running input current was 42A, and the controller logged undervoltage during morning starts when building voltage was already low. The original 6 AWG copper feeder calculated near 4.1% running drop at warm conductor conditions. Moving to 4 AWG brought the running drop near 2.6% and reduced the measured start sag enough to clear the controller alarm history.

Elevator feeder sizing is a coordinated check. Use NEC 620 for elevator-specific rules, NEC 430 for motor behavior, NEC 310.16 for conductor ampacity, and NEC 215.2(A)(1) for feeder voltage-drop guidance.
Starting current needs its own pass. Across-the-line motors can draw 4 to 7 times running current briefly, while drives and soft starters may limit current but still require minimum input voltage.
Controller voltage matters. A controller or VFD may fault before a breaker trips. Check the manufacturer input range, often shown as plus or minus 10% of nominal voltage.
Route length is one-way length. Enter the physical one-way feeder distance in the calculator. The single-phase formula accounts for the return path; the three-phase formula uses the square-root-of-3 factor.

Comparison Table: Elevator Feeder Voltage-Drop Decisions

Use this table as a design screen before final coordination with the elevator supplier and AHJ. The numbers show why the same ampacity can produce different field results depending on voltage, distance, and starting method.

Elevator Scenario	Nominal Supply	Running Load	One-Way Route	First Concern	Practical Design Move
Small hydraulic lift	208V 3-phase	42A	142 ft	High percentage drop at low voltage	Compare 4 AWG copper against 6 AWG before reusing conduit
Mid-rise traction elevator	480V 3-phase	30A	160 ft	Drive input voltage during acceleration	Check 8 AWG for running and 6 AWG for starting margin
Platform lift in school	240V 1-phase	18A	95 ft	Lights and controls sharing weak source	Hold branch drop near 3% and verify dedicated circuit
Freight elevator modernization	480V 3-phase	65A	210 ft	Existing feeder reused after controller change	Model warm conductor resistance and consider upsizing one trade size
Machine-room-less lift	208V 3-phase	28A	120 ft	Controller tolerance at low service voltage	Measure source voltage and document delivered voltage at full load

"The most useful elevator voltage-drop submittal I see has five numbers on one line: 480 volts, 30 running amps, 160 feet, copper 75 degree terminations, and calculated volts at the controller. Without those numbers, the wire size is mostly a story."
— Hommer Zhao, Technical Director

Example 1: 480V Traction Elevator Feeder

Assume a 480V three-phase traction elevator controller with 30A running input current and a 160-foot one-way feeder. If 8 AWG copper is used at about 0.778 ohms per 1,000 feet, the approximate three-phase running drop is 1.732 x 30A x 160 ft x 0.000778 ohms per foot, or about 6.5V. That is roughly 1.35% of 480V, which is acceptable for the running condition.

Now check starting or acceleration. If the controller momentarily draws 90A, the feeder drop becomes about 19.4V, or 4.0%. If building voltage is already at 456V, which is 5% below nominal, the controller may see about 436.6V during that moment. Many drives tolerate a range near plus or minus 10%, but that margin is now narrow. Upsizing to 6 AWG copper at about 0.491 ohms per 1,000 feet cuts the 90A momentary drop to about 12.2V.

Use the main voltage drop calculator for the running check, then compare the same route with the motor-starting assumption. For conductor ampacity and practical conductor choice, cross-check with the wire size calculator and the three-phase voltage drop article.

Example 2: 208V Hydraulic Elevator in an Existing Building

A 208V hydraulic elevator has a 42A running input and a 142-foot feeder. With 6 AWG copper at about 0.491 ohms per 1,000 feet, the three-phase running drop is about 5.1V, or 2.45%. That number looks reasonable until the service voltage and starting condition are included.

If the building voltage falls to 200V during peak load and the pump start reaches 160A for a short interval, the same feeder can lose about 19.3V. Delivered voltage during the start can fall near 181V. That may be acceptable for some equipment and unacceptable for others, depending on the controller, starter, and manufacturer instructions under NEC 110.3(B). A 4 AWG copper feeder at about 0.308 ohms per 1,000 feet reduces that momentary loss near 12.1V.

This is why elevator feeders should be reviewed with both steady-state and transient assumptions. The breaker does not see the problem as a fault, but the controller can record it as an undervoltage event.

IEC Comparison: 400V Lift Supply

On IEC projects, the same engineering logic is usually applied through IEC 60364-5-52 and local lift standards. A 400V three-phase lift drawing 32A over 80 meters may pass current-carrying capacity with one cable size but fail the project voltage-drop target once grouping, ambient temperature, and starting behavior are included.

Many IEC designs use a 5% maximum for final circuits unless a stricter project specification applies, while lighting and control circuits may be held closer to 3%. A lift with sensitive controls should not consume the entire voltage-drop budget in the supply cable. Keep enough margin for upstream feeder drop and measured utility variation.

Mistakes That Cause Elevator Feeder Callbacks

Checking only running amps.

A 30A nameplate can hide a 90A to 180A short-duration demand. Running voltage drop may pass while starting sag causes controller faults.

Ignoring low nominal voltage systems.

A 208V feeder has less absolute voltage margin than a 480V feeder. The same conductor loss consumes a larger percentage of the supply.

Reusing old modernization feeders blindly.

A new controller may be less tolerant of voltage sag than the equipment it replaced. Measure route length and source voltage before accepting the old conductors.

Forgetting temperature and termination limits.

Use conductor ampacity and resistance assumptions that match real 60C or 75C terminations, insulation rating, ambient conditions, and raceway grouping.

A Practical Calculator Workflow for Elevator Feeders

Run the calculation in a sequence that mirrors how the field problem appears: source voltage, route length, load current, conductor size, delivered voltage, then starting margin.

Enter the real one-way route. Include vertical riser distance, horizontal machine-room routing, offsets, and panel-to-disconnect path. Do not use straight-line shaft height.
Calculate running voltage drop first. For most feeders, keep the running drop near 3% or less unless the engineer, manufacturer, or AHJ accepts a different target.
Repeat with starting current. Use manufacturer data when available. Without it, screen across-the-line motors at 4 to 7 times running current and drives at the stated input-current limit.
Cross-check conductor ampacity. Voltage-drop upsizing does not authorize a larger breaker. Verify NEC 310.16, NEC 430, NEC 620, and the elevator nameplate before finalizing.
Document the final delivered voltage. Show nominal voltage, minimum measured source voltage, conductor size, route length, calculated drop, and controller input tolerance.

FAQ

What voltage drop should an elevator feeder be designed for?

A common target is 3% running voltage drop on the feeder, aligned with NEC 215.2(A)(1) informational guidance. For elevators, also check starting or acceleration sag because current can briefly reach 4 to 7 times running current.

Does NEC 620 give a fixed elevator voltage-drop percentage?

NEC 620 does not give one universal voltage-drop percentage for every elevator feeder. Designers usually combine NEC 620 elevator rules, NEC 430 motor rules, NEC 310.16 ampacity, and NEC 215.2(A)(1) voltage-drop guidance.

How much starting current should I use for a hydraulic elevator motor?

Use manufacturer data first. If it is not available for early screening, across-the-line hydraulic pump motors are often checked at 4 to 7 times running current; a 42A motor may momentarily demand 168A to 294A.

Can I upsize elevator feeder conductors without changing the breaker?

Yes. Upsizing from 8 AWG to 6 AWG copper to reduce voltage drop does not require increasing the overcurrent device. The breaker must still match NEC 430, NEC 620, nameplate data, and manufacturer instructions.

Why is 208V elevator equipment more sensitive to voltage drop?

Because each volt lost is a larger percentage of the supply. A 10V feeder drop is 4.8% at 208V but only 2.1% at 480V, before source voltage variation is included.

Should elevator voltage drop be checked at the controller or the motor?

Check the voltage at the equipment terminals specified by the manufacturer, usually the controller or drive input. NEC 110.3(B) makes listed equipment instructions part of the installation requirement.

Check the Elevator Feeder Before the Raceway Is Closed

Use the voltage drop calculator, wire size calculator, and three-phase calculator to compare conductor sizes before the elevator submittal, modernization order, or machine-room rough-in is locked. For a second review, send the voltage, running amps, starting data, route length, conductor material, and controller tolerance through the contact page.

Contact the Engineering Team Review More Guides