Okay, I understand. Converting DC motor data to AC load data for your distribution schedule can be tricky since you don't directly feed DC to the elevator motor. You are feeding 480V AC to a controller that then converts it to DC for the motor. Here's a breakdown of how to approach this

Understanding the System:
AC Input, DC Output

The key thing to remember is that you are dealing with an AC-to-DC conversion. The 480V/3-phase AC power you are supplying goes to the elevator controller (likely a solid-state drive). The controller then rectifies and controls the DC voltage and current to drive the DC elevator motor.

Controller Efficiency

The conversion process isn't 100% efficient. Some power is lost as heat. You'll need to account for this inefficiency.

Steps to Determine AC Load


Motor Horsepower (HP) is Your Starting Point

The 35 HP rating is the mechanical power output of the motor. This is the most reliable basis for your calculations.2.

Convert HP to Watts (Approximate DC Input Power)

1 HP = 746 Watts 35 HP 746 Watts/HP = 26,110 Watts (This is an approximate DC power input to the motor at full load).3.

Account for Controller Efficiency

This is CRUCIAL. Elevator drives are typically 85-95% efficient. Let's use 90% as a reasonable estimate. You should try to get the actual efficiency from the elevator control system documentation.

AC Input Power = DC Output Power / Efficiency AC Input Power = 26,110 Watts / 0.90 = 29,011 Watts4.

Calculate AC Apparent Power (kVA)

You need to convert the AC input power in watts to apparent power in volt-amperes (VA) or kilovolt-amperes (kVA) to properly size your distribution panel. To do this accurately, you need to estimate the power factor of the elevator drive. A typical power factor for a solid-state drive is between 0.7 and 0.
85. We will start with 0.85 Apparent Power (VA) = AC Input Power (Watts) / Power Factor Apparent Power (VA) = 29,011 Watts / 0.85 = 34,131 VA Apparent Power (kVA) = 34,131 VA / 1000 = 34.13 kVA5.

Calculate AC Line Current

Now you can calculate the AC current drawn from your 480V/3-phase supply. Use the following formula: I (Amps) = kVA 1000 / (√3 Voltage) I (Amps) = 34.13 kVA 1000 / (1.732 480V) I (Amps) ≈ 41.00 Amps6.

Consider Starting Current (Inrush)

Elevator motors, even with modern drives, can have a significant inrush current upon starting. This is very important for sizing breakers and conductors. Drives will limit this somewhat, but it still needs to be considered. Typically, you should assume an inrush current of 150-200% of the full-load current for a short duration. Consult the drive documentation for the exact inrush current specification. Assume Inrush is 150%: 41 Amps 1.5 = 61.5 Amps (peak) Assume Inrush is 200%: 41 Amps 2.0 = 82 Amps (peak)7.

Apply Code-Required Safety Factors



NEC 620.14 (Elevators, Dumbwaiters, Escalators, Moving Walks, Wheelchair Lifts, and Stairway Chair Lifts) outlines specific requirements for conductor sizing and overcurrent protection. You must consult this section of the National Electrical Code (NEC) for your specific installation. It will likely require you to size conductors and overcurrent protection at 125% of the full-load current of the elevator.

NEC 430 for motor circuits in general may also apply. Conductor Ampacity: 41 Amps 1.25 = 51.25 Amps (minimum ampacity for your conductors after considering temperature correction and derating factors). Select conductors with an ampacity greater than this value.8.

Include on Your Distribution Schedule



Load Description

Elevator # (1, 2, or 3).

Load Type

Motor (Elevator).

Voltage

480V, 3-Phase.

kVA

34.13 kVA (or the calculated value from Step 4).

Amps

41 Amps (or the calculated value from Step 5).

Breaker Size

Select a breaker size based on the inrush current and the requirements of NEC 620.14 and NEC 430, typically significantly larger than the calculated full-load current. Consult the drive manufacturer's documentation for recommended breaker types and sizes. Your existing 200A fused disconnect is a likely starting point, but may need adjustment.

Note that with newer VFDs, instantaneous trip settings need to be selected carefully to prevent nuisance tripping while still protecting the electrical system. For proper short circuit and ground fault coordination, current-limiting fuses may still be required depending on the specific installation.

Important Considerations and Recommendations



Elevator Controller Documentation is KEY

The most accurate way to determine the AC load is to consult the elevator controller documentation. This should provide the input kVA or full-load amps at 480V. This is far better than estimating.

Nameplate on Controller

Look for a nameplate on the elevator controller itself. It might list the AC input requirements.

Demand Factors

In a high-rise with multiple elevators, you might be able to apply a demand factor, assuming all elevators will not be running at full load simultaneously. However, this requires careful analysis of elevator usage patterns. Err on the side of caution, especially if it's a busy building. Check local codes regarding elevator demand factors.

Spare Capacity

Always include spare capacity on your new distribution panel for future expansion or changes.

Harmonic Distortion

Solid-state drives can generate harmonic distortion on the electrical system. Consider using harmonic mitigation techniques (e.g., line reactors or harmonic filters) if the distortion becomes excessive. Check with the elevator drive manufacturer for recommendations.

Licensed Professional Engineer (PE)



I STRONGLY recommend engaging a qualified, licensed professional engineer (PE) experienced in electrical distribution systems and elevator installations. They can perform detailed load calculations, ensure code compliance, and specify the correct equipment.

NEC Compliance

The NEC is the authority on electrical installations. Adhere to all applicable requirements.

Local Codes

Check local building and electrical codes, as they may have additional requirements.

Coordination Study

A coordination study may be required to ensure that the overcurrent protection devices (breakers and fuses) are properly coordinated to minimize outages.

In summary:*1. Get the AC input data from the elevator controller documentation (best option).
2. If that's not available, use the motor HP to estimate the AC load, accounting for controller efficiency and power factor.3. Calculate the AC current.
4. Consider inrush current.5. Apply NEC-required safety factors.
6. Consult with a licensed professional engineer.This detailed explanation should provide you with a solid understanding of the process. Good luck! Flag for review