You're right, the NEC's gradual push towards metric is a valid observation, and the absence of kW listings in the FLC (Full Load Current) tables for motors seems like a contradiction. It's a good question! Here's a breakdown of why this is the case and some potential reasons behind it

Why kW is Not in the NEC FLC Tables:
Historical Legacy

The NEC is deeply rooted in the traditional horsepower (HP) system. The FLC tables have been built and updated based on HP for decades. Changing them significantly would require extensive revisions, retraining, and potential for widespread confusion.

North American Market

While kW is globally prevalent, the North American motor market still largely relies on HP ratings for many applications. The NEC reflects this market reality.

Standardization Challenges

Creating a universally accepted and accurate kW-to-FLC conversion table presents challenges. Motor efficiency varies significantly based on design, manufacturer, and NEMA/IEC standards. A single kW-to-FLC value wouldn't be accurate for all motors of the same kW rating. The NEC tables aim for a conservative (i.e., higher current) value to ensure safety, and doing this accurately for all possible kW motors would be complex.

Ease of Conversion (Sort Of)

While not ideal, the NEC expects you to convert kW to HP using a simple conversion factor (1 HP = 0.746 kW). You're then expected to use the standard HP-based FLC tables. It's an extra step, but it's the current method.

Code Cycle Inertia

Changing major sections of the NEC takes considerable time and justification. The process involves proposals, public comments, and committee decisions.

Why This is a Problem (As You Point Out)



Increasingly Common kW Motors

As you've noted, the availability of motors rated only in kW is increasing, especially with imported equipment and the growing adoption of IEC standards.

Inconvenience and Potential for Error

Converting kW to HP and then looking up the FLC introduces an extra step where errors can occur. Rounding errors, misremembered conversion factors, or simply using the wrong table can lead to incorrect calculations and potentially unsafe installations.

Outdated Approach

Relying solely on HP feels increasingly anachronistic in a world that is rapidly adopting metric.

What You Can Do



Convert kW to HP

This is the current requirement. Use the conversion factor 1 HP = 0.746 kW. Divide the kW rating by 0.746 to get the equivalent HP. Example: A 1.5 kW motor is approximately 2 HP (1.5 / 0.746 = 2.01). Round up or down appropriately for safety considerations, often erring on the side of a slightly higher HP rating.

Look for Motor Nameplate Data

Always refer to the motor nameplate for the actual FLC (in Amps). The NEC FLC tables are minimum values; the nameplate value is the more accurate one for that specific motor. If the nameplate lists the current at the actual voltage that you will be using, then use the nameplate.

Consult Engineering Judgement

For critical applications or where you're unsure, consult with a qualified electrical engineer. They can help assess the situation, perform necessary calculations, and ensure compliance with the NEC and relevant standards.

Submit Proposals for Future NEC Cycles

The NEC is a living document that evolves through a formal proposal and revision process. If you feel strongly that kW should be included in the FLC tables, consider submitting a proposal to the NEC. This is the most direct way to influence the code's future direction. The key to a successful proposal is providing strong justification, clear language, and supporting documentation.

In Summary:

The lack of kW listings in the NEC FLC tables is primarily due to historical reasons, the continued prevalence of HP ratings in the North American market, standardization challenges, and the inherent inertia in changing established code practices. While it presents an inconvenience and potential for error in the modern era, the current expectation is to convert kW to HP and use the existing tables. As kW motors become more common, pressure will likely increase to update the NEC to reflect this reality.I hope this helps! Let me know if you have any other questions. Flag for review