What is the Difference in Sizing Between Motors and Non-Motor Feeders

Unraveling the Mystery: Sizing Differences Between Motors and Non-Motor Feeders

Did you know that the sizing process for motors and non-motor feeders differs significantly? In this article, we'll explore the key distinctions and why they matter for your electrical projects.

Motors: Full-Load Current and 125% Rule

When sizing motor feeders, the full-load current (FLC) is crucial. Based on the motor's FLC, branch-circuit conductors must have an ampacity of no less than 125%[2]. This accounts for the motor's higher starting current, which is typically greater than its running current[3].

Non-Motor Feeders: Total Load Current Calculation

For non-motor feeders, the total load current calculation is essential. This calculation takes into account continuous and non-continuous loads, ensuring the proper sizing of conductors and protection devices[6].

Feeder Overcurrent Protection

Feeder overcurrent protection devices are typically sized at 250% of the motor's full-load current for thermal-magnetic fixed-trip type breakers, while instantaneous magnetic-only breakers can be sized differently[5].

Conclusion

Understanding the difference in sizing between motor and non-motor feeders is crucial for proper electrical installations. By following the guidelines for each type of feeder, you can ensure safe and efficient operation. Got questions or comments? Share them below!

Sources:

1. https://franca-electricalengineer.blogspot.com/2023/04/sizing-mccb-for-motors-and-non-motor.html

2. https://franca-electricalengineer.blogspot.com/2023/04/the-difference-in-sizing-between-motors.html

3. https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/fuses/solution-center/bus-ele-tech-lib-fuses-diagnostic-sizing-charts.pdf

4. [4] https://forums.mikeholt.com/threads/sizing-motor-feeder-wires-correctly.111167/

5. https://www.globalspec.com/reference/59671/203279/3-8-motor-feeders-and-starters

6. https://site.ieee.org/icps-ehe/files/2015/11/13-9-NFPA-70_-National-Electrical-Code-NEC-Article-220.pdf

Related Articles:

• Understanding Motor Starter Types and Their Applications
• What Are the Different Types of Electrical Feeder Systems?
• Ground Fault Protection for Motors: What You Need to Know