Hi all,

Recently, we imported a batch of Japanese equipment and only specified a power requirement of 480V 60Hz.

They have indicated 32A on the FLA nameplate for this equipment.

Upon recently opening the control panel for inspection, I discovered that they might be in violation of some NEC regulations regarding circuit breakers and wire gauge.

They are using a 40A breaker as the main breaker and the main feeder size is 14mm2 .

I would like to know what changes I need to make to comply with NEC regulations with minimal modifications.

The panel consists of 11 servo drives, one 1HP water pump, and one controller.

The supplier explained that: Servo drives #1 to #4 do not operate simultaneously with #5 to #8, and #9 to #11 do not operate simultaneously with #1 to #8.
Servo drive #1~8 rated input current = 8.5A
Servo drive #9~11 rated input current = 4.6A

Therefore, they chose the circuit breakers/wire gauge based on the duty cycle. Additionally, NEC 409.20 seems to describe that duty cycles can be considered.

However, it seems NEC does not consider their previous logic interlock relationship? Is my understanding correct?

When selecting OCPD and conductors, NEC requires considering all continuous and non-continuous loads, regardless of any logic interlocks.

So, are servo drives considered continuous or non-continuous loads? Most of these servos operate below 50% load and do not run continuously; can they be classified as non-continuous loads?

I understand that NEC also describes VFDs should be calculated at 125% of the load, while NFPA79 states servos should be calculated at 115% of the load.

Which of the following calculations is correct?

1. (Calculating all servos as continuous loads or using the VFD calculation method. 8.581.25 + 4.631.25 + 2.1(1HP FLC)*1.25 = 104.875A should choose a 110A breaker

2. (Calculating all servos using NFPA79's 115% method) 8.581.15 + 4.631.15 + 2.1*1.25 = 96.695A should choose a 100A breaker

3. (Calculating all servos as non-continuous loads) 8.58 + 4.63 + 2.1*1.25 = 84.425A should choose a 90A breaker

Additionally, can I just change the conductor size without breaker change?

For example, only changing the conductor to AWG3 to meet NEC's current carrying capacity requirements, keeping the circuit breaker unchanged.

This logically seems feasible, as a 40A circuit breaker would still perform its function of disconnecting before damaging the conductor insulation.

But does this comply with NEC regulations?

As an aside, NEC only describes the current carrying capacity for AWG wire sizes. For IEC standard wire sizes, can I use the current carrying capacity described by the manufacturer?