Multiple motors on a branch circuit vs feeder circuit

[cppoly]

Looking at the code sections for connecting multiple motors or motor operated appliances on the same branch circuit compared to feeder circuit, I’m noticing a few differences.

Sizing a feeder OCPD per 430.62 requires calculations (largest motor OCPD + sum remaining motor FLCs, round down).

But sizing a branch circuit OCPD per 430.53 does not require calculations. It seems you can connect a lot more motors onto a single branch circuit (20A max / 120V ; 15A max 277V) using this method so long as any individual motor doesn’t exceed 1 HP or 6 amps. It seems strange that there’s no calculations required as we’ve been programmed to calculate the largest motor OCPD first followed by adding the remaining motor FLCs for feeder circuits.

An example would be connecting 45 motor indoor evaporator units (I know... excessive, but to prove a point) at 120V and .4 amps each. 45 x .4 = 18A = 20A circuit breaker per 430.53. In this example, there’s no calculation requirements other than not exceed a 20A circuit breaker. Am I missing something??

 

[mikeames]

No, your not missing anything. It makes sense. I know you know this but you are also comparing Feeders, and branch circuits. Thats different. The motors allowed on branch circuits are small, much like a general appliance. A feeder is sized for multiple larger motors where the inrush motor characteristics have a larger impact on circuit design. Small motors share the same characteristics but are less of a design issue when small. Imagine if you were going to run some 1/8 hp attic fans or bath vent fans, would a motor calc really need to be done if you had several on the same circuit?