Branch Circuits vs. Feeders for Motor Loads

Beginner Time: 20 min Type: Code Application Focus: Panel Design / NEC Core

After this module: Understand where a branch circuit ends and a feeder begins, and why motor loads require the 125% conductor multiplier from Article 430.

Prerequisites: NEC Code Reading Fundamentals

Purpose

This module clarifies the boundary between branch circuits and feeders in motor-load systems, explains why motor conductors require the 125% multiplier, and shows how to apply the Article 430 feeder formula when multiple motors share a common feeder.

Branch circuit vs. feeder — the boundary

The NEC defines a branch circuit as the conductors between the final overcurrent protective device (OCPD) protecting the circuit and the outlet or load. A feeder is everything upstream of that final OCPD, from the service or source panel up to but not including the branch-circuit OCPD.

The dividing line is the final overcurrent protective device.

Segment	From	To	NEC reference
Service conductors	Utility connection	Service OCPD	Art 230
Feeder	Service or source OCPD	Branch-circuit OCPD	Art 215
Branch circuit	Branch-circuit OCPD	Load (motor terminals)	Art 210, Art 430

For motor circuits, the branch-circuit OCPD is typically the fuse or circuit breaker that is selected from Table 430.52, not necessarily the one that also provides overload protection.

flowchart LR
  SVC["Service / Source Panel"]
  FOCPD["Feeder OCPD\n(Art 215)"]
  BOCPD["Branch-Circuit OCPD\nTable 430.52"]
  DISC["Disconnect\n(Art 430.102)"]
  OLR["Overload Relay\nArt 430.32"]
  MTR["Motor"]

  SVC --> FOCPD
  FOCPD -->|"Feeder conductors\nArt 430.24"| BOCPD
  BOCPD -->|"Branch-circuit conductors\nArt 430.22 (125%)"| DISC
  DISC --> OLR
  OLR --> MTR

  style BOCPD fill:#f5f5dc,stroke:#999
  style FOCPD fill:#dce8f5,stroke:#999

Article 430.22 — Branch-circuit conductor sizing (125% rule)

For a single motor, Art 430.22(A) requires that branch-circuit conductors have an ampacity of not less than 125% of the motor full-load current (FLC) from the NEC tables (Table 430.248 for single-phase, Table 430.250 for three-phase).

Do not use the nameplate FLA. Use the NEC table FLC value. The nameplate full-load amperes (FLA) reflects the actual motor, which may run cooler or hotter than assumed. The table values ensure the conductor is not thermally stressed under normal operation.

Formula:

Minimum conductor ampacity = FLC (Table 430.250) × 1.25

Example — 10 HP, 460 V, 3-phase motor:

Table 430.250 FLC = 14 A
Minimum conductor ampacity = 14 × 1.25 = 17.5 A
Select conductor ≥ 17.5 A → 12 AWG THHN at 75 °C = 25 A ✓

Article 430.24 — Feeder conductor sizing (multiple motors)

When a feeder supplies two or more motors, Art 430.24 sets the minimum feeder conductor ampacity as:

125% of the largest motor FLC + 100% of the FLC of all other motors

Formula:

Feeder ampacity = (FLC_largest × 1.25) + (FLC_motor2 + FLC_motor3 + ...)

Example — three motors on one feeder (460 V, 3-phase):

Motor	HP	Table FLC
Motor 1 (largest)	25 HP	34 A
Motor 2	10 HP	14 A
Motor 3	5 HP	7.6 A

Feeder ampacity = (34 × 1.25) + 14 + 7.6
               = 42.5 + 14 + 7.6
               = 64.1 A minimum

Select the next standard conductor size ≥ 64.1 A at 75 °C.

Key rules summary

Rule	Article	Requirement
Branch-circuit conductor ampacity	430.22(A)	≥ 125% of table FLC
Branch-circuit OCPD	430.52 + Table 430.52	Max % of FLC per device type
Feeder conductor ampacity	430.24	125% largest + 100% rest
Overload protection	430.32	Sized at 115–125% of FLA
Use NEC table FLC, not nameplate FLA	430.6(A)	Table values govern sizing

Common mistake — nameplate FLA vs. table FLC

A frequent field error is pulling the amperage value from the motor nameplate instead of the applicable NEC table.

Source	Value (10 HP, 460 V, 3Ø)	Status
Motor nameplate FLA	12.8 A (example)	Do not use for conductor sizing
Table 430.250 FLC	14 A	Use this for Art 430.22 and 430.24

The table value is almost always higher, providing a code-compliant thermal margin. The nameplate FLA may be used for overload relay setting (Art 430.32), but not for conductor ampacity calculation.

Practical takeaway

The branch circuit begins at the final OCPD (Table 430.52) and ends at the motor.
Size branch-circuit conductors at 125% of the NEC table FLC, never the nameplate FLA.
For shared feeders, apply the 430.24 formula: 125% of the largest motor FLC plus 100% of all others.
Overload relays are downstream of the disconnect and are sized separately from conductors and branch-circuit OCPDs.

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