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MotorsJourneymanMasterNEC 2026

Motor branch-circuit conductor sizing (NEC 430.22)

Short answer

Branch-circuit conductors for one continuous-duty motor must have an ampacity of at least 125% of the motor's table full-load current (NEC 430.22). Look up the full-load current in Table 430.248 or 430.250, multiply by 1.25, then pick the conductor from Table 310.16 in the column that matches the terminal temperature rating.

Updated Original problems, new numbers every time

Live practice

Practice: motor branch-circuit conductors

Each problem uses new numbers, so you practice the method rather than memorizing an answer.

Formula

Minimum ampacity (A) = 1.25 × table full-load current (A)
Conductor size = smallest size in Table 310.16, terminal temperature column, with ampacity ≥ minimum ampacity
SymbolMeaningUnit
FLCTable full-load current, Table 430.248 or 430.250A
AmpacityMinimum conductor ampacity, 125% of FLCA

Worked example

A 25 hp, 460 V, three-phase squirrel-cage motor (continuous duty) has a nameplate current of 29.9 A. The branch circuit uses THHN/THWN-2 copper conductors, and the motor and controller terminals are rated 75 °C. What is the minimum branch-circuit conductor size?

  1. Look up Table 430.250, 460 V column, 25 hp: 34.0 A. Use the table, not the nameplate (430.6(A)(1)).
  2. NEC 430.22: conductors for one continuous-duty motor carry at least 125% of the full-load current: 1.25 × 34.0 = 42.50 A.
  3. The terminals are rated 75 °C, so use the 75 °C copper column of Table 310.16 (110.14(C)), even though THHN is a 90 °C conductor.
  4. Look up Table 310.16, 75 °C copper column: the smallest conductor with at least 42.50 A is 8 AWG, rated 50 A.

Answer: 8 AWG

Motor branch-circuit conductors, explained

A motor draws its full-load current for long periods and much more while starting. NEC 430.22 makes the branch-circuit conductors for one continuous-duty motor big enough for 125% of the full-load current. The full-load current comes from Table 430.248 or 430.250, not the nameplate (430.6(A)(1)).

Pick the conductor from Table 310.16, using the column that matches the lowest temperature rating of the terminals, under 110.14(C). A THHN conductor is rated 90 °C, but if the terminals are rated 75 °C you size from the 75 °C column. Circuits of 100 A or less, or with 14 AWG through 1 AWG conductors, default to 60 °C unless the equipment is marked for 75 °C.

Motor circuits are an exception to the usual small-conductor limits in 240.4(D): the motor's short-circuit device and overloads protect the conductor, so a 14 AWG conductor at its 75 °C ampacity is fine for a small motor. The 2026 NEC also adds 430.22(H) for the new Design BE and CE motors, which can need larger conductors. The problems here use ordinary squirrel-cage motors.

How to solve it on the exam

  1. Look up the full-load current in Table 430.248 (single-phase) or Table 430.250 (three-phase) for the hp and voltage.
  2. Multiply by 1.25 (430.22).
  3. Find the terminal temperature rating; the question will say 60 °C or 75 °C.
  4. In Table 310.16, use that temperature column for copper or aluminum and pick the smallest conductor with an ampacity at least equal to your result.

Common mistakes

  • Sizing from the nameplate current instead of the table current.
  • Forgetting the 125% factor.
  • Using the 90 °C column because the conductor is THHN, when the terminals are rated 60 °C or 75 °C.
  • Using the copper column for aluminum conductors.
  • Applying the 125% again on top of a value that already includes it.

Exam tips

  • Write the chain on scratch paper: table FLC, × 1.25, column, size. Each step is one lookup.
  • On the Texas exam, treat conductors as copper unless the question says aluminum.

Questions people ask

How do you size conductors for a single motor?

Multiply the table full-load current by 125% and pick a conductor with at least that ampacity from Table 310.16. This is NEC 430.22 for one continuous-duty motor.

Why are motor conductors sized at 125%?

The 125% gives margin for a motor that runs at full load for long periods and may be slightly overloaded within its service factor. It is the same idea as sizing for continuous loads.

Which temperature column do I use for motor conductors?

Use the column for the lowest-rated terminal in the circuit, under 110.14(C). If the motor and controller are rated 75 °C, use the 75 °C column, even for 90 °C THHN.

Does 240.4(D) limit 14 AWG motor circuits to 15 A?

No. Motor circuits are protected under Article 430, and 240.4(G) lets those rules take the place of 240.4(D). The conductor is sized from 125% of the full-load current.

Sources

About the tables: The exam is open book. These problems cite the 2026 NEC section and table so you practice finding them in your own book. We never print NEC text or tables.