NEC · Article 430

Motor Full-Load Current & Sizing

The number one motor trap on the journeyman exam: conductors and branch-circuit OCPD are sized from the NEC table FLC value, not the motor nameplate FLA — and overload protection is the one place where the nameplate does apply.

NEC 2017 2020 2023 Last updated 2026-06-27

The core rule: table FLC, not nameplate FLA

Article 430 governs the wiring of motors, and the most frequently tested principle is also the most counterintuitive: when you size the branch-circuit conductors and the branch-circuit overcurrent protective device (OCPD) for a motor, you do not use the current shown on the motor's nameplate. Instead, you look up the full-load current (FLC) value from the NEC table — Table 430.248 for single-phase motors and Table 430.250 for three-phase motors — and you base your sizing on that number.

The table FLC and the nameplate full-load amperes (FLA) are often close but rarely identical. Using the wrong one is the mistake that exam questions are designed to catch. The NEC uses standardized table values so that the circuit design is independent of any particular motor's nameplate and remains consistent regardless of which motor is eventually installed.

The single exception to the "use the table" rule is overload protection. Overloads protect the motor windings themselves, and they must reflect how much current that specific motor actually draws — which is why 430.32 sends you back to the nameplate FLA for sizing overloads.

Conductor sizing: 430.22 and the 125% rule

Section 430.22 sets the minimum conductor ampacity for a single motor at 125 percent of the table FLC. The logic is the same as the 125% rule for continuous loads under 210.20 and 215.2: a motor running at full load is a continuous load, so the conductors must be sized above the expected running current to limit heat over long operating periods.

The formula is straightforward:

Minimum conductor ampacity = Table FLC × 1.25

After calculating the minimum ampacity, select a conductor from Table 310.16 (or the applicable table) whose ampacity equals or exceeds that value. Remember that the 125% multiplier applies to the table FLC, not the nameplate.

Branch-circuit OCPD sizing: 430.52 and Table 430.52

The branch-circuit OCPD — whether a fuse or a circuit breaker — must be large enough to allow the motor to start through its inrush current, which can be several times the running current. For this reason, 430.52 permits much higher OCPD ratings than the conductor ampacity calculation would suggest. The maximum OCPD size is expressed as a percentage of the table FLC and depends on the type of protective device:

Protective device type Maximum % of table FLC (per Table 430.52)
Non-time-delay fuse 300%
Dual-element (time-delay) fuse 175%
Inverse time circuit breaker 250%
Instantaneous-trip breaker (MCP) 800% (general); different limits may apply

These are maximum values. When the calculated result lands between standard OCPD sizes, 430.52 allows rounding up to the next standard size — within the limits stated in the section. Exam questions typically use the standard percentages from Table 430.52; only go beyond them if the question explicitly states the motor will not start with the standard calculation.

Overload protection: 430.32 and the nameplate

Overload protection covers the motor against sustained overcurrents that would overheat the windings — a separate concern from protecting the branch-circuit conductors. Section 430.32 sizes overloads from the motor nameplate FLA (not the table):

  • For motors with a service factor of 1.15 or greater, or with a marked temperature rise of 40°C or less: overload sized at not more than 125% of nameplate FLA.
  • For all other motors: overload sized at not more than 115% of nameplate FLA.

A convenient way to remember the split: conductors and OCPD come from the table; overloads come from the nameplate. Every motor question on the journeyman exam tests whether you know which source governs which calculation.

A worked example

Consider a 10 hp, 230V, three-phase motor. Table 430.250 gives a full-load current of 28 amperes for this rating. The nameplate on the actual motor reads 26.5 A FLA with a service factor of 1.15.

Use the table FLC (28 A) for conductor and OCPD sizing:

  • Minimum conductor ampacity: 28 × 1.25 = 35 A. Select a conductor rated at least 35 A at the applicable temperature column.
  • Maximum OCPD — dual-element fuse: 28 × 1.75 = 49 A. Round up to the next standard fuse size, 50 A.
  • Maximum OCPD — inverse time breaker: 28 × 2.50 = 70 A. 70 A is a standard breaker size, so no rounding needed.

Use the nameplate FLA (26.5 A) for overload sizing:

  • Overload (SF ≥ 1.15): 26.5 × 1.25 = 33.1 A maximum overload rating.

If an exam question gives you only a nameplate FLA and asks for the conductor size, pause before plugging that number into the 125% formula. The question may be testing whether you know to look up the table FLC first. If the question provides the table FLC directly or says "use the NEC table value," then proceed with that figure for conductors and OCPD. The motor FLC calculator walks through both steps with the correct source for each.

Practice questions on this rule

Real journeyman-exam practice questions from Loomi's bank — answer first, then reveal the explanation.

Q1 NEC 430.6(A)

A motor is built for low speed operation, rated less than 1200 RPM. How should its branch-circuit conductor ampacity be determined?

  1. A From the nameplate current rating, per 430.6(A)(2)
  2. B From the locked-rotor current as with torque motors
  3. C From Table 430.247-430.250, the same as a standard motor
  4. D From the horsepower rating interpolated against the standard tables
Show answer & explanation

Correct: A — From the nameplate current rating, per 430.6(A)(2)

430.6(A)(2) carves out low-speed (under 1200 RPM) motors, along with high-torque, canned pump, and multispeed motors, as exceptions to the table-based rule — their conductor ampacity, switch ratings, and protection all come from the nameplate current instead. The table method in 430.6(A)(1) applies only to standard motors.

Q2 NEC 430.6(A)

Regardless of whether a motor uses table current or nameplate current for its conductors, what value always determines separate motor overload protection?

  1. A Whichever value is higher
  2. B The branch-circuit short-circuit protective device rating
  3. C The table current from Table 430.247-430.250
  4. D The nameplate current rating
Show answer & explanation

Correct: D — The nameplate current rating

430.6(A)(2)(1) specifies that separate motor overload protection is always sized from the nameplate current rating, independent of whether conductor ampacity itself is based on table values or nameplate values.

Q3 NEC 430.22

What is the full-load current of a 25 HP, 460-volt, three-phase induction motor? (NEC Table 430.250)

  1. A 78.2 A
  2. B 68 A
  3. C 74.8 A
  4. D 34 A
Show answer & explanation

Correct: D — 34 A

Table 430.250 lists the full-load current of a 25 HP three-phase motor at 460 V as 34 A. The distractors are the FLC at other voltage columns — read the column for the motor's actual voltage.

Q4 NEC 430.22

What is the full-load current of a 50 HP, 460-volt, three-phase induction motor? (NEC Table 430.250)

  1. A 65 A
  2. B 143 A
  3. C 150 A
  4. D 130 A
Show answer & explanation

Correct: A — 65 A

Table 430.250 lists the full-load current of a 50 HP three-phase motor at 460 V as 65 A. The distractors are the FLC at other voltage columns — read the column for the motor's actual voltage.

All Motors practice questions (Article 430)

Frequently asked questions

Why does the NEC use table FLC instead of the nameplate FLA for conductor sizing?
Motor nameplate full-load amperes can vary between manufacturers for the same horsepower and voltage rating. The NEC tables provide a standardized, conservative value so that conductors and overcurrent devices are sized consistently enough to protect the circuit regardless of which motor is installed. Using the nameplate would make the circuit design dependent on the specific motor, which could change.
What is the difference between overload protection and branch-circuit overcurrent protection for a motor?
Overload protection (Article 430 Part III) guards the motor windings against sustained overcurrents that would overheat the motor — it is sized from the nameplate FLA. Branch-circuit overcurrent protection (Article 430 Part IV) protects the conductors and must be large enough to allow the motor to start through its inrush current — it is sized from the table FLC and the 430.52 percentages, which allow much higher values than conductor ampacity would suggest.
Can you go above the 430.52 maximum OCPD percentage?
In limited circumstances, yes. If the calculated maximum OCPD does not allow the motor to start, 430.52 permits going to the next standard size up from the calculated value, and in some cases further increases are allowed subject to absolute limits stated in the section. However, the default on a journeyman exam question is to use the standard percentages from Table 430.52 unless the question specifically says the motor will not start.
Related articles
Motor FLC Calculator Look up table FLC and size conductors and OCPD in one step. Motors — Topic Hub All Article 430 exam topics in one place. Overcurrent Protection How branch-circuit OCPD rules interact across all load types. Conductor Ampacity The general conductor sizing rules that Article 430 modifies for motors.
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