NEC Article 430 — Sizing and Code Compliance

Why Article 430 Matters

Electric motors are the single largest category of electrical load in commercial and industrial buildings. NEC Article 430 is the dedicated section of the National Electrical Code that governs how conductors, overcurrent protection, controllers, and disconnects must be sized and installed for motor circuits. Because motor starting currents can be six to ten times the full-load running current, the rules here differ from ordinary branch-circuit rules in Article 210. Understanding Article 430 is essential for passing your NCCER assessments and for working legally and safely on motor installations.

Structure of Article 430

Article 430 is divided into parts. The three parts you will use most often are:

• Part II (Sections 430.21–430.29): Conductor sizing for motor branch circuits and feeders.
• Part VII (Sections 430.81–430.91): Motor controllers — the devices that start, stop, and protect the motor.
• Part IX (Sections 430.101–430.113): Disconnecting means — the switch or circuit breaker used to isolate the motor and controller for maintenance.

Keep your codebook tabbed and annotated by part. During work on a real job or on an exam problem, you must be able to move quickly between these sections and the associated tables.

Part II — Sizing Branch-Circuit Conductors

Section 430.22 states that a conductor supplying a single motor must have an ampacity of not less than 125% of the motor's full-load current (FLC). The FLC is not read from the motor nameplate; it is taken from the NEC tables:

• Table 430.248 — Single-phase motors (120 V and 240 V)
• Table 430.250 — Three-phase motors (208 V, 230 V, 460 V, 575 V)

Using the table value rather than the nameplate protects the circuit from motors that may be rewound or replaced with a slightly different unit in the future.

Formula: Minimum conductor ampacity = FLC (from table) × 1.25

Once you have the minimum ampacity, select the smallest standard wire gauge from NEC Table 310.12 (or 310.16 for 60/75/90 °C conductors) whose ampacity equals or exceeds that value.

Part II — Overcurrent Protection (Branch-Circuit Short-Circuit and Ground-Fault Protection)

Section 430.52 governs the breaker or fuse that protects the branch-circuit conductors against short circuits and ground faults. This device is not sized at 125% of FLC like the conductors. Because of high inrush current during starting, it is sized using Table 430.52, which gives maximum percentages of FLC by motor type and protective device type. Common values include:

• Inverse-time (standard) circuit breaker: 250% of FLC (maximum)
• Dual-element (time-delay) fuse: 175% of FLC (maximum)
• Instantaneous-trip breaker: 800% of FLC (maximum, for certain motor-circuit types)

If the calculated value does not match a standard device rating, Section 430.52(C)(1) permits rounding up to the next standard size, provided the result does not exceed the maximums in Table 430.52. Standard sizes are listed in Section 240.6(A).

Part VII — Motor Controllers

A controller is any device used to start and stop the motor. It must have an ampere or horsepower rating sufficient for the motor. Magnetic contactors with overload relays — called motor starters — are the most common type. The overload relay provides overload protection (distinct from the branch-circuit overcurrent protection), tripping on sustained overcurrent caused by mechanical overload or a locked rotor. Overloads are sized according to Section 430.32, typically at 115–125% of motor nameplate FLA depending on the service factor.

Part IX — Disconnecting Means

Every motor and its controller must have an accessible disconnecting means (Section 430.102). The disconnect must:

1. Be in sight of the motor and the driven machinery (within 50 feet and visible) — or be lockable in the open position when in sight is not practical.

2. Have an ampere rating of at least 115% of the motor's FLC from the applicable table (Section 430.110).

3. Be capable of being locked open so workers can perform lockout/tagout (LOTO) before servicing equipment.

Safety: Lockout/Tagout and PPE

Motors store energy — electrical, mechanical (rotating parts), and sometimes thermal. Before any work on a motor or its control circuit:

• De-energize at the disconnect; verify absence of voltage with a properly rated meter or tester.
• Apply your personal lock and tag following your employer's LOTO program (OSHA 29 CFR 1910.147 for general industry; 29 CFR 1926.417 for construction).
• Verify that rotating parts have stopped before touching them.
• Wear appropriate PPE: safety glasses, insulating gloves rated for the voltage, and arc-flash PPE if an arc-flash hazard analysis requires it.

Never assume a motor is off because it is not turning — a motor stopped by a tripped overload can restart automatically when it cools.

Putting It Together

For any motor problem, follow this sequence:

1. Identify voltage and phase; find FLC in Table 430.248 or 430.250.

2. Multiply FLC × 1.25 → minimum conductor ampacity → select wire gauge.

3. Multiply FLC by the Table 430.52 percentage for your device type → select standard overcurrent device size.

4. Multiply FLC × 1.15 → minimum disconnect ampere rating.

5. Check that all selections comply with any additional conditions noted in Article 430.

Practice this sequence on every problem until it is automatic.