Explaining NEC Article 430 On Motors, Motor Circuits, and Controllers

Article 430 covers installation requirements for motors, motor circuits, controllers, overload and short-circuit protection, and disconnecting means.

The installation of motors is complex because they draw high inrush current at startup, often 6× their full-load current (FLC). This requires special protection and sizing rules beyond those for typical electrical equipment. Here is the overview of the main points of this article, along with the cables used for motors and motor equipment:

Conductor Sizing

• Conductors for a single motor must have ampacity ≥125% of the motor's FLC (per NEC Tables 430.147–430.150).

• For multiple motors, the conductors must be sized for the sum of all FLCs plus 25% of the highest-rated motor.

Overload Protection

• The purpose of overload protection is to protect motors and branch-circuit conductors from prolonged overcurrent that causes overheating, not from short circuits or ground faults.

• Overload protection is required for most motors, except in cases where it would introduce greater hazards (e.g., fire pumps).

• The trip settings for overload protection are:

• 125% of motor nameplate FLA if the motor has:

• A service factor ≥1.15 or

• A temperature rise ≤40°C

• 115% for all other motors

• Common overload devices are:

• Thermal overload relays

• Integral motor thermal protectors

• Embedded temperature detectors (for motors over 1500 HP)

• Properly rated dual-element fuses or breakers (if permitted)

Short-Circuit & Ground-Fault Protection

• Short-circuit & ground-fault protection protects motors, controllers, and conductors from sudden faults that can cause arcing, equipment damage, or fire.

• Must be separate from overload protection.

• Devices must allow for the motor's high inrush current at startup without tripping.

• Here is the sizing example - A 20A FLC motor may require a time-delay fuse rated at 175%–250 % of FLC, depending on type and duty.

• Protection methods include:

• Time-delay fuses

• Inverse time circuit breakers

• Instantaneous-trip breakers (only if adjustable and approved)

Controllers

• A motor controller starts/stops the motor and must:

• Be rated for the motor's horsepower and voltage

• Interrupt locked-rotor current

• Controllers may double as overload protection if rated accordingly

Disconnecting Means

• Must disconnect all ungrounded conductors and be in sight of the controller (i.e., within 50 feet and visible)

• Must have an ampacity ≥115% of the motor's FLC

• Acceptable disconnect types vary by motor size (e.g., circuit breaker, motor switch, plug/receptacle)

Control Circuits

• Must be protected from overcurrent and mechanical damage

• Must disconnect when the motor disconnect is opened

• Ground faults must not cause accidental motor startup

Cables Used in Motor Circuits and Motor Equipment

Power Feeds to Motors

THHN / THWN-2

• Used for motor branch and feeder circuits in conduit

• 600V rated; THWN-2 approved for wet locations

• Common in HVAC, pump, and equipment circuits in industrial settings

XHHW / XHHW-2

• 600V, 90°C wet/dry (XHHW-2)

• For motors in wet conduit or outdoor raceways

• Not for direct burial

RHH / RHW / RHW-2 / USE-2

• 600V, 90°C wet-rated (RHW-2, USE-2)

• RHW-2: Wet/dry conduit, above or below ground

• USE-2: Direct burial only, not for indoor use

• Used for long runs to outdoor motors (e.g., pumps)

MC Cable (Metal-Clad)

• Used for motor branch and feeder circuits in dry indoor locations without conduit

• Suitable for exposed or concealed runs in equipment rooms, mechanical spaces, and above ceilings

• Available with PVC or XLPE insulation; rated 600V

• Not approved for direct burial or wet locations unless specifically marked

Tray Cable (TC-ER)

• Used in cable trays or for exposed runs from control panels to motors

• Suitable for industrial environments with limited conduit

• Can include control conductors and be shielded

VFD Cable

• Specifically designed for motors controlled by Variable Frequency Drives

• Includes shielding to reduce EMI/RFI and insulation rated for high voltage spikes

• Prevents bearing pitting and signal interference

SOOW / SEOOW Flexible Cord

• Used for portable motor applications or equipment requiring flexibility

• Oil-, water-, and sunlight-resistant

• Common in maintenance setups, generators, and temporary motor installations

Internal Wiring in Motors and Equipment

Motor Lead Wires (Teflon/PTFE or XLPE insulated)

• High-temperature, abrasion-resistant, and compact

• Sized based on motor winding specs and typically terminated inside terminal housings

MTW (Machine Tool Wire)

• Used inside motor starters, controllers, and industrial machines

• Flexible, oil-resistant, flame-retardant; rated for 600V

• Common in control enclosures and machinery wiring

Hook-Up Wire (e.g., AWM, TEW)

• Used for internal wiring in motors, panels, and terminal boxes

• Typically used for light-duty internal circuits (not for power feeds)

• AWM (Appliance Wiring Material) varies widely in insulation and rating based on the type