NEC Article 440 — Air Conditioning and Refrigeration: Exam Guide

NEC Article 440 governs air-conditioning and refrigerating equipment — and it comes up on nearly every journeyman and master electrician exam. The rules are distinct enough from Article 430 (general motors) that many candidates mix them up. The key differences are nameplate-driven sizing, HACR-rated breakers, and a specific disconnect sizing formula.

This guide covers the Article 440 hierarchy, the four critical nameplate values, conductor sizing, overcurrent protection, and disconnect requirements — with worked examples for each.

Why Article 440 Exists — Hermetic Motor-Compressors

Standard electric motors have their windings accessible for testing and repair. A hermetic refrigerant motor-compressor seals the motor and compressor together inside a welded refrigerant-filled housing. You cannot test the motor separately, cannot measure its resistance easily, and the starting characteristics differ from open-type motors.

Because hermetic motor-compressors have higher inrush currents relative to their running currents and different thermal characteristics, the NEC gives them their own article rather than relying entirely on Article 430.

NEC 440.3 makes the hierarchy clear: Article 440 supplements or modifies Article 430. For hermetic compressors, use Article 440. For open-type motors in HVAC systems (condenser fan, evaporator fan, blower motor), use Article 430.

The Four Nameplate Values — 440.4(B)

The nameplate on A/C and refrigerating equipment must include four values that drive your circuit design:

The exam shortcut: On most A/C circuit questions, MCA drives conductor sizing, and MOCP drives breaker sizing. The nameplate gives you both — you do not calculate them from scratch (the manufacturer already did).

Why the Nameplate Values Matter

For equipment with multiple motors (compressor + fan motors), the MCA and MOCP account for all motors together. The manufacturer calculates:

MCA = 125% of the largest motor's FLA + 100% of all other loads

MOCP = largest OCPD permitted to let the compressor start without tripping

These are provided to you on the nameplate. On the exam, you are given these values and asked to size conductors and overcurrent devices — not calculate MCA and MOCP from scratch. However, understanding how they are derived helps you answer "why" questions.

Conductor Sizing — 440.32 and 440.33

Single Motor-Compressor — NEC 440.32

The branch circuit conductors must have an ampacity not less than 125% of the motor-compressor rated-load current or the branch-circuit selection current, whichever is greater.

In practice: the conductors must have an ampacity equal to or greater than the MCA on the nameplate. Use Table 310.16 to find the minimum wire size.

Example: A rooftop package unit has an MCA of 32A. What is the minimum copper conductor size?

From Table 310.16 (75°C column): 8 AWG = 50A, 10 AWG = 35A.

10 AWG has 35A ampacity ≥ 32A MCA ✓

Minimum conductor: 10 AWG copper THHN

Multiple Motor-Compressors — NEC 440.33

When a branch circuit supplies more than one motor-compressor (or a motor-compressor plus other motors/loads), the conductors must have an ampacity of at least the sum of all MCA values, or the value marked on the equipment nameplate, whichever is greater.

For multi-unit calculations, use the larger of:

• Sum of all rated-load currents + 25% of the largest rated-load current
• The combined MCA from the nameplate

Overcurrent Protection — 440.22

The MOCP Rule — NEC 440.22(A)

The branch circuit overcurrent device must not exceed the MOCP marked on the nameplate. If the MOCP is not a standard fuse or breaker size, round down to the next standard size.

Standard overcurrent device sizes per NEC 240.6(A): 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200A ...

Example: An A/C unit has MOCP = 45A marked on the nameplate.

45A is a standard size → use a 45A HACR-rated breaker (or 45A fuse).

Using a 50A breaker would violate NEC 440.22(A) — it exceeds the MOCP.

Example 2: An A/C unit has MOCP = 55A on the nameplate.

55A is not a standard size. Round down to 50A.

(Do not round up to 60A — that would exceed the MOCP.)

HACR Breakers — 440.22(A)

The overcurrent protection device must be listed and identified for use with motor-compressors — meaning it must be HACR-rated (Heating, Air Conditioning, Refrigeration). HACR-rated breakers have a higher withstand rating for inrush current.

Standard breakers in residential panels are often HACR-rated and will say "HACR" on the breaker face. If the breaker is not marked HACR, it is not suitable for A/C equipment per NEC 440.22(A).

When MCA and MOCP Are Both on the Nameplate

If the nameplate shows both MCA and MOCP:

• Conductors: ampacity ≥ MCA
• OCPD: ≤ MOCP (and must be HACR-rated)

The MOCP will always be larger than the MCA — the overcurrent device must allow the compressor to start while the conductor only needs to handle running current.

Sizing Without a Nameplate — 440.22(B)

When no MCA or MOCP is marked (older equipment), the overcurrent protection must not exceed:

• 175% of the rated-load current for time-delay fuses
• 225% of the rated-load current for inverse-time circuit breakers

If these values don't allow the motor-compressor to start, you may increase to:

• 225% for time-delay fuses
• 250% for inverse-time circuit breakers

These are similar to the Article 430 motor protection percentages but specific to hermetic motor-compressors.

Disconnecting Means — 440.12 and 440.14

Disconnect Sizing — NEC 440.12

The disconnect for A/C or refrigerating equipment must be rated at least 115% of the nameplate rated-load current or the branch-circuit selection current, whichever is greater.

Disconnect rating ≥ RLA × 1.15

Select the next standard disconnect size at or above that minimum.

Example: A condensing unit has a nameplate RLA of 24A. What is the minimum disconnect rating?

Minimum = 24A × 1.15 = 27.6A

Standard disconnect sizes: 30A, 60A, 100A ...

Next standard size ≥ 27.6A → 30A disconnect ✓

Disconnect Location — NEC 440.14

The disconnect must be:

• Within sight of the equipment (visible and not more than 50 feet away)
• Readily accessible to the operator

If the disconnect cannot be located within sight (unusual installations), it must be capable of being locked in the open position and the location must be marked at the equipment.

The panel circuit breaker may serve as the disconnect if it is within sight of the equipment. For most rooftop units, a separate safety disconnect (fused or non-fused) is installed adjacent to the unit.

Disconnect Type — NEC 440.12(A)

The disconnect must be a motor-circuit switch rated in horsepower, a molded-case circuit breaker, or a molded-case switch. A standard non-fused safety disconnect switch (with proper ampere and HP rating) is the most common choice installed adjacent to A/C condensing units.

Multi-Motor Equipment — Typical HVAC System

A typical split-system A/C installation has:

• Compressor (hermetic, governed by Article 440)
• Condenser fan motor (open-type, governed by Article 430)
• Evaporator fan / air handler (open-type, governed by Article 430)

The nameplate MCA and MOCP account for all components when they are part of listed equipment. When components are separately installed and wired, you may need to calculate each circuit individually:

For the condensing unit (compressor + condenser fan):

• Use MCA and MOCP from the condensing unit nameplate

For the air handler (evaporator fan motor):

• Use Article 430 motor rules: conductors at 125% FLA, overcurrent per Table 430.52

The Article 430 / Article 440 Comparison

This comparison is heavily tested on master exams:

The key takeaway: Article 440 uses nameplate values (MCA and MOCP) rather than calculated percentages of FLA. The manufacturer does the calculation; you read the nameplate and apply it.

Worked Exam Problem — Complete A/C Circuit

Problem: A 240V, single-phase condensing unit has the following nameplate data:

• RLA: 18A
• LRA: 90A
• MCA: 22.5A
• MOCP: 40A

Size the (a) branch circuit conductors, (b) overcurrent protection device, and (c) disconnecting means.

Solution:

(a) Branch circuit conductors: Must have ampacity ≥ MCA = 22.5A

From Table 310.16 (75°C column): 10 AWG copper = 35A ≥ 22.5A ✓

Minimum conductors: 10 AWG copper THHN

(b) Overcurrent protection device: Must not exceed MOCP = 40A. Must be HACR-rated.

40A is a standard size.

Use: 40A HACR-rated circuit breaker

(c) Disconnecting means: Minimum rating = RLA × 1.15 = 18A × 1.15 = 20.7A

Next standard disconnect size ≥ 20.7A = 30A

The disconnect must be within sight of the condensing unit.

Use: 30A non-fused disconnect switch (within sight of unit)

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Common Exam Traps

MCA vs. RLA: The conductors are sized to MCA (always ≥ RLA × 125%), not directly to RLA. Do not size conductors at just 125% of RLA yourself — use the nameplate MCA.

MOCP rounding: If the MOCP is not a standard size, always round down. Rounding up would exceed the nameplate MOCP and violate 440.22(A).

HACR vs. standard breaker: The exam will often ask whether a standard breaker or a HACR breaker is required. For hermetic compressor circuits: HACR required.

Disconnect must be within sight: The disconnect must be visible and ≤50 feet from the equipment — not just "nearby." If locked open is acceptable for the exam scenario, the question will specify it.

Article 430 fan motor vs. Article 440 compressor: In questions about a split-system installation with separate air handler and condensing unit circuits, apply Article 430 to the fan motor and Article 440 to the compressor.

Overload protection: Hermetic motor-compressors use thermal protectors built into the equipment by the manufacturer (440.52) rather than external overload relays. This is different from Article 430 open motors.

Key Takeaways

• Article 440 covers hermetic motor-compressors in A/C and refrigerating equipment — the sealed motor/compressor combination
• Conductors must have ampacity ≥ MCA (from nameplate) — NEC 440.32
• OCPD must not exceed MOCP (from nameplate), must be HACR-rated — NEC 440.22
• If MOCP is not a standard size, round down to the next standard size
• Disconnect must be rated ≥ 115% × RLA and located within sight (≤50 ft) of the equipment — NEC 440.12 and 440.14
• Article 440 overrides Article 430 for hermetic compressors; open-type fan motors in the same system still follow Article 430
• The manufacturer calculates MCA and MOCP — you read the nameplate and apply it