Air conditioners, heat pumps, and refrigeration equipment look like they should follow the same motor-sizing rules as any other electric motor, but they don't -- and that difference is exactly why NEC Article 440 exists as its own article instead of just being folded into Article 430's general motor rules. The reason comes down to one physical fact: the compressor motor inside a typical AC or refrigeration unit is a hermetic refrigerant motor-compressor, meaning the motor windings are sealed inside the same welded steel shell as the compressor mechanism, bathed directly in refrigerant and oil. You can't open it up, you can't measure its locked-rotor current with a clamp meter the way you can with an open drip-proof motor, and its electrical characteristics are affected by refrigerant pressure and temperature in ways an ordinary motor never sees. Article 440 exists to handle exactly that gap, and this article walks through the nameplate terminology, the sizing math, the disconnect and controller rules, and five worked examples so the logic makes sense instead of feeling like an arbitrary set of extra percentages layered on top of Article 430.
Why Hermetic Compressors Need Their Own Article
With an ordinary open motor, you can size everything from motor nameplate full-load current (FLC) and locked-rotor current (LRC), both of which are measurable, testable, standardized values published in NEC tables for common motor types. A hermetic compressor is different: because the motor is sealed inside the refrigerant circuit, its running current changes with refrigerant pressure, and its locked-rotor current can't be reliably standardized the same way an open motor's can. So instead of relying on NEC-published FLC tables, Article 440 requires the manufacturer to test and mark specific current values directly on the equipment nameplate, and the electrician's job becomes reading those marked values correctly and applying Article 440's percentage rules to them -- rather than looking anything up in a table the way you would for a standard motor under Article 430.
Nameplate Terms You Need to Know
Before any of the sizing math makes sense, you need to be fluent in the handful of terms that show up on every air-conditioning and refrigeration equipment nameplate:
- Rated-Load Current (RLC), also called Rated-Load Amps (RLA): the nameplate-marked running current of the compressor motor under rated load conditions -- this is the hermetic-compressor equivalent of an open motor's full-load current (FLC), except it's a manufacturer-tested marked value rather than a table lookup.
- Branch-Circuit Selection Current (BCSC): some manufacturers mark a BCSC value instead of, or in addition to, RLA. When BCSC is marked, it takes precedence over RLA for branch-circuit sizing calculations -- it's typically equal to or slightly higher than RLA and represents the current the manufacturer wants used specifically for circuit and overcurrent device sizing.
- Locked-Rotor Current (LRA): the current the compressor motor draws in the instant it starts, before it comes up to running speed -- typically several times higher than RLA. This spike is what makes controller and overcurrent device selection tricky, because a device sized only for running current would trip or fail every time the compressor starts.
- Minimum Circuit Ampacity (MCA): a single marked value, required on equipment with more than one motor (like a condensing unit with a compressor plus a condenser fan motor) or other combination loads, that tells the installer the minimum ampacity the branch-circuit conductors must have. The manufacturer has already done the 125%-of-largest-plus-100%-of-others calculation for you -- MCA is the answer, not a value you calculate yourself.
- Maximum Overcurrent Protection (MOCP), sometimes labeled "Max Fuse" or "Max HACR Breaker": the largest fuse or breaker size the manufacturer allows for the branch-circuit, already calculated to satisfy Article 440's short-circuit and ground-fault protection rules for that specific equipment.
The practical takeaway that surprises a lot of apprentices: for combination-load equipment (which is most modern packaged AC units, heat pumps, and condensing units), you are not expected to derive branch-circuit ampacity and overcurrent sizing from scratch using RLA and LRA. The manufacturer has already run that math and stamped MCA and MOCP directly on the nameplate. Your job is to read those two marked numbers correctly and size the conductors and breaker/fuse accordingly. The RLA/LRA-based calculation method below still matters -- both for single-motor-compressor equipment where MCA/MOCP might not be marked, and because you need to understand where MCA and MOCP numbers come from to answer exam questions and to sanity-check a nameplate that looks wrong.
Sizing Branch-Circuit Conductors
For a single hermetic compressor motor circuit (no other motors sharing the branch circuit), the conductor ampacity must be at least 125% of the rated-load current, or of the branch-circuit selection current if one is marked in place of RLA. This mirrors the same 125%-of-full-load-current logic used for ordinary continuous motor loads under Article 430 -- the extra 25% headroom exists for the same underlying reason: continuous-duty equipment needs conductor capacity above its steady running current.
For equipment with multiple motors or combination loads sharing one branch circuit -- the far more common real-world case -- the calculation is: 125% of the largest motor's rated-load current, plus the sum of the rated-load currents of all other motors and loads on that same circuit. But as noted above, on listed multimotor/combination-load equipment, the manufacturer is required to mark the MCA value directly on the nameplate, which is that exact calculation already performed for you.
Overcurrent Protection: Why It's Sized So Much Higher Than Running Current
This is the part of Article 440 that trips people up the most, because the overcurrent device ends up sized well above what looks like it should be needed for a device only drawing its RLA current during normal operation. The reason is locked-rotor current: a hermetic compressor can draw five, six, or more times its RLA for the brief moment it starts, and a fuse or breaker sized tightly to running current would trip on every single start cycle. Article 440 addresses this with percentage-based maximum overcurrent protection sizing referenced off the rated-load current (commonly cited figures run up to roughly 175% for many single-motor-compressor circuits, with an allowance to go higher, commonly cited around 225%, when the initial percentage value doesn't correspond to a standard fuse/breaker size and the equipment still won't start reliably) -- always confirm the exact current percentages and standard-size rounding rules against your code book, since this is one of the more detailed, table-driven parts of Article 440. In practice, for combination-load equipment, this entire calculation is again already done for you and marked as MOCP directly on the nameplate, which is the number you actually use in the field.
Disconnecting Means
Air-conditioning and refrigeration equipment requires a disconnecting means capable of disconnecting the equipment from all ungrounded conductors, and that disconnect generally must be located within sight of the equipment -- a commonly cited maximum sight-line distance is 50 feet -- unless a listed lockable disconnecting means is provided per the equipment-specific exception that allows the disconnect to be located elsewhere as long as it can be locked in the open position. The disconnect itself must be rated for at least 115% of the equipment's nameplate rated-load current or branch-circuit selection current (whichever applies), which gives a small margin above running current, distinct from the much larger margin built into overcurrent protection sizing for the locked-rotor starting spike.
Controllers Must Handle Locked-Rotor Current, Not Just Running Current
A "controller" in this context means the switching device -- a contactor, for example -- that actually starts and stops the compressor motor during normal operation, as distinct from the disconnecting means used for service and shutdown. Because the compressor draws locked-rotor current every time it starts, the controller has to be rated to interrupt that locked-rotor current, not merely the steady-state running current. A contactor sized only for RLA-level current would be a rapid failure point, arcing and pitting its contacts every single start cycle until it eventually fails. This is one of the most commonly tested distinctions in this article: running-current-only sizing is fine for some components (like conductor ampacity, which only needs 125% headroom above RLA), but is explicitly not fine for the controller, which has to be selected against the much higher locked-rotor figure.
Five Worked Examples
Example 1 — Reading MCA and MOCP Off a Combination-Load Nameplate
Problem: A packaged rooftop AC unit's nameplate reads: "MCA: 28.0A, Max Fuse/HACR Breaker (MOCP): 40A." What branch-circuit conductor size and breaker size does an electrician actually need to select?
Step 1 — Conductor sizing: Select conductors with an ampacity of at least 28.0A (the marked MCA) after accounting for any applicable temperature and conductor-count adjustments, the same way you would for any other branch circuit.
Step 2 — Overcurrent device sizing: Select a breaker or fuse no larger than 40A (the marked MOCP). A smaller standard size is permitted as long as it's not so small that it fails to handle the compressor's locked-rotor starting current — but 40A is the ceiling, not a target to hit exactly.
Result: 28A-rated conductors, up to a 40A breaker or fuse. No RLA/LRA math is needed here — MCA and MOCP are already the manufacturer's finished answers to those calculations.
Example 2 — Single Compressor Circuit, Sizing From RLA
Problem: A single hermetic compressor (no other motors on the same branch circuit) has a nameplate RLA of 18A and no marked BCSC. What's the minimum branch-circuit conductor ampacity?
Step 1: Since no BCSC is marked, use RLA. Minimum conductor ampacity = 125% × 18A = 22.5A.
Result: Conductors must have an ampacity of at least 22.5A — round up to the next standard conductor size that meets or exceeds this, following the same conductor-selection process used for any other branch circuit.
Example 3 — When BCSC Is Marked Instead of RLA
Problem: A compressor nameplate shows RLA of 16A and a marked Branch-Circuit Selection Current (BCSC) of 19A. Which figure governs the branch-circuit conductor calculation?
Answer: BCSC governs whenever it's marked — it takes precedence over RLA for this purpose. Minimum conductor ampacity = 125% × 19A = 23.75A, not 125% × 16A.
Result: Using RLA instead of the marked BCSC here would undersize the conductors — a classic exam trap, and a real-world mistake if someone skims a nameplate too quickly.
Example 4 — Condensing Unit With Compressor Plus Condenser Fan (No Marked MCA)
Problem: An older condensing unit has two motors on one branch circuit and, unusually, no MCA is marked on a worn nameplate: a compressor with RLA of 20A, and a condenser fan motor with FLA of 3A. What's the minimum conductor ampacity, calculated manually?
Step 1 — 125% of the largest motor load: 125% × 20A = 25A
Step 2 — Add the other motor's full running current: 25A + 3A = 28A
Result: Minimum conductor ampacity is 28A. This is exactly the calculation a manufacturer performs to arrive at a marked MCA value — walking through it manually here is what makes the marked MCA number on a normal, legible nameplate make sense instead of feeling like a mystery figure.
Example 5 — Disconnect Rating and Sight-Distance Check
Problem: The condensing unit from Example 4 (compressor RLA 20A, no BCSC marked) needs a disconnecting means. What minimum ampere rating does the disconnect need, and where can it be installed?
Step 1 — Minimum disconnect rating: 115% × 20A = 23A. Select a disconnect rated at least 23A (commonly the next standard disconnect size).
Step 2 — Location: The disconnect generally needs to be within sight of the equipment (commonly cited as within 50 feet), unless a listed lockable disconnecting means is used, which permits an alternate location as long as it can be locked in the open position.
Result: A disconnect rated for at least 23A, installed within sight of the unit (or a lockable alternative if sight-line placement isn't practical). Notice this 115% figure is meaningfully smaller than the 125%/175%+ figures used for conductors and overcurrent protection — the disconnect only needs modest headroom above running current, since it isn't expected to routinely interrupt locked-rotor starting current the way a controller is.
Room Air Conditioners: A Relaxed Subset of Rules
Article 440 Part VII carves out specific, somewhat relaxed provisions for room air conditioners -- the individual, typically cord-and-plug-connected units installed in a window or through-the-wall sleeve, as opposed to central/split-system equipment. Because these units are factory-assembled, listed appliances typically plugged into an existing receptacle rather than hard-wired into a dedicated new circuit, some of the disconnect and hard-wired-circuit provisions elsewhere in Article 440 don't apply the same way -- the attachment plug and receptacle can serve as the disconnecting means under specified conditions. Room air conditioners are also commonly cross-referenced with the ground-fault circuit-interrupter (GFCI) requirements found in Article 210 for 125-volt, 15- and 20-ampere receptacles in certain locations -- always confirm the current GFCI requirement scope for room AC receptacle circuits against your code book, since receptacle GFCI requirements have expanded across recent code cycles and this is an area worth double-checking rather than assuming from memory.
Common Mistakes
How This Connects to Article 430 and Basic Circuit Theory
Article 440 borrows its underlying logic directly from Article 430's general motor circuit rules -- percentage-above-running-current for conductors, a larger allowance for overcurrent protection to survive a high starting current, and a disconnecting means sized with modest headroom above running current. If you want a refresher on how that general motor-sizing logic works when you're not dealing with a sealed hermetic compressor, see our companion article on motor circuits under NEC Article 430. And because every one of these percentage calculations is, underneath it all, still just current, voltage, and resistance interacting under load, our Ohm's Law and basic circuit theory article is worth reviewing if the "why" behind starting-current spikes on any motor, hermetic or open, isn't fully clicking yet.
Frequently Asked Questions
What's the difference between RLA and FLA?
RLA (rated-load amps) is the term Article 440 uses specifically for the nameplate-marked running current of a hermetic refrigerant motor-compressor. FLA (full-load amps) is the more general term used elsewhere in the NEC (including Article 430) for ordinary motors. They serve the same functional role — the expected running current used as the basis for the 125% conductor-sizing calculation — just under different article-specific terminology.
If a nameplate shows both MCA and individual RLA/FLA figures, which do I use?
Use the marked MCA for branch-circuit conductor sizing — it's the manufacturer's already-completed combination-load calculation. The individual RLA/FLA figures are still useful for other purposes (like understanding what's inside the unit or troubleshooting), but MCA is the number the installer sizes conductors from.
Why does the maximum overcurrent protection allowed seem so much larger than the wire ampacity?
Because the overcurrent device has to survive the compressor's locked-rotor starting current every time it starts, while the conductor only needs headroom above steady running current. That's why MOCP is calculated using much larger percentage multipliers (and can end up rated well above the conductor's own ampacity) than the 125% figure used for conductor sizing.
Does Article 440 apply to heat pumps the same way it applies to air conditioners?
Yes — a heat pump's compressor is the same category of hermetic refrigerant motor-compressor Article 440 is written around, whether the unit is running in cooling mode or heating mode. The nameplate terminology (RLA, MCA, MOCP, etc.) and sizing rules apply the same way.
Can I use a standard motor-rated switch as the disconnecting means instead of a listed AC/refrigeration disconnect?
The disconnecting means needs to be suitable for the application and properly rated for the equipment's marked current, but the specific product-listing requirements can vary by installation. Always confirm the disconnect type is listed and appropriate for the specific equipment and installation conditions against your code book rather than assuming any general-purpose switch is automatically acceptable.
Do room air conditioners need a dedicated disconnect switch like central AC does?
Not necessarily — Part VII's relaxed provisions allow the attachment plug and receptacle to serve as the disconnecting means for a cord-and-plug-connected room air conditioner under specified conditions, rather than requiring a separate hard-wired disconnect switch the way central/split-system equipment does.
Key Terms
- Hermetic refrigerant motor-compressor: A motor and compressor welded together inside one sealed shell, running bathed in refrigerant and oil with nothing poking through the housing to the outside — the defining equipment type Article 440 is written around.
- Rated-Load Current (RLA): The nameplate-marked running current of a hermetic compressor motor, used as the basis for the 125% branch-circuit conductor calculation when BCSC isn't marked.
- Branch-Circuit Selection Current (BCSC): A manufacturer-marked current value that takes precedence over RLA for branch-circuit and overcurrent sizing when present on the nameplate.
- Locked-Rotor Current (LRA): The high current a compressor motor draws momentarily at start-up, before reaching running speed — the reason overcurrent devices and controllers need much more headroom than a simple running-current calculation would suggest.
- Minimum Circuit Ampacity (MCA): A manufacturer-marked value on multimotor/combination-load equipment giving the minimum required branch-circuit conductor ampacity, already calculated from the equipment's individual motor and load currents.
- Maximum Overcurrent Protection (MOCP): A manufacturer-marked value giving the largest fuse or breaker size permitted for the branch circuit, already calculated to accommodate the equipment's locked-rotor starting current.
Article 440 sits right at the intersection of electrical theory and HVAC/refrigeration equipment, so it pairs naturally with both sides of that world. Continue building your electrical foundation with our motor circuits (NEC 430) and Ohm's Law articles, or build your refrigerant-handling knowledge with our EPA 608 certification guide. Then put it into practice with our HVAC basic electrical practice test, HVAC air conditioning practice test, and HVAC heat pump practice test. You can also browse our full HVAC practice test and NEC code categories.
This article is a study aid meant to help you understand the concepts and practice the math behind NEC Article 440. It is not a substitute for the official NEC and any state or local amendments that apply in your jurisdiction. Always verify exact table values, percentages, and requirements against the current adopted code edition, the equipment nameplate, and your local authority having jurisdiction before performing real electrical work.