8.4 Air-Conditioning & Refrigeration Equipment

8.4 Air-Conditioning & Refrigeration Equipment

Air-conditioning equipment contains motors, but hermetic refrigerant motor-compressors use Article 440's nameplate-driven method. The equipment label usually provides the fastest and safest route to the answer.

Read the nameplate first

Common markings include:

• RLA or rated-load current for the compressor,
• BCSC or branch-circuit selection current where provided,
• fan-motor full-load current,
• MCA or minimum circuit ampacity, and
• MOCP/MOP or maximum overcurrent protective-device rating.

For field selection, a listed combination unit's MCA and MOCP markings generally control conductor ampacity and maximum fuse/breaker selection when installed as directed. On a calculation question that supplies individual components, use Article 440 formulas.

Do not replace compressor current with an Article 430 horsepower-table current. Article 440 directs use of the rated-load current or branch-circuit selection current for its compressor calculations.

Nameplate decision hierarchy

Treat MCA and MOCP as different instructions. MCA is the minimum allowable circuit-conductor ampacity after all applicable installation limitations; MOCP is the upper limit for the listed fuse or circuit breaker, not a command to use that exact rating. For equipment marked “MCA 31A, MOCP 50A,” select conductors with at least 31A allowable ampacity and an allowed standard OCPD no larger than 50A. Do not automatically size the conductors for 50A, and do not exceed a fuse-only marking by substituting a circuit breaker.

Conductor sizing

For a single compressor, branch-circuit conductors generally need an ampacity of at least 125% of the compressor rated-load current or branch-circuit selection current. For multimotor/composite equipment, add the other motors and loads that can operate at the same time using the article's method.

Example: a condensing unit has a compressor RLA of 22A and an outdoor fan FLA of 2A, with no listed MCA supplied in the question.

$MCA=(22\times1.25)+2=29.5\text{ A}$

Select a conductor with at least 29.5A allowable ampacity after applying terminal, ambient, bundling, and wiring-method restrictions. If the equipment nameplate lists an MCA, do not recalculate a different lower value and ignore the marking.

Overcurrent protection and overload

The branch-circuit fuse or breaker protects against short circuits and ground faults. It may be permitted at a percentage well above the conductor ampacity so the compressor can start. Compressor overload protection is furnished separately by the equipment's inherent protector, relay, or other approved means.

When the nameplate gives a maximum fuse or circuit-breaker size, do not exceed it. If the label distinguishes “maximum fuse” from “maximum breaker,” use only the permitted device type. An oversized breaker is not justified merely because a compressor trips during a mechanical fault.

This is the same conceptual separation used for Article 430 motors: conductor overload protection and branch short-circuit/ground-fault protection perform different jobs.

Disconnecting means

The HVAC disconnect must be within sight from and readily accessible from the equipment. Article 100's within-sight definition includes visibility and a maximum distance. The disconnect must open all ungrounded conductors and have an adequate ampere and horsepower rating.

Do not mount the disconnect on a removable or access panel that must be opened to service the unit. The location cannot obstruct required working space or safe access. Where a breaker is relied on under an allowed lockable arrangement, apply the permanently installed locking provision rule.

Service receptacle and GFCI

The receptacle required for servicing heating, air-conditioning, and refrigeration equipment is a separate outlet. Locate it within the maximum distance stated in Article 210, on the same level, and do not supply it from the equipment's load-side disconnect. Apply current Wisconsin GFCI rules and the assigned NEC edition.

Outdoor receptacles require weather-resistant devices and covers suitable for the exposure and whether a plug remains inserted. The HVAC disconnect enclosure and fittings likewise need the correct wet-location rating.

Room air conditioners

A cord-and-plug-connected room air conditioner can use the attachment plug and receptacle as the disconnect when the specific conditions are met. Article 440 limits cord length and addresses branch-circuit loading. A room air conditioner is not simply treated as an arbitrary portable appliance.

Feeder and service load

For feeder/service calculations, use the HVAC load required by Article 220 and the equipment nameplate. Heating and cooling may be noncoincident, but add any loads that operate with both modes. Heat-pump auxiliary heat may operate with the compressor under some control schemes, so do not always drop one of them.

Exam workflow

Circle MCA and MOCP if the nameplate provides them. Otherwise list compressor current, other motors, and simultaneous loads; calculate conductor ampacity; then calculate or select the permitted OCPD separately. Finish with disconnect, receptacle, weatherproofing, and GFCI checks. This prevents the common error of sizing everything from one current value.