What does MCA mean on an air conditioner nameplate?

Minimum Circuit Ampacity. NEC 440.4(B) requires the equipment nameplate to state it, and it is the number the manufacturer already calculated: 125% of the largest motor-compressor's rated-load current plus the full current of every other load in the unit. The branch-circuit conductors must have an ampacity at least equal to MCA. You read it, you do not recalculate it.

What does MOCP mean on a condenser?

Maximum Overcurrent Protection. It is the largest breaker or fuse rating the manufacturer allows for the unit, also stated on the nameplate under 440.4(B). The overcurrent device you install may be that size or smaller, never larger. On a typical residential condenser it reads something like 'Max Fuse/Ckt Bkr 40'.

How do you size the wire for a condenser?

Pick a conductor from Table 310.16 with an ampacity at least equal to the nameplate MCA, using the termination temperature 110.14(C) allows. A nameplate MCA of 31 amps, for example, is satisfied by 10 AWG copper at the 75 C column (35 A) if the terminations permit 75 C. You do not multiply the compressor current by 125% yourself, because the manufacturer did that inside the MCA figure.

How do you size the breaker for a condenser?

Any standard rating up to and including the nameplate MOCP. If the nameplate says maximum 40 amps, a 40-amp breaker is permitted, and so is 35 or 30 if the unit starts on them. The breaker may be larger than the conductor's ampacity would normally allow because, like a motor circuit, it is protecting against short circuits and ground faults, and the unit's own overloads protect the compressor.

Can the breaker be bigger than the wire on an AC circuit?

Yes, within the nameplate MOCP, and this is the part that looks wrong to anyone trained on general branch circuits. A 10 AWG conductor behind a 40-amp breaker is a correct condenser circuit when the nameplate reads MCA 31 and MOCP 40. Article 440 follows the motor-circuit logic of Article 430: the conductor is sized for running current, the device is sized to let the compressor start.

Why does the exam love this question?

Because it rewards reading over calculating, and candidates who know the 125% rule from Article 430 try to apply it a second time. The two wrong answers in almost every version are the compressor RLA multiplied by 125% (the math the manufacturer already did) and a breaker sized to the wire instead of to the MOCP.

Article 440 · NEC 440.4(B) deep-dive

MCA vs MOCP: The Two Numbers on the Condenser Nameplate

Four in ten candidates miss our condenser question, and nearly all of them miss it the same way: they start calculating. The nameplate already did the math. MCA sizes the wire. MOCP sizes the breaker. Here is what each one means, where it comes from, and the worked example the exam keeps rewriting.

Last reviewed September 2026

Where the two numbers come from

Section 440.4(B) requires the nameplate on a unit with a hermetic motor-compressor to state both figures. The manufacturer computes MCA the way Article 440 says to: 125% of the largest compressor’s rated-load current plus 100% of the other loads, the fan motor and any heaters. MOCP is the largest device the unit is listed to start and run behind. Both numbers already account for the rules you would otherwise have to apply by hand.

Worked example: MCA 31, MOCP 40

A residential outdoor condenser nameplate reads Minimum Circuit Ampacity 31 A and Maximum Overcurrent Protection 40 A. Size the circuit.

Conductor: at least 31 A of ampacity. Table 310.16 at 75 C gives 10 AWG copper 35 A, which clears it if the terminations are rated 75 C. At 60 C terminations 10 AWG is 30 A and does not, so 8 AWG.
Overcurrent device: any standard rating at or below 40 A. A 40-amp breaker is the usual answer.
Equipment ground: Table 250.122 on the 40-amp device gives 10 AWG copper.
Disconnect: within sight of the unit and readily accessible (440.14), which is the second question that rides along.

Notice what did not happen. Nobody multiplied anything by 125%. The compressor RLA on the same nameplate was never used. Those are the two wrong-answer factories.

Where candidates lose the point

Multiplying the compressor RLA by 125% and sizing the wire from that. The manufacturer already did it; that is what MCA is.
Sizing the breaker to the wire. A 10 AWG conductor behind a 40-amp breaker is correct here, because the device is set by MOCP, not by the conductor.
Going above MOCP because the next standard size is more convenient. MOCP is a ceiling, not a target.
Reading the 60 C column when the terminations allow 75 C, or the reverse. 110.14(C) decides which column.
Forgetting the disconnect within sight. It is the follow-up question on the same scenario.

How it shows up on the exam

The question hands you a nameplate with MCA, MOCP and usually the compressor RLA as a decoy, then asks for the conductor, the device, or both. The entire skill is knowing which number answers which question. MCA answers the wire. MOCP answers the breaker. The RLA answers nothing on the branch-circuit side; it is there to tempt the 125% reflex.

Is Article 440 costing you points?

The free 15-minute diagnostic scores equipment and motor questions separately and shows you which rule families you would miss today.

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MCA vs MOCP: The Two Numbers on the Condenser Nameplate

Where the two numbers come from

Worked example: MCA 31, MOCP 40

Where candidates lose the point

How it shows up on the exam

Is Article 440 costing you points?

FLA vs FLC vs MCA

Motor breaker sizing (430.52)

Table 310.16 ampacity

Motor conductor sizing (430.22)