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Reading an Appliance Nameplate for Circuit Sizing

Reference ServiceDelivery Updated Oct 28, 2026 ยท Electrical

Why this matters

The nameplate is the one document on site that the inspector, the manufacturer and the code all agree is authoritative, because 110.3(B) makes the installation instructions and labeling part of the installation. Read it wrong and you either oversize the breaker past what protects the compressor, or undersize the wire against a figure that already had the motor's margin built in. This card reads two labels the way an electrician sizes from them: an air-conditioning condenser, which states its own minimum wire and maximum breaker, and a cooktop, which states power and leaves the amps to you. The condenser and water heater HowTos lean on this card rather than re-explaining it.

Two kinds of nameplate

Equipment that sizes its own circuit. Air-conditioning and refrigerating equipment with more than one motor, or a motor plus other loads, is required by 440.4(B), as adopted, to be marked with a minimum supply circuit conductor ampacity and a maximum rating of the branch-circuit short-circuit and ground-fault protective device. Those are the MCA and MOCP. The manufacturer has already done the motor arithmetic. Your job is to obey the two numbers.

Equipment that states its power. A cooktop, an oven, a water heater or a baseboard heater gives watts or kilowatts at a voltage, sometimes a recommended circuit, and leaves the conversion to the installer. Your job is the arithmetic, and knowing which rule then sizes the circuit.

Label one: the condenser

+------------------------------------------------+
| SPLIT SYSTEM HEAT PUMP - OUTDOOR SECTION       |
| VOLTS 208/230   PHASE 1   HZ 60                |
| VOLTAGE RANGE  MIN 187  MAX 253                |
| COMPRESSOR    RLA 14.1    LRA 77.0             |
| FAN MOTOR     FLA 1.2     HP 1/6              |
| MIN CIRCUIT AMPACITY            18.8           |
| MAX FUSE OR HACR TYPE BREAKER   30             |
| USE COPPER CONDUCTORS ONLY                     |
+------------------------------------------------+
WHAT IT SAYS TO THE ELECTRICIAN
  wire     ampacity at least 18.8 A, copper
           -> 12 AWG copper (20 A NM, 25 A THWN at 75 C)
  breaker  not more than 30 A, fuse or HACR breaker
           -> 2-pole 30 A HACR, or 25 A if preferred
  check    MCA = 1.25 x 14.1 + 1.2 = 17.6 + 1.2 = 18.8

Reading it line by line:

  • VOLTS 208/230 and the voltage range. The unit is rated for either a 208 V or a 240 V supply. The range line, where the manufacturer prints one, is the band it must stay inside while running. The figures on this mock are 10 percent below 208 V and 10 percent above 230 V; your unit's label or instructions state its own. A house at 240 V nominal is fine. A unit in a commercial building on a 208Y/120 V system is fine too, but measure under load: a 208 V supply sagging to 185 V with the compressor running is outside the band. That reading is taken live at the disconnect's line terminals, which is energized work: a CAT III or better meter and the PPE your shop's NFPA 70E program assigns for the task, with nobody else's hands in the enclosure.
  • RLA (rated-load amps) and LRA (locked-rotor amps). RLA is the compressor's running current at rated conditions; LRA is the current at the instant of start. Neither is a number you size wire to directly on this equipment, because the MCA already incorporates the RLA. LRA matters for the disconnect's horsepower-equivalent rating under 440.12 and for whether a breaker below the MOCP will hold through start.
  • MCA, minimum circuit ampacity: size the wire to it. The circuit conductors' ampacity must be at least 18.8 A (440.35, as adopted). The check line shows where the figure comes from in substance: 125 percent of the largest motor's RLA plus the other loads at 100 percent. Do not apply the 125 percent again; it is already in the MCA.
  • MOCP, maximum fuse or HACR breaker: never exceed it. 30 A is the ceiling for the branch-circuit protective device (440.22, as adopted). A smaller device is allowed as long as it carries the starting current without tripping; a 25 A breaker works on many units this size. A 35 A or 40 A breaker is a violation, whatever wire is installed, because the MOCP protects the equipment's internal wiring and compressor, not just the circuit conductors.
  • HACR. Heating, Air-Conditioning and Refrigeration: a listing on the breaker for use with this kind of equipment. Most current residential breakers carry the HACR marking; look for it on the breaker before you install. A label that reads "MAX FUSE" without "OR HACR BREAKER" calls for fuses, and 110.3(B) holds you to that: a fused disconnect with fuses at or under the marked size.
  • 12 AWG on a 30 A breaker. This is legal here and only here. 240.4(D) normally caps 12 AWG at 20 A, but 240.4(G) sends air-conditioning equipment to Article 440, which allows the protective device to be sized from the MOCP while the conductors are sized from the MCA. See related 'Branch Circuit Wire and Breaker Pairing Card'.
  • Copper only. The terminal lugs inside the unit are listed for copper. Aluminum on this unit violates the listing whatever its ampacity.

The installed circuit: 12 AWG copper (NM inside the house, THWN-2 in raceway from the change of wiring method through the outdoor disconnect and the liquidtight whip, since NM is not permitted in a wet location), a 2-pole 30 A HACR breaker, a disconnect within sight of the unit, and terminations torqued to the values marked on the breaker, the disconnect and the unit with a calibrated tool (110.14(D)). The disconnect and whip are their own HowTo: see related 'How to Wire an AC Condenser Disconnect and Whip'.

Label two: the cooktop

+------------------------------------------------+
| ELECTRIC COOKTOP     240 V OR 208 V   60 HZ    |
| RATED  9.0 KW AT 240 V     6.8 KW AT 208 V     |
| CONNECT TO A 40 A BRANCH CIRCUIT               |
+------------------------------------------------+

This label gives power, not amps. Convert, then size.

Watts to amps, single phase: amps equal watts divided by volts. 9,000 W divided by 240 V is 37.5 A.

Why the 208 V rating is lower. The heating elements are resistances. On a resistance, power goes with the square of voltage, so dropping from 240 V to 208 V cuts power by the ratio (208 / 240) squared, which is 0.867 squared, or 0.751. 9.0 kW times 0.751 is 6.76 kW, which the label rounds to 6.8. The current drops in proportion to the voltage, not its square: 37.5 A times 0.867 is 32.5 A, and as a check, 6,760 W divided by 208 V is also 32.5 A. Both routes agree.

Sizing the circuit. For a single counter-mounted cooking unit, the branch-circuit load is its nameplate rating (the notes to Table 220.55, as adopted). The label also names a 40 A circuit, and 110.3(B) makes that instruction binding. A cooktop is not a continuous load, so no 125 percent: 37.5 A fits under a 40 A breaker, and 8 AWG copper NM carries 40 A from the 60 C column. At 208 V the same 40 A circuit is used; the label asks for it and the current only falls.

What the customer hears at 208 V. In an apartment or condo fed from a 208Y/120 V system, this cooktop delivers about three quarters of its 240 V heat (6.8 kW against 9.0 kW is 75.6 percent). Boil times get longer. That is not a wiring fault, and the customer should hear it from you at the walkthrough rather than as a callback.

The same conversion on a water heater element

A 4,500 W element rated at 240 V, installed on 208 V: power times 0.751 is about 3,380 W, current times 0.867 is 16.25 A (18.75 A at 240 V times 0.867). The tank recovers at about three quarters of its 240 V rate. Many water heaters ship with element options for 208 V; the label tells you which is installed. The circuit sizing, at 125 percent because 422.13 makes it continuous, belongs to 'Continuous Load and the 125 Percent Rule'.

Three-phase and motors: when the nameplate is not the number

  • Three-phase watts to amps: amps equal watts divided by (volts times 1.732). A 15 kW, 208 V three-phase heater draws 15,000 divided by (208 times 1.732), or 15,000 divided by 360.3, which is 41.6 A.
  • A plain motor, not inside AC equipment. For general motor applications, 430.6(A)(1), as adopted, sizes conductors and protection from the full-load current tables in Article 430, not from the motor's nameplate amps. The nameplate is used for the motor's overload protection. A pool pump or a well pump is the common case; see related 'How to Wire a Pool Pump Motor Circuit'.
  • Equipment with an MCA. If the label gives an MCA, use it. Do not rebuild it from the motor tables.

Where readings go wrong

  • Breaker sized to the wire instead of the label. The electrician pulls 8 AWG to a condenser for future capacity and puts a 40 A breaker on it "because the wire can take it." The label says 30 A maximum; the 40 A breaker voids the protection the MOCP exists for.
  • Wire sized to the MOCP. 10 AWG on the 30 A condenser circuit above is legal and wasted copper. The MCA is the wire number.
  • The 125 percent applied twice. 18.8 A times 1.25 is 23.5 A, which pushes some electricians to 10 AWG. The MCA already contains the factor.
  • kW read at the wrong voltage. A cooktop label showing two ratings: reading the 208 V kW and dividing by 240 V gives 28.3 A and a 30 A circuit the label does not permit.
  • The label behind the unit. Condenser labels fade and cooktop labels sit under the unit or in the installation manual. If you cannot read it, get the model number and the manufacturer's data sheet before you size; guessing an MCA is how a 25 A breaker ends up on a unit whose MOCP is 20.

References

  • NFPA 70, National Electrical Code, 2023 edition as adopted by your jurisdiction: 110.3(B), 110.14(D), Table 220.55 and its notes, 240.4(D), 240.4(G), 422.13, 430.6(A)(1), 440.4(B), 440.12, 440.22, 440.35
  • Manufacturer's installation instructions and nameplate for the equipment installed
  • See related: Branch Circuit Wire and Breaker Pairing Card; Continuous Load and the 125 Percent Rule
  • See related: How to Wire an AC Condenser Disconnect and Whip; How to Wire an Electric Water Heater Circuit

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