Conductor ampacity and equipment rating for hermetic compressors
NEC 440.6(A) Size conductors, disconnects, controllers, and overload protection off the nameplate rated-load current — or the branch-circuit selection current if the nameplate shows one.
Q1 NEC 440.6(A)
A hermetic refrigerant motor-compressor's equipment nameplate lists a branch-circuit selection current. Which of the following is sized using the rated-load current instead of the selection current?
- A The disconnecting means
- B The branch-circuit short-circuit and ground-fault protection
- C The branch-circuit conductors
- D The separate motor overload protection
Show answer & explanation
Correct: D — The separate motor overload protection
Per 440.6(A), where a branch-circuit selection current is marked, it replaces rated-load current for the disconnect, branch-circuit conductors, controller, and short-circuit/ground-fault protection — but not for separate motor overload protection, which stays based on rated-load current.
Multimotor/combination-load equipment nameplate requirements
NEC 440.4(B) Multimotor and combination-load equipment's nameplate must show a minimum supply ampacity (Part IV) and a maximum protective device rating (Part III), with narrow exceptions for single-circuit loads, room ACs, dwellings, and cord-and-plug gear.
Q2 NEC 440.4(B) Code lookup
A packaged rooftop HVAC unit contains multiple compressor motors and a condenser fan motor that can all operate simultaneously. The installing electrician needs to size the supply conductors and set the max branch-circuit protective device from the unit's nameplate. Which section requires the nameplate to list minimum supply circuit conductor ampacity and the maximum branch-circuit short-circuit and ground-fault protective device rating for this multimotor equipment?
- A 440.4(A)
- B 440.6(B)
- C 440.4(B)
- D 440.12(B)
Show answer & explanation
Correct: C — 440.4(B)
440.4(B) is the nameplate-marking rule for multimotor and combination-load equipment, requiring the maker's name, voltage/phase rating, minimum supply conductor ampacity, and max protective device rating. 440.4(A) instead covers the nameplate for a single hermetic refrigerant motor-compressor, and 440.6(B) addresses how the ampacity itself is determined rather than the nameplate marking requirement.
Sizing short-circuit/ground-fault protection for a single motor-compressor
NEC 440.22(A) Size the branch-circuit protective device at 175% of rated-load or branch-circuit selection current (whichever is greater), bump to the next standard size if needed, up to 225% if starting current demands it — never below 15 A.
Q3 NEC 440.22(A)
Under 440.22(A), what is the maximum percentage a motor-compressor's branch-circuit short-circuit and ground-fault protective device may be increased to if the 175% rating is not sufficient to carry the starting current?
- A 225 percent of the motor rated-load current or branch-circuit selection current, whichever is greater
- B 200 percent of the motor rated-load current or branch-circuit selection current, whichever is greater
- C 175 percent of the motor rated-load current only, with no further increase permitted
- D 250 percent of the motor rated-load current, matching typical inverse-time breaker sizing for other motor types
Show answer & explanation
Correct: A — 225 percent of the motor rated-load current or branch-circuit selection current, whichever is greater
440.22(A) allows the rating or setting to be increased beyond 175% when needed for starting current, but caps it at 225% of the motor rated-load current or branch-circuit selection current, whichever is greater. 200% and 250% are not the figures given in this section, and the rule explicitly permits an increase beyond 175% when justified.
Air-Conditioning Conductor Sizing (NEC 440.32)
NEC 440.32 Size the branch-circuit conductors for a single motor-compressor at 125% of the rated-load current (RLC) or the branch-circuit selection current (BCSC), whichever is greater (440.6, 440.32).
Q4 NEC 440.32
An air conditioner has a rated-load current of 24 A and a branch-circuit selection current of 28 A. What minimum branch-circuit conductor ampacity does NEC 440.32 require?
- A 28 A
- B 35 A
- C 30 A
- D 42 A
Show answer & explanation
Correct: B — 35 A
Per 440.6, use the greater value (28 A), and 440.32 requires 125%: 1.25 × 28 = 35 A. Distractors size from the RLC only, skip the 125%, or use the smaller value.
Sizing a disconnect for combined/multiple loads
NEC 440.12(B) When one disconnect serves multiple motor-compressors or motors/loads that can run at the same time, treat the sum as one giant motor: add full-load currents, add locked-rotor currents, then rate the switch at 115% of the combined full-load current.
Q5 NEC 440.12(B)
A single disconnecting means supplies a hermetic refrigerant motor-compressor and a separate fan motor that can operate at the same time. Per 440.12(B), how is the combined load treated?
- A Each motor gets its own disconnect rating and the larger value governs
- B The fan motor is ignored because it is not a hermetic refrigerant motor-compressor
- C As a single equivalent motor, using summed rated-load and summed locked-rotor currents
- D Only the hermetic compressor's rated-load current sets the disconnect rating
Show answer & explanation
Correct: C — As a single equivalent motor, using summed rated-load and summed locked-rotor currents
Under 440.12(B) and 440.12(B)(1), when loads may operate simultaneously on one disconnect, the combined rated-load current and combined locked-rotor current are treated as a single motor for sizing purposes — the fan motor's current is added in, not ignored or handled separately.
Overload protection methods for motor-compressors
NEC 440.52(A) Every motor-compressor needs overload and failure-to-start protection through one of four approved methods: separate relay, integral thermal protector, fuse/breaker, or protective system.
Q6 NEC 440.52(A)
Under 440.52(A), which of the following is NOT one of the approved means of protecting a motor-compressor against overload and failure to start?
- A An approved protective system furnished or specified for that motor-compressor
- B A general-purpose branch-circuit breaker with no time delay sized at 250% of rated-load current
- C A separate overload relay responsive to motor-compressor current
- D A thermal protector integral with the motor-compressor
Show answer & explanation
Correct: B — A general-purpose branch-circuit breaker with no time delay sized at 250% of rated-load current
440.52(A) lists exactly four approved means: a separate overload relay, an integral thermal protector, a fuse or inverse time circuit breaker rated at not more than 125% of rated-load current, or an approved protective system. A general-purpose breaker with no time delay sized at 250% matches none of these — it's neither an inverse time breaker at the correct rating nor any other listed option.
Sizing branch circuits for cord-and-plug room air conditioners
NEC 440.62 A cord-and-plug room AC counts as a single motor unit if it meets four conditions, then the branch circuit is sized by an 80% or 50% cap depending on what else it feeds.
Q7 NEC 440.62
Which requirement is NOT one of the four conditions for treating a room air conditioner as a single motor unit under 440.62(A)?
- A It is cord- and attachment-plug-connected
- B Its rating does not exceed 40 amperes and 250 volts, single phase
- C Total rated-load current is shown on the nameplate rather than individual motor currents
- D It is listed for use only in dwelling units
Show answer & explanation
Correct: D — It is listed for use only in dwelling units
440.62(A) lists four conditions: cord-and-plug connection, a 40 A/250 V single-phase rating cap, nameplate total rated-load current, and a protective device rating that doesn't exceed conductor ampacity or receptacle rating. There is no dwelling-unit-only listing requirement.
Hermetic motor-compressor nameplate marking
NEC 440.4(A) The nameplate's rated-load current — not motor horsepower tables — is what sizes conductors and protection for a hermetic refrigerant motor-compressor.
Q8 NEC 440.4(A)
A single-phase hermetic motor-compressor has a rated-load current of 7 amperes at 115 volts. Per 440.4(A), is locked-rotor current marking required on the nameplate?
- A Yes, because 7 A exceeds the 4.5 A threshold that applies at 115 volts
- B No, because locked-rotor current marking only applies to polyphase equipment
- C No, because 7 A is below the 9 A threshold for 115-volt single-phase units
- D Yes, because all single-phase motor-compressors require locked-rotor current marking
Show answer & explanation
Correct: C — No, because 7 A is below the 9 A threshold for 115-volt single-phase units
440.4(A) only requires locked-rotor current marking for single-phase motor-compressors with rated-load current over 9 A at 115 V (or over 4.5 A at 230 V). At 7 A, this unit falls under the threshold, so marking isn't mandated. The 4.5 A figure applies at 230 V, not 115 V, and polyphase units are a separate always-required category, not the only one.
Determining the highest rated (largest) motor
NEC 440.7 The largest motor in a group is the one with the highest rated-load current (or branch-circuit selection current, if marked) — not the one with the highest horsepower or nameplate amps.
Q9 NEC 440.7
When applying 440.7 to identify the 'highest rated (largest) motor' in a group for use with 430.24, which criterion governs?
- A The motor with the highest rated-load current
- B The motor with the highest locked-rotor current
- C The motor with the largest physical frame size
- D The motor with the highest nameplate horsepower
Show answer & explanation
Correct: A — The motor with the highest rated-load current
Section 440.7 defines the highest rated (largest) motor as the one with the highest rated-load current. Horsepower, frame size, and locked-rotor current are related motor characteristics but are not the deciding factor under this section.
Sizing protection for equipment with multiple compressors or mixed loads
NEC 440.22(B) When equipment has more than one compressor or a compressor plus other loads, whether the compressor is the largest load on the circuit decides which sizing formula applies.
Q10 NEC 440.22(B) Code lookup
A packaged rooftop unit has two hermetic refrigerant motor-compressors on the same branch circuit, with a third smaller motor also supplied. The largest connected load is a hermetic motor-compressor. Which section gives the maximum rating or setting for the branch-circuit short-circuit and ground-fault protective device in this case?
- A 440.22(B)(1)
- B 440.12(B)
- C 440.22(A)
- D 440.22(B)(2)
Show answer & explanation
Correct: A — 440.22(B)(1)
440.22(B)(1) governs sizing when a hermetic motor-compressor is the largest of multiple loads on the circuit: 440.22(A) value for the largest compressor plus the other loads' currents. 440.22(B)(2) applies instead when the motor-compressor is NOT the largest load, and 440.22(A) only covers a single motor-compressor with no other loads.
Short-circuit current rating for motor controllers
NEC 440.10 A motor controller or industrial control panel can't be installed where available fault current exceeds its marked short-circuit current rating, and that fault-current figure must be documented on site.
Q11 NEC 440.10
An industrial control panel for combination-load equipment is marked with a short-circuit current rating (SCCR) of 25,000 A. Site calculations show 30,000 A of available fault current. What does 440.10(A) require?
- A The panel may be installed if a licensed engineer signs off on the discrepancy
- B The panel must not be installed at this location
- C The panel may be installed as long as it is fed from an individual branch circuit
- D The panel may be installed if upstream overcurrent protection is increased
Show answer & explanation
Correct: B — The panel must not be installed at this location
Per 440.10(A), motor controllers or industrial control panels of multimotor and combination-load equipment shall not be installed where available fault current exceeds the marked SCCR. There is no engineering sign-off, individual-branch-circuit, or upstream-protection exception in this section — the marked rating is the limit.
Disconnect location and sight/accessibility rules
NEC 440.14 The AC/refrigeration disconnect must be within sight and readily accessible from the equipment, with narrow exceptions for locked industrial disconnects and cord-and-plug connections.
Q12 NEC 440.14
A technician wants to mount the disconnecting means for a rooftop condensing unit on a nearby electrical panel. Under what condition is this NOT permitted?
- A If the panel is outdoors rather than indoors
- B If the panel is more than 10 ft from the equipment
- C If the panel is designed to allow access to the air-conditioning or refrigeration equipment
- D If the panel serves other branch circuits in the building
Show answer & explanation
Correct: C — If the panel is designed to allow access to the air-conditioning or refrigeration equipment
440.14 specifically prohibits locating the disconnect on panels designed to allow access to the A/C or refrigeration equipment, or where it would obscure the equipment nameplate. Distance, other loads on the panel, and indoor/outdoor placement aren't the disqualifying factors under this section.
Disconnect compliance in series and high-horsepower (>100 hp) exception
NEC 440.12(D) Every disconnecting means in a compressor circuit must meet 440.12 sizing, except when the calculated load would need a disconnect over 100 hp — then 430.109(E) takes over.
Q13 NEC 440.12(D)
A refrigerant motor-compressor circuit has three separate disconnecting means in series between the feeder and the compressor. Per 440.12(D), which of these must meet the sizing requirements of 440.12?
- A All three disconnecting means
- B Only the disconnect closest to the compressor
- C Only whichever disconnect the installer marks as the primary means
- D Only the disconnect closest to the feeder
Show answer & explanation
Correct: A — All three disconnecting means
440.12(D) requires every disconnecting means between the point of attachment to the feeder and the point of connection to the compressor to comply with 440.12 — sizing isn't limited to a single 'main' disconnect in the chain.
Sizing a disconnect for a single hermetic motor-compressor
NEC 440.12(A) Size the disconnect at 115% of the nameplate rated-load current or branch-circuit selection current, whichever is greater — unless you're using a listed unfused motor circuit switch matched by equivalent horsepower.
Q14 NEC 440.12(A)
Per 440.12(A)(1), the ampere rating of a disconnecting means for a hermetic refrigerant motor-compressor must be at least what percentage of the applicable current?
- A 125 percent of the nameplate rated-load current, always
- B 115 percent of the nameplate rated-load current or branch-circuit selection current, whichever is greater
- C 115 percent of the locked-rotor current
- D 100 percent of the locked-rotor current
Show answer & explanation
Correct: B — 115 percent of the nameplate rated-load current or branch-circuit selection current, whichever is greater
440.12(A)(1) sets the ampere rating at 115% of the nameplate rated-load current or branch-circuit selection current, whichever is greater. The 125%-of-rated-load option and the locked-rotor-based options are confusions with other motor-circuit sizing rules, not what 440.12(A)(1) specifies.
Overload protection and plug ratings for cord-and-plug-connected equipment
NEC 440.55 Cord-and-plug motor-compressors on 15/20 A branch circuits need identified overload protection, a plug/receptacle rated no more than 20 A/125 V or 15 A/250 V, and a branch-circuit protective device with enough time delay to let the motor start.
Q15 NEC 440.55
A cord-and-attachment-plug-connected motor-compressor is installed on a 20-ampere, 120-volt branch circuit. What is the maximum permitted rating of the attachment plug and receptacle at 125 volts?
- A 20 amperes
- B 15 amperes
- C 25 amperes
- D 30 amperes
Show answer & explanation
Correct: A — 20 amperes
440.55(B) caps the attachment plug and receptacle (or cord connector) rating at 20 amperes at 125 volts (or 15 amperes at 250 volts). The 15-ampere option is the correct cap only for the 250-volt case, not 125 volts, and 25 and 30 amperes both exceed what 440.55(B) allows.
Overload protection for motor-compressor controller and branch-circuit conductors
NEC 440.52(B) The controller, disconnect, and branch-circuit conductors for a motor-compressor share the same overload protection as the motor-compressor itself — one device, one job.
Q16 NEC 440.52(B) Code lookup
A single-phase, hermetic refrigerant motor-compressor and its associated equipment are supplied by a 20-ampere branch circuit and are not cord- and attachment-plug-connected. Which section governs overload protection of the motor-compressor and equipment in this installation?
- A 440.52(B)
- B 440.53
- C 440.55
- D 440.54
Show answer & explanation
Correct: D — 440.54
440.54 specifically covers overload protection for motor-compressors and equipment on 15- or 20-ampere branch circuits that are not cord- and attachment-plug-connected. 440.55 is the parallel rule but only for cord- and attachment-plug-connected equipment, and 440.52(B) is the general branch-circuit/controller protection rule that explicitly defers to 440.54/440.55 for 15- and 20-ampere single-phase circuits.
Sizing conductors for multiple motor-compressors and motor loads
NEC 440.33 Conductor ampacity must cover every motor-compressor's rated-load or BCSC current, plus other motors' full-load current, plus 25% of the single largest motor-compressor or motor in the group.
Q17 NEC 440.33
A feeder supplies three motor-compressors with no interlock preventing simultaneous operation. How must the conductor ampacity be determined?
- A Sum the rated-load or branch-circuit selection current of all three compressors, then add 25% of the highest one's full-load current
- B Size for the largest compressor's rated-load current alone, since the others are considered standby
- C Use the average rated-load current of the three compressors multiplied by the total count
- D Sum the full-load currents of all three and add 25% for each additional compressor beyond the first
Show answer & explanation
Correct: A — Sum the rated-load or branch-circuit selection current of all three compressors, then add 25% of the highest one's full-load current
Per 440.33, without an interlock all motor-compressors are assumed to run together, so their rated-load or branch-circuit selection current (whichever is greater, per unit) is summed, then 25% of the single highest motor-compressor or motor FLC in the group is added. Sizing for only the largest unit, or adding 25% per additional unit, are not how the rule works.
Supply cord length and shock protection devices for room ACs
NEC 440.65 Room AC cords are capped at 10 ft on 120V or 6 ft on 208/240V, and every cord-and-plug unit needs a factory LCDI, AFCI, or HDCI within 12 in. of the plug.
Q18 NEC 440.65
A single-phase, cord-and-plug-connected room air conditioner is being installed. Which protection arrangement satisfies 440.65?
- A An LCDI built into the attachment plug
- B No protection device, since the unit is factory-listed
- C A GFCI receptacle installed at the wall outlet, with no device on the cord or plug
- D An AFCI device located 450 mm (18 in.) from the attachment plug on the supply cord
Show answer & explanation
Correct: A — An LCDI built into the attachment plug
440.65 requires the LCDI, AFCI, or HDCI to be a factory-installed integral part of the attachment plug, or located within 300 mm (12 in.) of the plug on the cord — an LCDI built into the plug meets this directly. A wall GFCI receptacle isn't the device 440.65 requires, a device set back 18 in. exceeds the 12 in. limit, and 'factory-listed' alone doesn't substitute for the required protection device.
Ampacity rule for multimotor equipment with fan/blower motors
NEC 440.6(B) For shaded-pole or PSC fan/blower motors in multimotor equipment, size everything off the nameplate full-load current, not a horsepower rating.
Q19 NEC 440.6(B)
A piece of multimotor HVAC equipment contains a permanent split-capacitor (PSC) blower motor. How should the branch-circuit conductors for this motor be sized?
- A Using the full-load current marked on the equipment nameplate for the fan or blower motor
- B Using the nameplate voltage and wattage to calculate an equivalent current
- C Using the horsepower rating from the motor tables in Article 430
- D Using the largest full-load current of any motor in the equipment
Show answer & explanation
Correct: A — Using the full-load current marked on the equipment nameplate for the fan or blower motor
Per 440.6(B), for shaded-pole or PSC fan/blower motors in multimotor equipment, the full-load current marked on the equipment nameplate is used instead of a horsepower rating to size the branch-circuit conductors (and other components). Sizing from Article 430 horsepower tables is the general motor approach that this rule specifically replaces for these motor types.
Branch-circuit selection current marking
NEC 440.4(C) If a hermetic compressor's protection system allows continuous current above the normal percentage of rated-load current, the nameplate must also show a branch-circuit selection current, and that higher value — not rated-load current — sizes the branch circuit.
Q20 NEC 440.4(C) Code lookup
A hermetic refrigerant motor-compressor is equipped with a protection system approved to allow continuous current above the percentage of nameplate rated-load current normally permitted for conductor and short-circuit protective device sizing. Which section requires the manufacturer to add an additional nameplate marking to account for this higher permitted current?
- A 440.4(A)
- B 440.6(A)
- C 440.4(B)
- D 440.4(C)
Show answer & explanation
Correct: D — 440.4(C)
440.4(C) is the section requiring a branch-circuit selection current marking when an approved protection system permits continuous current above the percentages in 440.52(B)(2) or (B)(4). 440.4(A) only covers the basic nameplate marking requirements for a single hermetic compressor, and 440.6(A) covers how rated-load current is used to determine ampacity, not the marking requirement itself.
Controller nameplate marking
NEC 440.5 A motor-compressor controller must be marked with enough data — voltage, phase, current or horsepower, and manufacturer info — to confirm it matches the motor-compressor it protects.
Q21 NEC 440.5
Under 440.5, which of the following is a required marking on a motor-compressor controller?
- A Maximum continuous branch-circuit conductor ampacity
- B Full-load and locked-rotor current (or horsepower) rating
- C Ambient temperature correction factor used for sizing
- D Short-circuit current rating of the disconnecting means
Show answer & explanation
Correct: B — Full-load and locked-rotor current (or horsepower) rating
440.5 requires the controller be marked with full-load and locked-rotor current (or horsepower) rating, along with manufacturer identification, voltage, and phase. Conductor ampacity, disconnect SCCR, and ambient correction factors are not controller marking requirements under this section.