Motor Overload Protection Practice Questions

A. Excessive heating of motors, motor-control apparatus and motor branch-circuit conductors from motor overloads and failure to start

An overload is the motor running and drawing more than it should, heating slowly, with nothing actually broken. That failure takes minutes, while a fault takes milliseconds, so a single device cannot cover both. The short-circuit part of the article says in its own opening that it does not protect against overload.

NEC 2026 430.31

B. The motor nameplate full-load current rating

The overload device is watching this particular motor, so it reads what this particular motor is rated to draw. That is the one place in a general motor application where the nameplate governs. Conductors, switches and the short-circuit device all come off the table instead.

NEC 2026 430.32, 430.6(A)(2)

C. 35 amperes

The rule reads 1.15 or greater, so a 1.25 service factor qualifies for the higher base percentage of 125, and 28 times 1.25 gives 35 amperes. The 32.2 answer is 115 percent, which applies to a motor with neither qualifying marking. The 39.2 answer is the permitted increase, which is only reached after the base selection fails to start the motor.

NEC 2026 430.32(A)(1)

D. 32.2 amperes

Neither qualifying marking is present, so the base percentage is 115 and 28 times 1.15 gives 32.2 amperes. A temperature rise above 40 degrees does not qualify, which is what the stem is checking. The 36.4 figure is this motor's permitted increase and not its base selection.

NEC 2026 430.32(A)(1)

A. A marked temperature rise of 40 degrees C or less

Both markings describe thermal headroom, which is why they earn the same treatment. A service factor above 1.0 means the manufacturer rates the motor to deliver more than nameplate horsepower under defined conditions, and a low temperature rise means the windings run further below what the insulation can take. A motor with neither marking gets the smaller multiplier.

NEC 2026 430.32(A)(1)

B. 39.2 amperes

The permitted increase for a motor with a marked service factor of 1.15 or greater stops at 140 percent of the nameplate current, so 28 times 1.4 gives 39.2 amperes. The 36.4 figure is the ceiling for a motor with neither qualifying marking. Reading the wrong ceiling row is the error, because both are on the same short list.

NEC 2026 430.32(C)

C. 36.4 amperes

The ceiling for a motor with neither qualifying marking is 130 percent, so 28 times 1.3 gives 36.4 amperes. Each of the three base percentages has a matching ceiling that sits above it, and the pairs have to be kept together. Mixing a base row with a different ceiling row is how 39.2 gets picked here.

NEC 2026 430.32(C)

D. The base percentage value, because the increase is a permission that only opens when the base selection fails

You size at the base percentage first, and the higher figure is available only where the device selected there will not start the motor or carry the load. A stem that never says the motor failed to start has not opened that door. Answering with the ceiling anyway is a wrong answer that looks like knowledge.

NEC 2026 430.32(C)

A. 13.6 amperes

The thermal protector allowance is set out as three bands by full-load current, and a motor at 9 amperes or less gets 170 percent, so 8 times 1.7 gives 13.6 amperes. Note that this percentage is applied to the table full-load current rather than to the nameplate, which is unusual inside the overload part of the article. The 12.48 answer is the middle band and 11.2 is the band for motors above 20 amperes, and both are on the list because people read the wrong row.

NEC 2026 430.32(A)(2)

B. 23.4 amperes

A full-load current from 9.1 through 20 amperes falls in the middle band at 156 percent, so 15 times 1.56 gives 23.4 amperes. Above 20 amperes the allowance drops to 140 percent, which produces the 21 ampere distractor. The bands step down as the motor gets larger, which is the opposite of what people expect.

NEC 2026 430.32(A)(2)

C. Motors used in a continuous duty application and rated more than 1 horsepower

Two conditions gate that subsection, the duty classification and the horsepower, and the subsections that follow pick up the motors it leaves out. Check the size and the duty before you reach for a percentage. A one horsepower motor and a hoist motor both land somewhere else.

NEC 2026 430.32

D. By one of the means the code lists for that case, including a separate overload device following the same percentage rule, a thermal protector or electronically protected motor, a device integral with the motor, or impedance protection

Automatic starting is what triggers this subsection, because nobody is standing there to notice the motor is not turning. The listed means are real alternatives rather than a preference order, and the separate overload device option follows the same percentages the larger motors use. A motor of that size started by hand is handled by the next subsection instead.

NEC 2026 430.32(B)

A. The branch-circuit short-circuit and ground-fault device may furnish the overload protection, and a separate exception allows any such motor on a 120 volt branch circuit protected at not over 20 amperes

Being within sight means a person can see whether the motor is running, which is the condition the relief is built on. The device furnishing that protection is still bounded by what the short-circuit part of the article allows. A motor of the same size that is not within sight from its controller goes back to the automatically started subsection.

NEC 2026 430.32(D)

B. Where a power loss would cause a hazard, such as in the case of fire pumps

The judgment is that a fire pump stopping is worse than a fire pump burning up, so the provisions do not require the device that would stop it. The same part of the article also states that it does not apply to motor circuits above the stated voltage limits. Neither of those releases has anything to do with horsepower.

NEC 2026 430.31

C. The full-load current from the Article 430 tables

That device is protecting the circuit rather than the motor, and it has to survive the starting current every time. Rather than send you chasing a locked-rotor figure for each unit, the code sets a maximum by motor type and device type and applies it to the standardized table value. Protecting the motor means nameplate, protecting the wire means table.

NEC 2026 430.6(A)(1), 430.52

D. Because it is built to ride through the starting current, so it does not need as much headroom above full-load current

Each column exists because that device type tolerates inrush differently, and the multiplier is set to whatever it takes to keep the device closed during a normal start. A fuse with no intentional delay needs three times the full-load current to survive that, and a time-delay fuse needs far less. Finding the right row and then reading the wrong column is the standard way to lose one of these items.

NEC 2026 Table 430.52(C)(1)

A. None, since it exists so the circuit can be opened for work on the motor

That is why the disconnect sits in a different part of the article from the two protective devices, with its own rules for what type qualifies and what current rating it carries. Its rating starts at 115 percent of the full-load current rather than the 125 percent people carry over from the conductor rule. The controller is a fourth thing again, and one enclosure often holds all three, which is precisely why the exam asks about them separately.

NEC 2026 430.109, 430.110(A)

B. 24.15 amperes

A switch is one of the three items the table governs, so the calculation starts from 21 amperes and not from the nameplate. That gives 21 times 1.15, or 24.15 amperes. The 25.88 answer applies 115 percent to the nameplate and the 26.25 answer applies 125 percent to the table value, and both are the mistakes this stem was written to catch.

NEC 2026 430.110(A), Table 430.250

C. Fuses or inverse time circuit breakers rated or set at not over 400 percent of the motor full-load current are in the circuit and operative during starting

Something has to be watching while the overload device is out of the circuit, so the code requires a device sized high enough to pass starting current and low enough to catch a real problem. It also requires that the shunting means cannot be left in the starting position. On an automatically started motor the shunting is not permitted at all except under a separate and much narrower set of conditions.

NEC 2026 430.35

D. In each ungrounded conductor and also in the grounded conductor

The general rule is a fuse in each ungrounded conductor, and this particular supply arrangement adds the grounded conductor to that list. It is a narrow case and the option list is built to make the general rule look sufficient. Read the supply system named in the stem before answering, because the answer changes with it.

NEC 2026 430.36

A. Three, one in each phase

The table is indexed by the kind of motor and the supply system, and every three-phase row asks for one unit in each phase. Single-phase rows generally ask for one, and two-phase rows for two. Answering with two on a three-phase motor is a habit left over from older installations and the table settles it.

NEC 2026 430.37, Table 430.37

B. Each half of the motor winding individually protected, with a trip current one-half of what would otherwise be specified

Each winding half carries about half the motor current, so a device sized for the whole motor would never see a problem in one half. The same section also cuts the branch-circuit short-circuit and ground-fault rating in half for each winding connection, with an exception where one device will let the motor start. Time-delay fuses under that exception are limited to 150 percent of the motor full-load current.

NEC 2026 430.4

C. From the control circuit table, which varies by conductor size and by whether the conductors leave the motor control equipment enclosure

The control circuit has its own section and its own table, with separate columns for separate protection, for conductors kept inside the enclosure and for conductors that extend beyond it. One exception releases the requirement to short-circuit and ground-fault protection only where opening the control circuit would create a hazard, such as on a fire pump. Whenever a stem says control circuit, start-stop station or pilot device, this is the section it is pointing at.

NEC 2026 430.72, Table 430.72(B)(2)

D. One rated or set at not more than 500 percent of the rated primary current

A transformer supplying a motor control circuit is excused from the general transformer overcurrent table and follows the motor control circuit section instead, which is a connection worth noticing before you meet it in a question. That section carries its own breakpoint below 2 amperes with a much larger multiplier. The other three answers are the general transformer percentages, offered because they are the ones people know.

NEC 2026 430.72(C)

A. By the branch-circuit short-circuit and ground-fault protective device, provided its rating or setting does not exceed what the branch-circuit device table allows

A motor that stops on its own before it can cook is a different thermal problem from one that runs all shift, so the code lets one device cover both jobs within a stated limit. The section also repeats that any motor application counts as continuous duty unless the driven apparatus cannot run continuously with load. That default is what keeps this relief from swallowing the general rule.

NEC 2026 430.33