Checked against primary sources 2026-08-24

Feeders for a group of motors, and the part everybody over-applies

Only one motor in the group gets the 125 percent. Applying it to all of them produces a number that looks careful and is wrong.

The rule is a sum of four things

When a feeder supplies several motors, or motors mixed with other loads, its conductors are sized from a sum with four parts (NEC 430.24).

1. 125 percent of the full-load current of the highest rated motor.
2. 100 percent of the full-load currents of every other motor in the group.
3. 100 percent of the non-motor load that is not continuous.
4. 125 percent of the non-motor load that is continuous.

All the motor currents come from the Article 430 tables, not from nameplates. 430.24 sends you to 430.6(A) for every one of them.

Two of the four parts carry a 125 percent and two carry 100 percent, and they interleave. That is what makes this easy to misremember.

Why only one motor gets the bump

The 125 percent on the largest motor is the same 125 percent that sizes the branch-circuit conductors for a single motor in 430.22. The code applies it once to the group rather than to every member.

It is worth being blunt about what it is not, because the usual explanation in the field is that the margin covers the largest motor starting. It does not. A motor draws several times its full-load current on start, not a quarter more, and starting current is the job of a completely different device sized from a completely different table (NEC 430.52).

So do not reason about this rule from inrush. Reason about it from where the number came from, which is the single-motor conductor rule, applied one time.

Highest rated does not mean highest horsepower

The highest rated motor is the one with the largest full-load current in the Article 430 tables, and the code says so in its own section rather than inside the sum (NEC 430.17).

On a group that is all the same voltage and phase, that is the same motor as the biggest horsepower. On a mixed group it can be a different motor. A single-phase motor and a three-phase motor of the same horsepower draw very different currents, and the smaller horsepower can be the larger current.

Sort the group by table current, not by the horsepower printed in the question. The question will sometimes list them in horsepower order to encourage the shortcut.

When two motors tie

Nothing in 430.24 or 430.17 breaks a tie, and nothing needs to. The sum asks for the highest rated motor at 125 percent and for all the other motors at 100 percent, so when two motors share the largest table current you take one of them as the largest and the other joins the rest.

Pick either. They carry the same current, so the total is identical whichever one you choose. The wrong answer is giving 125 percent to both, and that answer will be on the page because it is what a careful person does when they think a tie needs resolving.

Continuous and noncontinuous, on the non-motor side only

The continuous versus noncontinuous split applies to the non-motor load, not to the motors. Motors are already handled by the first two parts.

So a feeder carrying three motors and a bank of lighting gets: the largest motor at 125 percent, the other two motors at 100 percent, and the lighting at 125 percent because lighting on a commercial feeder is normally continuous.

Candidates who apply the continuous rule to the motors as well end up adding the same margin twice.

The feeder device is a different sum

The conductor and the device protecting it are not sized the same way, which is unusual and is exactly why it gets tested.

The conductor sum starts from a current: 125 percent of the largest table current, plus the others. The feeder device sum starts from a device: the largest branch-circuit short-circuit and ground-fault protective device of any motor on the feeder, plus the full-load currents of the other motors (NEC 430.62).

One term in that second sum is an ampere rating you already selected in a previous step. The other terms are currents. Mixing the two sums produces a plausible number either way, which is why neither wrong answer looks wrong.

Read 430.62 in your own book. It is short, and the difference between the two sums is the entire point of the section.

The four exceptions, and what they actually say

Three of the four turn on what kind of load is in the group rather than on the arithmetic, and the fourth arrived with the 2026 edition.

• A motor in the group running short-time, intermittent, periodic or varying duty is taken from the duty-cycle rule instead (NEC 430.22(E)).
• Motor-operated fixed electric space-heating equipment goes to Article 424 instead (NEC 424.4(B)).
• Where the circuitry is interlocked so that selected motors or loads cannot run at the same time, you may size on the combination that actually can run together and produces the highest total.
• A conductor temperature provision for Design BE and CE motors, new in the 2026 edition, which is where those motor designations enter Article 430.

Read them in your code book rather than working from this summary. Their conditions are specific and a paraphrase is not good enough to answer on.

Packaged equipment does not get calculated at all

A rooftop unit, a chiller or any other multimotor or combination-load assembly arrives from the factory with a minimum circuit ampacity marked on it, and the conductor ampacity comes off that marking rather than off the several-motors sum (NEC 430.25). The marking itself is required by NEC 430.7(D).

You do not open the cabinet and add up the internal motors. That is the point of the marking, and the manufacturer has already accounted for what runs together.

The one case that sends you back to 430.24 is equipment that is not factory wired and whose individual motor nameplates are visible. Then there is no assembly rating to rely on and you calculate.

This is not one of the 430.24 exceptions, whatever else you have read. It is a separate section, and knowing that it is separate is what stops you looking for it in the wrong place under time pressure.

What this page cites

• NEC 430.24 Conductors supplying several motors or a motor and other loads. Four exceptions: duty cycle via 430.22(E), motor-operated fixed electric space heating via 424.4(B), interlocked circuitry, and a Design BE and CE conductor temperature provision added in 2026. Text read in NFPA second revision 8015, panel 11, A2025 cycle.
• NEC 430.17 The highest rated or smallest rated motor is determined by rated full-load current selected from the Article 430 tables, for 430.24 and for 430.53(B) and (C).
• NEC 430.6(A)(1) Full-load currents for all of this come from the tables, not the nameplate.
• NEC 430.22 The single-motor 125 percent, which is where the 125 percent in the feeder sum comes from.
• NEC 430.22(E) The duty-cycle rule the first exception sends you to.
• NEC 430.25 Multimotor and combination-load equipment. Conductor ampacity comes from the minimum circuit ampacity marked on the equipment. Where the equipment is not factory wired and the individual nameplates are visible, you return to 430.24.
• NEC 430.7(D) The marking requirement that puts the minimum circuit ampacity on the equipment in the first place.
• NEC 430.52 The branch-circuit device rating that becomes the first term of the feeder device sum.
• NEC 430.62 Feeder short-circuit and ground-fault protection. A maximum, so it rounds down, and the next-higher permission in 430.52 does not carry over.
• NEC 424.4(B) Where the space-heating exception sends you.