Texas Electrician ExamTexas journeyman & master

Checked against primary sources 2026-08-24

Motor calculations, and the one distinction that decides them

A motor question hands you two different currents. Using the wrong one for the wrong step is how most people lose these points, and the wrong answer always looks reasonable.

On this page
  1. Two currents, and they are not interchangeable
  2. Where the nameplate wins the whole circuit
  3. Why the code works this way
  4. The sequence
  5. The 125 percent is not the continuous-load rule
  6. Rounding runs three different directions
  7. What to practice
  8. What this page cites

Two currents, and they are not interchangeable

Every motor problem involves two numbers that both describe current, and the code uses them for different jobs.

The first comes off a table in Article 430, selected by horsepower, voltage and phase. Call it the table current. The second is printed on the motor itself. Call it the nameplate current.

They are usually close. They are almost never equal. And the code is specific about which one belongs to which step (NEC 430.6).

One other place uses the nameplate, and it is the duty-cycle rule for a motor that is not continuous duty. Conductors for short-time, intermittent, periodic or varying duty come off a percentage of the nameplate current instead (NEC 430.22(E)). That is the exception people forget when they have learned the split as a slogan.

A question that gives you both numbers is testing whether you know which is which, and the distractor answers are built from the other current.

Where the nameplate wins the whole circuit

The table does not govern every motor, and the code says so in the same subsection that establishes it.

Motors built for low speeds, meaning under 1200 RPM, motors built for high torques, and multispeed motors are excluded from the table by the opening words of 430.6(A)(1). Those motors carry higher or speed-dependent full-load currents and the nameplate is what you use.

Two exceptions go further and hand the entire branch circuit to a marked current. One covers equipment with a shaded-pole or permanent-split-capacitor fan or blower motor marked with the motor type. The other covers a listed motor-operated appliance marked with both motor horsepower and full-load current. In each case the current marked on the equipment nameplate governs the conductors, the disconnect, the controller, the short-circuit device and the overload device together, not just one of them.

The 2026 edition tightened both. The fan and blower exception now also asks that the equipment nameplate marking be at least the current marked on the fan or blower motor itself, and the appliance exception now asks for both horsepower and full-load current on the appliance, where the 2023 text asked only for a motor type marking.

Why the code works this way

It looks arbitrary until you think about what each device is protecting against.

Overload protection is watching the motor. It cares what that specific motor actually draws, so it reads the nameplate.

Short-circuit and ground-fault protection is watching the circuit, and it has to survive the starting current every time the motor starts (NEC 430.52). Rather than make you chase a locked-rotor figure for every unit, the code sets a maximum by motor type and device type in a table and lets you work from the standardized table current.

Once you see that, you stop having to memorize which is which. Protecting the motor means nameplate. Protecting the wire means table. Then check whether the motor is one of the kinds the table does not cover.

The sequence

  1. Look up the full-load current in the Article 430 table using horsepower, voltage and phase (NEC 430.6(A)(1)). Check first that the motor is not low speed, high torque or multispeed, and that no equipment marking exception applies.
  2. Size the branch-circuit conductors at not less than 125 percent of that table current (NEC 430.22), then apply ambient and conduit-fill corrections from Article 310.
  3. Size the overload protection from the nameplate current (NEC 430.32).
  4. Size the branch-circuit short-circuit and ground-fault device from the percentage in the branch-device table, applied to the table current, then round up to the next standard rating (NEC 430.52).
  5. For a group, size the feeder conductor from the several-motors sum (NEC 430.24), taking 125 percent of the largest table current and 100 percent of the rest.
  6. Size the feeder protective device from the largest branch-circuit device in the group plus the full-load currents of the other motors, then round down (NEC 430.62).

Steps two and four both start from the table current and can be done in either order. Step three starts somewhere else entirely. Candidates who work straight down the list without noticing the source change get step three wrong every time.

The 125 percent is not the continuous-load rule

You already know a 125 percent rule from Article 210, the one for continuous loads. The motor rule looks identical and is not the same rule.

The Article 210 rule turns on whether the load runs for three hours or more. The motor rule turns on whether the application is continuous duty, which is a classification of the driven machine, not a stopwatch reading.

Any motor application is treated as continuous duty unless the thing it drives cannot run continuously under load. A conveyor that runs all shift and a hoist that runs in bursts are classified differently, and the hoist goes to the duty-cycle table, where the percentage is applied to the nameplate current and varies with both the duty classification and the time rating of the motor (NEC 430.22(E)).

So the duty-cycle case changes two things at once, the multiplier and the current it is applied to. Applying continuous-load reasoning to a motor gets the right number for the wrong reason on most questions and the wrong number on the ones that test duty cycle.

Rounding runs three different directions

Three rules in one problem all talk about standard ampere ratings and they do not agree, which is why this is a reliable place to lose a point.

Two of those say next higher and one says the opposite, and a candidate uses all three in the same question. Know which article and which part you are standing in before you round anything.

What to practice

Not the table values. You will have the book.

Practice the habit of writing both currents at the top of your scratch paper and labeling them before you start. Table current on the left, nameplate on the right. Then every step points at one of them.

Add one line above them: what kind of motor is this. If the answer is low speed, high torque, multispeed, or a marked appliance, the left column is empty and everything comes off the nameplate.

That habit is worth more on this section than any amount of memorization, because the arithmetic is easy and the sourcing is where the points go.

What this page cites

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Every rule here is cited to the section it comes from, and corrections are logged in public with the date. This is study material rather than electrical advice, and it does not replace your own code book or your inspector.