13.3 Motor Overload Protection
Key Takeaways
- Motor running overload protection is sized from nameplate FLA per 430.6(A)(2) and 430.32 — never from Table FLC
- For continuous-duty motors more than 1 hp with separate overload devices, 430.32(A)(1) generally permits not more than 125% of nameplate FLA when SF ≥ 1.15 or temperature rise ≤ 40°C; otherwise not more than 115%
- If the selected overload will not allow the motor to start or carry load, 430.32(C) permits a higher setting/size up to 140% (SF ≥ 1.15 or rise ≤ 40°C) or 130% (other motors) of nameplate — still not Table FLC
- Overload protects against prolonged overcurrent that overheats windings; it is not a substitute for branch-circuit short-circuit/ground-fault protection under 430.52
- Service factor and temperature rise on the nameplate are the decision keys for 125% vs 115% — read them before multiplying
Overload Is a Different Protective Job
Motor circuits need two layers of protection. Confusing them is the highest-yield Motors trap on the Arkansas JW exam:
| Layer | What it guards against | Typical sizing basis | Typical magnitude |
|---|---|---|---|
| Overload (Part III) | Sustained running current slightly above rating that cooks insulation over time | Nameplate FLA | About 115% or 125% |
| SC/GF (Part IV) | Faults and short circuits | Table FLC | Often 175%–300% (device type) |
A dual-element fuse or a breaker can sometimes serve dual roles in limited arrangements, but the calculations remain separate. This section is only overload.
Tab 430.6(A)(2), 430.32, and the nameplate SF / temperature-rise fields.
Continuous-Duty Motors More Than 1 hp — 430.32(A)(1)
For separate overload devices on continuous-duty motors rated more than 1 horsepower, the device is selected to trip or rated at not more than:
- 125% of motor nameplate full-load current rating, when the motor has a marked service factor of 1.15 or greater, or a marked temperature rise not over 40°C
- 115% of nameplate FLA for all other motors in this category
Decision tree (write this on your tab note)
- Is this separate overload protection for a continuous-duty motor > 1 hp? If yes, continue.
- Look at nameplate: SF ≥ 1.15 or temp rise ≤ 40°C?
- Yes → use 125% of nameplate FLA as the selection ceiling in 430.32(A)(1).
- No → use 115%.
- Do not open Table 430.250 for this step.
Worked example E — SF 1.15 path
Motor nameplate: 15 A FLA, SF 1.15, continuous duty, 5 hp.
Maximum separate overload selection under 430.32(A)(1) = 15 × 1.25 = 18.75 A.
Even if Table 430.250 FLC for that motor is 15.2 A or something nearby, overload math still starts at 15 A nameplate.
Worked example F — 115% path
Motor nameplate: 28 A FLA, SF 1.0, temperature rise 50°C (so neither 125% trigger applies).
Maximum = 28 × 1.15 = 32.2 A.
Wrong answer pattern: using Table FLC 28 A × 1.25 because “motors are always 125%.” The 125% conductor rule and the 125% overload rule are different sections and different currents.
Motors 1 hp or Less and Other 430.32 Cases
430.32 also addresses smaller motors, automatically protected motors, and impedance-protected motors. Prov stems that specify “integral thermal protection” or “impedance protected” are directing you to those subsections — do not force the separate-overload 125%/115% math onto a motor the stem says is already thermally protected in accordance with the section.
When the stem is silent and describes a separate overload relay in a starter for a >1 hp continuous-duty motor, use 430.32(A)(1).
When the Motor Will Not Start — 430.32(C)
If the overload sensing element or setting selected under 430.32(A) or (B) is not sufficient to start the motor or to carry the load, 430.32(C) permits a higher size or setting, not to exceed:
- 140% of motor nameplate FLA for motors with SF ≥ 1.15 or temperature rise ≤ 40°C
- 130% of nameplate FLA for all other motors
Worked example G — higher setting ceiling
Nameplate FLA 14 A, SF 1.15. The 125% selection is 17.5 A, but the motor will not start with that heater/setting.
430.32(C) ceiling = 14 × 1.40 = 19.6 A.
You still do not jump to Table 430.52’s 250% breaker math and call it “overload.” Overload remains a nameplate-percentage world; SC/GF remains a Table-FLC-percentage world.
Overload vs Fuse/Breaker That Also Provides Running Protection
Some arrangements use a dual-element fuse sized to provide overload protection as well as SC/GF protection. When a stem asks specifically for overload sizing, stay in 430.32 and nameplate percentages. When it asks for branch-circuit short-circuit and ground-fault maximums, go to Table 430.52 and Table FLC (§13.4).
If the stem says “maximum dual-element fuse for branch-circuit protection,” that is usually a 430.52 question (often 175% of Table FLC), not a 125% nameplate overload question — read the exact protective function named.
Number of Overload Sensing Elements
430.37 and related rules address how many overload units are required based on the number of phases and whether a grounded conductor is present. Classic exam themes:
- Three-phase motors generally need overload sensing in each phase path as required by the table/section.
- Do not assume a single overload unit in one phase protects a three-phase motor.
Open 430.37 when the stem asks “how many overload units” rather than inventing a field practice answer.
Controllers, Heaters, and Setting Language
On Prov items, “heater size,” “overload relay setting,” and “maximum overload device rating” all point at Part III. Match the stem language to the calculation:
- Maximum permitted → apply the 115%/125% (or 130%/140% under 430.32(C)) ceiling.
- Minimum conductor ampacity → leave this section; that is 430.22.
- Maximum breaker for short-circuit protection → leave this section; that is Table 430.52.
Exam Workflow — Overload Stems
- Confirm the ask is overload / running protection / heater, not SC/GF.
- Take nameplate FLA only.
- Read SF and temperature rise.
- Apply 125% or 115% under 430.32(A)(1).
- If the stem says the motor will not start with that selection, apply 430.32(C) caps (140%/130%).
- Reject any option that used Table FLC for overload.
Timed Open-Book Tips for §13.3
- Circle SF and temperature rise the instant you see them.
- Write
NPL = ____ Aon scratch paper so you do not accidentally copy a Table FLC from an earlier calculation on the same motor. - Remember: conductors love Table FLC × 1.25; overloads love nameplate × 1.15/1.25.
- 430.32(C) is a relief valve with a hard ceiling — not unlimited upsizing.
- Motors ≤ 1 hp or with integral protection may leave the separate-device percentages — open the matching subsection.
Per NEC 430.6(A)(2), separate motor overload protection is generally based on which current?
A continuous-duty motor rated more than 1 hp has a nameplate FLA of 20 A, a service factor of 1.15, and a separate overload device. What is the maximum overload selection permitted by 430.32(A)(1) before considering 430.32(C)?
A continuous-duty motor more than 1 hp has nameplate FLA 16 A, service factor 1.0, and temperature rise 50°C. What maximum separate overload rating does 430.32(A)(1) generally permit?
If an overload selected under 430.32(A)(1) will not allow a motor with SF 1.15 to start, what is the maximum higher setting generally permitted by 430.32(C)?