Practice: motor full-load current
Each problem uses new numbers, so you practice the method rather than memorizing an answer.
Pick the answer: sizes and ratings come from your code book.
Worked solution
Formula
| Symbol | Meaning | Unit |
|---|---|---|
| FLC | Table full-load current for the motor hp and voltage | A |
| FLA | Nameplate full-load current marked on the motor | A |
| hp | Motor horsepower rating | hp |
Worked example
A 5 hp, 230 V, three-phase squirrel-cage induction motor has a nameplate full-load current of 13.4 A. What current must you use to size its branch-circuit conductors and its short-circuit and ground-fault protection?
- NEC 430.6(A)(1): for conductors and short-circuit protection, use the full-load current from the NEC tables, not the nameplate.
- Look up Table 430.250, 230 V column, 5 hp: 15.2 A.
- The nameplate current (13.4 A) is used only for the separate overload protection, 430.6(A)(2).
- Current to use: 15.2 A.
Answer: 15.2 A
Motor full-load current, explained
Every motor calculation starts with a current. NEC 430.6(A)(1) says that for conductor ampacity, switch ratings, and branch-circuit short-circuit and ground-fault protection you use the full-load current from the NEC tables, not the current on the motor nameplate. The tables are a bit conservative, so a replacement motor with a different nameplate still fits the circuit.
Table 430.248 covers single-phase motors and Table 430.250 covers three-phase induction motors. Find the row for the horsepower and the column for the motor voltage. Use the motor voltage column, such as 460 V for a motor on a 480 V system, or 208 V for a motor on a 208Y/120 V system.
The nameplate current is still needed. Separate overload protection (430.32) is sized from the nameplate, under 430.6(A)(2). Many exam questions give both numbers on purpose, so read which one the task needs.
How to solve it on the exam
- Decide if the motor is single-phase (Table 430.248) or three-phase (Table 430.250).
- Find the horsepower row and the motor voltage column.
- Use that table value for conductors, short-circuit and ground-fault protection, and feeders.
- Use the nameplate current only for separate overload protection.
Common mistakes
- Using the nameplate current to size conductors or the breaker.
- Using the table current to size overloads.
- Reading the 230 V column for a 208 V motor, or the 460 V column for a 575 V motor.
- Using the three-phase table for a single-phase motor.
Exam tips
- Tab Tables 430.248 and 430.250 together. Almost every motor question on the exam starts with one of them.
- Circle the nameplate value in the question and write "overloads only" next to it.
Questions people ask
Do you use nameplate or table current to size motor conductors?
Use the table current. NEC 430.6(A)(1) requires the full-load current from Table 430.248 or 430.250 for conductors and short-circuit protection; the nameplate current is used for overloads.
What is the full-load current of a motor?
It is the current the motor draws at its rated horsepower and voltage. The NEC gives standard values in Tables 430.248 and 430.250 for sizing circuits.
Which column do I use for a motor on a 480 V system?
Use the 460 V column. Motors on 480 V systems are rated 460 V, and Table 430.250 lists the motor voltage, not the system voltage.
Sources
- TDLR: Electrician examination information
- PSI: Texas electrician candidate information bulletin
- IEC: 2026 NEC changes to Chapter 4
About the tables: The exam is open book. These problems cite the 2026 NEC section and table so you practice finding them in your own book. We never print NEC text or tables.