Pick the horsepower, the phase and the voltage, and read the full-load current the code makes you use, the branch-circuit conductor, the overload setting and the largest device each of the four types is allowed. Table values are the 2026 edition as printed.
Three-phase reads Table 430.250, single-phase reads Table 430.248.
Only the voltage columns the table prints. A 480 volt system reads the 460 volt column, and a 240 volt system reads the 230 volt column.
Rows the table leaves as a dash at that voltage are left out of this list.
Sized from the 75 C column of Table 310.16, with the 60 C answer called out underneath when the two differ.
This row sets four percentages, one for each device type. A wound rotor motor gets 150 percent everywhere, which is why it is the row people miss.
Read this off the motor, not off the table. It is usually close to the table figure and rarely equal to it.
The first two get 125 percent, everything else gets 115 percent.
This page holds Table 430.248, Table 430.250, Table 430.52(C)(1), Table 240.6(A), Table 250.122 and Table 310.16 so you get four answers off one horsepower. The motor tool on the calculators page makes you type each table value in from your own book, because the lookup is the thing the exam is testing.
Use this one on the job. Use that one the week before the test, and read the motor calculations study page for the order the four steps go in and why each one uses a different current.
A motor circuit is four calculations that share a horsepower and nothing else. The conductors, the branch-circuit device, the overload device and the grounding conductor each start from a different number, and mixing those numbers up is the single most common way to get a motor question wrong.
The first number is the full-load current, and 430.6(A)(1) says where it comes from. For general motor applications the value in Table 430.248 or Table 430.250 is used instead of the current marked on the motor, and it sets the conductor ampacity, the switch ratings and the branch-circuit short-circuit and ground-fault protection. A 10 hp three-phase motor at 460 volts is 14 amperes, whatever its nameplate says.
Conductors come next. Section 430.22 asks for an ampacity of not less than 125 percent of that table current for a motor in a continuous duty application, so 14 amperes becomes 17.5 amperes, and the smallest 75 C copper row in Table 310.16 that carries it is 14 AWG at 20 amperes. Section 430.22(G) will not let a small motor go below 14 AWG whatever the arithmetic says.
Watch the termination temperature here. Section 110.14(C)(1)(a) holds equipment rated 100 amperes or less to the 60 C column unless the equipment is listed and identified for higher, and 110.14(C)(1)(a)(4) is the permission that lets a motor marked design letter B, C or D use 75 C conductors. At the 60 C column that same 17.5 amperes needs 12 AWG, so the two columns give different answers and the exam knows it.
Section 240.4(D) does not apply. It opens by deferring to 240.4(G), and 240.4(G) sends motor and motor-control circuit conductors to Article 430. The small conductor rule that caps 14 AWG copper at 15 amperes on an ordinary branch circuit has nothing to say about a motor circuit.
The overload device is the one that goes back to the nameplate. Section 430.32(A)(1) rates a separate overload device at no more than 125 percent of the nameplate full-load current where the motor is marked with a service factor of 1.15 or greater or a temperature rise of 40 C or less, and 115 percent for everything else. Where that size will not start the motor or carry the load, 430.32(C) allows the trip current up to 140 percent, or 130 percent for the other motors.
The branch-circuit short-circuit and ground-fault device is last and it is the loose one. Table 430.52(C)(1) gives a percentage of the full-load current for each of four device types, and the table current is the base, not the nameplate. An ac polyphase motor other than wound rotor gets 300 percent on a nontime delay fuse, 175 percent on a dual element time delay fuse, 800 percent on an instantaneous trip breaker and 250 percent on an inverse time breaker.
Then the rounding rule, and read it carefully, because it does not say nearest. Section 430.52(C)(1)(a) says that where the value from the table does not correspond to a standard ampere rating or setting in 240.6, the next higher standard rating or setting is permitted. Older editions printed this as an exception; in the 2026 edition it is subdivision (a) of 430.52(C)(1). So 42 amperes goes up to 45, never down to 40, and 35 amperes stays at 35 because 35 is already standard.
One more permission sits under it and it is not free. Section 430.52(C)(1)(b) lets the device go higher still where the rating from the table will not carry the starting current, to 400 percent on a nontime delay fuse, 225 percent on a dual element fuse, and 400 percent on an inverse time breaker for full-load currents of 100 amperes or less. That is for a motor that trips the smaller device on starting, not a number you reach for first.
The grounding conductor closes it out. Section 250.122(F)(1) sizes the equipment grounding conductor from Table 250.122 on the rating of the branch-circuit short-circuit and ground-fault protective device, so the device you picked decides it. Where that device is an instantaneous trip breaker, 250.122(F)(2) sends you to the largest dual element time delay fuse 430.52(C)(1)(a) would have allowed instead.
Take a 10 hp three-phase motor on 460 volts, an ac polyphase motor other than wound rotor, with 13 amperes and a service factor of 1.15 on the nameplate. Table 430.250 gives 14 amperes at the 10 hp row and the 460 volt column, and that is the figure 430.6(A)(1) makes you use for everything except the overload.
Conductors: 14 amperes at 125 percent is 17.5 amperes, and the smallest 75 C copper row in Table 310.16 that reaches it is 14 AWG, which carries 20 amperes. At the 60 C column the answer would be 12 AWG.
Overload: 13 amperes on the nameplate at 125 percent, because the service factor is 1.15, is 16.25 amperes. If the motor will not start on that, 430.32(C) allows up to 140 percent, which is 18.2 amperes.
Branch-circuit device, all four of them from the same 14 amperes. The inverse time breaker at 250 percent is 35 amperes, which is already a standard rating, so it stays at 35. The nontime delay fuse at 300 percent is 42 amperes, which is not standard, so 430.52(C)(1)(a) takes it up to 45 amperes. The dual element time delay fuse at 175 percent is 24.5 amperes and goes up to 25. The instantaneous trip breaker at 800 percent is 112 amperes and goes up to a setting of 125.
Grounding conductor: on the 35 ampere breaker, Table 250.122 falls in the row for a device not over 60 amperes, which is 10 AWG copper. Section 250.122(A) does not require it to be larger than the circuit conductors, and those are 14 AWG here. Set those inputs above and the calculator prints the same figures.
The value used for your inputs is read from NEC 2026 Table 430.248, Table 430.250, Table 430.52(C)(1), Table 240.6(A) and Table 250.122, the way you would read it in the exam room, and the working above names the row it came from. The tables themselves belong to NFPA and are not printed on this page. Bring your own copy of the 2026 code, which is what the exam requires anyway, and check the row there.
Footnote 1 to Table 430.52(C)(1) puts time-delay Class CC fuses in the nontime delay column. Footnote 3 holds a low-torque, low-speed synchronous motor that starts unloaded to 200 percent rather than the 300 percent the row prints.
You do not calculate it, you look it up. NEC 430.6(A)(1) says the current used to size conductors, switches and the branch-circuit protective device comes from Table 430.248 for a single-phase motor and Table 430.250 for a three-phase one, read at the horsepower and the voltage. A 10 hp three-phase motor at 460 volts is 14 amperes. The nameplate figure is used for the overload device and for very little else.
Because the conductors and the branch-circuit device are sized before anyone knows which motor gets installed, and two motors of the same horsepower can carry different nameplate amperes. Section 430.6(A)(1) fixes the design current at the table value so the circuit does not have to be rebuilt when the motor is swapped. Section 430.32(A)(1) then sends the overload device back to the nameplate, because that device is protecting the actual machine.
Table 430.250 gives 14 amperes, 430.22 asks for 125 percent of that, which is 17.5 amperes, and the smallest 75 C copper row in Table 310.16 that carries it is 14 AWG at 20 amperes. Read the 60 C column instead, which 110.14(C)(1)(a) calls for on equipment rated 100 amperes or less unless it is listed for higher, and the same load needs 12 AWG.
For an inverse time breaker on an ac polyphase motor, Table 430.52(C)(1) sets the maximum at 250 percent of the full-load current. On 14 amperes that is 35 amperes, which is already a standard rating in Table 240.6(A). Where the percentage lands between standard ratings, 430.52(C)(1)(a) allows the next one up, so a nontime delay fuse at 300 percent, which is 42 amperes, becomes 45 amperes.
Section 430.32(A)(1) rates a separate overload device at no more than 125 percent of the nameplate full-load current for a motor marked with a service factor of 1.15 or greater or a temperature rise of 40 C or less, and 115 percent for everything else. Where that size will not start the motor or carry the load, 430.32(C) allows the trip current up to 140 percent, or 130 percent for the other motors.
They protect against two different things and they are sized from two different currents. The overload device watches a motor drawing more than it should over minutes, and it comes off the nameplate at 115 or 125 percent. The branch-circuit short-circuit and ground-fault device clears a fault in a fraction of a second, and it comes off the table current at up to 250 or 300 percent. A device set to do one of those jobs cannot do the other.
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