Why use the table FLC instead of the nameplate?

NEC 430.6(A) requires using the full-load current values in Tables 430.248 and 430.250 for sizing branch-circuit conductors, the short-circuit and ground-fault device, and the disconnect — not the motor nameplate. The nameplate FLA is used only for the separate overload protection. This tool reads FLC straight from those tables.

How is the conductor sized?

Per 430.22, a single continuous-duty motor's branch-circuit conductors must carry at least 125 percent of the table full-load current. The tool multiplies FLC by 1.25 and selects the smallest 75 degree Celsius copper conductor whose ampacity meets that value, before any ambient or conduit-fill derating.

What sets the maximum overcurrent device size?

Table 430.52 gives a multiplier of the FLC by protection type: 250 percent for an inverse-time breaker, 175 percent for a dual-element time-delay fuse, 300 percent for a non-time-delay fuse, and 800 percent for an instantaneous-trip breaker. The result is rounded up to the next standard size under 430.52(C)(1) Exception 1 if the motor will not otherwise start.

Is the overload device the same as the breaker?

No. Branch-circuit protection (the breaker or fuse) guards against short circuits and ground faults, while overload protection under 430.32 — typically heaters or an electronic overload in the starter — guards the motor against sustained overcurrent. Overload is sized from nameplate FLA at 115 or 125 percent depending on service factor and temperature rise.

Does this account for derating or multiple motors?

No. It sizes one motor's branch circuit at 75 degree Celsius copper without ambient or conduit-fill adjustment, and it does not size feeders supplying several motors. Apply the relevant correction and adjustment factors and use 430.24 for feeder sizing when more than one motor shares a circuit.

NEC Article 430 Motor Circuit Summary Calculator

Designing a motor branch circuit means pulling five related numbers in the right order: the full-load current, the conductor, the short-circuit and ground-fault device, the overload, and the disconnect. NEC Article 430 ties them together but spreads them across several tables and sections. This calculator reads the table values and applies each rule so you get the complete circuit summary in one step.

How it works

Full-load current comes directly from NEC Table 430.248 for single-phase motors or Table 430.250 for three-phase, indexed by horsepower and voltage. Every downstream value is derived from that FLC:

Conductor (430.22):      ampacity >= 1.25 x FLC
Max OCPD (Table 430.52): multiplier x FLC, rounded up to a standard size
   inverse-time breaker  250%   dual-element fuse  175%
   non-time-delay fuse   300%   instantaneous trip 800%
Overload (430.32):       115% or 125% of nameplate FLA
Disconnect (430.110):    >= 1.15 x FLC

The conductor is chosen from the 75 degree Celsius copper column of Table 310.16, and the OCPD is rounded up to the next standard size from 240.6(A) as permitted by 430.52(C)(1) Exception 1.

Example and notes

A 10 HP, three-phase, 460 V motor has a table FLC of 14 A. The conductor must carry 17.5 A, which a 12 AWG 75°C copper conductor satisfies. With an inverse-time breaker the maximum OCPD is 250 percent of 14, or 35 A, which is already a standard size. The overload sizes to roughly 16 to 17.5 A from nameplate, and the disconnect must be rated at least 16.1 A.

Remember the table FLC drives conductor, OCPD, and disconnect, while only the overload uses the nameplate FLA. When several motors share a feeder, size the feeder under 430.24 and apply ambient and conduit-fill corrections to the conductor ampacity shown here.