430.52 Rating or Setting for Individual Motor Circuit
|Type of Motor||Percentage of Full-Load Current|
|Nontime Delay Fuse1||Dual Element (Time-Delay) Fuse1||Instantaneous Trip Breaker||Inverse Time Breaker2|
|AC polyphase motors other than wound-rotor||300||175||800||250|
|Squirrel cage — other than Design B energy-efficient||300||175||800||250|
|Design B energy-efficient||300||175||1100||250|
|DC (constant voltage)||150||150||250||150|
|Note: For certain exceptions to the values specified, see 430.54.|
|1The values in the Nontime Delay Fuse column apply to time-delay Class CC fuses.|
|2The values given in the last column also cover the ratings of nonadjustable inverse time types of circuit breakers that may be modified as in 430.52(C)(1), Exceptions No. 1 and No. 2.|
|3Synchronous motors of the low-torque, low-speed type (usually 450 rpm or lower), such as are used to drive reciprocating compressors, pumps, and so forth, that start unloaded, do not require a fuse rating or circuit-breaker setting in excess of 200 percent of full-load current.|
Exception No. 1: Where the values for branch-circuit short-circuit and ground-fault protective devices determined by Table 430.52 do not correspond to the standard sizes or ratings of fuses, nonadjustable circuit breakers, thermal protective devices, or possible settings of adjustable circuit breakers, a higher size, rating, or possible setting that does not exceed the next higher standard ampere rating shall be permitted.
Exception No. 2: Where the rating specified in Table 430.52, or the rating modified by Exception No. 1, is not sufficient for the starting current of the motor:
- The rating of a nontime-delay fuse not exceeding 600 amperes or a time-delay Class CC fuse shall be permitted to be increased but shall in no case exceed 400 percent of the full-load current.
- The rating of a time-delay (dual-element) fuse shall be permitted to be increased but shall in no case exceed 225 percent of the full-load current.
- The rating of an inverse time circuit breaker shall be permitted to be increased but shall in no case exceed 400 percent for full-load currents of 100 amperes or less or 300 percent for full-load currents greater than 100 amperes.
- The rating of a fuse of 601—6000 ampere classification shall be permitted to be increased but shall in no case exceed 300 percent of the full-load current.
Informational Note: See Informative Annex D, Example D8, and Figure 430.1.
Informational Note No. 1: Instantaneous trip circuit breakers are also known as motor-circuit protectors (MCPs).
Informational Note No. 2: For the purpose of this article, instantaneous trip circuit breakers may include a damping means to accommodate a transient motor inrush current without nuisance tripping of the circuit breaker.
Exception No. 1: Where the setting specified in Table 430.52 is not sufficient for the starting current of the motor, the setting of an instantaneous trip circuit breaker shall be permitted to be increased but shall in no case exceed 1300 percent of the motor full-load current for other than Design B energy-efficient motors and no more than 1700 percent of motor full-load current for Design B energy-efficient motors. Trip settings above 800 percent for other than Design B energy-efficient motors and above 1100 percent for Design B energy-efficient motors shall be permitted where the need has been demonstrated by engineering evaluation. In such cases, it shall not be necessary to first apply an instantaneous-trip circuit breaker at 800 percent or 1100 percent.
Informational Note: For additional information on the requirements for a motor to be classified "energy efficient," see NEMA MG 1—2016, Motors and Generators, Part 12.59.
Exception No. 2: Where the motor full-load current is 8 amperes or less, the setting of the instantaneous-trip circuit breaker with a continuous current rating of 15 amperes or less in a listed combination motor controller that provides coordinated motor branch-circuit overload and short-circuit and ground-fault protection shall be permitted to be increased to the value marked on the controller.
Exception: For a multispeed motor, a single short-circuit and ground-fault protective device shall be permitted to be used and sized according to the full-load current of the highest current winding, where all of the following conditions are met:
- Each winding is equipped with individual overload protection sized according to its full-load current.
- The branch-circuit conductors supplying each winding are sized according to the full-load current of the highest full-load current winding.
- The controller for each winding has a horsepower rating not less than that required for the winding having the highest horsepower rating.
Informational Note: Proper application of self-protected combination controllers on 3-phase systems, other than solidly grounded wye, particularly on corner grounded delta systems, considers the self-protected combination controllers' individual pole-interrupting capability.