with a motor that protects the motor against damage due to failure to start shall be permitted (1) if the motor is part of an approved assembly that does not subject the motor to overloads, or (2) if the assembly is also equipped with other safety controls (such as the safety combustion controls on a domestic oil burner) that protect the motor against damage due to failure to start. Where the assembly has safety controls that protect the motor, it shall be so indicated on the nameplate of the assembly where it will be visible after installation.
(4) Impedance-Protected. If the impedance of the motor windings is sufficient to prevent overheating due to failure to start, the motor shall be permitted to be protected as specified in 430.32(D)(2)(a) for manually started motors if the motor is part of an approved assembly in which the motor will limit itself so that it will not be dangerously overheated.
FPN: Many ac motors of less than 1/20 hp, such as
clock motors, series motors, and so forth, and also
some larger motors such as torque motors, come
within this classification. It does not include split-phase
motors having automatic switches that disconnect the
starting windings.
(C) Selection of Overload Device. Where the sensing el ement or setting or sizing of the overload device selected in accordance with 430.32(A)(1) and
430.32(B)(1) is not sufficient to start the motor or to carry the load, higher size sensing elements or incremental settings or sizing shall be permitted to be used, provided the trip current of the over load device does not exceed the following percentage of motor nameplate full-load current rating:
Motors with marked service factor 1.15 or 140%
greater
Motors with a marked temperature rise 40°C or 140%
less
All other motors 130%
If not shunted during the starting period of the motor as provided in 430.35, the overload device shall have sufficient time delay to permit the motor to start and accelerate its load.
FPN: A Class 20 or Class 30 overload relay will provide a longer motor acceleration time than a Class 10 or Class
20, respectively. Use of a higher class overload relay may preclude the need for selection of a higher trip current.
(D) One Horsepower or Less, Nonautomatically
Started.
(1) Permanently Installed. Overload protection shall be in accordance with 430.32(B).
(2) Not Permanently Installed.
(a) Within Sight from Controller. Overload protection shall be permitted to be furnished by the branch-circuit short-circuit and ground-fault protective device; such device, however, shall not be larger than that specified in Part IV of Article 430.
Exception: Any such motor shall be permitted on a nominal 120-volt branch circuit protected at not over 20 amperes.
(b) Not Within Sight from Controller. Overload protection shall be in accordance with 430.32(B).
(E) Wound-Rotor Secondaries. The secondary circuits of wound-rotor ac motors, including conductors, controllers, resistors, and so forth, shall be permitted to be protected against overload by the motor-overload device.
430.33 Intermittent and Similar Duty. A motor used for a condition of service that is inherently short-time, intermittent, periodic, or