relationship between motor current and motor temperature changes when the motor is operated by an adjustable speed drive. In certain applications, overheating of motors can occur when operated at reduced speed, even at current levels less than a motor's rated full-load current The overheating can be the result of reduced motor cooling when its shaft- mounted fan is operating less than rated nameplate RPM. As part of the analysis to determine whether overheating will occur, it is necessary to consider the continuous torque capability curves for the motor given the application requirements. This will assist in determining whether the motor overload protection will be able, on its own, to provide protection against overheating. These overheating protection requirements are only intended to apply to applications where an adjustable speed drive, as defined in 430.2, is used.
For motors that utilize external forced air or liquid cooling systems, overtemperature can occur if the cooling system is not operating. Although this issue is not unique to adjustable speed applications, externally cooled motors are most often encountered with such applications. In these instances, overtemperature protection using direct temperature sensing is recommended [i.e., 430.126(A)(1), (A)(3), or (A)(4)], or additional means should be provided to ensure that the cooling system is operating (flow or pressure sensing, interlocking of adjustable speed drive system and cooling system, etc.).
(B) Multiple Motor Applications. For multiple motor applications, individual motor overtemperature protection shall be provided as required in 430.126(A).
(C) Automatic Restarting and Orderly Shutdown. The provisions of 430.43 and 430.44 shall apply to the motor overtemperature protection means.
430.128 Disconnecting Means. The disconnecting means shall be permitted to be in the incoming line to the conversion equipment and shall have a rating not less than 115 percent of the rated input current of the conversion unit.
XI. Over 600 Volts, Nominal
430.221 General. Part XI recognizes the additional hazard due to the use of higher voltages. It adds to or amends the other provisions of this article.
430.222 Marking on Controllers. In addition to the marking required by 430.8, a controller shall be marked with the control voltage.
430.223 Conductor Enclosures Adjacent to Motors. Flexible metal conduit or liquidtight flexible metal conduit not exceeding 1.8 m (6 ft) in length shall be permitted to be employed for raceway connection to a motor terminal enclosure.
430.224 Size of Conductors. Conductors supplying motors shall have an ampacity not less than the current at which the motor overload protective device(s) is selected to trip.
430.225 Motor-Circuit Overcurrent Protection.
(A) General. Each motor circuit shall include coordinated protection to automatically interrupt overload and fault cur rents in the motor, the motor- circuit conductors, and the motor control apparatus.
Exception: Where a motor is vital to operation of the plant and the motor should operate to failure if neces- sary to prevent a greater hazard to persons, the sensing device(s) shall be permitted to be connected to a super- vised annunciator or alarm instead of interrupting the motor circuit.
(B) Overload Protection.
(1) Type of Overload Device. Each motor shall be pro- tected against dangerous heating