PHASE CONVERTERS

70-457 455-7. Overcurrent Protection. The single-phase supply conductor and phase converter shall be protected from overcurrent at not more than 125 percent of the phase converter nameplate single-phase input full-load amperes. Exception No. 1: Where the phase converter supplies specific fixed loads, the overcurrent protection shall have a rating not greater than 250 percent of the sum of the full-load, 3-phase current rating of the motors and other loads served where the input and output voltages of the phase converter are identical. Where the input and output voltages of the phase converter are different, the current as determined by this section shall be multiplied by the ratio of output to input voltage. Exception No. 2: Where the required fuse rating or circuit breaker setting does not correspond to a standard rating or setting, the next higher standard rating or setting shall be permitted. 455-8. Disconnecting Means. Means shall be provided to disconnect simultaneously all ungrounded single-phase supply conductors to the phase converter. (a) Location. The disconnecting means shall be readily accessible and located in sight from the phase converter. (b) Type. The disconnecting means shall be a switch rated in horsepower, a circuit breaker, or a molded-case switch. Exception: Where only nonmotor loads are served, an ampere-rated switch shall be permitted. (c) Rating. The ampere rating of the disconnecting means shall not be less than 115 percent of the rated maximum single-phase input full-load amperes. Exception No. 1: Where the phase converter supplies specific fixed loads, and the input and output voltages of the phase converter are identical, the disconnecting means shall be permitted to be a circuit breaker or molded-case switch with an ampere rating not less than 250 percent of the sum of the following: a. Full-load 3-phase current ratings of the motors, and b. Other loads served. Where the input and output voltages of the phase converter are different, the current shall be multiplied by the ratio of the output to input voltage. Exception No. 2: Where the phase converter supplies specific fixed loads, and the input and output voltages of the phase converter are identical, the disconnecting means shall be permitted to be a switch with a horsepower rating. The horsepower rating shall be equivalent to 200 percent of the sum of the following: a. Nonmotor loads, b. The 3-phase locked-rotor current of the largest motor as determined from Table 430-151, and 70-458 NATIONAL ELECTRICAL CODE c. The full-load current of all other 3-phase motors operating at the same time. Where the input and output voltages of the phase converter are different, the current shall be multiplied by the ratio of the output to input voltage. 455-9. Connection of Single-Phase Loads. Where single-phase loads are connected on the load side of a phase converter, they shall not be connected to the derived phase. 455-10. Terminal Housings. A terminal housing shall be provided on a phase converter, and the terminal housing shall be in accordance with the provisions of Section 430-12. B. Specific Provisions Applicable to Different Types of Phase Converters 455-20. Disconnecting Means. The single-phase disconnecting means for the input of a static phase converter shall be permitted to serve as the disconnecting means for the phase converter and a single load if the load is within sight of the disconnecting means. 455-21. Start-Up. Power to the utilization equipment shall not be supplied until the rotary phase converter has been started. 455-22. Power Interruption. Utilization equipment supplied by a rotary phase converter shall be controlled in such a manner that power to the equipment will be disconnected in the event of a power interruption. (FPN): Magnetic motor starters, magnetic contactors, and similar devices, with interruption. manual or time delay restarting for the load, will provide restarting after power 455-23. Capacitors. Capacitors that are not an integral part of the rotary phase conversion system but are installed for a motor load shall be connected to the line side of that motor overload protective device.