Article 455

Phase Converters

Part I. General

Scope. This article covers the installation and use of phase converters.
Definitions.Manufactured Phase. The manufactured or derived phase originates at the phase converter and is not solidly connected to either of the single-phase input conductors.Phase Converter. An electrical device that converts single- phase power to 3-phase electric power.Informational Note: Phase converters have characteristics that modify the starting torque and locked-rotor current of motors served, and consideration is required in selecting a phase converter for a specific load.Rotary-Phase Converter. A device that consists of a rotary transformer and capacitor panel(s) that permits the operation of 3-phase loads from a single-phase supply.Static-Phase Converter. A device without rotating parts, sized for a given 3-phase load to permit operation from a single- phase supply.
Other Articles. Phase converters shall comply with this article and with the applicable provisions of other articles of this Code.
Marking. Each phase converter shall be provided with a permanent nameplate indicating the following:
1. Manufacturer’s name
2. Rated input and output voltages
3. Frequency
4. Rated single-phase input full-load amperes
5. Rated minimum and maximum single load in kilovolt- amperes (kVA) or horsepower
6. Maximum total load in kilovolt-amperes (kVA) or horse‐ power
7. For a rotary-phase converter, 3-phase amperes at full load
Equipment Grounding Connection. A means for attach‐ ment of an equipment grounding conductor termination in accordance with 250.8 shall be provided.
Conductors.
1. Ampacity. The ampacity of the single-phase supply conductors shall be determined by 455.6(A)(1) or (A)(2).Informational Note: Single-phase conductors sized to prevent a voltage drop not exceeding 3 percent from the source of supply to the phase converter may help ensure proper starting and operation of motor loads.
  1. Variable Loads. Where the loads to be supplied are varia‐ ble, the conductor ampacity shall not be less than 125 percent of the phase converter nameplate single-phase input full-load amperes.
  2. Fixed Loads. Where the phase converter supplies specific fixed loads, and the conductor ampacity is less than125 percent of the phase converter nameplate single-phaseinput full-load amperes, the conductors shall have an ampacity not less 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.
2. Manufactured Phase Marking. The manufactured phase conductors shall be identified in all accessible locations with a distinctive marking. The marking shall be consistent through‐ out the system and premises.
Overcurrent Protection. The single-phase supply conductors and phase converter shall be protected from over‐ current by 455.7(A) or (B). Where the required fuse or nonadjustable circuit breaker rating or settings of adjustable circuit breakers do not correspond to a standard rating or setting, a higher rating or setting that does not exceed the next higher standard rating shall be permitted.
1. Variable Loads. Where the loads to be supplied are varia‐ ble, overcurrent protection shall be set at not more than125 percent of the phase converter nameplate single-phase input full-load amperes.
2. Fixed Loads. Where the phase converter supplies specific fixed loads and the conductors are sized in accordance with 455.6(A)(2), the conductors shall be protected in accordance with their ampacity. The overcurrent protection determined from this section shall not exceed 125 percent of the phase converter nameplate single-phase input amperes.
Disconnecting Means. Means shall be provided to disconnect simultaneously all ungrounded single-phase supply conductors to the phase converter.
1. Location. The disconnecting means shall be readily acces‐ sible and located in sight from the phase converter.
2. Type. The disconnecting means shall be a switch rated in horsepower, a circuit breaker, or a molded-case switch. Where only nonmotor loads are served, an ampere-rated switch shall be permitted.
3. 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 or, for specific fixed loads, shall be permitted to be selected from 455.8(C)(1) or (C)(2).
  1. Current Rated Disconnect. The disconnecting means shall be a circuit breaker or molded-case switch with an ampere rating not less than 250 percent of the sum of the following:
    1. Full-load, 3-phase current ratings of the motors
    2. Other loads served
    (2) Horsepower Rated Disconnect. The disconnecting means shall be a switch with a horsepower rating. The equivalent locked rotor current of the horsepower rating of the switch shall not be less than 200 percent of the sum of the following:
    1. Nonmotor loads
    2. The 3-phase, locked-rotor current of the largest motor as determined from Table 430.251(B)
    3. The full-load current of all other 3-phase motors operat‐ ing at the same time
4. Voltage Ratios. The calculations in 455.8(C) shall apply directly where the input and output voltages of the phase
ARTICLE 460 — CAPACITORS 460.10
converter are identical. Where the input and output voltages of the phase converter are different, the current shall be multi‐ plied by the ratio of the output to input voltage.
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 manufactured phase.
Terminal Housings. A terminal housing in accordance with the provisions of 430.12 shall be provided on a phase converter.

Part II. Specific Provisions Applicable to Different Types of Phase Converters

Disconnecting Means. The single-phase disconnecting means for the input of a static phase converter shall be permit‐ ted to serve as the disconnecting means for the phase converter and a single load if the load is within sight of the disconnecting means.
Start-Up. Power to the utilization equipment shall not be supplied until the rotary-phase converter has been started.
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.Informational Note: Magnetic motor starters, magnetic contac‐ tors, and similar devices, with manual or time delay restarting for the load, provide restarting after power interruption.
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.

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