Article 455 provides the requirements for installing phase converters [Sec. 455.1]. Before installing a phase converter, read the nameplate to ensure the unit you have matches the drawings and specifications. The nameplate must be permanent and provide the six bits of info required by Sec. 455.2 (seven requirements if it’s a rotary-phase converter).
How do you determine the ampacity of the conductors? It depends on whether the loads are variable or fixed. If the loads are:
- Variable, the conductor ampacity must be at least 125% of the phase converter nameplate single-phase input full-load amperes [455.6(A)(1)].
- Fixed, determine if the conductor ampacity meets the requirements for variable loads. If it’s less than that, the ampacity must be at least 250% of the sum of the full-load, 3-phase current rating of the motors and other loads served but only if the input and output voltages (of the converter) are identical. If these voltages differ, determine the current per Sec. 455.6, and multiply by the ratio of output to input voltage [Sec. 455.6(A)(2)].
The manufactured phase conductors must be identified at all accessible locations with a distinctive marking that is consistent throughout the system and premises [Sec. 455.6(B)].
How do you determine overcurrent protection? As with conductor ampacity, it depends on whether the loads are variable or fixed. If the loads are:
- Variable, the conductor ampacity must be at most 125% of the phase converter nameplate single-phase input full-load amperes [Sec. 455.7(A)].
- Fixed, protect the conductors per their ampacity. But don’t exceed 125% of the phase converter nameplate single-phase input full-load amperes [Sec. 455.7(B].
What about a disconnecting means? It’s required, and you have to install it in sight from the controller and make it readily accessible [455.8(A)]. It has to be a switch (rated in horsepower if motor loads are used), a circuit-breaker, or a molded-case switch [Sec. 455.8(B)]. Its ampere rating must be at least 115% of the rated maximum single-input full-load amperes [Sec. 455.8(C)]. But if its used for specific fixed loads you can select the rating from Sec. 455.8(C)(1) or (2), which are for a current rated disconnect or a horsepower rated disconnect respectively.
If you connect single-phase loads on the load side of a phase converter, do not connect them to the manufactured phase [Sec. 455.9].
Part II is brief and it applies specific provisions to different types of phase converters. For example, if you have a rotary-phase converter then power can’t be supplied to the utilization equipment until the converter has been started [Sec. 455.21].
