3.3. AC Input Connection
Warning
Disconnect AC power from the mains and measure the AC input terminals to ground to ensure 0 Vac is present before attempting any installation procedure.
AC power is wired to the MT Series MagnaDC power supply by attaching three cables plus ground. A safety ground wire must be connected to the stud labeled with a ground symbol at the rear of the power supply. The MT Series is insensitive to phase orientation, so the three phase conductors may be connected to the input studs in any order.
The AC input connection points are four (4) 3/8-16 studs mounted in 1.5 inch copper buses, located behind the rear access panel. Magna-Power recommends cables per the recommendations of the National Electrical Code or Suggested Ampacities of 4-Conductor Type S or SO Cable, crimped to ring terminals and securely fastened to the studs.
Note
The cable recommendations provided are for reference purposes only. Always consult local electrical code requirements to ensure compliance.
Given the input currents involved, verify that every connection is tight before energizing the supply. A loose connection at these current levels will overheat the bus and the cable termination.
This programmable DC power supply is designed to be permanently connected to the power source, requiring a readily accessible disconnect device incorporated into the fixed wiring. The integrated AC input breaker described in Circuit Breaker is not a substitute for that disconnect device.
3.3.1. AC Input Current
The following table provides the maximum input current rating per phase for the available AC input voltages and power levels of the MT Series. All AC input currents factor in efficiency and power factor. With the product’s AC soft-start circuitry, there is no additional in-rush current; the numbers in the following table provide the peak AC current draw at full load. These same AC input current ratings are also specified on the product’s serial label. These ratings, in combination with the conductor ampacity tables above, guide AC input conductor selection.
Note
For master-slave systems, each cabinet draws the current listed above and must be provided with its own branch circuit sized accordingly.
3.3.2. Circuit Breaker
The MT Series MagnaDC power supply is equipped with an integrated three-phase AC breaker rated for the full power of the supply, mounted behind the rear access panel and accessible from the rear of the cabinet. This is a difference from the smaller MagnaDC products, which protect the power stage with input power and control fuses instead: the MT Series has no input fuses to inspect or replace.
The breaker serves two purposes. It provides overcurrent protection for the power processing circuitry, and it isolates the unit from the mains for service. The breaker must be in the on position for the supply to operate.
If the breaker trips, or if the breaker has not been engaged after turning on control power at the front panel control power switch, the fuse (FSE) alarm will indicate. Investigate the cause before re-engaging the breaker: a tripped breaker usually indicates a power stage failure, often requiring factory attention, though it can also be caused by power surges from lightning storms or other AC transient events. After engaging the breaker to the on position, clear the FSE alarm as described in Fuse (FSE).
Warning
Lethal voltages may be present inside the power supply even when the AC input breaker is open and the AC input voltage is disconnected. Only properly trained and qualified personnel should remove covers and access the inside of the power supply.