3.4. 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 ML 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. The ML Series is insensitive to phase orientation, so the three phase conductors may be connected to the input bus bars in any order.

The user AC connection is made at the harmonic neutralizer, which is where the system circuit breaker is located. On 500 kW models the neutralizer is part of the connected three-cabinet assembly; on 1000 kW models it is the second cabinet, interconnected as described in Harmonic Neutralizer Interconnection.

The AC input connection points are three copper bus bars located behind a cover/access panel at the rear of the cabinet, dimensioned in Fig. 2.5. Conductors should be terminated with a 3/8” ring terminal to mate with the provided hardware. The recommended torque for the AC input connection is 240 in-lbf (27.1 Nm). Each bus bar accepts connections on both faces, so conductors may be landed from either side.

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 bus bars.

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 well before any protective device responds.

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.

Table 3.2 Suggested Ampacities of Various Conductors as Recommended by the National Electrical Code

Wire Size	60 °C Types	75 °C Types	85 °C Types	90 °C Types
	RUW, T, TW	FEPW, RH, RH, RUH, THW, THWN, XHHW, ZW	V, MI	TA, TBS, SA, AVB, SIS, FEP, FEPB, RHH, THHN, XHHW
14 AWG	25 Aac	30 Aac	30 Aac	35 Aac
12 AWG	30 Aac	35 Aac	40 Aac	40 Aac
10 AWG	40 Aac	50 Aac	55 Aac	55 Aac
8 AWG	60 Aac	70 Aac	75 Aac	80 Aac
6 AWG	80 Aac	95 Aac	100 Aac	105 Aac
4 AWG	105 Aac	125 Aac	135 Aac	140 Aac
3 AWG	120 Aac	145 Aac	160 Aac	165 Aac
2 AWG	140 Aac	170 Aac	185 Aac	190 Aac
1 AWG	165 Aac	195 Aac	215 Aac	220 Aac
10 AWG	195 Aac	230 Aac	250 Aac	260 Aac
20 AWG	225 Aac	265 Aac	290 Aac	300 Aac
30 AWG	260 Aac	310 Aac	335 Aac	350 Aac
40 AWG	300 Aac	360 Aac	390 Aac	405 Aac
250 MCM	340 Aac	405 Aac	440 Aac	455 Aac
300 MCM	375 Aac	445 Aac	485 Aac	505 Aac
350 MCM	420 Aac	505 Aac	550 Aac	570 Aac

Table 3.3 Suggested Ampacities of 4-Conductor Type S or SO Cable

Wire Size	Maximum Current
18 AWG	7 Aac
16 AWG	10 Aac
14 AWG	15 Aac
12 AWG	20 Aac
10 AWG	25 Aac
8 AWG	35 Aac
6 AWG	45 Aac
4 AWG	60 Aac
2 AWG	80 Aac

3.4.1. 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 ML 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.

Table 3.4 AC input current ratings for ML Series MagnaDC power supply

Power Level	AC Input Voltage	AC Input Current
500 kW	440 Vac, 3Φ	760 Aac
500 kW	480 Vac, 3Φ	697 Aac
1000 kW	440 Vac, 3Φ	1519 Aac
1000 kW	480 Vac, 3Φ	1362 Aac

Note

For master-slave systems, each cabinet draws the current listed above and must be provided with its own branch circuit sized accordingly.

3.4.2. Circuit Breaker

The ML Series MagnaDC power supply is equipped with an integrated three-phase AC breaker rated for the full power of the supply, housed in the harmonic neutralizer section 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 ML 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.