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Page 8 MX28B200/400 –48 VDC User’s Manual (990-9133)
Ventilation
The rectifier modules for this system have fans that provide front-to-rear airflow for
internal cooling. The MX28B housing should mounted such that there is free airflow to
the front, top, and bottom of the unit. [Refer to Section 6.6 for environmental
characteristics.]
Free airflow should be ensured so that the power system can provide full power at a
given ambient temperature rating without de-rating.
3.3. AC Power Connections
WARNING: Ensure that all of the external DC and AC circuit
breakers are in the OFF position prior to connecting service to
the power plant. Confirm that all voltages have been removed
including any battery sources before proceeding.
The MX28B DC power plant requires the supply of 208/220/240/277 VAC single-phase,
50/60 Hz power through individual external 20-amp circuit breakers to the AC input
terminal block connections for each rectifier module in the system. Two rectifier modules
are required to accommodate the full AC input voltage range. The 1MRF28H54BV
rectifier is designed for the standard 208/220/240 VAC input service, while the
1MRF28H54BV50 is used for the 277 VAC input. The AC wiring, from the AC input
terminal block connections to the hot-pluggable AC input connector for each rectifier, is
factory installed.
The AC input enclosure, located at the top right rear of the MX28B housing, is provided
with two one-inch conduit entry holes and an access cover. Inside, a terminal strip(s) for
AC input power connection and a separate “Earth Ground” bar for connection of the
safety ground wire(s) are provided. The terminal block(s) is labeled as Position 1 through
Position 4 (Position 1 through Position 8 for the 400-amp unit) with each position having
inputs designated “L1” and “L2/N” for connection of the two AC wires. Positions 1-4
correspond to the top rectifier shelf positions from left to right. Positions 5-8 are
applicable to the 400-amp unit only and correspond to the lower rectifier shelf positions
from left to right.
The suggested wire size is #10 AWG rated at 90°C or higher; however, the ambient
temperature and number of wires in a conduit must also be considered in accordance
with NEC requirements. It is suggested that feeds for four rectifiers (8 wires) and one
safety ground wire be run in a one-inch conduit; however, be sure to follow any local
electrical wiring codes.
If the AC input power is provided from a three-phase distribution panel, the circuit breaker
positions should be selected such that the load is balanced as much as possible.