MX28B 13
5.1.6 Mounting
Both front mounting on standard 23-inch rails and optional wall mounting are available.
5.1.7 Ventilation
The rectifiers 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 4.9 for environmental characteristics.]
5.2 AC Service and Ground Connections
***** WARNING *****Ensure that all of the dc and external 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 208/220/240V ac, single-phase, 50/60 Hz
power through individual external 20-amp two-pole circuit breakers to the ac input terminal
block connections for each rectifier in the system. (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” 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.
5.3 Battery Connections
5.3.1 Battery Disconnect
An external circuit breaker (not supplied) is required in the negative line (located at the
battery end) to protect the cables from the battery to the MX28B dc power plant. The power
plant can monitor auxiliary contacts from this breaker.
5.3.2 Cable Sizing Considerations
The battery cable(s) should be sized sufficiently large to limit the voltage drop from the
MX28B dc power plant to the battery during charging per system design requirements. The