Emerson Static Transfer Switch user manual Input Junction Box Installation-Optional

Power and Control Wiring

Figure 3 Typical static transfer switch one-line diagram

SOURCE 1		STS1	STS2	SOURCE 2
	CB1			CB2
	K1			K2
K2 K3	CB4		CB3	K1 K3	CB5

OUTPUT

The input and output power wire size should be based on the upstream overcurrent protection device, observing the NEC and local codes.

The molded case switches contained in the Liebert STS2 are typically non-automatic circuit breakers that rely on the upstream and/or load overcurrent protection. Upstream overcurrent protection should be rated equal to or less than the rating of the Liebert STS2 molded case switches.

The Liebert STS2 input and output power and ground and neutral bus bars accommodate a wide range of wire sizes. The Liebert STS2 bus bars accommodates standard 2 hole lugs.

Table 2	Input/output conduit plate specifications
Rating		Max. number and size
100-250A		6	— 3" conduit
400-600A		9	— 4" conduit
800-1000A		12	— 4" conduits

5.2Input Junction Box Installation—Optional

The input junction box option is available to simplify input connections to the Liebert STS2. Two input junction boxes and the associated flexible 10 foot long (3 meter) input cables are provided with this option.

This option is available only with bottom cable entrance, typically when the unit is located on a raised floor.

If the input junction boxes will be used, they may be shipped either with the unit or in advance to be installed during the rough-in stage of construction.

Locate the junction boxes a maximum of 8 feet (2.4 meters) from the planned location of the Liebert Static Transfer Switch.

Due to a lack of clearance for the cables below the unit, the cables are also shipped loose from the unit for installation at the site. The input cables connect from the input junction boxes to the input power bus bars inside the Liebert STS2.

The standard configuration for the input junction boxes and cables is for 3-wire-plus-ground feeds. If the input neutral is required, special 4-wire-plus-ground input cables and junction boxes are required. See Figure 29 for wiring details.

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