Emerson 115-480 Manuel D’Utilisation

1. Consider the grounding configuration of the UPS system before finalizing module placement. For 

optimal ground performance, the Liebert

®

 APM

™

 modules should be close together. See 3.2.5 - 

2. For optimal load-sharing performance, the UPS bypass input cables and output cables should be 

approximately the same length, plus or minus 20 percent.

3. Position modules in such a way as to minimize the length of power cables and control wiring 

between UPS modules and the paralleling cabinet.

Consider the grounding configuration of the UPS system before finalizing module placement. See 

3.2.5 - Cabling Guidelines.
Emerson recommends matching the impedance in the bypass path of paralleled systems as closely as 

possible.
The impedance mismatch can be minimized by controlling the wiring length of each unit. The design 

and the layout of the UPS system and associated panels and cabling should be examined closely to 

ensure that cable lengths and impedances are closely matched. The Liebert 1+N UPS module is 

supplied with a sharing reactor to minimize the impact of cable impedance mismatch. The cabling 

impedance must be carefully controlled to ensure good bypass current sharing. 
For Liebert APM

™

 systems, the cabling impedances must be within 10% from maximum to minimum. 

If the cabling impedances must be greater than 10%, contact your Emerson representative to 

calculate whether the system will result in an overload condition when operating on bypass.
When bringing the 1+N system online for the first time or after removing one unit, Emerson 

recommends checking the bypass current mismatch. To check the bypass current mismatch:
1. Place a load on the bypass of each UPS module.
2. View the output current of each unit.
The accuracy of the currents displayed on the UPS module is sufficient for this check. If the mismatch 

is greater than 10%, the bypass impedances must be balanced or the load must be limited to less than 

the maximum rating.

The 45kVA frame consists of a single cabinet housing the UPS components and the internal battery 

string. The 90kVA frame, also a single cabinet, does not accommodate internal batteries, but does 

provide for an internal 4-breaker bypass, or an internal transformer. The internal transformers are 

available with either 480V:208V or 600V:208V input primaries.
Optional battery cabinets are available for each Liebert

®

 APM

™

 model to provide extended run time. 

Each battery cabinet houses a single string of batteries per cabinet that operate in parallel with the 

Liebert APM’s internal batteries (45kVA frame only). The battery cabinets are designed to be bolted 

to the left side of the UPS (see Figure 1). Refer to 4.4 - External Battery Cabinet Installation for 

details.
Optional Liebert BDC

™

 units are available. These cabinets house the components necessary to 

provide an external wraparound maintenance bypass switch for servicing the UPS.
Liebert BDCs are designed to be bolted to the right side of the UPS (see Figure 1). Refer to 5.3 - 

A UPS system can comprise a number of equipment cabinets, depending on the system design 

requirements—e.g., UPS cabinet, External Battery Cabinet and External Bypass Cabinet. In general, 

all cabinets used will be the same height and are designed to be positioned side-by-side to form an 

aesthetically appealing equipment suite.