Emerson 40-200KVA Mode D'Emploi

The parallel redundant system can noticeably improve system reliability. In normal condition, none of 

the UPS modules work at full load. That means that even if the load is increased, the system will not 

transfer to bypass. And when a UPS module shuts down due to any failure, the remaining UPS 

modules can still power and protect the load. When redundancy is lost due to module failure or load 

increase, the parallel system will trigger an alarm.

The parallel system also has operation modes such as normal, battery, bypass and maintenance 

bypass. All UPS modules in the parallel system operate in coordination.

• Normal Mode Operation

The load is powered by the inverters of all the UPS modules in the system. If the frequency of 

bypass is within the synchronous range, the inverter will be synchronized with the bypass. 

Otherwise, the system will operate at nominal frequency.

• Battery Mode Operation

The batteries of all UPS modules power the load through their inverters. The system operates at 

nominal frequency.

• Bypass Mode Operation

The condition to transfer to bypass mode is essentially the same as that of single module system. 

The bypass of all the UPS modules powers the load.

• Maintenance Bypass Mode Operation

The sequence to transfer to maintenance bypass mode is the same as for transferring a single-

module system. The maintenance bypass switches should be switched on as synchronously as 

possible. Thus the system can be repaired without interrupting the power supply to critical load. 

If ECO mode is selected, the double-conversion UPS operation is inhibited at most times for the 

purpose of saving energy. In this mode of operation, not unlike UPS of line-interactive or standby 

technology, the bypass is the preferred source. Only when the voltage and/or frequency of the 

bypass supply is beyond pre-defined and adjustable limits is the critical AC load transferred to 

the inverter.

The basic installation procedure of parallel system is the same as that of single module system. The 

following sections introduce only the installation procedures specific to the parallel system.

• Each UPS module must have the same bypass source.
• The outputs of all UPS modules are connected altogether.
• The main inputs can be from different sources, but the phase rotation sequence of main inputs, 

bypass inputs and outputs must be correct and the same.

• The parallel logic cable and load sharing cable must be connected in a ring correctly (see 

Risk of creating parallel systems with incorrect power ratings. Can cause equipment damage.
When paralleling UPS’s with different power ratings, the power rating of the larger UPS can 

be no more than four times the power rating of the smaller UPS.
• 40-80kVA Liebert

®

 NX

™

 units can be installed in parallel with 80-120kVA Liebert NX 

units.

• 80-120kVA Liebert NX units can be installed in parallel with 160-200kVA.
• 40-80kVA Liebert NX units must not be installed in parallel with 160-200kVA Liebert NX 

units.