Figure 4-9: Principle Of Paralleled Ups Systems - Eaton 93PM User And Installation Manual

MOB's
Module Output Breakers (MOBs) allow the output of the UPS to be disconnected from the other
UPSs and system load for maintenance and service. Design considerations assume that each UPS
has a Module Output Breaker (MOB). The breaker shall not disconnect neutral.
The MOB must have a Form "C" auxiliary contact. The N.C contact is connected to the corresponding
UPS's input used for signal input. The N.O. contact is used to disconnect the Bypass Pull-Chain when
the MOB is open. Figure 4-9: Principle of paralleled UPS systems on page 49 shows the principles
of paralleled UPS systems including MOBs and outputs from UPSs.
MOB Override
Users without MOBs installed can simply leave the MOB signal input disabled. The user should be
aware that systems without MOB have limited maintenance capability.
Parallel system wiring

Figure 4-9: Principle of paralleled UPS systems

Required parallel system wiring length must be equal to ensure approximately equal current sharing
when in Bypass mode.
For proper operation the following must be true: 1A+1B=2A+2B=3A+3B=4A+4B.
Any difference in wire length will result in decreased capacity and improper operation of the UPS
system while on bypass.
P-164000249 30-200 kW 49
Revision 2 User's and Installation Guide