Emerson Liebert PSA Line-Interactive UPS 500-1500VA User Manual

The UPS and monitoring computer can be connected in either of two ways: serial connection or 

contact closure. A serial connection cable permits access to Liebert MultiLink’s complete 

functionality, but may be used only for those UPS models listed in Table 1. Any other UPS model 

must use contact closure. 
Liebert MultiLink requires a custom cable. The software will NOT function properly with ordinary 

serial cables. Proper cables can be purchased from Emerson or made with readily available materials.
To make your own cable, follow the instructions in this section. With the exception of Step 5, the 

instructions are identical for both the serial connection cable and the contact closure cable. (You may 

purchase a Liebert MultiLink UPS cable by contacting your local Emerson representative, 

value-added reseller or distributor. See Table 15 for part numbers.)
You should prepare and attach the cable before installing Liebert MultiLink so that the system will 

be ready to use the software.

• Two connectors, one with pins, the other with sockets, either DB25 or DB9 
• RJ11 or RJ12 cable 
• Two connectors, RJ11 or RJ12, depending on the cable being used

Follow these directions to build the cable:
1. Determine the connector your UPS needs

Examine your UPS. 

• Does it have a 9-socket or 25-socket connector?

This connector should be a socket or pin connector and look similar to one of the diagrams 

below. You will need to obtain a corresponding pin or socket connector.

• The diagrams in Figure 4 - Serial Port Connectors will help determine the type of 

connector you have. The circles denote pins and the dots denote sockets.

Examine your computer. 

• Does it have a 9-pin or 25-pin connector?
• Is the connector a pin or socket type? (A pin connector has protruding pins; a socket connector 

has holes.)

• If the UPS has a socket connector, the cable connector must have pins and vice versa.
• The diagrams in Figure 4 - Serial Port Connectors will help determine the type of 

connector you have. The circles denote pins and the dots denote sockets.

Measure the distance between the UPS and the computer. The cable must be long enough to reach 

each machine’s connector and to go around obstructions. Keep the cable as short as possible, 

preferably less than 25 feet. Do not lay the cable near electromagnetic interference sources such 

as AC power lines, fluorescent lights and induction motors.