Liebert EM User Manual

The OpenComms EM must be connected to a modem to send pager alerts when a sensor reading 

crosses a user-defined threshold (see 5.5.2 - Modem Setup for more information). 
The unit is compatible with modems that have DB9 or DB25 serial COM ports. A proper cable must 

be constructed to allow communication between the unit and the modem. This cable connects the 

RJ45 connector labeled Modem on the back of the unit to the serial port on the modem. 
Refer to Table 13 for a pinout guide for building the correct cable. For more information on construct-

ing this type of cable, call Liebert Monitoring Application Support at 1-800-222-5877 or contact your 

local Liebert representative. 

All OpenComms EM models can 

accommodate a contact closure cable in 

either sensor port. Contact closure cables 

are available separately from Liebert in 

various lengths (see Table 3).
To make your own contact closure cable, 

refer to Table 14 for the pinout for this 

cable. 

• Pin 2 is the contact that may be 

defined as either Normally Open or 

Normally Closed. 

• Pins 6 and 8 must be tied together to 

form the common.

The serial cable included with 

OpenComms EM PDU and vEM-14 con-

trollers is designed for connecting the 

OpenComms EM unit to an MP 

Advanced power strip. 
To make your own cable, refer to 

Table 15 for the pinout for this cable.

1

DTR

Data Term Ready

20

4

2

CTS

Clear to Send

5

8

3

GND

Signal Ground

7

5

4

TXD

Transmit Data

2

3

5

RXD

Receive Data

3

2

6

CD

Carrier Detect

8

1

7

RTS

Request to Send

4

7

8

DSR

Data Set Ready

6

6

1

—

2

Normally Open or Normally Closed

3

—

4

—

5

—

6

Common - tied to Pin 8

7

—

8

Common - tied to Pin 6

1

8

2

3

3

2

4

5

5

4

6

Not Connected

7

Not Connected

8

1