# Using an alternative power supply

You can use a power supply other than the NMS power supply. This power supply must provide:

- DC voltage to provide talk battery power to the station telephones.

- AC and DC ring voltage, if your application involves ringing station telephones. The AC voltage provides the ringing power. The DC voltage provides loop current that signals the CX board when the telephone goes on or off hook.

This topic specifies the power supply requirements for different boards and describes how to connect an alternative power supply.

Note: If you are using CX 2000C-32-R boards with the on-board ringing option enabled, you do not need to provide external ring voltage. However, you still need to provide the talk battery power.

## Power supply requirements

The tables in this topic specify power supply requirements for different boards, cable lengths, and resistive loads.

Cables between the power supply and the board must be rated for 2 A per board or greater. Twisted pair cabling is recommended for noise reduction.

Warning: | In the worst case, the ring voltage must not exceed 92 V AC, and the DC voltage must not exceed 52 V DC.

An AG 2000 power supply can be substituted for the rack mount supply for one CX 2000C board. The cable supplied with the AG 2000 power supply will mate with the connector on the board.

### CX 2000C-32 and CX 2000C-48 power supply requirements

For CX 2000C-32 and CX 2000C-48 boards, AC voltage is required only if you are enabling ringing of station phones.

Note: In this type of installation, all cables must be a minimum of 8000 feet to control heat.

Length of 24 AWG cable | Maximum resistive load | Recommended output
--- | --- | ---
Talk battery | Ring voltage (only if ringing required)
0 to 18,000 feet | 1500 Ohms | -30/-48 V DC | 80 to 89 V AC and -48 V DC
0 to 2000 feet | 600 Ohms | -24 V DC | 55 to 89 V AC and -24 V DC
0 to 8000 feet | 800 Ohms | -30 V DC | 55 to 89 V AC and -30 V DC
8000 to 18,000 feet | 1500 Ohms | -48 V DC | 80 to 89 V AC and -48 V DC

The dual output -30/-48 V DC supply is preferred. However, if the cable lengths to all stations fit into one of the other categories listed above, a supply with a single DC output is satisfactory.

The ring signal circuitry in the power supply must be equivalent to the following illustration:

Ring signal schematic (for CX 2000C power supply)

### CX 2000C-32-R power supply requirements

For CX 2000C-32-R boards, AC voltage is required only if you want to enable ringing, and are not using the on-board ringer option. In this case, CX 2000C-32-R power supply requirements are identical to those of the CX 2000C-32 and CX 2000C-48.

Length of 24 AWG cable | Max resistive load | Recommended output
--- | --- | ---
Talk battery | Ring voltage (only if ringing required)
0 to 8000 feet | 1500 Ohms | -30/-48 V DC | N/A
0 to 2000 feet | 600 Ohms | -24 V DC | N/A
0 to 8000 feet | 800 Ohms | -30 V DC | N/A
> 8000 feet | Not supported.

The dual output -30/-48 V DC supply is preferred. However, if the cable lengths to all stations fit into one of the other categories listed above, a supply with a single DC output is satisfactory.

## Connecting an alternative power supply

Connect the power supply to the TELCO POWER connector on the rear I/O transition board. The following illustration shows the power connector pinouts for the CX 2000C (rear I/O transition board):

Power connector pinouts

The mating connector is Molex 43025-1000 with Molex 43030-0001 or Molex 43030-007 pins.

If only one DC output is available, it must be connected to both the high battery input and the low battery input.

For more information, refer to Connecting to a CompactPCI chassis telecom power bus.