AT&T 3.0 manual Installing the Basic Carrier, Unit Loads for Key or Behind Switch Mode

Installing the Basic Carrier

Unit Loads for Key or Behind Switch Mode

In a Key or Behind Switch system with four or fewer modules, no calculation is needed. The power supply (model 391A1) generally supports four modules of any type.

Auxiliary Power Units

The power supply provides 54 unit loads to each carrier. If the unit load requirement for a carrier exceeds 54, an auxiliary power unit is needed to allow that carrier to support up to an additional 27 unit loads.

CAUTION:

Running the system with more than 54 unit loads per carrier may not appear to do harm. However, this can cause the system to malfunction, creating “NO Trouble Found” situations, such as malfunctioning LEDs on multiline telephones or power unit failure.

Any extension that is connected to the modules in the last two slots receives power from the auxiliary power unit instead of from the power supply.

If an auxiliary power unit is required, refer to “Installing the Auxiliary Power Unit,” later in this chapter, for instructions.

Installing the Basic Carrier

Continue with this procedure only if you have met all of the requirements discussed earlier in this chapter.

NOTE:

When you mount the basic carrier onto the backboard, leave 29 in. (73.66 cm) of backboard to the right. This allows you to easily install and remove the control unit cover, and also allows enough room for system expansion to the right for the total length of up to three carriers.

Installing the Control Unit 2-17