Model 4821/4820 Control/Communicator Installation Manual
4-12 150964
4.10 AC Power Transformer
The Model 9227 is an external transformer that is included with the 4821/4820. The trans-
former output is 18 VAC, 50VA and provides power and battery charging for the system. The
transformer plugs directly into a conventional 120 VAC unswitched outlet.
The earth terminal on the 4821/4820 main circuit board provides a convenient method for
connecting the 4821/4820 metal cabinet to an earth ground. (See Figure 4-6.)The earth con-
nection is also used for increased transient protection on the telephone interface. All circuitry
in the Model 4821/4820 system is electrically isolated from this earth terminal on the 4821/
4820 main circuit board. There should be no connections to this terminal other than the earth
connection for grounding the metal cabinet.
Figure 4-6 Model 9227 Connection to Model 4821/4820
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