A.O. Smith DSE-5 Service Handbook page 42

120 VAC Transformer Wiring - 480 Volt Models
This is a multiple or "multi" tap transformer that can accept 2 different input voltages to it's
primary winding. This transformer outputs 120 VAC power from it's secondary winding which
powers the CCB (page 50) and the contactor coils. The input power wiring to the primary
winding of this transformer must be configured to match the power supply voltage to the
water heater. Incorrect wiring can cause output voltage from the transformer's secondary
winding to be too low or too high. This can cause "contactor chatter" (contacts open and
close rapidly) and may permanently damage the contactors and/or the CCB. The
instructions below show how to properly configure the input power wiring to the transformers
primary winding.
Service Note: The 380 Volt H2 tap is used for international applications. Ensure you do not
connect the second wire to the H2 tap for standard 480 volt applications.
1 Determine power supply voltage to the water heater - see pages 12 - 14. Ensure the power supply wiring to
the 120 VAC transformer's primary winding are connected to the proper terminals as shown in the table
below.
2 Only one wire needs to be moved on the transformer's primary winding terminals to configure for a
different voltage. Do not move or change the wire connected to the H1 terminal on the primary winding. Do
not move or change either wire at the secondary winding X1 or X2 connections.
WATER HEATER POWER SUPPLY VOLTAGE
Servicing should only be performed by a Qualified Service Agent
OPERATION & SERVICE
380 VAC
480 VAC
Primary Winding
Secondary Winding
PRIMARY WINDING CONNECTIONS
H1 Common & H2 (380)
H1 Common & H3 (480)
40
H1 H2 H3
120 VAC
X1 X2