Electrical Connections - All Models; Electrical Wiring; Power Supply Connections - A.O. Smith BTH 120 Service Handbook

ELECTRICAL CONNECTIONS – ALL MODELS
The water heaters covered in this Service Handbook require a 120 VAC, 1Ø (single phase), 60Hz, 15 amp
power supply and must also be electrically grounded in accordance with local codes or, in the absence of
local codes, with the National Electrical Code, ANSI/NFPA 70 or the Canadian Electrical Code, CSA C22.1.
POWER FLUCTUATIONS AND ELECTRICAL NOISE
The water heater's control system requires a source of stable clean electricity for proper operation. Connecting
the water heater to a branch circuit that is subject to fluctuations in voltage level or electrical line noise
such as EMI (electro magnetic interference) or RFI (radio frequency interference) may cause erratic control
system operation and malfunction.
A high quality power supply filter/suppressor must be installed if the above conditions exist. Call the technical
support phone number listed on the back cover of this Service Handbook for more information.
Note: Malfunctions caused by power supply and costs to install power supply filters are not covered under
the limited warranty.
DEDICATED POWER WIRING AND BREAKERS
Dedicated power supply wires, ground wiring and dedicated circuit breakers often reduce electrical line noise
and are required when installing the water heater.

ELECTRICAL WIRING

All electrical work must be installed in accordance with the National Electrical Code, ANSI/NFPA 70 or the
Canadian Electrical Code, CSA C22.1 and local requirements.
When installed, the water heater must be electrically grounded in accordance with local codes or, in the
absence of local codes, with the National Electrical Code, ANSI/NFPA 70 or the Canadian Electrical Code,
CSA C22.1.
If any of the original wire as supplied on the water heater must be replaced, it must be replaced with UL Listed
Power Limited Circuit Cable of the same size and rating as original wiring.

POWER SUPPLY CONNECTIONS

The 120 VAC black (hot) wire from the power supply must connect to the black lead wire or the "L1" terminal
block location in the junction box and the 120 VAC white (neutral) wire must connect to the white lead wire
or the "Neutral" terminal block location in the junction box for correct polarity. See "Junction Box Assembly"
Figure on next page.
Power supply connections must be made as follows:
1. Turn off the electrical circuit breaker that serves the water heater.
2. Remove the junction box cover.
3. Connect the 120 VAC black (hot) wire from the power supply to the black lead wire or the terminal
block location marked "L1" inside of the junction box located on top of the water heater. If the black
lead wire is used make the connection inside of the junction box with a properly sized wire nut. See
"Junction Box Assembly" Figure on next page and "Wiring Diagrams" on Page 52 and Page 53.
Note: If electrical connection is made directly to terminal block remove black lead wire before making
connection.
4. Connect the 120 VAC white (neutral) wire from the power supply to the white lead wire or the
terminal block location marked "Neutral" inside of the junction box located on top of the water
heater. If the white lead wire is used, make the connection inside of the junction box with a properly
sized wire nut. See "Junction Box Assembly" Figure on next Page and "Wiring Diagrams" on Page
52 & Page 53.
Note: If electrical connection is made directly to terminal block remove white lead wire before making
connection.
Servicing should only be performed by a Qualified Service Technician 35