Checking Single Phase Power - A.O. Smith DSE-5 Service Handbook

Checking Single Phase (1Ø) Power
A single phase power supply will be connected to the L1 and L2 terminals of the Power Distribution
Block or directly to the contactor on models equipped with a single element. On 208/240/480 volt
power supplies both wires are "hot" with voltage present. On a 277 volt power supply one of the two
wires is a "neutral" and does not have any voltage present. Check power supply voltage as follows:
1 With the power supply to the water heater turned on set the volt meter to an AC voltage range above the
expected voltage (600 VAC or higher range initially).
2 Measure and record voltage between the [L1 & L2] terminals at the water heater's Power Distribution Block
or at the contactor on a single element model. Models equipped with a single element and a 4 pole
contactor will require two voltage readings; one voltage reading between the first and second terminals of
the contactor and a second voltage reading between the third and fourth terminals of the contactor.
3 Measure and record the voltage between the L1 terminal and the ground wire connection to the water
heater. Check between L2 and ground in the same way. Note: models equipped with a single element and
a 4 pole contactor will require four voltage readings; between the each of the 4 poles of the contactor and
ground. On 208/240 volt power supplies each reading to ground should be approximately 120 volts. On
480 volt power supplies each reading to ground should be approximately 277 volts. On 277 volt power one
of the wires is a neutral wire and will normally read approximately zero volts to ground.
Service Warning: Zero volt readings between terminals and ground can be due to an inadequate earth
ground. TREAT ALL WIRES AS BEING HOT until it has been determined there is no voltage present.
If the voltage readings between terminals (step 2) or the voltage between any of the terminals and
ground (step 3) was less than expected (< 95% expected): check the power supply to the water
heater. Contact a Qualified/Licensed electrician to restore power. If the voltage readings taken in
Step 2 above are a standard voltage (277/208/240/480) but do not match the listed voltage on the
water heater's rating label secure power to the water heater. DO NOT place the water heater back in
service. Call the toll free Technical Support phone number listed on the back cover of this manual for
further assistance.
208/240/480 Volt 1Ø Power
Measure power supply
voltage to water heater
on single element models
at upper terminals of the
contactor.
OPERATION & SERVICE
Measure power supply
voltage to water heater
on models with more
than one element at the
Power Distribution Block
Power Distribution Block
3 Pole Contactor
Servicing should only be performed by a Qualified Service Agent
L1 L2
4 Pole Contactor
13
277 Volt 1Ø Power
Measure power supply
to heating elements on
all models at the lower
terminals of the
contactor(s).