Voltage - A.O. Smith ST1302 Manual

10

Voltage

Level 2
VOLTAGE
Most dual voltage (115/230V) motors are con-
nected at the factory for 230 volts for two rea-
sons. First, the highest percentage of motors are
installed on the higher voltage. Second, if a
motor is connected for 230 volts and 115 volts are
applied in the field, the motor will hum and trip
the overload. If connected for 115 volts and 230
volts are applied, it burns out immediately.
Motors are designed to operate at plus or
minus 10% of the nameplate rating. This means
the motor will operate at 103 volts to 126 volts on
the 115 volt connection; and, 207 volts to 253
volts on the 230 volt connection. At 207 volts, the
amps will be higher and the RPM will be approx-
imately 25% lower.
If the system is rated at 208 volts or 200 volts,
a motor specifically designed for these ratings
should be used since the voltage could go as low
as 187 or 180. Specific 208 and 200 volt single
phase motors are not normally stocked for
replacement. The alternative is to use the next
higher horsepower motor. For example, use a 1
horsepower, 230 volt motor when a 3/4 horsepow-
er 208 volt motor is needed. Three phase motors
have some greater ability to operate at 208 volts.
But, the next higher horsepower should be used if
a 200 volt motor is required.
NEMA no longer recognizes 208 volt systems.
The standard is now 200 volts.
Pump Motors
A.O.Smith