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What is allowable voltage range at a wall receptacle outlet in a house?
Tuesday, June 19, 2018
The nominal voltage in the United States is 120 volts, but the National Electrical Code [NEC 210.19 (A)] specifies an acceptable drop of 5% to fartherest outlet, which is 114 volts. The NEC does not specify maximum voltage, but plus 5% is the accepted standard. This puts the acceptable voltage range of a nominal 120-volt receptacle at between 114 and 126 volts.
You will rarely get a reading of exactly 120.0 volts. Voltage is typically set a little higher at the tap at the electric utility’s transformer to allow for voltage drop between it and the residence. The farther away the house is from the a transformer, the more the voltage drop. Then there is secondary voltage drop induced by the wiring between the main electric panel and a receptacle.
We test the voltage at a receptacle as part of an inspection, along with resistance to ground. An example of an acceptable reading is shown below.
Both excessively high or low voltage can cause problems with electrical devices in a home, but the effects of low voltage, or voltage drop when a major appliance such as a central air conditioner starts up, is most often noticed by a homeowner. Incandescent lights may flicker or sensitive electronic equipment like computers and laser printers may suddenly stop functioning.
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To learn more about electrical wiring, devices, and receptacles, see these other blog posts:
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