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:

 • What is the difference between what trips a GFCI (ground fault) receptacle and a circuit breaker?

• What is the code requirement for GFCI protection for receptacles near a wet bar sink? 

• What is the requirement for a service receptacle outlet for heating, air conditioning, and refrigeration (HACR) equipment? 

• Why is an opening in the wall around the side of an electrical receptacle outlet a safety defect?  

• When was GFCI-protection for kitchen dishwasher receptacle outlet first required? 

• What is allowable voltage range at a wall receptacle outlet in a house?

• When should I replace electric receptacle outlets? 

• Does an electric receptacle outlet in a storage shed require GFCI protection? 

• What are "self-contained" electrical receptacle outlets and switches?

• What is the difference between an electrical receptacle, an outlet, and a plug?

• Does a washing machine receptacle outlet require GFCI protection?

• What is the building code requirement for receptacle outlets at stairs and stair landings?

• Can I remove a 240-volt range receptacle and hard-wire the range? 

• What is a "backstab" receptacle outlet? 

• How many electrical receptacles (outlets) are required in a hallway?  

• What problems does having too many electric receptacle outlets on a single circuit cause? 

• Is a house required to have outdoor electric receptacle outlets?

• How I can tell if a receptacle outlet is tamper resistant?

• Why is there a GFCI breaker in the electric panel for the bathroom shower light and exhaust fan?

• What is a false ground, bootleg ground, or cheated ground receptacle? 

• How can adding wood paneling or a wainscot create an electrical safety hazard?

• How far apart should electric receptacles be spaced in a bathroom? 

• Is an ungrounded electric receptacle outlet dangerous?

• Why is there no bathroom electric receptacle in this old house?

   Visit our ELECTRICAL page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.