Get Voltage Tolerance Boundary

NEMA tolerances on most standard equipment is +10/-15%. Motors are +/-10%. ANSI gives standard voltages with generally -5% for utilization so set transformer to 120 V but equipment is designed for 110-115 V (there is some variation) or multiples.

At the electrical service, the electric utility should attempt to keep the voltage ±5% of nominal. The electrician needs to be aware of the acceptable electric utility fluctuation and plan to keep the voltage at the point of utilization between +5/-10% of nominal.

Voltage Tolerance: The range within which the output voltage can vary while still the meeting specifications. Load Regulation: How well the regulator maintains the voltage when the load changes. Line Regulation: The ability to maintain voltage despite variations in the input voltage.

Most electric utilities in the U.S. try to maintain the voltage level within plus or minus 5% of the nominal voltage level (e.g. 480V +/-5%), however for short periods the voltage level may be as much as 6% high or 13% low (ing to ANSI Standard C84. 1).

NEMA tolerances on most standard equipment is +10/-15%. Motors are +/-10%. ANSI gives standard voltages with generally -5% for utilization so set transformer to 120 V but equipment is designed for 110-115 V (there is some variation) or multiples.

The specification is that the nominal 120 V line should be long term within +/-5% which is 114 to 126 Volts. Brief excursions are allowed up to about +/-10% which is 108 to 132V.

Often a tolerance of 5% from scheduled voltage is considered acceptable. On the transmission system, greater variances are sometimes acceptable. If voltage is too high, protective breakers will open to prevent damage to equipment, causing portions of the grid to lose power.

The National Electrical Code allows up to a 5% drop. There can be a <3% drop in a feeder and an additional <3% drop in individual branch circuits. Utilities actively regulate distribution voltages slowly by means of tap changing regulators and by switching capacitors to follow changes in load.