Acceptable Voltage Ranges

Voltage Relationships Based on Voltage Ranges in ANSI C84.1-1989

Voltage Ranges 

Voltage is divided into two ranges: A and B. Each voltage range is listed for locations: service, utilization and lighting. Service voltage is measured at the point of delivery; utilization voltage is measured at the terminals of the utilizing equipment. These are detailed in Table. The difference between service and utilization voltage allows for voltage drop in facility wiring between the point of utility delivery and the utilization equipment. The National Electrical Code (NEC), recommends that voltage drop in branch circuits (sub panel to utilization equipment) be less than three percent. It also recommends that feeder (between main panel and subpanel) voltage drop be less than three percent, with the combined voltage drop of branch plus feeder being less than five percent.

Range A (Favorable Zone)

Voltage range A is the favorable zone, where voltage level is near optimal.

Service Voltage

Most utilities supply systems are designed and operated so that most service voltage levels are within the limits specified for range A. The occurrence of service voltages outside these limits is to be infrequent. 

Utilization Voltage

Customer systems are to be designed and operated so that, with service voltage levels within range A limits, most utilization voltage levels will also be within the limits specified for range A. Utilization equipment shall be designed and rated to give fully satisfactory performance throughout this range. 

Lighting Voltage

Customer systems are to be designed and operated so that, with service voltage levels within range A limits, most utilization voltage levels will also be within the limits specified for range A. Lighting equipment shall be designed and rated to give fully satisfactory performance throughout this range.

Range B (Tolerable Zone)

Voltage range B is the tolerable zone, where voltage level is acceptable but not optimal. Range B includes voltage levels above and below range A limits that necessarily result from operating conditions. Although such conditions result in a practical system, they should be limited in extent, frequency, and duration. Within a reasonable time, corrective measures should be taken to upgrade voltage levels that lie in range B to those of range A. In some cases, sustained voltage levels will fall outside range B. In these instances, utilization equipment may not operate satisfactorily and protective devices may need to operate to protect equipment. Such cases should be considered temporary and subject to immediate improvement.

Table For Acceptable Industry Standard Nominal Voltage

Voltage Point of Measurement Standard Voltages
120 208 240 277 480		 Percent Of Nominal Voltage
     
Service Entrance Voltage High Range A 126 218 252 291 504 105%
Service Entrance Voltage Low Range A 114 198 228 263 456 95%
   
Utilization High Voltage Range A 125 217 250 289 500 105%
Utilization Low Voltage Range A 110 191 220 254 440 91.7%
   
Utilization High Voltage Range A Lighting 121 209 241 278 482 N/A
Utilization Low Voltage Range A Lighting 103 178 205 237 410 N/A
   
Service Entrance Voltage High Range B 127 220 254 293 508 105.8%
Service Entrance Voltage Low Range B 110 191 220 254 440 91.7%
   
Utilization High Voltage Range B 127 220 254 293 508 105.8%
 Utilization Low Voltage Range B  106 184 212 245 424 88%
 

Utilization High Voltage Range B Lighting 116 202 233 269 466 N/A
Utilization Low Voltage Range B Lighting 095 165 191 220 382 N/A