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Glossary
Electrical Theory & Applications for HVACR
U
Underwriters Laboratories (UL)
an independent tesƟng agency for electrical appliances
uƟlity transformer
a transformer that steps down the uƟlity supply voltage for use in a facility
V
VAC
abbreviaƟon for volts alternaƟng current
valance electrons
the number of electrons in the outer orbit of the atom determine whether the material is a
conductor, insulator or semiconductor
variable frequency drive (VFD)
an electronic device that varies frequency and voltage to control the speed of an AC motor
variable speed drive (VSD)
an electronic device that varies voltage through the use of pulse width modulaƟon to control the
speed of an AC or DC motor
VDC
abbreviaƟon for volts direct current
VMAX
the maximum voltage in an AC cycle
volt
unit of electromoƟve force
voltage drop
the amount of voltage loss from the source through a conductor or load
voltage root mean square (VRMS)
the average voltage in a circuit; equal to peak voltage Ɵmes 0.707
volt‐ampere (VA)
unit of apparent electrical power
volt‐ohm‐milliammeter (VOM)
a meter with mulƟple funcƟons and ranges, usually including voltage, current, and resistance