TRANSFORMER: (1) electric device that changes voltage in direct proportion to currents and in inverse proportion to the ratio of the number of turns of its primary and secondary windings (2) see primary and secondary

TRANSIENT: any increase or decrease in the excursion of voltage, current, power, heat and so forth, above or below a nominal value that is not normal to the source

TRANSIENT VOLTAGE: (1) refers to several parameters of a transient: (a) the peak or maximum voltage reached, (b) the rate of rise of the transient (dv/dt), and (c) the duration of the transient (2) generated when inductive loads such as solenoids, contactors, motors, relays, and so forth, are de-energized

VOLT (V): (1) unit of electromotive force (2) the difference of potential required to make a current of one ampere flow through a resistance of one ohm

VOLTAGE: term most often used (in place of electromotive force, potential, potential difference, or voltage drop) to designate electrical pressure that exists between two points and is capable of producing a flow of current when a closed circuit is connected between the two points

VOLTAGE DROP: voltage loss experienced by electrical circuits due to two principal factors: wire size and length of wire runs

VOLT/AMP (VA) RATING: the product of rated input voltage, multiplied by the rated current; this establishes the “apparent energy” available to accomplish work

WATT: common unit of electrical power; one watt is dissipated by a resistance of one ohm through which one ampere flows

WIRE: slender rod or filament of drawn metal

ZONE: (1) specific area of protection (2) portion of a large protected area (3) power supply to operate equipment

Ohms Law

In electrical systems, there is a relationship between current, voltage, and resistance. This is known as ohms law, and can be written in many different forms, but always boils down to V=IR, where V is voltage, I is current, and R is resistance.

This equation holds true whether we are dealing with AC, DC, Capacitive, Inductive, Three Phase, or any other type of circuit. However, it should be noted that sometimes the values for current and/or voltage are no longer simple values. The V and I of Ohms' Law can be replaced by complex mathematical expressions, but they still represent the current and voltage.

In fact, it isn't that the equations change, it is the values of current and voltage, which become complex. For example, we may replace the simple term "I" with the complex term "I*cos(p)",I*cos(p)",I*cos(p)", where p represents a shift in the phase angle, or timing, of the current.

Ohm's law can be written in different forms, but are still the same equation. The three common forms of Ohms law are:

V=I *R

I=V/R

R=V/I

In an electrical circuit, voltage applied to a conductor will cause electrons to flow. E or Voltage is the force and electron flow or I (Amperage) is the motion. The rate at which work is done is called power and is represented by the symbol "P". Power is measured in watts and is represented by the symbol "W". The watt is defined as the rate work is done in a circuit when 1 amp flows with 1 volt applied

Power consumed in a resistor depends on the amount of current that passes through the resistor for a given voltage. This is expressed as voltage times current.

P = E x I or P =E I

The formula can also be written as: Watts = Voltage x Amperage or Amps = Watts/Voltage

Solving a Power Problem

In the following illustration, power can be calculated using any of the power formulas.

P=EI

P=12 volts x 2 amps

P=24 watts

P=I² R

P=(2 amps)² x 6 W

P=4 x 6

P=24 watts

P=E² / R

P=(12 volts)² / 6 W

P=144/6

P=24 watts