__Ohm's Law__

E = IR

where E = voltage in volts

I = current in amperes

R = resistance in ohms

By simple algebra this equation may be written:

__Power__

P = IE

where P = power in watts

I = current in amperes

E = voltage in volts

This equation for power may also be transposed to:

From Ohm's law it is known that E = IR. If this expression for voltage is substituted in the power law, we can derive the additional equation: P = I^{2}R

If we use the equation for current from Ohm's law, I = E/R, the equation for power becomes:

^{*}See "Ugly's Electrical Reference" (SEBD0983) for additional information.

__Resistance__

Series Circuits R_{T} = R_{1} + R_{2} + R_{3} + ... R_{N}

where R_{N} = resistance in the individual resistors

R_{T} = total resistance in circuit

__Reactance__

X_{L} = 2 π f L

where X_{L} = inductive reactance in ohms

f = frequency in hertz

L = inductance in henries

π = 3.1416

where X_{C} = capacitive reactance in ohms

f = frequency in hertz

C = capacitance in farads

π = 3.1416

__Impedance__

where Z = impedance in ohms

R = resistance in ohms

X_{L} = inductive reactance in ohms

X_{C} = capacitive reactance in ohms

Note that the impendance will vary with frequency, since both X_{C} and X_{L} are frequency dependent. In practical AC power circuits, X_{C} is often small and can be neglected. In that case, the formula above simplifies to:

__Transformer Voltage Conversion__

where V_{S} = secondary voltage

V_{P} = primary voltage

N_{S} = number of secondary turns

N_{P} = number of primary turns

__Power Factor__

In mathematical terms, the power factor is equal to the cosine of the angle by which the current leads or lags the voltage. If the current lags the voltage in an inductive circuit by 60 degrees, the power factor will be 0.5, the value of the cosine function at 60 degrees. If the phase of the current in a load leads the phase of the voltage, the load is said to have a ** leading power factor**; if it lags, ** a lagging power** factor. If the voltage and current are in phase, the circuit has a ** unity power factor**.

__Equation Summary Diagram__

__Three Phase Connection Systems:__

__Electrical Enclosure Protection = IEC__

The degrees of protection provided within an electrical enclosure is expressed in terms of the letters IP followed by two numerals. Mechanical protection against impact damage is defined by an optional third numeral.

Example: An IP55 enclosure protects its contents against dust and spray from water jets.

**Reference: **DIN 40050 of July 1980, IEC 144 of 1963, IEC 529 of 1976, NF C 20-010 of April 1977

__Electrical Enclosure Protection - NEMA__

__Electrical Tables__

**Table 1 Electrical Formulae**

**Table 2 KV·A of AC Circuits**

**Table 3 Copper Wire Characteristics**

**Table 4 Single-Phase AC Motors Full Load Currents in Amperes**

**Table 5 Three-Phase AC Motors - 80% Power Factor Full Load Current in Amperes - Induction-Type, Squirrel Cage and Wound Rotor**

**Table 6 Direct Current Motors Full Load Current in Amperes**

**Table 7 Conduit Sizes for Conductors**

**Table 8 Allowable Current-Carrying Capacities of Insulated Copper Conductors**

**Table 9 Code Letters Usually Applied to Ratings of Motors Normally Started on Full Voltage**

**Table 10 Identifying Code Letters on AC Motors**

**Table 11 Conversion - Heat and Energy**

**Table 12 Approximate Efficiencies - Squirrel Cage Induction Motor**

**Table 13 - Approximate Electric Motor Efficiency to Use in Calculating Input**

**Table 14 Reduced Voltage Starters**