# Basic Electrical Theory

Electricity is the movement of charge. No matter how the charge is created, chemically (like in batteries) or physically (friction from socks and carpet), the movement of the discharge is electricity. The flow of electrical charge is referred to as electric current.

## Simple Electrical Circuits

An Electric Circuit is a closed path for transmitting an electric current through the medium of electrical and magnetic fields. The flow of electrons across the loop constitutes the electric current. Electrons enter the circuit through the “Source,” which can be a battery or a generator.

### Series Circuits

When several elements are connected in linear series with an energy source, the circuit is known as a series circuit. For a series circuit, the same amount of current flows through each element and voltage is divided. Because the elements are connected in a line, if there is faulty element among them, the circuit will open.

### Parallel Circuits

In a parallel circuit, all of the elements are connected to the source at a common point and the other terminal of the elements are connected to the other terminal of the source at a common point. In parallel circuits, the voltage remains the same in the parallel elements while the current changes. If there is any fault among parallel elements, there is no effect on the rest of the circuit.

### Common vs. Ground

Ground and Neutral are two important conductors apart from the hot (or phase or live) wire in a typical application. The neutral wire acts as a return path for the “hot lead” while Ground acts as a low impedance path to “ground” fault current. Neutral is normally a current carrying conductor whereas Ground is normally not a current carrying conductor.

## Simple DC Theory

Direct current (also known as DC) is the flow of charged particles in one unchanging direction (most commonly found as electron flow through conductive materials). DC can be found in just about every home and electronic device, as it is more practical (compared to AC from power stations) for many consumer devices.

### Ohm’s Law

States the relationship between voltage, current and resistance. Given the relationship between these three elements, once you know any two of them, it is possible to calculate the third.

#### Electromotive Potential

Measured in Volts, electromotive potential is represented by the letter V (or E).

• V = IR
• Volts = Amps x Ohms

#### Current

Measured in Amperes, is represented with the letter I.

• I = V/R
• Amps = Volts / Ohms

#### Resistance

Measured in Ohms, is represented by the letter R (or the Greek letter Ω).

• R = V/I
• Ohms = Volts / Amps

#### Power

Measured in watts, is represented by the letter (W). Watt’s Law is similarly useful in figuring out the relationship between power, voltage and current.

• W = VI
• Watts = Volts x Amps
• V = W/I
• Volts = Watts / Amps
• A = W/V
• Amps = Watts / Volts

## Simple AC Theory

Alternating current is an electric current which periodically reverses direction and changes its magnitude continuously with time. AC comes in several forms, as long as the voltage and current are alternating. AC currents can be converted to and from high voltages with ease by using transformers.

### Peak Voltage (VPK)

The maximum instantaneous value of a function as measured from the zero-volt level. For the waveform shown above, the peak amplitude and peak value are the same, since the average value of the function is zero volts.

• VPK = 0.5 x VPP
• VPK = 1.414 x Vrms
• VPK = 1.571 x Vavg

### Peak-to-Peak Voltage (VPP)

The full voltage between positive and negative peaks of the waveform; that is, the sum of the magnitude of the positive and negative peaks.

• VPP = 2 x VPK
• VPP = 2.828 x Vrms
• VPP = 3.141 x Vavg

### RMS Voltage (Vrms)

The root-mean-square or effective value of a waveform, equivalent to a DC voltage that would provide the same amount of heat generation in a resistor as the AC voltage would if applied to that same resistor.

• Vrms = 0.707 x VPK
• Vrms = 0.353 x VPP
• Vrms = 1.111 x Vavg

### Average Voltage (Vavg)

The level of a waveform defined by the condition that the area enclosed by the curve above this level is exactly equal to the area enclosed by the curve below this level.

• Vavg = 0.637 x VPK Graph of a sine wave voltage versus time (in degrees of angle) with RMS, peak, and peak-to-peak marked.

## Single Phase vs. Three Phase

Single-phase power is a two-wire alternating current (ac) power circuit. Typically, there is one power wire (the phase wire) and one neutral wire, with current flowing between the power wire (through the load) and the neutral wire. Three-phase power is a three-wire ac power circuit with each phase ac signal 120 electrical degrees apart.

Residential homes are usually served by a single-phase power supply, while commercial and industrial facilities usually use a three-phase supply.

A three-phase power supply delivers power at a steady, constant rate. In a three phase power supply, during one cycle of 3600, each phase would have peaked in voltage twice. Also, the power never drops to zero.

This steady stream of power and ability to handle higher loads makes a three phase supply suitable for industrial and commercial operations. Single-phase systems can be derived from three-phase systems.

### Why 3 Phase Power in Data Centers?

Short answer: Efficiency. Delivers power at a steady, constant rate. Less voltage transformation is required when power is fed directly to the racks vs. using 208/120V.

### AC Voltage Formula

• Single Phase Volts x 1.732

### Power Formulas in Single Phase AC Circuits

• P = V x I x Cos Ф
• P = I2 x R x Cos Ф
• P = V2 / R (Cos Ф)

### Power Formulas in Three Phase AC Circuits

• P = √3 x VL x IL x Cos Ф
• P = 3 x VPh x IPh x Cos Ф
• P = 3 x I2 x R x Cos Ф
• P = 3 (V2 / R) x Cos Ф