Whether you are new to the industry or are well seasoned and want to review some of the basic information that you learned in the past, these courses and lessons will clearly outline what you are looking for. “Power Systems Electric” is On-Line training that bridges the gaps between textbook theories and practical power systems experience. As a retired electrical engineer who has gone through the experience of developing a career in electrical power systems, I know how frustrating it can be to try and find the answers, so I put together these courses that I feel would have been a major help to me in my development. I have also taken suggestions from students of what they would like to see in addition to these courses which I have given live in person.

Basic Electrical Learning

For those new to the industry, there is a beginner’s group of courses that cover the “Fundamentals of Electricity ” including DC and AC Circuit Analysis. These lessons examine such basics as Ohm’s Law, Series, and Parallel Circuits. The first, and perhaps most important, relationship between current, voltage, and impedance, “Ohm’s Law”, and its relevance to Series and Parallel Circuits. Subsequently, this will lead to the development of Kirchhoff’s Laws as they help to further analyze Network Analysis & Metering Circuits.

Conductors and Insulators are investigated along with their connected components, Capacitors, Inductors, and how they are influenced by Electromagnetism.

Alternating Current (AC – an electric current that periodically reverses direction) is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions, fans, and electric lamps into a wall socket.

The abbreviations AC and DC are often used to mean simply alternating and direct, as they are applied to current or voltage.

These AC courses deal specifically with sinusoidal waveforms and will provide the student with the basic understanding of working with circuits involving Alternating Current, which includes sinusoidal waveforms, vectors & phasors, reactance & impedance of R,L,C circuits, as they relate to the basic laws and theorems of electricity. This includes working with AC Power, Power Factor, Resonance, Complex Numbers, Reactance, and Impedance

Advanced Electrical Learning

These Courses involve subjects such as “Short Circuit Analysis for HV Three-Phase Systems ” which introduces the student to the basic concepts of fault studies on a high voltage three-phase system. System modeling is then used in order to aid in this process, with the ability to move between asymmetrical and symmetrical systems. With hey Searle and extensive study of “Per Phase” & “Per Unit” methodologies system faults are analyzed with the use of symmetrical components.

“A Per-Unit System ” is the expression of system quantities as fractions of a defined base unit quantity. Calculations are simplified because quantities expressed as per unit do not change when they are referred from one side of a transformer to the other.

In these courses, you will learn exactly what Per Unit Analysis is, the main advantages of using it, how manufacturers of equipment use and rate their products, and the technique of converting to and from the Per Unit system.

Several examples of working with Per Unit are demonstrated in this crisp clear presentation. When you finish you will have a though understanding of this subject.

It is important for all power engineers and technicians to be familiar with the concept of Per Unit as it is being used and referred to every day in power flow, short circuit evaluation, and motor starting studies.

The method of “Symmetrical Components ” is used to simplify asymmetrical three-phase voltages and current analysis by converting the unbalanced system into two sets of balanced phasors and a set of single-phase phasors, or symmetrical components. These sets of phasors are called the positive, negative, and zero sequence components.

An understanding of this method is essential for the understanding of fault analysis and modern-day protection schemes. These courses will provide you with the knowledge to comprehend the concept and how it is applied.

Supplemental Electrical Lessons

In all power electrical analyses, the student will encounter special Trigonometric and Mathematical identities and equations. This site contains special supplemental lessons that zero in on those identities and equations. For example, there are lessons that take you from the “Fundamentals of Trigonometry ” to the more sophisticated requirements in electrical engineering. As you work and study in electrical engineering you are going to run into proofs and equations that are based on trigonometry. A good example of this is when studying AC current, voltage, and impedance calculations, phasors or vectors are used and combined mathematically. Further adventures into complex power will also require a knowledge of trig functions and identities. As a student of this course, you will be introduced to these or at least re-introduced to these that may have been long since forgotten.
In mathematics, “The Derivative of a Function ” of a real variable measures the sensitivity to change of the function value (output value) with respect to a change in its argument (input value). Derivatives are a fundamental tool of calculus. For example, the derivative of the position of a moving object with respect to time is the object’s velocity: this measures how quickly the position of the object changes when time advances.

Specialized Electrical Lessons

Specialized lessons include the “Protection & Control(P & C)” principles of high voltage stations. HV Bus Differential Protection is studied along with restrictions due to CT saturation & mismatch and its solution, “Restraint Differential Protection”.

High Voltage Circuit Breakers are examined as to the various Types (Oil, Vacuum, Air Blast, SF6), their Controls as well as the introduction of potential transformers & current transformers, and their use in conjunction with the relevant instruments such as ammeters, voltmeters, watt meters, and energy meters.

Other lessons include the study of “Transformers ” including core construction along with losses, cooling, and mitigation techniques. Three-phase transformer configurations are studied along with harmonic distortion, CT saturation, and on-load tap-changer problems and how these problems are dealt with. Over-current and restraint differential transformer protection is developed along with a look at some examples of ” Old School relays” as well as modern IDE (intelligent Electrical Devices) relays.

Transformer Connections: (Y – Y; Delta – Delta; Y – Delta; Delta – Y & Y – Zag Zig) are examined along with Transformer Clock System Vector Nomenclature.

Lastly, there is a special section dedicated to “Single and Three-Phase Metering “, including old analog and new digital kilowatt-hour meters.

Conclusion

Regardless of whether or not you are new to the industrial power system, you’ll find what you’re looking for on this site in the way of training. In order to review or select any of these courses, left-click on any of the blue highlighted hyperlinked words of this posting or on “14 Courses Available” from the top menu of the landing page. All of the courses have a free introduction

As a bonus and in the way of a thank you, for your interest in PSPT’s WEB (and Blog) page, I’m making available my 50-page “Electrical Power” crib sheets. These were prepared for use with my courses that are available on this site. There is one section associated with each course and is extremely valuable while viewing the course, as well as a recall of the pertinent formulas and information after the fact. The contained information is also useful during any technical career as a quick reference from time to time. Simply click here or on the picture to the right to be taken to where you can download this item.

October 07, 2022

Blog #10- Light Switch Wiring

October 07, 2022/ Graham VanBrunt

Electricity is a mystery to many people, but some electrical projects — like wiring a switch — are so simple that anyone can do it. With just a few simple steps and the right knowledge, anyone can easily and safely wire a switch.

Always turn the power off at the breaker before starting any electrical project. Once you’ve turned your power off, remove the switch cover and use a current detector to make sure there’s no power going to any of the wires in the electrical box, if there’s no power, you’re ready to move on to the first step.

Electrical wires and screw terminals are color-coded to help you match each wire to the correct terminal. But this doesn't mean that color-coding is always a reliable guide. For example, sometimes white wires are used in place of black wires, and some devices, like outlets and lamps, can be wired backward and still work (even though this creates a potential shock hazard). Understanding the basics of electrical circuits and color-coding will help you assess existing wiring and avoid some common mistakes with new installations.

A simple standard electrical circuit has a black or red "hot" wire that carries power from the power source to the device (e.g., switch, fixture, outlet, appliance), a white neutral wire that carries the power back to the power source, and a green or bare copper ground wire that connects the device to the home's grounding system.

A black or red wire usually connects to a brass-colored screw terminal or black wire lead on electrical devices. A white neutral wire usually connects to a silver-colored terminal or white wire lead. A green or bare ground wire almost always makes a ground connection—to a ground screw on a device, electrical box, or appliance case or to a green wire lead.

Of course, there are always exceptions to the rule, and there are many legitimate and not-so-legitimate ways to wire devices that don't follow the basic color-coding, so never make assumptions based on color-coding alone.

In this simple circuit, a single-pole single-through (SPST) switch has only two terminals, plus a ground screw (for newer switches). The switch terminals connect only to the hot wires in a circuit and are interchangeable, so the terminal screws are the same color. These switches don't typically connect to the neutral, so there is no terminal for the neutral wire. This is a simplistic schematic of what is going on. The hot wire is switched to the light with a neutral returning to the source.

There are two ways that a switch can be wired to control a light. First of all there will always be a two wire cable connecting the switch to the light. Let's call it the connecting cable. A two wire cable will have a black wire and a white wire and usually a ground wire. Then power has to be introduced to this circuit arrangement which is also done with a two wire cable. Let's call it the power cable. It can be either brought in to the light box which holds the light or the power can be brought into the switch box which holds the switch. Then connections are made in the boxes that hold the light and the switch.

This diagram shows the connections made inside the light box and the switch box for the situation where the power cable comes into the light box. The first thing to note is that the incoming ground wire from the power cable is connected to the outgoing ground wire in the connecting Cable. The ground wire is also connected to the light box and the switch box. There are ground screws in both of these boxes which are indicated in our diagram by a round green spot. Newer switches will have a ground screw which must be connected to the ground wires.

The white wire from the power cable is connected to one of the terminals of the light which is either a screw or a white wire.

The black wire from the power cable is connected to the white wire of the connecting cable. This white wire enters the switch box and it's connected to one of the two screws on the side of the single pole single throw switch. The black wire from the connecting cable is connected to the other screw of this switch.

The black wire from the connecting cable entering the light box is connected to the other terminal of the light which is either a screw or a black wire.

The above is an updated version of the previous arrangement. Because the electrical code as of the 2011 update may require a neutral wire in most new switch boxes, a 3-wire cable runs between the light and switch. The red and black are used for hot and the white neutral wire at the switch box allows for powering a timer, remote control, or a programmable switch.

Here a single-pole single-through switch controls the power to a light fixture. The power source is at the switch and a 2-wire cable runs from there to the light. The source hot wire is connected to one switch terminal and the other terminal is connected to the black cable wire running to the light. The neutral wire from the source is spliced to the white cable wire and continues on to the light. At the light, the white wire connects to the neutral terminal and the black wire connects to the hot terminal.

Here two switches are wired in the same double-ganged switch box, to control two separate lights. The source is at the switch box and a 2-wire cable is run to each light. One source is spliced to each switch with a pigtail to power the two lights.

The diagram to the left illustrates the wiring for a split receptacle with the top half controlled by SW1 and the bottom half always hot. The receptacle is split by breaking the connecting tab between the two, brass-colored terminals. The tab between the neutral, silver terminals should remain intact.

Here, the source is at the outlet and 2-wire cable runs from there to SW1. The circuit neutral wire is connected to one of the neutral terminals on the outlet, it doesn't run to the switch. The hot source is spliced to a pigtail that connects to the bottom, always-hot half on the receptacle and to the white cable wire running to SW1. The black cable wire runs to the SW1 connecting it to the hot on the top half of the split outlet.

In this updated diagram to the left, a 3-wire cable runs between the receptacle and switch and the red cable wire is used to carry the hot source to the switch. The neutral from the source is spliced through to the switch box using the white wire and in this diagram, the white wire is capped with a wire nut. This represents a change in the NEC code that requires a neutral wire in most new switch boxes. The white neutral wire at the switch box allows for powering a timer, remote control, or a programmable switch.

Three-way switches allow for controlling a light fixture from two separate locations, these are usually used at the top and bottom of a flight of stairs or at two different entrances to a room. Following are several wiring diagrams that can be used to map 3 way lighting circuits depending on the location of the power source in relation to the switches and lights.

Three-way switches have 3 terminals to carry circuit electricity and one terminal for a ground wire. Of the three circuit terminals, one is called the common and the other two are known as travelers. The common terminal may be labeled and is usually a different color than the traveler terminals. Depending on the manufacturer, the travelers may be on opposite sides of the device or the two terminals may be on the same side. In any case, the common terminal will be distinguished from the travelers in some way.

The common terminals will always be connected to a hot wire, either from the source or on the light fixture. These connections can be reversed if it's more convenient, as long as one of the 3 way common terminals connects to the hot source and the other one connects to the hot on the load. The traveler terminals will always be connected from switch to switch. Travelers never connect to a device load or to a source wire. It doesn't matter which traveler terminal is used for which traveler wire, reversing them will make no difference.

In the above diagram, the electrical source is at the first switch and the light is located at the end of the circuit. Three-wire cable runs between the switches and 2-wire cable runs to the light. The black and red wires between SW1 and SW2 are connected to the traveler terminals. The hot source is connected to the common terminal on SW1 and the common terminal on SW2 connects to the hot terminal on the light.

The power source in the above circuit is at the first switch and the light fixture is located between SW1 and SW2. Three-wire cable runs between each switch and the light fixture. The hot source wire is connected to the common terminal on SW1. The common terminal on SW2 is connected to the hot terminal on the light. The traveler wires are spliced at the fixture box to run between the traveler terminals on the switches, they are not connected to the light.

In this diagram, the power source for the circuit is at the light fixture and the two switches come after. Two-wire cable runs from the light to SW1 and a 3-wire cable runs between SW1 and SW2. The hot source wire is spliced at the lightbox to the white cable wire running to the first switch box. There it is spliced to the black wire running to the second switch box, which is then connected to the common terminal on SW2. When a white wire is used for hot like this, it's marked with black tape or paint at the ends to identify it as hot.

Back at the light fixture, the hot terminal on the light is connected to the black wire running to the common terminal on SW1. At SW1, the red and white wires running to SW2 are used as travellers connecting the traveler terminals between the two switches. Again, the white wire is marked with black on the ends to identify it as hot.

In this arrangement, the power source for the circuit is at the light fixture which is located in the middle of the circuit. A 3-wire cable runs to the switches on each side of the light. At the light, the hot source wire is spliced to the black wire running to the common terminal on SW2. The hot terminal on the light fixture is connected to the black wire running to the common terminal on SW1. The red and white cable wires are spliced in the fixture box and run to the traveler terminals on both switches. They don't connect to the light fixture. It is good practice to mark the white wire if it is being used as a hot wire. In this case, the white wire is marked with black tape on both ends to identify it as hot.

The following 4 graphic slides demonstrate the functioning of a 4-way switch and two 3-way switches to control lights.

Any number of these DPDS switches can be used as long as they're placed between the three way switches.

The wiring diagrams on the above slide make use of three 4 way switches located between two 3-way switches to control lights from five locations. Two wire cable is used between the power source and the first three way switch and the light in the second three-way switch. Three wire cable is used between the five switches. The red and black wires in the cables are connected to the traveler screws on the five switches. All of the white wires are spliced together in each switch box and connected to the neutral of the light. The Black hot wire coming from the source is connected to the common terminal of the first three way switch and the common of the second three-way switch is connected through the two-wire cable to the hot terminal of the light.

In this basic 4 way light circuit, a 3-wire cable runs between all the switches and a 2-wire cable runs from the last switch to the light.

The electrical source is at the first 3 way switch and the hot wire connects to the common there. The circuit neutral is spliced at each switch box through to the light fixture using the white wire. The black and red wires running between the boxes are connected to the travelers on each switch. The common terminal on the 3 way switch at the end of the circuit connects to the black wire running to the hot terminal on the light.

Take note that the traveler wires from SW1 are connected to the T1 pair on the 4 way switch and the travelers going to SW2 are connected to the T2 pair. Each pair of traveler terminals on the 4 way must be connected to only one 3 way switch. Don't mix up the pairs or the circuit will not work properly.

Here two 4-way and two 3-way switches are used to control lights from four different locations. The two 4-ways are located between the two 3-way switches.

Two wire cable is used between the power source and the first three way switch and the light in the second three-way switch. Three wire cable is used between the four switches. The red and black wires on the cables are connected to the traveler screws on the four switches. All of the white wires are spliced together in each switch box and connected to the neutral of the light. The Black hot wire coming from the source is connected to the common terminal of the first three way switch and the common of the second three-way switch is connected through the two-wire cable to the hot terminal of the light.