Electrical Fundamentals PDF

Electrical Fundamentals RACM-150 Learning Outcomes Demonstrate knowledge of the fundamental concepts of electricity. Demonstrate knowledge of electrical circuits and loads. Demonstrate knowledge of conductors, relays, switches, contactors, overloads and transformers, and their operation...

Electrical Fundamentals RACM-150 Learning Outcomes Demonstrate knowledge of the fundamental concepts of electricity. Demonstrate knowledge of electrical circuits and loads. Demonstrate knowledge of conductors, relays, switches, contactors, overloads and transformers, and their operation. Demonstrate knowledge of electronic controls and their operation. Demonstrate knowledge of electrical wiring diagrams. Demonstrate knowledge of the procedures used to measure voltage, resistance, current and power, and to calculate their interrelationships. Conductors Good conductors have few electrons in the outer shell of the atom. Good conductors of electricity are generally good conductors of heat. Conductors carry the current through the circuit. Conductors have low resistance to electron flow. Metallic materials generally make good conductors. Copper and aluminum examples of good conductors. Conductor Ampacity Conductors have resistance. As the conductor gets larger, the resistance becomes LOWER. Conductors are sized by their ampacity rating. Sizing conductors is done by a certified Electrician. However, if you need to purchase a whip it is good to have a base understanding. Ampacity Chart Insulators The opposite of conductors. Insulators have several electrons in their outer shell. The electrons are difficult to free from the outer shell, making it difficult for the electrons to move from one atom to another. Non-metallic materials make good insulators. Ex. Glass, air, rubber, and plastic. Magnetism and Electricity Magnets have 2 poles, north and south. The north and south pole are attracted to each other, creating lines of force. When a conductor (wire) is placed between these lines, the outer electrons in atoms found in the wire are freed. The result is more electrons on one side of the conductor (wire) than the other. This potential difference of electrons is voltage. Current (A) Current is the amount of electrons flowing. Measured in amperes(amps) can be described as the amount of work being done. Two types exist, direct current and alternating current. Current takes the path of least resistance. Current will flow until there is no difference in charge. Direct Current (DC) Travels in one direction, hence the name direct current. Electrons flow from the negative charge to the positive charge. DC power supplies a constant voltage. DC power is typically generated by chemical reactions. Alternating current can produce DC current with the use of a rectifier. A battery is a good example of a DC power source. Alternating Current (AC) Continually and rapidly reverses the current flow. Most electricity generated for public use is AC. More practical to transmit long distances. The voltage can be readily changed. Single phase and three phase can be utilized. AC vs DC Notice the waveform on the AC current goes back and forth from negative to positive. The amount of negative to positive waves per second is know as the frequency or Hz. 60Hz means 60 cycles per second. Voltage (EMF) Electromotive force (voltage) is speed at which the electrons are moving. Voltage is a measurement of potential difference. If we measure voltage on the same line of power with a closed switch, we get 0V. This is because there is no difference in charge on the same line of power. 1 volt is the amount of force needed to allow 1 amp of current to flow through 1 ohm of resistance. Resistance The resistance of a circuit can be described as the opposition of current flow. When the resistance increases, the current flow decreases**. The most common unit of measurement is Ohms. 1 ohm is present when 1 volt causes a current of 1 amp to flow. Power The term power refers to rate at which electrical energy is transferred or stored. Power is measured in wattage (W) or Kilowattage (Kw) Power companies measure power in Kw/h. This is simply the amount of kilowatts being used in an hour. Power(w) = voltage x amperage. Ohms Law (V = I x R) Ohms law can be described as the relationship between voltage, current, resistance and power. Electromotive force(V) = amperage(I) x resistance(R) This allows you to calculate the approximate value of one of the following listed above. Place your finger over the value to solve for. Ohms Law Applied What is the resistance of a heating element if we have 120V circuit and it is drawing 3 Amps? R = E/I = 120V/3 = 40 ohms What is the voltage of a circuit drawing 2A at 60 ohms? V=IxR = V=2x60 = 120V. What is the current draw of a 120v circuit with 20 ohms of resistance? I=E/R=120/20= 6A Watts Law (P = V x I) Watts law can be described as the relationship between voltage, amperage and useful power. It is expressed as watts(p)=volts(v) x amps (I). What is the wattage of a 120V circuit drawing 6 amps? P=VxI=120x6=720 watts. Electrical Measurements Watts = power consumption (W) Kilowatts = W/1000 Amperage = current (A) Voltage = force (V) Ohms = Resistance (Ω) Basic Electrical Circuit Terms Magnetism A magnetic field is generated around a conductor (wire) whenever current is flowing. If the wire is formed into a loop, the magnetism is stronger. If the wire is wound into a coil, the magnetism is even stronger. The coil of wire carrying an electrical current is known as a solenoid. The solenoid will pull/attract an iron bar into the coil. This iron bar is the plunger. Inductance Inductance – the fluctuation of the magnetic strengths in an AC circuit or conductors cutting through more than magnetic field, induces a voltage that counteracts the original voltage. Ex. When a motor spins, back emf (voltage) is created, opposing the flow of current. This occurs because of the magnets in the motor, and the coil being wound tightly. Motors, solenoids, and coils are inductive loads. A quick cheat sheet on back emf in under 5 mins Inductive/Capacitive Reactance Reactance in the resistance the alternating current faces when it changes direction. The resistance in a DC circuit is the only factor that affects the current flow. In AC circuits, resistance, inductive reactance, and capacitance reactance affect current flow. Capacitance reactance is caused in circuits using capacitors, the circuit resists the change in voltage. How it Affects the Circuit Inductive reactance – the opposition to change the flow of AC current. This causes the voltage to lead the current. Capacitive reactance – the opposition to change the voltage in an AC circuit, causing the current to lead the voltage. Impedance = total resistance of a circuit. Inductive reactance + capacitive reactance + resistance = impedance. Transformers Transformers are electrical devices that produce a secondary voltage through electromagnetic induction. Step up transformer – more windings on the secondary side, increasing the voltage. Step down transformer – more windings on the primary side, decreasing the voltage. Transformer Application Transformer are rated in volt-amps (VA). Step down transformers are typically used to step down line power to 24v control power. They can also be used to step down higher line voltage, to a lower line voltage to operate different components. Ex. 575 V to 120 V to run a inducer motor on an RTU. Step up transformers are can be used to increase the voltage to supply a motor. They can also be used to increase the voltage to create a spark for gas ignition. Ex. 120v to 10,000V. Capacitance A capacitor is a device in an electric circuit that stores electrical energy for later use. A capacitor has capacitance, this is simply the amount of charge that can be stored. The rating of a capacitor is in microfarads (uf). If replacing a capacitor and the exact uf rating is not available, you can increase it by up to 10 %. Short Circuits A short circuit is an undesigned path to ground, or line to line. Electricity takes the path of least resistance, naturally it travels to the short. Shorts can occur to ground, or line to line. A short circuit = too low of resistance. The low resistance causes an unwanted spike in current flow. The high current will blow a fuse or trip a breaker. Series Circuits Series circuits allow only one path of current flow. Switches and controls are typically wired in series. A simple way to think about ‘series’ is inline. The switch is inline with the bulb. Parallel Circuits In a parallel circuit, the current can travel in more than one path. Electrical loads are arranged in parallel circuits so that each load are connected to both supply voltage lines. Series-Parallel Circuits Series-parallel circuits are combination circuits. They allow all of the loads to be connected in parallel to the supply lines. They also allow the switches for each load to be wired in series with the individual load. Resistance and Current Calculations In series circuits, the total resistance is the sum of all resistances added together. Rt=R1+R2+R3…and so on. In series circuits, the current draw is the same throughout the whole circuit because there is only one path for the electrons to flow. C(t) = C1=C2=C3…and so on. In parallel circuits, the total resistance is calculated as the inverse. 1/Rt=1/R1+1/R2+1/R3..and so on. In parallel circuits, the current is the sum of all loads. Ct=C1+C2+C3..and so on. Reading Schematics/Diagrams How to Read AC Schematics and Diagrams Basics Type of Relays and Contactors Common Relays Used in HVAC/R!