Common electrical units

 Volt - unit of electrical potential or motive force - potential is required to send one ampere of current through one ohm of resistance

 

Ohm - unit of resistance - one ohm is the resistance offered to the passage of one ampere when impelled by one volt

 

Ampere - units of current - one ampere is the current which one volt can send through a resistance of one ohm

 

Watt - unit of electrical energy or power - one watt is the product of one ampere and one volt - one ampere of current flowing under the force of one volt gives one watt of energy

 

Volt-ampere (VA) - is a measurement of power in a direct current ( DC ) electrical circuit. The VA specification is also used in alternating current ( AC ) circuits, but it is less precise in this application, because it represents apparent power , which often differs from true power .

 

Kilovolt Ampere - one kilovolt ampere - KVA - is equal to 1000 volt amperes

 

Power Factor - ratio of watts to volt amperes

 

Most important Formulas:

 

Voltage V = I × R = P / I = √(P × R) in volts V         

Current I = V / R = P / V = √(P / R) in amperes A

Resistance R = V / I = P / I2 = V2 / P in ohms Ω    

Power P = V × I = R × I2 = V2 / R in watts W

 

 

Electrical Potential - Ohm's Law

 

Ohm's law can be expressed as:

 

V = R I         (1a)

 

V = P / I         (1b)

 

V = (P R)1/2         (1c)

 

Electric Current - Ohm's Law

 

I = V / R         (2a)

 

I = P / V         (2b)

 

I = (P / R)1/2         (2c)

 

Electric Resistance - Ohm's Law

 

R = V / I         (3a)

 

R = V2/ P         (3b)

 

R = P / I2         (3c)

 

Electric Power

 

P = V I         (4a)

 

P = R I2         (4b)

 

P = V2/ R         (4c)

 

where

 

P = power (watts, W), V = voltage (volts, V)

 

I = current (amperes, A), R = resistance (ohms, Ω)

 

Electric Energy :Electric energy is power multiplied time, or

 

W = P t      (5)

 

where

 

W = energy (Ws, J), t = time (s)

 

Electrical Motors : Electrical Motor Efficiency

 

μ = 746 Php / Pinput_w         (6)

 

where

 

μ = efficiency

 

Php = output horsepower (hp)

 

Pinput_w = input electrical power (watts)

 

or alternatively

 

μ = 746 Php / (1.732 V I PF)         (6b)

 

Electrical Motor - Power

 

P3-phase = (V I PF 1.732) / 1,000         (7)

 

where

 

P3-phase = electrical power 3-phase motor (kW)

 

PF = power factor electrical motor

 

Electrical Motor - Amps

 

I3-phase = (746 Php) / (1.732 V μ PF)         (7)

 

where

 

I3-phase = electrical current 3-phase motor (amps)

 

PF = power factor electrical motor

Electrical measurements

Quantity	Name	Definition
frequency f	hertz (Hz)	1/s
force F	newton (N)	kg•m/s²
pressure p	pascal (Pa) = N/m²	kg/m•s²
energy E	work joule (J) = N•m	kg•m²/s²
power P	watt (W) = J/s	kg•m²/s³
electric charge Q	coulomb (C) = A•s	A•s
voltage V	volt (V)= W/A	kg•m²/A•s³
current I	ampere (A) = Q/s	A
capacitance C	farad (F) = C/V = A•s/V = s/Ω	A²•s4/kg

How To Wire Lights in Series?

 

How to Connect Lights Points in Series?

In today basic electrical wiring installation tutorial, we will show how to wire lighting points in sires?. Although, we know that series connection for household wiring like fans, switches, light bulbs etc is not a preferred way instead of parallel or series-parallel wiring. But in some case, we need to wire and connect electrical appliances in series as well.

How To Wire Lights in Series?

In above fig, all the three light points are connected in series. Each lamp is connected to the next one i.e. the L (Line also known as live or phase) is connected to the first lamp and other lamps are connected through middle wire and the last one wire as N (Neutral) connected to the supply voltage then.

according to the series circuit analogy, the flowing current is same in all these incandescent bulbs / lamps but the voltage are different as opposed to the parallel circuit where voltage are same at each point where current are different.

One of the major disadvantage of series lighting circuit, adding or removing one lamp from the circuit will affect the over all circuit i.e. others lamps will dim in light and other connected devices and appliances will not get the sufficient or required operated voltage because the voltage in series circuit is different at each point but the flowing current is same.

Any number of lighting points or load can be added (according to the circuit or sub-circuit load calculation) in this kind of circuit by simply extending the L and N conductors to other lamps but they will not glowing according to the rated output efficiency. in short, adding more light bulbs in series circuit will dim the rest of the light points.

another major defect of series lighting circuit is that as all lamps or bulbs are connected between Line L and Neutral N accordingly, if one of the light bulb gets faulty, the rest of the circuit will not work as the circuit will be open as shown in fig below. Here, you can see there is a cut in the line wire connected to lamp 3, so the bulb is switch OFF and the rest circuit is working properly i.e. bulbs are glowing.

Lights connected in Series

Disadvantages of Series Lighting Circuit.

• The break in the wire, failure or removal of any single lamp will break the circuit and cause all of the others to stop working as there is only one single path of current to flow in the circuit.
• If more lamps are added in series lighting circuit, they will all be reduced in brightness. because voltage are shared in series circuit. If we add more loads in series circuit, the over voltage drop is increases which is not a good sign for electrical appliances protection.
  
• Series Wiring is “ALL or NONE” type wiring mean all the appliances will work at once or all of them will disconnect if fault occurs at any one of the connected device in series circuit.
• High supply voltage are needed if we need to add more load (light bulbs, electric heaters, air conditioner etc)  in the series circuit. For example, If five, 220V Lamps are to be connected in Series, Than Supply Voltage would have to be: 5 x 220V = 1.1kV.
  
• The overall series circuit resistance increases (and current decreases) when more load added in the circuit.
• According to future need, only those electrical appliances should be added in the current series circuit if they has the same current rating as current are same at each point in series circuit. However, we know that electrical appliances and devices i.e. light bulbs, fan, heater, air conditioner etc have different current rating, therefore, they can not be connected in series circuit for smooth and efficient operation.

Advantages:

• Less size of wire cable is required in series wiring.
• We use to protect the circuit to connect fuse & circuit breakers in series with other appliances.
• Series circuit don’t get overhead easily due to high resistance when more load added in the circuit.
• The lifespan of battery in series circuit is more as compared to parallel.
• It is most simple method of electrical wiring and fault can be easily detect and repair as compared to parallel or series-parallel wiring.

Disadvantages of Series Lighting Circuit

How to Wire a Light Switch? Controlling a Lamp by Single Way Switch

In today basic home electrical wiring installation tutorial, we will show how to wire a light switch to control a light point by one way or single way switch.

We will use the basic SPST (Single Pole Single Through) switch in this tutorial to control a lamp / bulb from single location.

Before go in details, we have to show the basic construction and operating mechanism of single way switch which is shown in fig below:

Below is a simple step by step tutorial with schematic and wiring diagram which shows how to wire a light switch to control the bulb/lamp from single place with the help of one way or single way switch?

Requirements:

• Single Way Switch (SPST = Single Pole Single Through) x 1 No
• Lamp (Light Bulb) x 1 No
• Short pieces of cables x 3 No

Procedure:

This is just like a series circuit i.e. all the components are connected in series. Just connect the Neutral wire directly to the light bulb and then connect the light bulb to the switch through middle wire. And then connect the live wire to the switch as shown in fig below. Fig given below shows the basic connection of light switch and their position i.e. when the switch is OFF, the circuit acts like an open circuit and the bulb won’t glow. To switch on the bulb, switch S₁ must be closed to complete the circuit and glow the light bulb.

Wiring a Light Switch

In fig below, schematic and wiring diagrams of light switches are shown which shows how to wire a light switch?

How to Wire a Light Switch

Also note that home wire colors may vary according to different areas. In addition, always use and connect the earth wire (direct naked wire to switches, and electrical appliances from earth link in the distribution board to reduce the risk of electric shock and hazard) which is not shown in the figures above.

How To Wire Switches In Series?

In today basic home electrical wiring installation tutorial, we will learn how to wire and connect two switches in series to control and operate a single light point.

Mostly, this is not a proffered method to wire single way switches in series as parallel or series-parallel connection is used in common electrical wiring installation. In some case, it may seems useless connection, but there are some possibilities where we have to control single load from two places while both switches must be switch ON to operate the load.

Before go in details, we will see the basic construction and operating mechanism of single way switch which is shown in fig below:

Below is a simple step by step tutorial with schematic and wiring diagram which shows how to wire single way switches in series ?

Requirements

• Single Way Switches (SPST = Single Pole Single Through) x 2 No
• Lamp (Light Bulb) x 1 No
• Short pieces of cables x 4 No

Procedure:

Connect the two single way switches, light bulb in series to the power supply as shown in fig below. Keep in mind that both switches S1 and S2 must be closed to complete the circuit.

If there are more switches connected in series with electrical appliance i.e. light point, all of them must be at ON position to operate the load. If one of the single switch is open, the circuit won’t work then.

How To Wire Switches In Series?

The circuit will only complete if both of the switches are at ON position. In other words, If one of the switch are open or at OFF position, the light bulb will not glow. This is the same case for other loads as well which are connected in series to control by two single way switches.

Below are the different positions of single way switches and light point when connected in series.

Switches in Series Different Positions of Switches & Light Bulb

To get the switching position in ON condition for light bulb, the above operation is same as the Digital Logic AND Gate  truth table which is given below.

In simple words, there are four switching positions and if both the switches are at ON position, the light bulb will glow. On the other hand, if one of the switch is at OFF position, the current will not flow in the circuit as the circuit behaves like an open circuit, hence bulb will not glow. No matter all of other connected switches are at OFF or ON positions.