Fuse vs. Circuit Breaker: What’s Best for Your Application?

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When designing or upgrading an electrical system, one of the most critical decisions you'll face is choosing the right overcurrent protection device. Fuses and circuit breakers are the two primary options, each with distinct characteristics, advantages, and applications. Understanding their differences is essential to ensuring safety, efficiency, and cost-effectiveness in your electrical installations.

What Are Fuses?

A fuse is a simple yet highly effective protective device designed to prevent overcurrent conditions. It consists of a metal filament or wire that melts when exposed to excessive current, thereby breaking the circuit and stopping the flow of electricity. Once a fuse operates (commonly referred to as "blowing"), it must be replaced with a new one.

Fuse Diagram:

Time-Current Characteristic Curve:

Advantages of Fuses:

• Simplicity and Reliability: Fuses have no moving parts, making them less prone to mechanical failure.

• Fast Response Time: They react quickly to overcurrent situations, providing superior protection for sensitive electronic devices.

• Cost-Effective: Fuses are inexpensive to purchase, making them ideal for budget-conscious applications.

• Compact Design: They take up less space in control panels compared to some circuit breakers.

Disadvantages of Fuses:

• Single-Use: Once blown, a fuse needs to be replaced, leading to potential downtime.

• Inconvenience: Replacing a fuse can be time-consuming, especially in critical systems where rapid power restoration is needed.

• Limited Flexibility: Fuses have fixed ratings, offering little room for adjustment once installed.

What Are Circuit Breakers?

A circuit breaker is an electromechanical device designed to automatically interrupt electrical flow in the event of an overcurrent or short circuit. Unlike fuses, circuit breakers can be reset manually or automatically after tripping, making them reusable.

Circuit Breaker Diagram:

Advantages of Circuit Breakers:

• Reusability: After tripping, circuit breakers can be reset without replacing any components, reducing maintenance costs.

• Adjustability: Many circuit breakers allow for adjustable trip settings, offering flexibility for various load requirements.

• Ease of Use: Resetting a circuit breaker is faster and more convenient than replacing a fuse.

• Comprehensive Protection: Circuit breakers can protect against both overcurrent and short-circuit conditions.

Disadvantages of Circuit Breakers:

• Higher Initial Cost: Circuit breakers are more expensive upfront compared to fuses.

• Slower Response: They typically react slower than fuses, which can be a disadvantage when protecting highly sensitive equipment.

• Maintenance Requirements: Circuit breakers may require periodic maintenance to ensure optimal performance.

Key Factors to Consider When Choosing Between Fuses and Circuit Breakers

1. Application Type

• Fuses: Ideal for applications where rapid response to overcurrent is critical, such as in sensitive electronic equipment.

• Circuit Breakers: Better suited for systems requiring frequent switching operations or quick power restoration after a fault.

2. System Complexity and Maintenance Needs

• Fuses: Suitable for simpler systems with infrequent overcurrent events.

• Circuit Breakers: Preferred in complex installations where ease of resetting and adjustability are essential.

3. Cost Considerations

• Initial Cost: Fuses are cheaper to purchase, but replacement costs can add up over time.

• Long-Term Savings: Circuit breakers, despite higher initial costs, may be more cost-effective in the long run due to their reusability.

4. Safety and Reliability

• Fuses: Offer better protection for highly sensitive equipment due to their fast reaction time.

• Circuit Breakers: Provide consistent performance and protection, especially in high-current applications.

Common Applications

• Residential: Circuit breakers are commonly used in homes due to their convenience and ease of resetting.

• Industrial: Fuses are often preferred in industrial applications for their fast response to short circuits, especially when protecting motors and sensitive equipment.

• Commercial: A combination of both is frequently used, depending on the specific requirements of different systems.

Fuse vs. Circuit Breaker: A Quick Comparison

Feature	Fuses	Circuit Breakers
Response Time	Faster	Slower
Reusability	No (single-use)	Yes (resettable)
Cost	Lower initial cost	Higher initial cost
Maintenance	None after installation	Requires periodic checks
Adjustability	Fixed ratings	Adjustable trip settings
Downtime After Trip	Requires replacement	Quick reset

Choosing between a fuse and a circuit breaker depends on your specific application needs. Fuses offer fast response times and cost-effective protection, making them ideal for sensitive electronic equipment and industrial applications. On the other hand, circuit breakers provide convenience, reusability, and flexibility, making them the preferred choice for residential and commercial installations.

For critical systems, a combination of both may be the best solution, leveraging the advantages of each device. Always consult relevant sources and standards, such as the ABB Electrical Installation Handbook, and local electrical codes to ensure compliance and safety.

References

• ABB Electrical Installation Handbook

• National Electrical Code (NEC)

• Van Meter: Fuses vs. Circuit Breakers

• C3 Controls: Circuit Breaker or Fuse

How to Wire a Photocell Switch to Lighting Loads with a Contactor

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We have already discussed how to install and wire a photocell switch in a lighting installation and how to size a photocell for a lighting installation. We noted that the photocell switch is an energy saving device used to help conserve energy during the day and switch on the lighting installation during night-time.

Photocell sensors or switches come in various voltage and current ratings. For lighting loads under 5 Amps, it may be possible to wire the photocell switch directly to the lighting load circuit.

However, with large lighting loads, the photocell sensor has to be used indirectly to switch on and off the lighting load using a contactor. For example, let us say you have twenty (24) pieces of 250W High Pressure Sodium Lamps providing lighting to a small sized industrial complex, evidently it is not possible to wire the photocell sensor directly to the lighting loads!

What will be required is a higher current rated 3-phase contactor to power the lights, while a photocell can be wired to energize the contactor coil. During the day, the lights will be switched off and during the night when the photocell activates as a result of increased resistance, the lights come on.

How do we then Wire a Photocell with a Contactor?

The schematic wiring diagram below shows how to wire a photocell switch with a 3-phase contactor to power nine (9), 250W lighting loads:

Note that on the photocell sensor, L1 is the live wire, N is the neutral wire and Lo, is the load wire which goes to energize the contactor coil which must be rated for the phase voltage (L1-N or L2-N or L3 -N). Common phase voltage levels are 120V, 208V or 240V.

As shown in the schematic above, power goes into the circuit breaker (used for overload as well as short circuit protection). From the circuit breaker, power goes through the power contactor. During the day time, the Photocell sensor switch is off and the lamps are off. During the night time, the photocell sensor comes on energizing the coil of the contactor thereby supplying light to the lighting loads.

 

How to Size a Portable Generator for Home Use

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Portable Generators are a reliable source of power in the absence of utility power. They provide electrical power to supply our critical power needs when the utility company is unable to supply us electrical power due to fault in their transmission system or during maintenance interventions in their power infrastructure or in the worst case of a natural disaster such as earthquake or a hurricane that has destroyed section of the power grid.

What Size of Portable Generator Do I need ?

The size of portable generator you need depends on your power requirement when the need arises to use the generator. Do you require the generator to power all of your electrical appliances at once? Or do you require the generator to power some critical electrical load during power outage? The bigger your power needs, the bigger the size of your generator and the more expensive your portable generator will be!

Running Watts of an Electrical Appliance

The running watts of an electrical appliance is the power it can draw continuously with rated voltage and current. It is usually calculated as:

Running Watts = Rated Voltage x Rated Current.

Note that the above formula will give power in volts-amps or VA but assuming a power factor = 1 which is rarely the case, we get power in watts. This approximation is done to enable easy sizing of a portable generator for home use.

The running watt can easily be calculated by using the rated voltage and current on the name plate of the appliance. Generators are also rated for their running watts. It is the power the generator can deliver continuously at rated voltage, current and frequency. A generator must not be made to continuously carry load beyond its running watts for a very long time otherwise the generator’s life will be shortened and the device becomes damaged in a short time.

Surge Watts or Start up Power of an Electrical Appliance

Certain devices and appliances have an electric motor or compressor in them. They require additional watts to start them. This additional watt may also be referred to as the surge watt of the device. The surge watts required by these devices may sometimes be two or three times the watts required to run the device. Heat producing devices also called resistive loads such as light bulbs, toasters or coffee makers do not require surge watts at start up. A generator must have enough surge watts capacity to handle devices that require surge watts at start up to prevent a nuisance tripping of the main power breaker in the generator.

As shown above, a generator must have sufficient surge capacity to carry loads requiring additional power during start up. Consider a refrigerator that works for one third of the time within a given time cycle. Each time the refrigerator compressor starts, a generator powering the refrigerator must have sufficient surge power for the compressor each time it comes on!

How to Calculate the Size of Portable Generator Required

To properly size a generator, care should be taken to analyse the load the generator is to power so that both running watts and surge watts can be correctly calculated. To calculate the size of generator:

Add up the total running and surge watts for each appliance. Multiply the total sum gotten by a contingency of 15 – 20 % to get the capacity of your generator.

As a guide during the sizing calculation for domestic application;

Surge watts for refrigerators and air conditioners = 2 x running watts 

Surge watts for motors (surface or submersible pumps) = 3 x running watts

Microwave Oven = 1.5 x running watts

Sample Sizing Calculation

Suppose the following loads are to be powered by a portable generator:

Electrical Load	Number	Running Watts (W)
Refrigerator	1	800
Submersible pump	1	800
Lighting loads	lot	150
Air Conditioner (1hp)	1	800
Deep Freezer	1	500
Microwave	1	600
Computer	1	300
TV	1	400

Determine power rating for generator  as shown below:

Electrical Load	Number	Running Watts (W)	Surge Watts (W)
Refrigerator	1	800	2 x 800 = 1,600
Submersible pump	1	800	3 x 800  = 2,400
Lighting loads	lot	150	0
Air Conditioner (1hp)	1	800	2 x 800 = 1,600
Deep Freezer	1	500	2 x 500 = 1,000
Microwave	1	800	1.5 x 800 = 1200
Computer	1	300	0
TV	1	400	0
Total		4,350	7,800
Total Power Required	= 4,350 + 7,800 = 12,150W
Add 15% contingency	= 12,150 x 1.15 =13,972.5W
Size of Generator needed			= 15,000W or 15KVA   standard Size

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How UPS (Uninterruptible Power Supply) Systems Works

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UPS stands for Uninterruptible Power Supply. A UPS system is an autonomous source of alternate power that is used to supply sensitive electronic loads such as computer centers, telephone exchanges and many industrial-process control and monitoring systems. These applications require power that is availability and of good quality.

A UPS solution for sensitive electrical loads is used to provide a power interface between the utility and the sensitive loads, providing voltage that is:

1. Free of all disturbances present in utility power and in compliance with the strict

        tolerances required by loads.

2. Available in the event of a utility outage, within specified tolerances

UPS systems satisfy requirements in 1 & 2 above in terms of power availability and quality by:

1. Supplying loads with voltage complying with strict tolerances, through use of an

        inverter

2. Providing an autonomous alternate source, through use of a battery

3. Stepping in to replace utility power with no transfer time, i.e. without any interruption in the               supply of power to the load, through use of a static switch.

These characteristics make UPS units the ideal power supply for all sensitive applications because they ensure power quality and availability, whatever the state of utility power.

Basic Parts of a UPS System

A UPS comprises the following main components:

1. Rectifier/charger, which produces DC power to charge a battery and supply an inverter

2. Inverter, which produces quality electrical power free of all utility-power disturbances, notably           micro-outages and that is within tolerances compatible with the requirements of sensitive                     electronic devices.

3. Battery, which provides sufficient backup time to ensure the safety of life and property by                   replacing the utility as required

4. Static switch, a semi-conductor based device which transfers the load from the

        inverter to the utility and back, without any interruption in the supply of power

Types of Static UPS Systems

Types of static UPSs are defined by standard IEC 62040. The standard distinguishes three operating modes for UPSs which are:

1. Passive standby (also called off-line)

2. Line interactive

3. Double conversion (also called on-line)

These definitions concern UPS operation with respect to the power source including the distribution system upstream of the UPS. IEC Standard 62040 defines the following terms:

a. Primary power: power normally continuously available which is usually supplied by

        an electrical utility company, but sometimes by the user’s own generation

b. Standby power: power intended to replace the primary power in the event of

        primary-power failure

c. Bypass power: power supplied via the bypass

UPS Operating in Passive Standby Mode

Operating Principle:

The inverter is connected in parallel with the AC input in a standby as shown below:

UPS in Passive Standby Mode. Photo Credit: Schneider Electric

Normal Mode Operation

In normal mode operation, the load is supplied by utility power via a filter which eliminates certain disturbances and provides some degree of voltage regulation (IEC 62040 specifies some form of power conditioning). The inverter operates in passive standby mode.

Battery Backup Mode Operation

In battery backup mode operation, when the AC input voltage is outside specified tolerances for the UPS or the utility power fails, the inverter and the battery step in to ensure a continuous supply of power to the load following a very short less than 10 ms transfer time. The UPS continues to operate on battery power until the end of battery backup time or the utility power returns to normal, which causes transfer of the load back to the AC input (normal mode).

Application

This configuration is a compromise between an acceptable level of protection against disturbances and cost. It can be used only with low power ratings less than 2 kVA.

Limitations

This UPS operates without a real static switch, so a certain time is required to transfer the load to the inverter. This time is acceptable for certain individual applications, but

incompatible with the performance required by more sophisticated, sensitive systems

(large computer centers, telephone exchanges, etc.). Furthermore, the frequency is not regulated and there is no bypass.

UPS Operating in Line-interactive Mode

The inverter is connected in parallel with the AC input in a standby configuration, but also charges the battery. It thus interacts with the AC input source as shown below:

UPS in Line-interactive Mode. Photo Credit: Schneider Electric

Normal Mode Operation

In normal mode operation, the load is supplied with conditioned power via a parallel connection of the AC input and the inverter. The inverter operates to provide output-voltage conditioning and/or charge the battery. The output frequency depends on the AC-input frequency.

Battery Backup Mode Operation

In this mode of operation, when the AC input voltage is outside specified tolerances for the UPS or the utility power fails, the inverter and the battery step in to ensure a continuous supply of power to the load following a transfer without interruption using a static switch which also disconnects the AC input to prevent power from the inverter from flowing upstream. The UPS continues to operate on battery power until the end of battery backup time or the utility power returns to normal, which provokes transfer of the load back to the AC input (normal mode).

Bypass Mode Operation

This type of UPS may be equipped with a bypass. In the bypass mode, If one of the UPS functions fails, the load can be transferred to the bypass AC input (supplied with utility or standby power, depending on the installation).

Application and Limitation

This UPS configuration is not well suited to regulation of sensitive loads in the medium to high-power range because frequency regulation is not possible. For this reason, it is rarely used other than for low power ratings.

UPS Operating in Double Conversion (On-line) Mode

Operating Principle:

In this type of UPS, the inverter is connected in series between the AC input and the application as shown below:

UPS in Double-Conversion Mode. Photo Credit: Schneider Electric

Normal Mode Operation

During normal operation, all the power supplied to the load passes through the rectifier/charger and inverter which together perform a double conversion (AC to DC to AC), hence the name.

Battery Backup Mode Operation

In battery backup mode, When the AC input voltage is outside specified tolerances for the UPS or the utility power fails, the inverter and the battery step in to ensure a continuous supply of power to the load following a transfer without interruption using a static switch. The UPS continues to operate on battery power until the end of battery backup time or utility power returns to normal, which causes transfer of the load back to the AC input (normal mode).

Bypass Mode Operation

This type of UPS is generally equipped with a static bypass, sometimes referred to as a static switch. The load can be transferred without interruption to the bypass AC input (supplied with utility or standby power, depending on the installation), in the event of UPS failure, load current transient (inrush or fault currents) or load peaks. The presence of a bypass assumes that the input and output frequencies are identical and if the voltage levels are not the same, a bypass transformer is required.

For certain types of load, the UPS must be synchronized with the bypass power to ensure load-supply continuity. Furthermore, when the UPS is in bypass mode, a disturbance on the AC input source may be transmitted directly to the load because the inverter no longer steps in. Another bypass line, often called the maintenance bypass, is available for maintenance purposes. It is closed by a manual switch.

How to Size a Photocell for a Lighting Installation

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Now that you know how to install and wire a photocell in a lighting installation. The next step would be to know how to determine the current rating of the photocell for a given application so that when installed, it does not burn off easily and create problems for the lighting installation.

Consider the simple lighting installation below where a photocell has been used.

Let LP 1 =LP2 = LP3 = LP4 = 250W

Power supply Voltage, V = 240V

Power Factor = 0.5 (discharge lamps see Typical power factor for common electrical loads)

Power in a single phase circuit is given by:

$P = VICosՓ$       ((see Voltage Drop and Power Formulas for Electrical Engineers)

Where I is the rated current of the photocell.

Now from the above formula for power, we get : 

$I = \frac{250}{(240 * 0.5)} = 2.0833 Amps$ 

Now the photocell should be able to withstand the inrush current of a discharge lamp which is about 1.6 times nominal current.

Hence actual current rating of photocell = 1.6 x 2.0833 = 3.33 Amps

A photocell rated 5 Amps should just do for the above application with four (4) discharge lamps. However as the number of lamps to be controlled increases, it becomes impractical to use a photocell switch to carry the lighting loads directly.

What is normally done is to use a power contactor with a higher current rating to carry the load while the photocell switch will be used to power the contactor coil. 

See How to Wire a Photocell Switch to Lighting Loads with a Contactor

How to Install and Wire a Photocell Switch in a Lighting Installation

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A photocell switch is essentially a light dependent resistor, LDR. Its resistance decreases with increasing incident light intensity. They are used in many applications for on-off control especially in lighting installations.

In lighting applications, Photocells are placed in streetlights to control when the lights are ON or OFF. During daylight, light falling on the photocell causes the streetlights to turn off and during night hours or darkness to turn on. Thus energy is saved by ensuring the lights are only on during hours of darkness.

How to Wire a Photocell 

A photocell used in lighting application has three terminals labelled as:

1. Load line (Lo)

2. Neutral line (N)

3. Supply or live line (LI)

In most photocells, the load line wire is RED, the neutral wire is WHITE and the Supply line is black. 

This colour code is not universal. It may change depending on the manufacturer of the photocell switch.

The picture of the terminals of a brand of photocell is shown below:

Photocell Terminal Markings

Wiring and installing a photocell is pretty straight forward as shown below:

How to Wire a Photocell Switch in a Lighting Installation

As shown above, the load wire (Lo) goes to the lighting installations connected in series while the neutral (N) wire through a breaker is looped to all the lights. The supply line through a breaker supplies the photocell electrical power.

See also How to wire a photocell switch to lighting loads with a contactor

How to size a photocell for a lighting installation

Voltage Drop and Power Formulas for Electrical Engineers

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Working with single phase, three-phase and DC (direct current circuits) and you quickly need to reference formulas for voltage drops and power calculations for a given conductor? The table below provides a quick reference for these calculations.

Voltage Drop and Power Calculation Formulas For Single Phase Circuits

Electrical Parameters	Formulas
Voltage Drop	$∆V = 2*I*L*(rCosՓ + xSinՓ)$
% Voltage Drop	% $∆V  =  \frac{∆V}{V_r}*100$
Active Power	$P = V*I*CosՓ$
Reactive Power	$Q = V*I*SinՓ$
Apparent Power	$S =  V*I = \sqrt{{P^2} +{Q^2}}$
Power Factor	$CosՓ = \frac{P}{S}$
Power Loss	$P_L = 2*L*r*I^2$

Voltage Drop and Power Calculation Formulas For Three-Phase Circuits

Electrical Parameters	Formulas
Voltage Drop	$∆V = \sqrt{3}*I*L*(rCosՓ + xSinՓ)$
% Voltage Drop	% $∆V = \frac{∆V}{V_r}*100$
Active Power	$P = \sqrt{3}*V*I*CosՓ$
Reactive Power	$Q = \sqrt{3}*V*I*SinՓ$
Apparent Power	$S = \sqrt{3}*V*I = \sqrt{{P^2} +{Q^2}}$
Power Factor	$CosՓ = \frac{P}{S}$
Power Loss	$P_L = 3*L*r*I^2$

Voltage Drop and Power Calculation Formulas For Direct Current (DC) Circuits

Electrical Parameters	Formulas
Voltage Drop	$∆V = 2*I*L*r$
% Voltage Drop	% $∆V = \frac{∆V}{V_r}*100$
Active Power	$P = V*I$
Reactive Power	$ - $
Apparent Power	$ - $
Power Factor	$ - $
Power Loss	$P_L = 2*L*r*I^2$

Meaning of symbols used in the formulas above:
$L$       =   Total length of conductor
$r $       =    Resistance of conductor per unit length
$x$       =    Reactance of conductor per unit length
$∆V$    =   Voltage drop 
$P$       =   Active power
$Q$      =    Reactive power
$I$        =   Current

Formulas For Star - Delta Transformations in Three - Phase Electrical Circuits

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In three - phase electrical circuits, there is often the need to transform from a Delta configuration to a Star configuration and vice versa. The formulas for making these conversions are detailed below:

For a Star  to Delta Transformation, as shown in the formula above:



$Z_{12} = Z_1 + Z_2  + \frac{Z_1 Z_2}{Z_3}$

$Z_{23} = Z_2 + Z_3  + \frac{Z_2 Z_3}{Z_1}$

$Z_{13} = Z_3 + Z_1  + \frac{Z_3 Z_1}{Z_2}$




For a Delta to Star Transformation, we have:
$Z_1 = \frac{Z_{12} Z_{13}}{Z_{12}+Z_{13}+ Z_{23}}$

$Z_2 = \frac{Z_{12} Z_{23}}{Z_{12}+Z_{13}+ Z_{23}}$

$Z_3 = \frac{Z_{23} Z_{13}}{Z_{12}+Z_{13}+ Z_{23}}$

With the above formulas, you can easily transform from a Delta configuration to a Star configuration or vice versa.

How to Size the Neutral Conductor in an Electrical Installation

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In a balanced three phase systems, the current in the neutral conductor is theoretically zero. However in a practical electrical installation, this is not the case. In fact there is always some current flow in the neutral although small if the loads in the three phase are sufficiently balanced. However increasing current will flow through the neutral in an installation with high harmonics necessitating the need to appropriately determine the minimum cross sectional area of the neutral that will be safe for the installation.

Given the implications of under sizing the neutral conductor, the neutral conductor, shall have the same cross section as the line conductor:

1. in single-phase, two-wire circuits whatever the section;

2. in poly-phase and single-phase three-wire circuits, when the size of the line conductors is less             than or equal to 16mm2 in copper, or 25mm2 in Aluminium.

The cross section of the neutral conductor can be less than the cross section of the phase conductor when the cross section of the phase conductor is greater than 16mm2 with a copper cable, or 25mm2 with an aluminium cable, if both the following conditions are met:

1. The cross section of the neutral conductor is at least 16mm2 for copper conductors and 25mm2          for aluminium conductors;

2. There is no high harmonic distortion of the load current. If there is high harmonic distortion (the          harmonic content, THD, is greater than 10%), as for example in equipment with discharge                  lamps, the cross section of the neutral conductor cannot be less than the cross section of the                phase conductors.

The table below shows the minimum cross sectional area of the neutral conductor in a given electrical installation under different types of circuits:

Type of Circuit	Phase Conductor Cross Section, S, (mm2)	Minimum Neutral Conductor Cross Section, SN (mm2)
Single Phase/Two Phase Circuits - Copper/Aluminium	Any	S
Three-Phase Circuits - Copper	S ≤ 16	S
	S > 16	16
Three - Phase Circuits - Aluminium	S ≤ 25	S
	S > 25	25

Basics of Harmonics in Electrical Systems:

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Harmonics are essentially distortions in the electrical power systems. An electrical power system can be represented by a sinusoidal waveform which varies with time. The harmonic with frequency corresponding to the period of the original waveform is called fundamental and the harmonic with frequency equal to “n” times that of the fundamental is called harmonic component of order “n”. The presence of harmonics in an electrical system is an indication of the distortion of the voltage or current waveform and this implies such a distribution of the electric power could result in the malfunctioning of equipment and protective devices.

The harmonics are nothing less than the components of a distorted waveform and their use allows the analysis of any periodic non-sinusoidal waveform through different sinusoidal waveform components. 

Harmonics Distortions Waveform. Photo Credit: ABB

Causes of Harmonics in Electrical Systems

Harmonics are generated by nonlinear loads. When we apply a sinusoidal voltage to a load of this type, we shall obtain a current with non-sinusoidal waveform.

The main equipment generating harmonics are:

1. personal computer

2. fluorescent lamps

3. static converters

4. continuity groups

5. variable speed drives

6. welders.

7. Transformers (mostly third harmonics which becomes insignificant with increasing loading of the transformer).

In general, waveform distortion is due to the presence, inside of these equipment, of bridge rectifiers, whose semiconductor devices carry the current only for a fraction of the whole period, thus originating discontinuous curves with the consequent introduction of numerous harmonics.

Effects of Harmonics in Electrical Systems

The effects of harmonics can be felt in both the current and voltage.

The main problems caused by harmonic currents are:

1) overloading of neutrals

2) increase of losses in the transformers

3) increase of skin effect.

The main effects of the harmonics voltages are:

4) voltage distortion

5) disturbances in the torque of induction motors (since Torque is proportional to supply voltage)

Total Harmonic Distortion (THD) in an Electrical System

If the rms values of the harmonic components are known, the total rms value can be easily calculated by the following formula:

Total Harmonic Distortion (THD)

The total harmonic distortion is defined as:

The harmonic distortion ratio is a very important parameter, which gives information about the harmonic content of the voltage and current waveforms and about the necessary measures to be taken should these values be high.

For THDi < 10% and THDu < 5%, the harmonic content is considered negligible and such as not to require any provisions

Comparison of Common Lamps Used in Electrical Installations

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Below are the characteristics of the common lighting technology in use in different electrical installations. Also stated are their place of application, advantages and disadvantages:

Lighting Technology	Application	Advantages	Disadvantages
Standard Incandescent	Domestic use Localized decorative lighting	Direct connection without intermediate Switchgear. Reasonable purchase price. Compact size Instantaneous lighting Good colour rendering	Low luminous efficiency and high electricity consumption. Significant heat dissipation. Short service life.
Halogen Incandescent	Spot lighting. Intense lighting	Direct connection Instantaneous efficiency Excellent colour rendering	Average luminous efficiency
Fluorescent tube	Shops, offices, workshop. Outdoors	High luminous efficiency. Average colour rendering	Low light intensity of single unit. Sensitive to extreme temperatures
Compact fluorescent lamp	Domestic use. offices. Replacement of incandescent lamps	Good luminous efficiency. Good colour rendering	High initial investment compared to incandescent lamps
HP Mercury Vapor	Workshops, halls, hangars. Factory floors	Good luminous efficiency. Acceptable colour rendering. Compact size Long service life	Lighting and relighting time of a few minutes
High-Pressure Sodium	Outdoors Large halls	Very good luminous efficiency	Lighting and relighting time of a few minutes
Low-Pressure Sodium	Outdoors Emergency lighting	Good visibility in foggy weather Economical to use	Long lighting time (5 mins). Mediocre colour rendering.
Metal halide	Large areas Halls with high ceilings	Good luminous efficiency. Good colour rendering. Long service life.	Lighting and relighting of a few minutes
LED	Signaling (3-colour traffic lights, exit signs and emergency lighting	Insensitive to the number of switching operation. Low energy consumption. Low temperature	Limited number of colors. Low brightness of single unit

Typical Power Factors for Common Electrical Loads

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Power factor is very critical for calculating or measuring the electrical power consumed by an electrical device on an alternating current supply. To be able to determine electrical power on alternating current (AC) systems, you need to know the power factor of the electrical load. Below is listed the  typical power factors for common electrical loads:

Electrical Load	Power Factor (CosՓ)	Reactive Demand Factor (TanՓ)
Transformers (No load condition)	0.1 - 0.15	9.9 - 6.6
Motor (Full load)	0.7 - 0.85	1.0 - 0.62
Motor (No load)	0.15	6.6
Metal Working Apparatuses:
Arc Welding	0.35 - 0.6	2.7 - 1.3
Arc Welding  Compensated	0.7 - 0.8	1.0 - 0.75
Resistance Welding	0.4 - 0.6	2.3 - 1.3
Arc Melting Furnance	0.75 - 0.9	0.9 - 0.5
Fluorescent Lamps:
Compensated	0.9	0.5
Uncompensated	0.4 - 0.6	2.3 - 1.3
Mercury Vapor Lamps	0.5	1.7
Sodium Vapor Lamps	0.65 - 0.75	1.2 - 0.9
AC DC Converters	0.6 - 0.95	1.3 - 0.3
DC Drives	0.4 - 0.75	2.3 - 0.9
AC Drives	0.95 - 0.97	0.33 - 0.25
Resistive Load	1	0

How To Select Batteries for Any Application

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The selection of batteries for any application is a critical exercise. A number of factors must be considered in selecting the best battery for a particular application. The characteristics of each available battery must be weighed against the equipment requirements and one selected that best satisfy these needs. The considerations that are important and influence the selection of the battery are tabulated below

How to Determine Voltage Drop in an Electrical Conductor

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Owing to the effect of voltage drop on electrical equipment, determination of the voltage drop of an electrical conductor is very important in helping to predict voltage drop level and ensure that it is in line with the relevant standard.
For an electrical conductor with impedance Z, the voltage drop is calculated by the following formula:

Where:
K   =     a coefficient equal to 2 for single phase and two phase systems.
             SQRT(3) for three phase systems
IB   =     load current in Amps. if no information are available, the cable carrying   
             Capacity of the conductor shall be considered.
L    =     Length of conductor in Km
n     =     is the number of conductors in parallel per phase
R    =     is the resistance of the single cable per kilometre in (Ω/km)
X    =     is the reactance of the single cable per kilometre in (Ω/km)

CosФ = power factor of the load

Resistance and reactance values

How Voltage Drop Affect Electrical Equipment and Installations

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In an electrical installation, determination of voltage drop from the point of supply to the load is very important. Excessive voltage drop on the supply line impacts most electrical equipment but not to the same degree. The effect of voltage drop on some key electrical equipment is given below.

Effects of Voltage Drop
Electric Motors
In an electric motor, the torque is proportional to the square of the supply voltage. Therefore, if the voltage drops the starting torque will also decrease, making it more difficult to start up motors. The maximum torque will also decrease .

Incandescent Lamps
The more the voltage drops the weaker the beam becomes and the light takes on a reddish tone.

Discharge Lamps
In general, they are not very sensitive to small variations in voltage, but in certain cases, great variation may cause them to switch off.

Electronic Appliances
They are very sensitive to

Classes of Explosive Atmospheres – EU Classification

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An understanding of this classification is required because often motors and other electrical equipment are required to be installed in these hazardous or explosive atmospheres. A clear understanding of the classes of explosive atmospheres will help in the selection and specification of electrical equipment in such environment.

Classes of Explosive Atmospheres
The EU (European Union) ATEX directive 99/92/EC distinguishes between two types of explosive atmospheres: GAS and DUST. Areas subjected to these two kinds of explosive atmospheres are each divided into three zones. Each zone characteristics are identical for gas and dust, but their numbering is different. Zones 0, 1, 2 refer to gas and zones 20, 21, 22 refer to dust. 

The various classes of explosive atmospheres are listed below

Basics of Explosive Atmospheres

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An explosive atmosphere is an atmosphere that develops explosively because of an uncontrollable combustion. Explosive atmosphere consists of air and some sort of combustible material such as gas, vapours, mists or dust in which the explosion spreads after ignition. Typical examples of productions where combustible dust is of major concern, is the handling of cereals, animal feed, paper, wood, chemicals, plastics and coal.

Sources of Ignition

Sources of ignition that can cause the atmosphere to explode are listed below:

How to Identify Three Phase Windings

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A procedure has been adopted by the IEC for identifying three phase winding connections. Letters and numbers are used as follows. The high voltage (HV) terminals have upper-case letters e.g. A-B-C, R-Y-B, U-V-W, L1-L2-L3 and the low voltage (LV) terminals have lower-case letters e.g. a-b-c, r-y-b, u-v-w, l1-l2-l3. Each winding has a start numbered 1 and a finish numbered 2.
The choice of letters and numbers tends to be a national preference, see the table below for a rule of thumb guide:

Types of Protection for Hazardous Areas

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Most electrical equipment consists of live or active static parts, and in some cases such as motors, solenoid valves and relays have moving mechanical parts, encased in an enclosure. The electrically live conductors are kept out of touch to prevent electric shock hazards. The detrimental effects of the environment e.g. rain, sprayed water, fine dust and particles are kept out of contact with the conductors, insulation, bearings and the like.

The design of the enclosure of electrical equipment with regard to hazardous area applications is defined by several lower case letter codes, mostly single digits for electrical power equipment but occasionally two digits for very low energy electronic equipment. The most frequently encountered codes are d, e, n, p and i. The lesser used codes are o, m, s and q. The table below gives a brief description of each code:

How to Convert KVA to Amperes for Single and Three Phase Circuits Using Tables

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The following tables list the current in amperes for different KVA values for both single and three phase circuits for 120, 240, 480 and 600V circuits. To get the corresponding value of AMPS for a given KVA, simply read off the current value at the required voltage for the given KVA rating.

KVA Rating to AMPS for Single Phase Circuits