Basic Electricity – Understanding Current, Voltage, Resistance, and Power

Green electricity integrates renewable energy sources such as solar PV, wind turbines, and hydropower into smart grids, improving power quality, decarbonization, efficiency, and reliability for industrial loads and utility-scale networks.

What is green electricity?

Green electricity is renewable-source power via smart grids to cut emissions and enhance system efficiency.

✅ Integrates PV, wind, hydro with power electronics and converters

✅ Enhances grid stability via inverters, FACTS, and smart protection

✅ Reduces CO2, improves efficiency, supports microgrids and storage

Green electricity is a term describing what is thought to be environmentally friendly sources of electricity. Typically, this refers to renewable and non-polluting energy power sources. For a broader perspective on how different technologies contribute, see this overview of sources of electricity across modern grids.

Green electricity includes natural energetic processes which can be harnessed with little pollution. Anaerobic digestion, geothermal power, wind power, small-scale hydropower, solar power, biomass power, tidal power and wave power fall under such a category. Some versions may also include power derived from the incineration of waste. Comparisons with other clean options are summarized in this guide to alternative electricity solutions used worldwide.

Energies Wind Electricity 
The winds that blow across the UK can be harnessed by turbines to provide Green electricity. Wind turbines sited in suitable locations already provide a small, but growing percentage of the UK's electricity, and are used successfully all around the world. In fact wind power is the world's fastest growing energy source! Wind turbine technology has greatly improved over the last ten years, making wind turbines quieter and more efficient so that electricity generated from the wind is now often competitive with traditional coal-fired and nuclear power stations. Wind turbines are also beginning to be built at sea — in the future much of our electricity could come from these offshore windfarms. Understanding how turbines integrate into national systems is covered in this primer on electricity generation methods and planning.

Solar Electricity
Many people believe that we don't get much solar Green electricity here in the UK. In fact solar power is already being used to provide essential power for many types of equipment being used in both remote and urban areas across the country. A solar photovoltaic (PV) module works by converting sunlight directly into electricity (even on cloudy days) using semiconductor technology. The vast majority of solar modules available today use "waste" silicon from the computer chip industry as the semiconductor material. They can be integrated into buildings and even made into roof tiles virtually indistinguishable from normal tiles. 
Solar Electricity can also be used to heat water directly using specially designed collectors. Even in winter a useful amount of hot water can be produced from roof top collectors. A third way to use solar energy is simply to design buildings to make maximum use of the sun. Using this so-called 'passive solar' approach, much of the energy that we currently use for heating, lighting and air conditioning can be saved. Homeowners can explore practical steps to generate electricity with rooftop PV and storage.

Hydro Electricity
Water turbines have been used to provide Green electricity for over 100 years and presently provide over 1% of the UK's electricity. Although most of the possible sites for large hydropower stations in the UK have already been developed, there is a large potential for smaller schemes. These can either use a small dam or work as a 'run of the river' system which has a minimal impact on the local environment. Design considerations for small schemes are outlined in this resource on water electricity systems for communities.

Wave Electricity
Many different devices have been designed over the years to try and capture some of this huge energy resource — the latest one has recently started generating Green electricity on the isle of Islay, off the West Coast of Scotland. In this machine waves hitting the shore are channelled into a large tube to power a specially designed turbine. With the proper support, wave power could provide a significant proportion of the UK's electricity needs in the future.

Tidal Electricity
Tidal power has been used in Britain for over a thousand years — at the time of the Doomsday book over 5,000 tide powered mills were recorded. Unlike other Green electricity renewable energy sources, which depend on the weather, tidal power is as predictable as the tides themselves. One way to capture tidal energy is to build a barrage across an estuary, storing water behind it as the tide rises and then releasing the stored water through turbines at low tide. Several sites around the UK could be suitable for this type of tidal system, the largest being the Severn Estuary. Another way is to use 'marine current turbines', which work like underwater wind turbines, harnessing tidal currents instead of the winds.

Geothermal Electricity
Geothermal energy comes from hot rocks deep underground. In some parts of the world steam comes to the surface and can be used to run steam turbines to produce Green electricity directly. In other places water can be pumped down and heated by the rocks to make steam. Geothermal energy can also be used to provide hot water and heating for buildings. Case studies of enhanced systems are available in this overview of geothermal electricity projects worldwide.

Biomass Electricity
Either agricultural wastes or specially grown plants can be used as a fuel to run small Green electricity power stations. As plants grow they absorb carbon dioxide (the main gas responsible for climate change) which is then released when the plants are burnt. So using biomass does not add any extra carbon dioxide into the atmosphere. Specially grown 'energy crops' provide not only an environmentally sound source of electricity, but also an important new opportunity for farmers. Analyses of supply chains and grid impacts appear in this review of electricity production from biomass and other renewables.

Landfill gas Converted to Electricity
As rubbish decomposes in the landfill sites where our household waste is dumped, it gives off methane gas. This gas can be captured and burnt in a gas turbine to produce an attractive Green electricity tariff. Burning the gas does give off carbon dioxide but since methane, which is emitted from the landfill site, is in fact a much more powerful greenhouse gas it is better to burn it than to allow the methane to escape into the atmosphere. There are already many landfill gas systems operating in the UK.

Waste Incineration Electricity
The UK generates an enormous amount of waste, and space at landfill sites is quickly running out. The best solution would be to recycle as much of the waste as possible, but instead incinerators are being constructed to burn the waste. In some cases the energy is being used to generate green electricity. However many environmentalists are still concerned about the emission of harmful dioxins and also about the loss of a valuable resources that could have been recycled. You can read about Greenpeace's views on incineration.

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Saving electricity through energy efficiency, power factor correction, load balancing, and demand response integrates smart meters, VFDs, and SCADA to cut losses, optimize voltage, and improve grid reliability in industrial and commercial systems.

What Is Saving Electricity?

Saving electricity applies engineering methods to cut losses, optimize loads, and improve efficiency and reliability.

✅ Implement power factor correction capacitors to reduce reactive power.

✅ Use VFDs for motor speed control and peak demand reduction.

✅ Deploy smart meters, SCADA, and analytics for load balancing.

Saving electricity becomes an increasingly important issue the more the cost of power increases. There is no such thing as cheap electricity. That is a basic fact in today's world of increasing costs for all forms of energy. It's a common fact that vast amounts of electric power are wasted every year in the world, mostly in areas where power is cheap and abundant. However, in recent years, as the supply of electricity generation has remained static and at the same time demand for power continues to increase, the power prices have increased dramatically. For a refresher on the fundamentals, see this brief guide to what electricity is to better frame consumption trends.

One of the leading cost inputs of electric energy is the cost of generation energy inputs. For instance, if all power generation came from oil, you can imagine what the cost of power would be. Since most power is generated from burning coal and natural gas, as the cost of these commodities increases, so does the cost of electric generation. A quick overview of primary sources of electricity clarifies how fuel price volatility feeds into rates.

Saving electricity, on the other hand, is one of the least expensive ways to generate large amounts of power is from the use of water in hydroelectric generation stations. Hydropower is covered among methods that generate electricity efficiently when geography permits.

The other least expensive way to generate power is from the use of uranium in nuclear power stations. Yes, nuclear power stations are very expensive to build but given the amount of power they generate, plus the fact that they operate 24 hours a day, makes them a very cost-effective way to generate electric power. Alongside nuclear, many regions are expanding alternative electricity options to diversify supply.

Using Less, Quickly
Energy conservation can be accomplished quickly when each home saves electricity through less consumption. This is accomplished by turning lights off when not needed. You can also turn off appliances and use less heat. First, power saver improvements can be made to the electrical equipment such that consumers receive the same services but with less power consumed. (These are sometimes called “efficiency improvements”). In the second case, the energy consumer takes deliberate measures to reduce energy use through changes in operations or procedure which may also cause inconvenience and result in a loss of service. These are typically called “behavioral” changes. For step-by-step ideas, practical checklists on how to save electricity can help households prioritize actions without sacrificing comfort.

Technical Efficiency Improvements
The technical measures to save consumption quickly are similar to those used to save power slowly except that they may be implemented with greater intensity by combining them with special subsidies or delivery schemes. Three examples are described below.

Retrofits—especially retrofits of large, energy-using facilities—are attractive targets during an energy crisis. About 8% of industrial power consumption is used to make compressed air, much of which is lost through system leaks. Understanding the relationship between electricity and power helps target leaks and idle loads more effectively.

Lighting replacements have been the most frequently used retrofit strategy. Replacing incandescent light bulbs with compact fluorescents (CFLs) was used in Brazil, California, and New Zealand. California consumers installed nearly eight million CFLs during the crisis period, resulting in almost 500 MW of demand reduction (Pang 2003). California cities replaced millions of traffic lights with LED lamps, each saving about 80 watts. California aggressively encouraged consumers to replace older appliances with new units qualifying for the Energy Star endorsement of high efficiency. While there is no such thing as truly free power, discussions about free electricity often highlight bill-lowering strategies and policy incentives.

When it comes to saving electricity, there are many techniques one can easily apply. Conservation (or using less) is the best and most extreme way. But when using less is not possible, the next best thing for energy conservation is the use of more energy efficient electrical equipment, such as:

• Energy efficient electric Motors. Electric motors consumer 75 per cent of all power consumed by industry and any large consumer of power will save money by installing more energy efficient electric motors.
• Variable frequency drives that operate and control electric motors and are good at saving electricity. These devices control the speed and torque and starting characteristics of large horsepower motors and one of the best ways for using less and earning more.
• Energy efficient electric lighting is also good at saving electricity. There are lots of more efficient electric lighting technologies and control systems on the market today.
• Energy efficient home appliances like refrigerators and dishwashers and clothes washers and dryers can make a large impact on your power bill.
• A High-Efficiency Energy heating system saves heating and money.
• Off-peak electric utility rates from electric utilities reward customers for saving electricity because they can provide consumers with an incentive to shift their power consumption into periods of the day when the electric utility is not at or near full generating capacity like late at night.

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Nominal voltage is the standard voltage level assigned to electrical equipment or systems for identification. It helps ensure compatibility, performance, and safety across devices without indicating actual operating voltage, which may vary slightly.

What is Nominal Voltage?

Nominal voltage refers to the labelled voltage value of an electrical system or device.

✅ Represents standard system voltage, not an  exact measurement

✅ Helps match equipment compatibility and safety standards

✅ Common in power distribution, residential, and industrial systems

Nominal voltage (NV) is a vital aspect of electrical systems, serving as a reference point for designing, manufacturing, and testing equipment. Additionally, it affects the performance, efficiency, and safety of electrical systems, with voltage regulation ensuring that voltage levels (V) remain within acceptable tolerances. Understanding the differences between nominal voltage, operating voltage (OV), and rated voltage (RV) is crucial for professionals and enthusiasts to ensure the effective operation and maintenance of electrical systems. To better understand how nominal voltage fits within broader system design, see our comprehensive overview on voltage.

It is vital to understand the definition and importance of nominal voltage in electrical systems. NV refers to the standard voltage value assigned to an electrical system, typically the voltage that electrical equipment is designed to operate under normal conditions. This value is crucial because it serves as a reference point for designing, manufacturing, and testing electrical equipment to ensure satisfactory performance. Maintaining voltage stability is essential—learn how voltage drop impacts performance and how to accurately calculate it.

Determining nominal voltage for electrical systems involves considering factors such as the type of equipment being used, the overall power requirements, and the voltage standards set by industry organizations. In some cases, the NV is set by the equipment manufacturer, while in others, it depends on the power grid's Voltage levels. Standard nominal voltages have been established to streamline equipment design and manufacturing processes. Use our voltage drop calculator to determine how wiring distance and load affect nominal voltage in real applications.

The terms NV, OV, and RV often appear in discussions about electrical systems. While they may seem interchangeable, each has a distinct meaning. As previously mentioned, nominal voltage is the standard voltage value designated for an electrical system. On the other hand, OV is the actual voltage at which equipment functions during operation. Similar to nominal voltage, RV refers to the maximum voltage at which equipment can operate continuously without sustaining damage. See how voltage regulators are used to maintain nominal levels and protect sensitive equipment.

Nominal voltage has a direct impact on the performance of electrical systems. Equipment designed for specific NVs operates safely within a particular voltage range. Operating outside this range can result in equipment damage, decreased efficiency, and even electrical fires. Therefore, it is essential to maintain the voltage levels as close as possible to the NV. Our guide to what is voltage explains the differences between nominal, operating, and actual voltage in power systems.

Electrical systems worldwide adhere to common national voltage (NV) standards for alternating (AC) and direct (DC) systems. For AC systems, NV  ranges include 110V, 220V, and 380V, while DC systems typically have NVs of 12V, 24V, or 48V. These standardized voltage levels enable the compatibility and interoperability of electrical equipment across various regions and industries. Learn how wattmeters and voltmeter tools help monitor nominal and real-time voltage values in field diagnostics.

Voltage regulation plays a critical role in controlling an electrical system's output voltage to ensure it remains within the acceptable voltage tolerance. Voltage regulation can be achieved through various means, including transformers, voltage regulators, and software algorithms in modern power systems. By maintaining NV, the electrical system The voltages more efficiently and safely, ensuring the longevity of the equipment.

The voltage tolerance is the range of voltage deviation from the nominal voltage value within which equipment can still operate effectively and safely. Different electrical systems have different voltage tolerances depending on the nature of the equipment and its intended use. For instance, a residential electrical system may have a voltage tolerance of +/- 5%, while an industrial system might tolerate a deviation of +/- 10%. Maintaining the acceptable V tolerance is crucial for the satisfactory operation of electrical equipment.

Nominal Voltage (NV) vs Operating Voltage (OV)

Nominal voltage and OV are two related yet distinct concepts in electrical engineering systems. Understanding the different essentials to ensure electrical systems' safe and efficient operation.

Nominal voltage refers to the standard or reference voltage level assigned to an electrical system, circuit, or device. It is the ideal voltage at which the equipment is designed to operate under normal conditions. NV is a baseline value that allows manufacturers, engineers, and technicians to design, test, and rate electrical equipment consistently.

Conversely, OV is the actual voltage level at which a particular electrical system, circuit, or device is functioning during real-time operation. Unlike nominal voltage, OV can fluctuate due to factors such as load changes, temperature variations, and power supply issues. Although electrical equipment is designed to operate optimally within a specified voltage range around the nominal voltage, slight variations in the operating V are often unavoidable.

In essence, NV serves as the benchmark or target voltage level, while OV reflects the real-world voltage conditions experienced by the electrical equipment. To ensure the efficient and safe operation of electrical systems, it is crucial to maintain the OV as close as possible to the NV. When the operating voltage falls within the acceptable voltage tolerance range, electrical equipment can function efficiently and safely without the risk of damage or performance degradation. Discover how alternating current systems rely on standardized nominal voltages like 120V or 240V for safe and consistent operation.

Nominal Voltage (NV) vs Rated Voltage (RV)

Nominal voltage and RV are related terms in electrical engineering but have distinct meanings and implications. Understanding the difference between the two is crucial for designing, operating, and maintaining electrical systems and devices properly. Differences between high voltage, medium voltage, and low voltage categories are based on standardized nominal values used in system classification.

It refers to the standard or reference voltage level assigned to an electrical system, circuit, or device. It is the ideal voltage at which the equipment is designed to operate under normal conditions. NV serves as a baseline value that enables manufacturers, engineers, and technicians to design, test, and rate electrical equipment consistently across various industries and applications.

On the other hand, RV is the maximum voltage at which an electrical device or component can operate continuously without incurring damage or experiencing a significant reduction in performance. RV is a critical parameter to ensure electrical equipment's safe and efficient functioning. Operating an electrical device within its RV range prevents excessive stress on the device, thereby reducing the risk of failure or shortened lifespan. Understanding the concept of electrical resistance is key to managing voltage drop and maintaining nominal voltage across circuits.

Nominal voltage is the target or reference Voltage level for the design and operation of electrical systems. In contrast, RV defines the maximum allowable Voltage for the continuous operation of electrical equipment. To ensure the efficient and safe performance of electrical systems, it is essential to maintain the operating voltage within the acceptable voltage tolerance range around the nominal voltage and not exceed the RV.  The relationship between power factor and nominal voltage affects system efficiency, especially in industrial electrical networks.

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Capacitors in series lower the total capacitance but increase voltage handling. This configuration is widely used in electronics, circuit design, and energy storage to balance voltage and improve reliability.

What are Capacitors in Series?

Capacitors in series describe a circuit configuration where capacitors are connected end to end, affecting capacitance and voltage distribution.

✅ The total capacitance is always less than the smallest capacitor value

✅ Voltage divides across each capacitor based on its capacitance

✅ Improves voltage rating of circuits while lowering equivalent capacitance

They play a critical role in various electronic applications, and understanding their characteristics, advantages, and potential drawbacks is essential for designing and implementing successful circuits. By mastering the concepts of capacitance, voltage distribution, and energy storage, one can leverage capacitors in series to create optimal circuit designs. To fully understand how capacitors (caps) behave in different setups, it helps to compare Capacitance in Parallel with series connections and see how each affects circuit performance.

Capacitors are fundamental components in electronic circuits, and their applications are vast, ranging from simple timing circuits to sophisticated filtering applications. This article delves into the intricacies of caps connected in series, highlighting their characteristics, advantages, and potential drawbacks.

To understand capacitors in series, it's essential first to grasp the concept of capacitance, which represents a capacitor's ability to store electric charge. Caps consist of two conductive plates separated by a dielectric material that can store energy when an applied voltage is present. The amount of energy stored depends on the capacitance value, voltage rating, and the dielectric material used. Engineers often study Capacitance and its capacitance definition to calculate charge storage and predict how components will interact in series circuits. 

When caps are connected in series, their individual capacitance values contribute to the total equivalent capacitance. The series connection is achieved when the positive plate of one capacitor is connected to the negative plate of the subsequent capacitor. This forms a continuous path for current flow, creating a series circuit.

Calculating the total capacitance for capacitors in series is different from parallel capacitors. In a series connection, the reciprocal of the total equivalent capacitance is equal to the sum of the reciprocals of the individual capacitance values. Mathematically, this is represented as:

1/C_total = 1/C1 + 1/C2 + 1/C3 + ... + 1/Cn

Where C_total is the total equivalent capacitance, and C1, C2, C3, ... Cn are the individual capacitance values of the number of caps connected in series.

In a series connection, the electric charge stored in each capacitor is the same. However, the voltage across each capacitor varies depending on its capacitance. According to Kirchhoff's voltage law, the sum of voltages across individual capacitors must equal the applied voltage. Thus, higher capacitance values will have lower voltage drops, while lower capacitance values will have higher voltage drops.

There are both advantages and disadvantages to connecting capacitors in series. On the plus side, the voltage rating of the series connection increases, allowing the circuit to handle higher voltage levels without risking damage to the caps. This feature is particularly useful in high-voltage capacitors in series applications. Alongside capacitors, Amperes Law and Biot Savart Law provide deeper insight into the electromagnetic principles that govern current and voltage distribution.

However, there are also drawbacks to this arrangement. The total equivalent capacitance decreases as more capacitors are added to the series, which may limit the energy storage capabilities of the circuit. Moreover, in the event of a capacitor failure, the entire series connection is compromised.

Different capacitor types and values can be combined in a series configuration, but care must be taken to consider each capacitor's voltage ratings and tolerances. For instance, mixing capacitors with different dielectric materials may lead to uneven voltage distribution and reduced overall performance. Since Capacitors are essential to energy storage and timing circuits, learning their behavior in a Capacitors in Series arrangement is key for advanced electronics design.

Determining the total energy stored in a series connection of caps involves calculating the energy stored in each individual capacitor and then summing those values. The formula for energy storage in a capacitor is:

E = 0.5 * C * V^2

Where E is the energy stored, C is the capacitance, and V is the voltage across the capacitor. Calculating each capacitor's energy and adding the results can determine the total energy stored in the series connection.

Compared with parallel configurations, the total capacitance increases in parallel connections while it decreases in series. In parallel, the total capacitance is the sum of the individual capacitance values:

C_total = C1 + C2 + C3 + ... + Cn

A crucial aspect of working with capacitors in series is charge distribution. As mentioned earlier, the electric charge stored in each capacitor is the same, but the voltage distribution varies depending on the capacitance values. This characteristic influences the circuit's behaviour and must be considered when designing complex electronic systems. Uneven voltage distribution can affect the entire system's performance, making choosing caps with appropriate capacitance values and voltage ratings for a specific application is vital.

Another important factor to consider is the plate area. In general, caps with larger plate areas have higher capacitance values. Therefore, when connecting capacitors in series, it is essential to evaluate how the plate area of each capacitor influences the overall capacitance of the series connection. Understanding these factors will enable engineers and hobbyists to make informed decisions when designing and constructing electronic circuits.

Capacitors in series are versatile and valuable configurations for various electronic applications. By understanding the principles of capacitance, voltage distribution, energy storage, and the influence of dielectric materials, one can harness the full potential of capacitors connected in series. Additionally, being mindful of the advantages and disadvantages of this configuration and considering the compatibility of different capacitor types and values will enable the creation of efficient, reliable, and effective electronic circuits. As electronics evolve, they will remain critical in developing innovative devices and systems. A solid foundation in Basic Electricity makes it easier to grasp why capacitors in series lower overall capacitance but increase voltage handling.

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Ground electricity underpins grounding and earthing practices, managing earth potential and fault current. It ensures equipotential bonding, surge protection, and safety compliance per IEC/NEC standards for power systems, electronics, and lightning protection.

What Is Ground Electricity?

Ground electricity is the earth reference and return path that stabilizes systems and safely carries fault current.

✅ Provides low-impedance fault current paths to trip protection

✅ Uses earth electrodes, bonding, and grounding conductors

✅ Reduces touch voltage, EMI, and lightning surge damage

Understanding Ground Electricity 

Ground Electricity is a general term that is often used loosely to refer to “Bonding” (Safety Grounding) and “Earth Grounding”.  Personnel of major industries have often misinterpreted grounding to mean that anything in contact with the earth is considered to be grounded. For foundational context, see our overview on how electricity works to understand why grounding concepts are sometimes conflated.

Electrical Grounding is the reference zero for the electrical system.  When we talk about 120 Volts RMS, it represents 120 units above the zero electrical reference.  In residential settings, this reference is commonly tied to service equipment, as explained in our guide to home electricity and typical distribution practices.

Electrical Grounding is the reference zero for the electrical system and all the equipment should be at this same equipment potential plane. Maintaining that equipotential plane is central to electricity safety because it minimizes touch voltage hazards.

According to accident reports, most electrical accidents occur when the earth is used as the safety grounding system (Bonding).   These incidents underscore the broader dangers of electricity when protective paths are improperly designed.

Accident reports details the hazards of using earth as a safety grounding and the practice of electrical grounding the equipment through local grounds. (grounding each individual piece of equipment with a separate ground rod, driven into the earth).  Improper local grounds can also complicate fault clearing during a system electrical fault, increasing damage and downtime.

The best method for ensuring the safety of personnel is to use a “Bonding Conductor”. This conductor should be continuous, with sufficient ampacity and the lowest impedance path back to the circuit interrupting devices, which insures positive operation of the protective devices. A robust bonding network ensures rapid clearing of a ground fault by providing a low-impedance return path for protective devices.

Once a system that connects all the metallic frames of electrical equipment together has been established, then the grounding system must be placed at “Zero Reference Potential”.  The earth grounding electrode should have the lowest resistance value possible, preferably 5 ohms or less.   Coordinating equipment bonding with proper transformer grounding helps maintain stable reference potential across the installation.

This low resistance to earth ground electricity will limit the potential of the electrical system to earth (limiting the stresses placed on components such as switches, insulators and transformers).

It will also reduce the effects of static charges on the electrical system and will protect against lightning strokes, lightning induced voltages, and minimizes the effects of transient over-voltages.

Visit Our Electrical Grounding and Bonding Course 

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Voltage drop occurs when electrical voltage decreases as current flows through a conductor. It can cause poor equipment performance, energy loss, and overheating. Discover how selecting the proper wire size and material can help minimize voltage drop in electrical systems.

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What is Voltage Drop?

Voltage drop (VD) is a common issue in electrical systems where the voltage (V) at the end of a circuit is lower than at the beginning due to resistance in the wiring.

✅ A decrease in V along a wire or circuit due to resistance or impedance

✅ Leads to reduced equipment performance and higher energy consumption

✅ Prevented by proper wire sizing, shorter runs, and low-resistance materials

Voltage Drop Definition

Voltage drop can lead to inefficient equipment operation or even failure. Solving electrical potential drop involves ensuring proper wire sizing, minimizing long-distance wiring runs, and using materials with lower resistance. Calculating the voltage drop for specific circuits and adjusting the installation accordingly helps maintain optimal performance and prevent power loss.

Any length or size of wires will have some resistance, and running a current through this dc resistance will cause the voltage to drop. As the length of the cable increases, so does its resistance and reactance increase in proportion. Hence, circuit V drop is particularly a problem with long cable runs, for example, in larger buildings or on larger properties such as farms. This technique is often used when properly sizing conductors in any single-phase, line-to-line electrical circuit. This can be measured with a voltage drop calculator.

Electrical cables have a carrying capacity of current that always presents inherent resistance, or impedance, to the flow of current. Voltage drop is measured as the amount of loss which occurs through all or part of a circuit due to what is called cable "impedance" in volts.

Too much resistance in wires, otherwise known as " excessive voltage drop ", in a cable's cross-sectional area can cause lights to flicker or burn dimly, heaters to heat poorly, and motors to run hotter than normal and burn out. This condition causes the load to work harder with less energy, pushing the current.

Voltage Drop per 100 Feet of Copper Wire (Single Phase, 60 Hz, 75°C, 120V Circuit)

(Values are approximate, in volts, for a 2% limit)

Key Takeaways

• Larger wires (lower AWG numbers) carry more current with less VD.

• Longer distances require thicker wires to stay within VD limits.

• A 2% VD is often used as a conservative design target in electrical systems.

How is this solved?

To decrease the voltage drop in a circuit, you need to increase the size (cross-section) of your conductors – this is done to lower the overall resistance of the cable length. Certainly, larger copper or aluminum cable sizes increase the cost, so it’s essential to calculate the voltage drop and determine the optimum wire size that will reduce voltage drop to safe levels while remaining cost-effective.

How do you calculate voltage drop?

Voltage drop refers to the loss of electricity that occurs when current flows through a resistance. The greater the resistance, the greater the voltage drop. To check the voltage drop, use a voltmeter connected between the points where the voltage drop is to be measured. In DC circuits and AC resistive circuits, the total of all the voltage drops across series-connected loads should add up to the V applied to the circuit (Figure 1).

Fig. 1. Measuring voltage drops across loads

Read our companion article Voltage Drop Calculator. For more information, see our article: Voltage Drop Formula.

Each load device must receive its rated power to operate properly. If not enough is available, the device will not operate as it should. You should always be certain that the V you are going to measure does not exceed the range of the voltmeter. This may be difficult if the V is unknown. If such is the case, you should always start with the highest range. Attempting to measure a V higher than the voltmeter can handle may cause damage to the voltmeter. At times you may be required to measure a V from a specific point in the circuit to ground or a common reference point (Figure 8-15). To do this, first connect the black common test probe of the voltmeter to the circuit ground or common. Then connect the red test probe to whatever point in the circuit you want to measure.

To accurately calculate the drop for a given cable size, length, and current, you need to accurately know the resistance of the type of cable you’re using. However, AS3000 outlines a simplified method that can be used.

The table below is taken from AS3000 electrical code, which specifies ‘Amps per %Vd‘ (amps per percentage VD) for each cable size.  To calculate the dop for a circuit as a percentage, multiply the current (amps) by the cable length (metres); then divide this Ohm number by the value in the table.

For example, a 30m run of 6 mm² cable carrying 3-phase 32A will result in a 1.5% drop: 32A × 30m = 960A / 615 = 1.5%.

Learn more about real-world voltage drop issues on our Voltage Dropping in Power Quality page.

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