“Electrical load” refers to the electrical component or equipment that consumes real power, and converts electricity into another energy shape, like heat, light or motion.
Electrical load Example
- light bulbs
- home appliances
- motors
- control circuit components like, contactors and relays
- electric transformers
What are electrical load types?
Three fundamental loads are present within circuits:
- capacitive
- inductive
- resistive loads
Resistive Loads
The loads that contains any heating element are categorized as resistive loads.
In resistive loads, the voltage and current remain in phase. Therefore the power factor is unity.
Talking about the units, resistive loads are measured in Ohms, while power is measured in watts.
Resistive loads include heaters, incandescent lighting or any non-motor loads.
Inductive Loads
All devices and equipment with coils are inductive in nature.
Contrary to a resistive load, in an inductive load, the current and voltage are out of phase.
We measure inductive load in Henry and its power in VAR. While, the power is the sum of Reactive and real power.
For more information about Active (apparent) Power, Read My article here. And, if you need more information about Reactive Power, Read my article here.
Capacitive Load
In the field of engineering, capacitive loads are rare compared to resistive and inductive loads. It’s much common in electronic circuits.
Capacitance is measured in Farads, while its power in VAR. The value of VAR in capacitive load is negative because the polarity of reactive power is negative.
In capacitive loads, changes in voltage lag behind changes in current.
What are the examples of three phase loads?
Three phase induction motors are the majority loads, but not the only loads in the power system.
Three phase heaters are an example of three phase loads, they are widely used in electric furnaces. These furnaces are common loads in iron and steel factories.
Hereunder some examples of three phase loads:
- Three phase motors.
- Three-phase rectifiers
- Three phase heaters.
- Three phase capacitor banks.
Leading and Lagging three-phase loads
- A three-phase leading load uses active power; however, its deliver reactive power back into the system. This creates an over-excited system.
- Three-phase lagged load consumes both reactive and active power simultaneously and makes the system overexcited.
There are some examples of lagging loads such as arc furnaces and three-phase transformers.
Leading loads are utilized exclusively to correct the power factor of the alternators, such as capacitor banks, series compensators or a series combination of capacitors and resistors.
The TCR (thyristor-controlled reactors) are utilized to increase the efficiency of power systems.
Is battery Considered an electrical load?
Batteries are primarily used to store Direct Current then, feed DC loads. They are sources, in most cases!
However, they have an internal resistance , because of the non-conductive nature of electrolytes and plates compared to the material used in the conductor.
In case of charging the battery, it’s considered as a load to the charger. It consumes power! isn’t it?
Think about it, when you are charging a your cell phone, the charger gets hot due to the power consumed by the battery. It draws current from the
After that, the battery feeds your cell phone with DC current, it acts like a DC power source in this case.
What is electrical load list?
The Electrical Load List is an estimated and detailed list of electrical loads of a distribution system. We can do a load list once the load data has been collected which is achieved after:
- We have a complete load layout
- We choose a basic distribution panels system of the project and know how we will distribute loads
- We assign all loads to individual load center and MCC (motor control center).
A load schedule can help find out the power needed for the installation. The information can then be used to correctly determine the proper size of conduits and conductors and the proper overload protection and other control systems.
The loads list makes it easy to identify and assist with the required quantities and equipment ratings that must be utilized to power the installation and design phase of the project.
A load plan should be established as early as possible during the design phase. It is essential to know the main voltage levels needed in the construction and all the other aspects of the purpose of the building or facility, and the nature of non-process and process loads.
The benefits of a load schedule:
- Provides an accurate estimation of the electrical load in the normal and peak load.
- The load list determine the power required for the project and for each load.
- The estimation assists in determining the size of conduits, conductors, the control and protection equipment and of course the cost estimation.
How to calculate electrical load schedule for a house?
Here’s a method used to calculate the load Schedule for a house:
- Take the total wattage capacity of all branches of lighting circuits.
- Include the wattage rating of each outlet plug-in circuit.
- Incorporate the wattage ratings of every permanent appliance (ranges dryers, stoves, water heaters, etc.)
- Subtract 10,000.
- Then multiply this answer by 40% (0.4).
- Then Add 10,000.
- Check the full wattage rating for permanent air conditioners and the wattage rating of heating appliances and then add either Larger Value from both of these. Because (You can’t cool and heat simultaneously; therefore, you don’t have to include each number.)
- Divide the sum by the total voltage if your electricity connection is three-phase then value will be different for each phase also need to calculate the load separately for three phase appliances’ in-case of three phase you have to divide the sum of total by phase-to-phase voltage not with single phase voltage.
This formula gives the recommended amperage required to supply the home with enough power. It is easy to evaluate the current electricity service applying this formula.
Some recommended simpler guidelines:
- 100-amp service is typically enough to supply a small-medium-sized or larger home’s main branch circuits as well as one or two electrical appliances like a cooking range or water heater, or clothes dryer. If the heating appliances use gas, the service could be adequate for homes with less than 2500 square feet.
- 200-amp service can take on the same amount of load as 100-amp service. It also includes electric appliances and electric heating and cooling equipment for homes that are up to 3,000 square feet.
- 300or 400-amp services are recommended to big homes (more than 3500 square feet) with all-electric appliances and electric heating and cooling equipment. This service size is suggested for homes where the anticipated electric heat load exceeds the 20,000-watt mark. 300- or 400-amp service is typically offered by installing two panels, one offering 200 amps and the second one that provides 100 amps or 200 amps.
Electrical load calculations, formula and examples
Calculating electrical loads can be performed by calculating load power or load current.
Let’s begin with calculating electrical current.
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Single-Phase current calculation
Single Phase Load current, I = P ÷(V× PF)
Where, P is power in watt, V is operating voltage and PF is the power factor.
Let’s Take the values of P (Watt) and Voltage,
P= 800W
V= 230V
(power factor) P. F= 0.9
Now put these values into the formula
Load current, I = 800 / (230× 0.9)
Single Phase Load current (I) = 3 Amp
Three-Phase current calculation
Three Phase Load current, I = P÷ √3 V × P.F
Let’s Take the values of P and Voltage
P=1000 W
V= 440 V
P.F = 0.9
Now, put these values into the formula
I (3 phase)=1000 ÷ (1.73 × 400 × 0.9)
Three Phase Load current, I = 1.60 Ampere
Now, let’s calculate load power, Power can be real or apparent power. Real power is calculated in KW, and apparent power is calculated in KVA.
Load in KW Calculation formula
The unit used to estimate the real power is KW, we calculate power in KW in case of resistive loads or calculating real power of the load.
Single-Phase Load Power Calculation
P (KW)= (V × I × PF) ÷ 1000
Example:
Let’s assume the values of current and volts
V (Voltage)=220 Volts
I (Current)=5 Amp
Power factor = 0.9
P (KW)= (220 x 5 x 0.9) ÷ 1000 = 0.99KW
Three Phase Load Power Calculation
P(KW)= (√3 x V x I x P.F) ÷ 1000
Example:
Let’s assume the values of current and volts,
V= 435 Volts and I=25 Amp
Now put all values in Formula
Load power= (1.732 x 435 x 25 x0.9) ÷1000 =16.95 KW
Where V is voltage,
I is load current,
PF is power factor
KVA load calculation
The unit that calculates apparent power is KVA, we use it with generators and transformers loads.
Single-Phase Load in KVA
S (KVA)= (V × I) ÷ 1000
Example:
V (Voltage)=220 Volts
I (Current)=5 Amp
Put the values in formula
S(apparent power)= (220 x 5)÷ 1000, Load Power = 1.1KVA
Three-Phase Load in KVA
S(KVA)= (V × I× 1.732) ÷ 1000
Let’s assume the values of current and volts
V= 435 Volts
I=25 Amp
Now put all values in Formula
Load apparent power, S= (435 x 25× 1.732)÷1000= 18.835 KVA
Difference Between kW load and kVA load
The primary difference between kW (kilowatt) and the kVA (kilovolt-ampere) is their power factors.
KW is the term used to describe the load real power unit, and kVA is the load apparent power unit.
Although as well-known, the power ratio is consequently an approximate figure (typically 0.8). When comparing kW to kVA calculations, the value of kVA will always be greater than the kW value.
For industrial and commercial generators, the kW number is the most frequently used in US generators. Most of the rest of the world utilizes kVA as the main generator set.
What is the measuring Unit of Electrical Load?
The measuring Unit of the Electric Load is Watt and Kilowatt.
Electrical power is expressed in power units known as Watts, named in honor of James Watt, the inventor of the steam engine.
One Watt is just a small quantity of energy. Some devices need only some Watts to function, whereas others require more. Power consumption for smaller devices is typically measured in Watts. In contrast, bigger devices are measured using Kilowatts (kW), equivalent to 1,000 Watts.
Electricity generation capacity is typically expressed in multiples of Kilowatts in megawatts (MW) and gigawatts (GW). One megawatt is 1000 thousand kW (or one million Watts), while one gigawatt is 1000 milliwatts (or 1,000,000 Watts).
What type of load is electric motor?
Induction motors are the most common motor type in the network. Electrical motors, single or three phase, are inductive loads. They are the most common inductive loads in the power system.
Motor are used in a wide range of consumers commercial, residential and industrial loads.
This is why we use capacitive loads, capacitor banks, to compensate the inductive loads of large industrial buildings, i.e power factor correction.
Is a transformer an inductive or a capacitive load?
The transformer draws an inductive current to perform its operation. The magnetizing current required for setting the flux needed within the iron core of the transformer is inductive.
The secondary current could be either inductive, resistive, or capacitive, based on the kind of load being connected to secondary side of the transformer.
If the primary side of the transformer is connected to a capacitive load, the primary current will be capacitive.
The primary current is inductive if the secondary is connected to an inductive load.
It’s all depends on the type of load connected by the secondary side of the transformer.
- If the secondary is an open circuit, the primary acts as a high inductance coil.
- If the secondary is connected with a resistor, it acts in sequence with the leakage inductance. Practically, if the leakage inductance is negligible, the transformer will appear like a pure resistor. The resistance is changed up or down depending on the ratio of turn.
- The same as capacitors on the secondary; however, the capacitance will be changed in inverse proportion to the turn ratio. The main will remain the capacitor with a low inductance when in series.
What is critical load in power system?
Critical loads are those loads where the power supply needs to be maintained in any conditions. The power supply to these loads shouldn’t ever be cut off.
These types of loads are classified as Critical loads, those loads that directly affect the capability for an organization to run.
Special measures are implemented to ensure a continuous supply of power to these loads, even if the power supply to the industry fails because, these loads need to be maintained running (without interruption in power) when the mains power source is shut down in a timely way to avoid computer crashes or data corruption, as well as life-shortening hardware damages.
This is why uninterruptible power supply and other standby power solutions like generators play a crucial function in ensuring continuity of business by providing immediate backup to the essential electronic devices, systems, and equipment in the event of a significant power outage.
Critical loads are often found in processing plants where processes cannot be stopped.
In my work, we have a small airport, the critical loads are the devices that are used to communicate with the pilots and direct them during take off and landing process.
We use UPS (ninterruptible power supply) to feed these devices during any power outage till the emergency generator run, these devices has no outage time.
Think bout hospitals, surgery rooms requires power all the time. No outage is allowed, these are critical loads.
Factors To Classifying Loads as Critical or Non-Critical:
load is classified as critical or non-critical is based on the importance it has to the company in relation to:
- Health care centers and hospitals.
- Financial penalties, loss of business, and impacts on customer service
- Service delivery
- Productivity and production lost
- Quality, safety, and health as well as environmental protection systems
- Security breaches and the loss of control
- Stakeholder trust and reputation of the company
After critical loads have been discovered, they need to be prioritized according to their importance and the length of time they will need to remain in operation during a primary outage.
For specific critical loads, such as local file servers, the server may need to be protected from shutting down a secure system.
Like the medical systems for life or telecom networks, others might require maintaining the longest time it is feasible.
What is the function of an electrical load in circuit?
The circuit’s load is the actual device that performing the necessary task like the dishwasher, television, and toaster or oven.
A circuit could be nothing without an associated load. The load takes the required current to enable the device to function.
The cool thing about electrical energy is that it can be converted to other shapes of energy like heat or mechanical energy. Electrical loads are the part of the electrical system that do such thing.
- Electric motor is a load, its function is to convert electricity into mechanical energy to drive a mechanical load.
- Light bulb is a load, its function is to convert electricity into light energy.
- Space heater is a load, its function is to convert electricity into heat.
