Why Did the U.S. Transition from 110V to 120V Supply?

Why Did the U.S. Transition from 110V to 120V Supply?

In the early days of electricity in the U.S., the standard household voltage was 110 volts, largely influenced by Thomas Edison’s DC systems and early incandescent lighting technology, which was optimized for around 100–110V. However, as technology advanced, electrical loads increased, and better transmission efficiency was needed, engineers and utility companies started looking at ways to improve the power supply system without completely overhauling infrastructure.

One major reason for the shift to 120V was the introduction of AC (alternating current) and modern appliances. AC power systems, promoted by Nikola Tesla and Westinghouse, allowed for long-distance power transmission at higher voltages with lower losses. As demand for more power-hungry appliances like refrigerators, washing machines, and heaters increased, so did the need for a higher and more consistent voltage level. Increasing the voltage from 110V to 120V allowed for more efficient energy delivery to homes and reduced line losses, especially over longer distances.

Another factor was the standardization of equipment and safety regulations. As electrical codes and standards evolved in the U.S., it became necessary to define a nominal system voltage that allowed a range for fluctuation. The National Electrical Code (NEC) and utilities gradually defined the standard voltage as 120V ±5%, allowing for variations while still ensuring safe and consistent operation of equipment.

Importantly, the shift was not abrupt. Utility companies incrementally increased the voltage at transformers to compensate for line drops and improve efficiency. The infrastructure (such as transformers and appliances) was gradually designed or retrofitted to handle 120V without the need to drastically replace household wiring or plugs, which still largely resemble those used in the 110V era.

🔍 Summary:

The U.S. moved from 110V to 120V to improve efficiency, support modern appliances, reduce power losses, and meet updated safety and performance standards. This transition allowed for better compatibility with growing residential loads without major rewiring, as 120V systems could still support legacy 110V devices.

Why are there only 3- phase power system? why not 6- phase or 9- phase?

The three-phase power system is the global standard primarily because it provides the best balance between efficiency, simplicity, and cost. In a three-phase system, the voltage waves are spaced 120 degrees apart, creating a constant and smooth transfer of power. This smooth and balanced energy flow ensures that motors run efficiently with less vibration and wear.

Compared to single-phase power, three-phase systems deliver more power using less conductor material, which reduces cost and improves system performance, especially for industrial applications. The design of electrical machines (motors, transformers, generators) is also optimized for three-phase input, making the system more compact and cost-effective.

Now, while higher-phase systems like 6-phase or 9-phase are technically possible and sometimes used in special applications (such as high-voltage transmission lines or specialized rectifiers), they are not widely adopted because they complicate the infrastructure. More phases mean more conductors, more complex switching equipment, and more expensive transformers and protection systems. The added complexity doesn't provide a proportional benefit for general power generation and distribution. For most real-world uses, the three-phase system hits the "sweet spot" — offering efficiency, ease of design, and economic practicality without unnecessary complexity.

Here's a more detailed breakdown:

1. Cost and Complexity:

Fewer Components:

Three-phase systems require fewer components than higher-phase systems, leading to lower installation and maintenance costs, according to BTB Electric.

Simpler Equipment:

Three-phase equipment is generally simpler and more readily available than equipment for systems with more phases.

Reduced Wiring:

While increasing the number of phases increases the number of wires needed for transmission, three-phase systems strike a balance between power delivery and wire usage. 

2. Efficiency and Power Delivery:

Constant Power Delivery:

Three-phase systems offer a more consistent power delivery than single-phase systems, which experience pulsating power. 

Optimized for Motors:

Three-phase motors are highly efficient and provide a smooth, rotating magnetic field, crucial for many industrial applications. 

Diminishing Returns:

The efficiency gains from increasing the number of phases beyond three are often minimal, making the added complexity and cost not worthwhile, according to BTB Electric. 

3. Practical Considerations:

Industry Standards:

The widespread adoption of three-phase systems means that most electrical equipment is designed for it, simplifying integration and reducing the need for specialized components. 

Load Balancing:

Three-phase systems inherently help balance the electrical load across the phases, preventing overloading and improving overall system stability. 

Neutral Current:

In a balanced three-phase system, the current in the neutral wire is typically zero, further simplifying wiring and reducing losses. 

In essence, three-phase power offers a sweet spot in terms of cost, complexity, and efficiency, making it the most practical choice for widespread power distribution despite the theoretical possibilities of higher-phase systems.

Summary:

Three-phase power is the standard because it offers efficient, smooth power delivery with minimal cost and complexity. While higher-phase systems exist, they are rarely used due to added equipment costs and operational challenges without significant advantages for everyday applications.

Automatic changeover switch setup

This is a simplified and easy-to-understand layout of a residential power backup system using an automatic changeover switch (ATS). The setup is designed to automatically switch the power supply between the utility grid (from the transformer) and a diesel generator (DG set) in case of a power outage.

Starting from the top-right, the transformer brings electricity from the grid (utility supply). It is connected to one side of the automatic changeover switch, supplying the normal (grid) input. On the left side, the DG set (diesel generator) is connected, serving as the backup power source. These two inputs are wired into the automatic transfer switch (ATS), which intelligently selects the available source.

The automatic changeover switch (ATS) is the brain of this setup. When the grid supply from the transformer is available, it allows that power to pass through to the house. But if the grid supply fails, it detects the failure and automatically switches to the generator, assuming the DG is turned on or starts automatically. Once the grid is restored, the ATS shifts back to grid power. This switching helps avoid manual intervention and ensures an uninterrupted supply.

Below the changeover switch, the output power is routed through an MCB (Miniature Circuit Breaker) before entering the house. The MCB provides overcurrent protection, preventing electrical fires or damage to wiring and appliances due to short circuits or overloads. From the MCB, power is safely distributed to the house’s internal wiring, sockets, and appliances.

In summary, this system ensures that the home always receives power either from the grid or the generator with automatic switching, and it also includes basic protection via the MCB to safeguard the house's electrical infrastructure.

Transformers are rated in KVA but motors are rated in KW, why?

Transformers are rated in kVA (kilovolt-amperes) because they supply both active (real) and reactive power, and their losses depend mainly on voltage and current—not on the power factor of the load. Since a transformer doesn’t "know" what kind of load will be connected (whether resistive, inductive, or capacitive), it’s rated based on the total apparent power it can handle without overheating.

On the other hand, motors are rated in kW (kilowatts) because they convert electrical energy into mechanical power, and this mechanical output is only based on the real power consumed. The motor’s efficiency and power factor are already considered in its kW rating, as what matters most is the actual usable power delivered to perform mechanical work.

Details: 

The reason transformers are rated in kVA (kilovolt-amperes) and motors are rated in kW (kilowatts) lies in how each device handles power and the nature of the losses involved.

Here’s a detailed explanation:

1. Transformer Rated in kVA:

Power Factor Independence: A transformer does not consume power on its own but rather transfers electrical power from the primary to the secondary side. The power factor (the ratio of real power to apparent power) depends on the load connected to the transformer, which can vary. Since the transformer’s operation is independent of the load's power factor, manufacturers rate transformers in terms of apparent power (kVA), which does not consider the power factor.

Losses in Transformers: The two main types of losses in a transformer are:

Copper losses (I²R losses): Dependent on the current.

Iron (core) losses: Dependent on the voltage. These losses are not directly influenced by the power factor, so transformers are rated in terms of kVA, which combines both current (amperes) and voltage (volts).

2. Motor Rated in kW:

Power Factor Consideration: Motors convert electrical energy into mechanical energy (real power), which is measured in kilowatts (kW). The kW rating specifies the amount of real power a motor can provide to carry out mechanical work. The power factor is already accounted for in motor design, so the real power rating (kW) is what matters for motors.

Energy Conversion: Motors are primarily concerned with the real power (kW) they can generate for mechanical work. The electrical energy converted into useful work is reflected in the kW rating, which represents the power consumed and converted into mechanical motion.

Key Difference:

kVA (apparent power) in transformers represents the combination of real power and reactive power, without assuming a specific power factor.

kW (real power) in motors reflects the actual power used to do useful work, where the power factor is inherently part of the motor's efficiency.

Why is aluminum used instead of copper for overhead lines?

Why is aluminum used instead of copper in overhead lines?

Aluminum is used instead of copper in overhead power lines mainly because it is much lighter and more cost-effective, even though copper has better conductivity.

In long-distance transmission, the weight of the conductor plays a significant role—aluminum's lighter weight puts less mechanical strain on the poles and towers, making it easier and cheaper to install and support.

Although copper conducts electricity better, aluminum's lower density means thicker wires can be used to match the current-carrying capacity without significantly increasing cost or weight.

Additionally, aluminum is more resistant to corrosion, especially in outdoor environments, which increases the lifespan of overhead lines. These advantages make aluminum the preferred choice for power transmission despite its slightly lower electrical performance.

Aluminum vs Copper 

For the wires used in the home, copper core wires are basically used at this stage. The earliest aluminum wires have been basically replaced, and rarely appear in home decorations. But you will find that some overhead lines outside are basically made of aluminum cores.

- So why not use copper wire for outdoor wires?

- Why not use copper wire for outdoor wires?

- Copper wire conducts electricity better, so why use aluminum wire?

- Why aren’t the outside cables indicated here made of copper wires, but of aluminum wires? Yet, the conductivity of copper wire is significantly superior to that of aluminum wire. 

- What causes this to occur?

That is, you are still unfamiliar with the installation conditions of outside wire circuits. Five reasons for this situation will be told so that everyone can understand.

The characteristics of overhead lines determine the use of aluminum wires for overhead lines, you will know that the wires are hung in the air by means of poles or towers.

There are specifications for the weight of the wires since overhead circuit cables are hanging in the air.

Aluminum actually has the second-highest conductivity, behind copper.

Aluminum’s conductivity is roughly two-thirds that of copper, while its density is only one-third that of copper.

As a result, in the overhead state, aluminum wire is preferable.

Outdoor wires are also affected by their own gravity and environmental influences.

The simplest point, for example, will be impacted by changes in air and temperature, which is our ordinary thermal expansion and contraction.

The ability of the aluminum wire to withstand thermal expansion and contraction is better than that of copper wire, so it is more suitable to use aluminum wire for overhead wires.

The unique characteristics of aluminum wires under outdoor conditions determine the use of aluminum wires.

What's difference between MCB and MCB?

MCB (Miniature Circuit Breaker) vs MCCB (Molded Case Circuit Breaker)

An MCB (Miniature Circuit Breaker) and an MCCB (Molded Case Circuit Breaker) are both protective devices used to interrupt electrical faults, but they differ mainly in their capacity and applications. 

MCBs are designed for low current circuits, typically up to 125 amps, and are commonly used in residential and small commercial settings to protect lighting and socket circuits.

They have a fixed trip setting and a lower breaking capacity, usually up to 10kA.

In contrast, MCCBs are built for higher current ratings—up to 2500 amps or more—and are used in industrial and large commercial applications to protect heavy equipment like motors and transformers.

MCCBs offer adjustable trip settings, higher breaking capacities (up to 100kA), and are physically larger and more robust.

While MCBs are simpler and more economical, MCCBs provide more flexibility and are better suited for high-load and high-risk environments.

Why is a capacitor used in 1- phase and not in a 3- phase motor?

A capacitor is used to create a rotating magnetic field, which is necessary for the motor to start and run.

Single-phase motors lack the natural rotating magnetic field present in three-phase motors, and a capacitor helps generate a second phase, allowing the motor to self-start and improve its running performance. 

Here's a more detailed explanation:

1. Single-phase motors are not self-starting:

Unlike three-phase motors, single-phase motors don't inherently produce a rotating magnetic field.

This means the rotor (the rotating part of the motor) won't start turning on its own.

A capacitor is used to introduce a phase shift in the current, effectively creating a second phase and enabling the motor to generate a rotating magnetic field. 

2. How the capacitor works:

A capacitor is connected in series with an auxiliary winding (also called the starting winding) of the motor. 

When the motor starts, the capacitor provides a surge of current to the auxiliary winding, creating a phase difference between the current in the main winding and the auxiliary winding. 

This phase difference, along with the physical separation of the windings, creates a rotating magnetic field that allows the rotor to begin rotating. 

Once the motor reaches a certain speed, a centrifugal switch (or other switching mechanism) disconnects the capacitor and auxiliary winding, and the motor continues running on the main winding. 

3. Types of capacitors and their roles:

Start capacitor:

Used for a short period during motor startup to generate a strong starting torque. 

Run capacitor:

Used to improve the motor's efficiency and power factor during continuous operation. 

Dual run capacitor:

Combines the functions of both start and run capacitors, often found in applications like air conditioners. 

4. Benefits of using a capacitor:

Improved starting torque:

Capacitors help the motor generate enough torque to overcome inertia and start rotating. 

Enhanced running performance:

Capacitors can improve the motor's efficiency and power factor, leading to better overall performance. 

Increased reliability:

By providing a starting boost and optimizing running conditions, capacitors contribute to the motor's longevity and reliability.

Summary:

A capacitor is used in a single-phase motor because single-phase power does not create a rotating magnetic field on its own, which is necessary to start and run the motor. The capacitor provides a phase shift that creates a second, out-of-phase current in an auxiliary winding, producing a rotating magnetic field that starts the motor. In contrast, a three-phase motor naturally generates a rotating magnetic field due to the three-phase supply, eliminating the need for a starting capacitor.