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Single- Vs. Three-Phase Electricity: What’s the Difference Between the Two?

As a property owner or manager in New York City, you may have heard discussions about single- vs. three-phase electricity. Unless you work in electrical contracting, you might be wondering what’s the difference between the two. You may have even been told by Con Edison, the power utility for the city, that you need one or the other, without really knowing why. Here’s an explanation so you can better understand how each works. This will help you if you plan to upgrade, renovate, or resize your property in the future.

Two Types of AC Electrical Power

Single- vs. three-phase electricity

While back in the early days of electricity in New York City, there was a competition between alternating current (AC) and direct current (DC) power, AC electricity eventually won out. With this type of power distribution, the power changes regularly, both in direction and magnitude. Alternating current can be utilized in two different ways: as single- or three-phase electricity. Let’s take a look at the mechanism, as well as the pros and cons of each.

Single-Phase Power

How it works

A single-phase electrical system uses two wires. One is called the phase (AKA hot, line, or live). The other is a neutral wire. You might recall that AC power can be graphed as a sinusoidal wave. When examining the voltage in a single-phase electrical supply, it peaks at 90 degrees on that sinus wave. Its low point is at 270 degrees.

The current is carried to the load by the phase wire, and the return path goes through the neutral wire. With this type of power, the electrical supply rises and dips, which means the load never receives constant power.

Advantages

The anatomy of a single-phase power supply is quite simple. It’s actually not very complicated for electricians to work on. It is the most common type of power supply in single-family homes and other small buildings because the appliances and devices used in these structures don’t require a huge amount of power. Typically, loads up to 2,500 watts can be run on a single-phase electrical system.

Disadvantages

The main disadvantage of this type of power supply is that some motors require more electricity during their startup. To provide adequate torque, you’d have to add motor starters to the circuit. Clearly, you can’t operate industrial motors with single-phase power. So, if you’re doing work on a property that uses a single-phase electrical supply, you’ll need to use an external source of power for tools and heavy-duty equipment.

Three-Phase Power

How it works

As the name implies, three-phase electrical power uses three phases (wires). Sometimes a neutral wire is used as well, depending on if you have a star or delta type of system (a star connection uses four wires in total).

Each of the three power signals in a three-phase system is 120 degrees out of phase with the others. When this is graphed, it looks like three separate but overlapping versions of the sinus wave created with a single-phase AC power system. For each 360-degree cycle, each phase peaks twice, and the power never diminishes to zero.

Advantages

Because three-phase electricity offers constant current, it can handle heavier loads. This makes it ideal for commercial and industrial uses. (In Europe, three-phase power is also used for small residential supply.) This eliminates the need for motor starters in three-phase circuits, as the power supply can handle the heavier demands of the startup mode.

Furthermore, three-phase electrical power is more efficient overall. It requires less wire to install. You can even create three single-phase supplies, using one three-phase supply split into three (usually accomplished with a transformer in the US, whereas in the EU, it is done directly).

Disadvantages

There aren’t many downsides to three-phase power supply. Although it is slightly more complex to install, a competent electrical contractor can still do it for you. With its higher voltage, three-phase electricity may require more insulation. Also, overload is more damaging with this type of system, which could result in higher repair costs for the property owner.

Which Type of AC Power Is Right for Your Needs?

It depends on your requirements

As mentioned above, sometimes Con Edison weighs in on which type of power supply a property should have based on assumptions about its size and electrical needs. This normally isn’t an issue unless you need to make changes to the electrical demands of the building.

For instance, you may wish to subdivide a large single-family property into four or more individual apartments, each with its own air conditioning units and large appliances that would run simultaneously. In that case, installing a three-phase system makes sense.

Likewise, a small commercial building where a lot of industrial or manufacturing work is done relative to its square footage might require a three-phase system. If you wish to install an elevator or piece of equipment that uses a heavy-duty motor, single-phase electricity will probably not be adequate.

Call Bolt Electric for Electrical Upgrades and Repairs

New York City’s hyper-local blue-chip electricity experts

The larger established apartment buildings and commercial properties where we work already have three-phase electrical supply. Therefore, it makes sense to understand how it works if you encounter a problem or intend to do work on the property.

If you are planning to increase the electrical demands on your property, we can help you upgrade so your service is able to accommodate tools, equipment, appliances, and HVAC. We can also assist with your electrical repairs for common problems like flickering lights, malfunctioning outlets, and old electrical panels, whether you have a single-phase or a three-phase system.

Call Bolt Electric today at 212-434-0098 to learn more, or reach out online to schedule an appointment at your convenience.