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Asco Transfer Switches

An Introduction to Transfer Switches: Single Phase and Three Phase

What is a Transfer Switch?

Transfer Switches are an integral part of any generator system, but many don’t know what they are, or overlook their significance. Simply said, Transfer Switches are important – so much so that your diesel generator power system could not safely function without them.

Despite the Transfer Switch’s importance, it’s a relatively simple component in any backup power system. A Transfer Switch is a device that transfers electrical loads from one source to another source. There are a variety of Transfer Switch configurations that perform various complex functions, though the most common are Manual Transfer Switches and ATS Transfer Switches.

Manual Transfer Switches

Most people are familiar with Manual Transfer Switches, but don’t realize it. A Manual Transfer Switch resembles the common household circuit breaker – by toggling the switch, the electrical load is transferred elsewhere. Manual Transfer Switches are commonly used in combination with small, portable generators designed for recreational use or as a cheap means of temporary backup power during power outages.

ATS Transfer Switches

ATS Transfer Switches, however, are another story. “ATS” stands for “Automatic Transfer Switch” which means that should a utility or the regular power source fail unexpectedly, the ATS Transfer Switch changes the electrical load to the backup diesel generator power system. ATS Transfer Switches are available in both Single Phase and Three Phase applications.

Keep in mind that the ATS Transfer Switch only transfers the load source to the diesel generator system. That’s key – and that’s why any Transfer Switch is necessary in a diesel generator backup power system. Specifically, the Transfer Switch isolates your backup power system from the utility – it transfers the load from the utility to the backup generator system.

Three Phase Transfer SwitchIf the Transfer Switch did not change the load from the utility to the backup generator system, all kinds of havoc could ensue due to “back-feed”. Back-feed occurs when power travels back through the utility lines – which in the case of a blackout, could cause fires, damage your generator system, and endanger the lives of utility workers who are expecting the power lines to be dead. 

In more complex systems, a backup diesel generator system equipped with an ATS Transfer Switch has several functions. For one, the ATS Transfer Switch will send a signal to start the backup generator power system. It also monitors the electrical system’s connection to outside utilities or regular power sources, and once that regular power source is sustained for a minimum amount of time, the ATS Transfer Switch transfers the load back, shutting down the backup generator power system in the process.

ASCO Transfer SwitchSingle Phase and Three Phase Transfer Switches

Transfer Switches are designed for both Single Phase and Three Phase diesel generators, and in general, the two stay in their respective realms. In case you are asking yourself what the terms “Single Phase” and “Three Phase” mean, here’s a quick lesson to help you distinguish between them.

The Bicycle Analogy: Single Phase Systems

Imagine you are riding a bicycle. As you pump your legs, the pedals rise and fall, and occasionally both pedals are at the top or bottom of the wheel at the same time. A Single Phase Generator is similar, in that when both pedals are at the top or bottom for the briefest of an instant, your pedaling power drops off. The drop in power is so fast that you barely notice it, but it’s still there.

In more technical terms, a Single Phase generator system carries alternating current in which the supply voltages vary together.  A hot wire carries the electrical load, while the neutral wire (or ground wire) returns the load.

This doesn’t mean Single Phase Systems are inferior, by any means. In fact, if your home is wired to the national grid, it most likely operates from Single Phase power! Below are a few quick notes on the advantages of a Single Phase System:

  • Single Phase has numerous applications
  • Single Phase is carries AC power the most efficiently up to 1000 watts
  • Single Phase designs are less complex and less expensive
  • The Bicycle Analogy: Three Phase Systems

Phase system operates much like if you were riding your bike, but instead of two legs, you had three legs with which to pedal. With three legs and three pedals, there is never a moment in which all three pedals intersect at the bottom or top of the wheel – providing a smoother ride.

A Three Phase system uses at least three wires, each at 120 degrees, to provide continuous, efficient power distribution. Three Phase systems are generally used in industrial settings, though they occasionally find their way to residential areas. Though a single family home commonly runs from Single Phase power, an apartment block downtown likely utilises Three Phase power distribution. Listed below are a few advantages of utilising a Three Phase system:

  • Lower installation costs and fewer safety risks
  • Greater power distribution efficiency
  • Allows higher power loads for high powered equipment
  • Generator Power is Here to Help

As you’ve guessed, generator installation can become complicated quickly. The good news is that Generator Power has your back. Our experts are available for consultation, ready and willing to help you find the genset that meets and exceeds your needs and expectations. In the meantime, look for more articles here to help you find the information you need to make an informed choice.


A word from the editor

Aaron Generator PowerMy name is Aaron Robins, I’m the sales manager at Generator Power. I have been in the generator game for over 10 years. I have supplied generators to residential and commercial clients for a wide range of various uses. My aim in writing this short article it that I may be able to arm you with the right information in order to help you make a wise decision. There are many people who make poorly informed decisions in my industry. This commonly results in loss of finances, wasted time and bucket loads of stress. I believe in doing a job right the first time and with as little stress possible. As a result I aim to educate potential customers so that people avoid these issues before they happen.


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