In the modern 3-phase transmission or distribution system, we need a transformer to distribute single phase power to our homes and offices, for example a 480V 3-phase to 240V single phase power. So, how is it done?

It is done by the help of a single phase transformer. A 480V to 240 V single phase step down transformer can be used here to do the job. But there are more than one configuration or way to perform the work with the same equipment.

Here in this article my prime focus will be to show you how a 480v 3-phase to 240v single phase transformer works, how to wire it and the basics that you will need to know in order to master the topic.

480v 3 Phase To 240v Single Phase Transformer

What Is The Difference Between A 3-Phase And Single Phase Line?

In short, A 3-phase line has three separate cables that carries electricity, there may or may not be a neutral cable depending on the type of the 3-phase. A star connected 3-phase line will have a neutral while a delta connected will not have a 3-phase line. On the other hand, a single phase line only consists of a electricity carrying cable and a neutral.

Can You Get 240V Single Phase From 480V 3-Phase?

Yes, you can get 240V single phase output from a 480V 3-phase. In this case you can implement a transformer in 2 different ways. That is what I am going to show you right now. But before that you need to know about the 2 types of 3-phase connections.

2 types of 3-Phase Connection:

3-phase Delta and Star connection
Figure: 1: 3-phase Delta and Star connection

In figure 1(a) you can see a 3-phase delta connection. In this type of connection, you can see there are 3 wires. The voltage between any two phases is equal to the line voltage. That means if, this is a 480V system, then any two terminals like Va1-a2=Vb1-b2=Vc1-c2= 480 V.

On the other hand, figure 1(b) is a star connection which is mainly a 3-phase 4 wire system. The common point of the 3-terminals acts as the neutral. Here, The voltage between any two phases will be 480 which is the line voltage. But the voltage of a single phase, that is, the voltage between a phase and a neutral is 480/√3=277V.

480V 3-Phase To 240V Single Phase Transformer:

Now that we know the characteristics of a 3-phase connection, we can figure out a way to convert a 480V 3-phase to 240V single phase. In this case, the first thing we need is a single phase transformer with the correct rating.

About choosing the transformer we have two options here-

  1. The transformer is a 480V to 240V step down single phase transformer
  2. The transformer is a 277V to 240V step down single phase transformer

One thing you should keep in mind is the KVA rating of the transformer. That part should be considered depending upon the amount of load you are going to connect to the transformer.

How To Connect The Transformer To Get 240V Single Phase Output?

Basically, you need to connect the higher voltage to the primary winding of the transformer. And the secondary output will give the single phase output. But there are some other facts.

If you are using a 480V/240V transformer, you will need to apply 480V in the primary side. To do so, you should connect any two of the phases of the 3-phase supply as you have seen in figure-1. In this case, you can use both delta or star connected 3 phase supply.

If you are using a 277V/240V transformer, you will need to apply 277V to the primary winding. To get 277V out of a 480V 3-phase system, you should use a star connected 3-phase supply and connect only one of the phases and the neutral to the primary winding of the transformer. Doing so, you will get a 240 output in the secondary winding. In homes you may use 240V or 208V in that case knowing how to wire 208V single phase will come really handy.

480V 3-Phase To 240V Single Phase Transformer Wiring:

I am going to show you the wiring diagram for both the options I have mentioned above. Let’s start with the first option where we are going to use a 480V/240V single phase transformer.

For a delta connected supply use the following wiring method:

480V 3-Phase To 240V Single Phase Transformer Wiring
Figure: 2(a)

You can connect any two phases here. Because the voltage between any two of the phases is 480V.

For a star connected supply use the following wiring method:

For a star connected supply use the following wiring method
Figure: 2(b)

The same rule goes for the star connection also. Use any of the phases since the voltage difference between the phases are 480V.

Now, if you decide to use a 277V/240V transformer you should use a star connected 480V 3-phase supply. Since the voltage difference between any of the phases and the neutral is 277V as shown earlier. The wiring diagram should be like figure 3:

Figure: 3
Figure: 3

Using any of the given wiring methods you can convert a 480V 3-phase to 240V single phase. The same technique can be followed to convert 3-phase to single phase 220V. In that case, the rating of the transformer will vary a bit.

Things To Keep In Mind:

Use proper protection systems to save the equipment from any type of fault. Use the proper circuit breakers. Use a double pole breaker where necessary, know whether can you use two single pole breakers for 220V before using.

Pay attention to the KVA rating of your single phase transformer. This is very important since overloading is harmful to your device.

Bottom Line:

Our main transmission and distribution lines are mostly 3 phase systems. So, learning to convert a 3-phase to single phase is really important since we need single phase for your homes and offices. This article serves you the right way for that purpose as it covers all the things you need to know regarding the conversion.

Besides all these, if you are going to work in a factory someday, you will need to know how to handle 480V 3-phase as well as converting it to a single phase 240V. Use this article as a basic guide to you journey. Good luck…