A one page crash course in electrical systems


Back | Main page

Do I need to understand this to plug in my laptop and shaver abroad?

No. This page is aimed at those who want to understand the different electrical systems and those who need to use high power equipment. There is a lot of information for travellers on Steve Kropla's site. I suggest that travellers visit his site to learn how different voltages/frequencies affect electrical appliances.

Is this advanced?

This is definitely not rocket science and anyone with some knowledge electricity should be able to follow. However, I suggest you read it from top to bottom since I've refrained from repeating the information. If you want to learn the basics of electricity, visit HowStuffWorks electricity pages

How does a 115/230 V or 230/460 V DC system work?

This is the simplest system, originally used by Edison and therefore called a Edison system. Assume we have a light bulb that won't work at a higher voltage than 115 V. Next, assume we want to distribute electric power in a city to run these bulbs. Easy enough, everyone knows how to connect a light bulb to a battery. Connecting two is just as simple:
 - 115V battery -             - 115V battery - 115V battery -
| | -- light bulb -- OR | |
| | -- light bulb - - light bulb -
-- light bulb --
The only problem is that copper is expensive, and therefore we want to minimize the current. The wires in the circuit to the left carries twice the current compared to those in the circuit to the right. This means that we will need to use wires with at least twice as much copper. The cicruit to the right means that both light bulbs have to be on at the same time. Somewhat unpractical. The obvious way to solve this problem is to use two 230 V bulbs instead, but we don't have those yet. But what if we introduce an extra wire between the two batteries?
 - 115V battery - 115V battery -
| | |
-- light bulb - - light bulb -

Voila! We have cut the current to half in both wires and can operate the lights independently. Although we need copper for the extra wire, it is still less than before. We save money. This system can be applied on a larger scale. Just insert house where is says light bulb above.

OK, now I understand 230/460 V DC but how do you get 230/460 V AC?

This has to do with how the secondary side of the transformer is wired. (If you wonder how a transformer works, visit [remember to insert suitable site])

Take a single phase transformer, which is like a battery: It can be wired for 230 V only or 230-0-230 V. In the first case, there are only two wires from the transformer, one from each side of the secondary winding. In the second case, there are three wires, one from each end of the winding and one connected at the center of the winding. This is therefore called center tapped single phase. It works just like the two batteries in the DC case. Easy, isn't it?

[remeber to include schematics]

There has been heated debate whether this constitutes single phase or two-phase. In my opinion, single phase denotes a system with a single voltage, and the 2-phase denotes a hardly ever used system with a 90 phase angle. In this case the phase angle is 180. The debate thus misses the target. It's center tapped single phase or 180 two phase. The term Edison system is sometimes used, although it more properly refers to DC systems. You can also have two out of three phases plus the common (neutral) conductor in a service cable. This is sometimes called Vee-phase. Possibly it could also be called 120 two phase.

OK, now I get center tapped single phase (230/460 V), but what is three phase (230/400 V)?

Now it gets a bit more difficult. You don't need to understand the math behind, just what happens. Any book on electrical theory should cover three phase. HowStuffWorks have a few words on it too. Instead of the three wires we had in the center tapped single phase case, we now have four wires: One - the common (neutral) wire - has 230 volts to any of the other three wires. Between the other three wires - called phases - there is square root of 3 x 230 = 400 volts. Before, we needed two bulbs to balance out each other. Now we need three. This means that this system is a bit harder to balance than the centertapped single phase, but on the other hand: The current in each of the three wires is only one third of what it had been if this had been a 230 V single phase system.
 
That wasn't very hard, was it? There's more to three phase: It makes it possible to build cheap and efficient electric generators and motors. Therefore, virtually all industries and power plants in the world use three phase. If we have a 3-phase power plant, we can use transformers to convert it to the other systems described here, with the exception of the 2-phase system. Not surprisingly, the 2-phase system is today confined to text books.

What are the 127/220 V and the 230 V three phase systems?

The 127/220 V, is the predecessor of the 220/380 V (230/400 V) system and works the same way. A few countries, most notably Brazil, Mexico and Saudi Arabia still have 127 V systems in use and appliances for this voltage are still sold there. In most other countries however, 127 V appliances are few and far between these days. Therefore even single phase loads are connected between two phases and the utilities often won't even supply the neutral. To see how such a system can be earthed, look at the page about earthing systems.
 
230 V can also be a corner grounded delta system. In this case, one of the phases is earthed for lack of a neutral. An advantage of this system compared to the 230V wye system without neutral is that you can use the TN earthing system.

What about 115/230 V three phase?

A three phase system where the lower voltage is half of the higher is called a center tapped delta system. In this case two more transformers have been added to a center tapped single phase transformer, to form a delta configuration. This is a curious system, as you get three different voltages: 230 V between the phases, 115 V between the neutral and two of the phases and finally 200 V between the neutral and the third phase. The only case where this system is useful is when you have a limited 115 V load, but a significant 230 V load.

Where do you find 400/690 V, 277/480 V or 347/600 V?

These are industrial voltages. The 277/480 V system is common in industries in the United States and in other countries with 60Hz. 347/600 V is the Canadian equivalent. 400/690 V is an offical IEC standard industrial voltage for 50Hz countries. However, these systems (380/660-415/720 V) are uncommon, as the standard 220/380-240/415 V is enough for most needs.

Other lists have a field "Number of wires supplied"?

That information originally comes from the US Department of Commerce. It is in fact in the database, but it is not presented on the webpage. The reason is that the number of wires depend on three factors: The type of earthing used, if the neutral is provided or not and the number of phases supplied. It also doesn't state which type of service this information refers to: Industrial or residential. The Department of Commerce has undertaken a major task in collecting information, something which we should be grateful for, but this particular piece of information is not very useful.
 
The relevant factors when designing or selecting appliances are the number of phases and if the neutral is provided or not. Useful information would look something like this:
 
Phases supplied: 1 + N
Only a single phase service is supplied for residential services.
 
Phases supplied: 2/2 + N
Two out of two phases plus neutral, i.e. center tapped single phase, are supplied. (2/3 + N would mean two out of three phases plus neutral.)
 
Phases supplied: 3
Three phases without neutral are supplied for residential services.

Why do you write 115/230 V and not 110/220 V or 240/120 V ?

I've used 230 V rather than 220 V or 240 V throughout just to keep things simple. This page aims to present concepts, not to describe the actual systems used in a specific country.
 
I've choosen to write the lower voltage before the slash, but some people write the higher voltage first. I don't know what the official standard is, but this way seems to be the most common.

I want to learn more!

You can start at ePanorama. The page is a bit messy, but it is stuffed with information and links.