Single-Phase Two Wires (each line is 110 VAC) Working Principles

Thread Starter

Thank you

Joined Feb 20, 2019
4
Why some electrical loads are required Single-Phase two wires (each line is 110 VAC) connection such as Water heater and some Refrigerator, while others not ? Is it possible to hook up for example a Single-Phase two wires (each line is 110 VAC) into a Single -Phase one wire and one neutral (110 VAC) loads such as laptop charger ?

Lastly, I know that in a two wires connection, they are both 110 VAC 180 degree out of phase, but I can not understand how 220 VAC is passing inside the load at the same time when "I think" only 110 VAC is passing each time...
 

Ya’akov

Joined Jan 27, 2019
5,669
Welcome to AAC.

Maybe this will help. Each phase has ~120V (I am referring to the 110VAC you mentioned) with respect to neutral and the two phases have ~240V with respect to each other. No source has an abstract potential, it is always measured with respect to some other source.

So what you are calling "110V phases" are not. They are two phases with ~240V across each other and ~120V between each and the neutral. They have no independent identity as "110V" they only get an identity when you specify the other side of the circuit

Is it possible to hook up for example a Single-Phase two wires (each line is 110 VAC) into a Single -Phase one wire and one neutral (110 VAC) loads such as laptop charger ?
No, it doesn't even make sense, and what would be the benefit?
 

Thread Starter

Thank you

Joined Feb 20, 2019
4
No, it doesn't even make sense, and what would be the benefit?
Trying to understand the behavior of the laptop charger if it could accept not only one hot ( 120 ~220 VAC ) one neutral, but also two hots wires. I thought it should accept it.

Likewise, Water Heater, should accept one hot wire ( 220 VAC ) and one neutral since it only asks for 220 V, it doesn't matter what is the connection.

It puzzles me that most electrical and electronic devices require one hot ine neutral connection, so why the designers made such device that only accept two hot wires if it doesn't accept one hot one neutral wiring connections..

Sorry for my sketchy knowledge, I am a beginner :)
 

Ya’akov

Joined Jan 27, 2019
5,669
Trying to understand the behavior of the laptop charger if it could accept not only one hot ( 120 ~220 VAC ) one neutral, but also two hots wires. I thought it should accept it.

Likewise, Water Heater, should accept one hot wire ( 220 VAC ) and one neutral since it only asks for 220 V, it doesn't matter what is the connection.

It puzzles me that most electrical and electronic devices require one hot ine neutral connection, so why the designers made such device that only accept two hot wires if it doesn't accept one hot one neutral wiring connections..

Sorry for my sketchy knowledge, I am a beginner :)
The neutral is not involved in the ~240V power, only the two of the split phases. The neutral is the center tap of a transformer that produces the ~240V, the neutral is a way to get ~120V out of that. So no matter what you are powering with it, when ~240V is used, the neutral is not involved.

The neutral is bonded to ground, though they are distinct connections, so the safety ground on a ~240V appliance will have continuity to neutral. If an appliance uses ~240V and ~120V, then both phases are used to get the former and one plus neutral to get the latter.

The problem is, I can't understand what you are trying to accomplish in the case of something like a laptop charger. You could run it from ~240V, but since ~240V outlets are not commonly installed in the walls of a house, using ~120V is much easier. There is no practical benefit to using ~240V in this case.

What are you thinking you would gain, or even do, with 2 ~120V inputs? Most things, laptop chargers included, do not benefit from the increased power available at lower current available at ~240V so what use two ~120V circuits?

[EDIT: fixed "increased current"]
 
Last edited:

BobTPH

Joined Jun 5, 2013
4,927
The advantage of using 240V for the water heater is that is uses half the current it would if powered by 120V. You may notice that it is usually high current appliances that use 240, often ones involving heaters.

I am mot sure why we do it this way. Most if the world uses single phase 240 for everything.

Bob
 

Ian0

Joined Aug 7, 2020
5,162
I am mot sure why we do it this way. Most if the world uses single phase 240 for everything.

Bob
I read somewhere that some US gas company argued in court that anything over 100V was far too dangerous, and the judge gave them a 10% leeway which they took full advantage of, hence 110V. Maybe it’s true - perhaps not.

The split-phase arrangement is used on British building sites and other outdoor situations with 110V power tools so that no wire is ever more than 55V to ground.
 

crutschow

Joined Mar 14, 2008
29,818
I am mot sure why we do it this way.
What I've read is that the early carbon filament light bulbs couldn't be made to work on 240V, so all the early home wiring was 120V split-phase 240.
By the time tungsten filament light bulbs became available that could operate on 240V, there were too many homes already with 120V in the USA, so that became the standard.
 

MaxHeadRoom

Joined Jul 18, 2013
25,226
It puzzles me that most electrical and electronic devices require one hot ine neutral connection, so why the designers made such device that only accept two hot wires if it doesn't accept one hot one neutral wiring connections..
@Thank you
Here is another poser for you.
At one time it was mandatory for duplex outlets installed in kitchens to be wired with one 120v, L1 on the top outlet and 120v, L2 on the bottom outlet, both outlets shared the same neutral, (3 wire cable).
If a 120v 10amp load was plugged into the top outlet and a 120v 10A load plugged into the bottom, What current does the neutral carry? :)
 

Ian0

Joined Aug 7, 2020
5,162
If you look at the efficiency graphs for universal-voltage switched-mode controllers they are generally more efficient at 240V than at 120V.
So, if you connect one between the two lives instead of live to neutral, you’ll save money, and it won’t be any more dangerous because there is still no voltage greater than 120V from earth.
 

Ya’akov

Joined Jan 27, 2019
5,669
If you look at the efficiency graphs for universal-voltage switched-mode controllers they are generally more efficient at 240V than at 120V.
So, if you connect one between the two lives instead of live to neutral, you’ll save money, and it won’t be any more dangerous because there is still no voltage greater than 120V from earth.
How much efficiency do you gain? It'w not so trivial to just wire it that way. You'd need a spec outlet. Could the efficiency bonus really be enough to make it practical?
 
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