Stupid Neutral ?

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  #1  
Old 11-27-04, 07:33 PM
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Stupid Neutral ?

I understand the purpose of a neutral in 120v is actuaaly the return to the source (power co.)

Why does 220/240 volt in some cases not have a neutral, only two hots and one ground??

John
 
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Old 11-27-04, 09:14 PM
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A 240 volt line could have one side grounded and work OK. The system we have was agreed upon long ago and is just the way it's done, but it's not the only way it could be done. Over the years a separate gound wire was added for additional safety in case a neutral wire would become open. I Germany they use 220 volts 50 cycles in a simular manner that we use 110 volts. They just have a different standard over there. If you study the existing system a little, two hots and a neutral makes sense and offers some flexability between the power requirements of larger appliances, safety of the users, and the necessary wire sizes in the walls. If Edison had his way, we would all be trying to get by using DC. Westinghouse had a better idea with AC and I'm glad he won the battle years ago.
 
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Old 11-27-04, 11:02 PM
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Technically, a simple 120-volt branch circuit does not have anything called a "neutral". It has an "ungrounded conductor" (which most people call the "hot"), and a "grounded conductor" (which most people imprecisely call the "neutral").

Any circuit, be it alternating current or direct current, 120 volts or 240 volts, needs exactly the same thing: one wire to carry electrons out to the load and a second wire to carry electrons back from the load. There is nothing fundamentally different between how a 120-volt circuit works and how a 240-volt circut works.

A pure 240-volt circuit never has a neutral. This is what you see on a 240-volt power saw, welder, compressor, or hot water heater. When you see two hot wires plus one neutral wire, what you're actually seeing is two circuits, one 240-volt circuit and one 120-volt circuit (although technically it is still called one branch circuit by the code). This is what you see on most ranges and electric clothes dryers (e.g., the heating element of a dryer uses 240 but the drum motor uses 120). The 240-volt part of the circuit doesn't use the neutral at all (it uses only the two hots), but the 120-volt part does. In addition to the neutral, the 120-volt part of the circuit shares one of the hots with the 240-volt part.
 
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Old 11-28-04, 04:35 AM
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Techinically I would say you have 3 circuits not 2.
One 240 volt circuit and two 120 volt circuits. One 120 volt circuit from each hot to neutral.
 
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Old 11-28-04, 08:02 AM
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I think one of the reasons we didn't use DC from power companies was because DC wasn't able to be transmitted of long distances at the high voltages AC was. I'm a little foggy on that but it seems to come to mind from EE101.

I think we'll see a rebirth of DC when they figure out how to send power wirelessly. It would seem to make more sense.

In many other countries (Iraq for example) they classify all their circuitry as 220V (or similar). Only problem is, there are no retail supplies of for electrical or plumbing, so if you can spell the word electrician, congrats, you are one!
 
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Old 11-29-04, 06:24 AM
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Originally Posted by SkyKing
I think one of the reasons we didn't use DC from power companies was because DC wasn't able to be transmitted of long distances at the high voltages AC was. I'm a little foggy on that but it seems to come to mind from EE101.
Actually the main problem with DC power transmission (which if I recall correctly was the scheme that Edison supported) is the difficulty in converting to high voltage for distance transmission and back down again. A transformer (which only operates with AC) is a highly efficient, reliable, and inexpensive method of stepping voltages up or down.
 
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Old 11-29-04, 09:41 AM
SkyKing
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Could very well be. I'm foggy on debate.
 
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