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#8285 03/16/02 01:27 AM
Joined: Feb 2002
Posts: 11
L
Looee Offline OP
Member
I'm an electrician student so I'm kind of new to this. Why is it that 240V circuits don't use a neutral? I have asked my teacher but I'm not sure he understood what I was asking, and nobody else in my class seems to know either.

#8286 03/16/02 07:05 AM
Joined: Oct 2000
Posts: 5,392
S
Member
A good Q.
This has had much past attention in this forum, especially via Scott who moderates the theory section.
Consider that some countries have no nuetral in thier grid, and the maladies it causes us in ours... [Linked Image]

#8287 03/16/02 12:01 PM
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Posts: 182
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Bob Offline
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Looee
Some 240 volt circuits do require a neutral.
A dryer circuit requires a neutral because besides the motor there are components that
require 120 volts. Therefore the neutral serves a the return conductor for these components. If a device such as a 240 volt welder is used, the power is conducted over the 2 energized conductors. There is no need for the neutral. A grounding conductor would be needed to ground the welder frame.

#8288 03/16/02 12:38 PM
Joined: Oct 2000
Posts: 2,722
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A quick and dirty answer is:

The "Neutral" [Better known as the Grounded Circuit Conductor] is no different than any other circuit conductor - only it is usually Grounded.

On a simple 1 phase 3 wire system, the "Neutral" is derived from a "Center Tap" on the secondary winding.
This center tap effectively cuts the winding's normal output voltage of 240 VAC by half, so from each "End" of the secondary winding to the Center Tap, the Voltage is 120 VAC.

It does not need to be Grounded for this to function properly - nor any other "Common Grounded Circuit Conductor".

If you have further questions, I would suggest starting a thread in the Theory area.

Also take a look at some of the Transformer schematics in the Technical Reference area, as they will help explain things better.

Scott SET


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
#8289 03/17/02 10:52 PM
Joined: Dec 2001
Posts: 444
S
Member
Looee....

Some 240V circuits, like a motor, baseboard heater, AC compressors, welders, etc. carry a balanced load (basically, each conductor carries equal amounts of current). So therefore, a neutral is not required to return the unbalanced current. As mentioned elsewhere, some 240V circuits, like a stove or dryer use current other then for the heating element or require 120V at the appliance, so the load is not always balanced, and thus a neutral is required to carry the unbalanced load.

[This message has been edited by Sandro (edited 03-17-2002).]


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