How does return work

There is always a closed path, for DC or AC current flow.

In unusual or exotic situations the air can be the return path (extremely high-voltage low-current stuff) or the ground/earth can be part of the path.

The only thing seemingly (but not actually) open-ended is RF (radio frequency) generation / transmission.

Dave

In Alaska we have at least one operational distribution line in a remote part of NW Alaska that uses an earth return. There are also numerous earth return distribution lines in rural Canada. There was also another near the Alaska Highway between Dot Lake and Tok Junction, a distance of about 30 miles, that existed for many years until an inspector wrote it up as a violation to the National Electrical Safety Code. The engineers studying the Alaska Highway route for the Gas Pipeline were concerned about this, knowing that the pipeline would become a convenient return path for this line.

As I remember the Pacific intertie on the west coast (the million volt DC line) uses earth (pacific ocean) for a return.

I am not sure what you mean. In any event, a closed circuit is required.

-- Ferme le Bush

That is only needed when one of the two (± 500kV) high voltage lines is out of service. Otherwise, the two high voltage lines run close to balanced.

Bill

-- Ferme le Bush

On Mon, 20 Feb 2006 15:07:24 -0800, "Carl Lovejoy" Gave us:

Don't think "equipment". Think "circuit".

ALL electrical circuits MUST have a return to function. It goes along with the physical law that in order to observe something, one changes it.

So, even for a device that seems to have a sensor or probe that is single ended, there is still an action reaction taking place.

Most circuits DO have a "hard return". Some are capacitively coupled to ground, or inductively coupled to the device they feed.

Look at the operation of a radio transmitter and receiver as examples.

On 20 Feb 2006 16:33:35 -0800, snipped-for-privacy@electrician.com Gave us:

The HUGE DC intertie between Washington state and LA Calif. has an Earth return. It is 800 miles long.

On Tue, 21 Feb 2006 02:02:01 GMT, Salmon Egg Gave us:

Not according to them.

Are you talking about the "neutral"? That is the grounded side of a 120v circuit (USA). It does provide "return" current to the transformer that camer out on an ungrounded leg (hot).. There are 2 ungrounded legs from opposite windings of the transformer and when used together you have 240v. If you have a 240v load the current "returns" down the other leg of the circuit

I can't see how that would mean anything even if they were balanced... unless "balance" means one sends power north while the other sends power south? What's the point though... ;-)

Unfortunately, WINTEL machines do not seem to interpret the combined + and - signs correctly and substitutes a ? For a ± (shift-option8 on a Mac).

If currents are the equal and opposite in the + 500kV and -500kV lines there is no necessity for return to carry any current. And power will travel in the same direction on both halves.

Bill

-- Ferme le Bush

Actually, electromagnetic radiation does not require a "return". That becomes more clear when you think of space communications where waves transfer energy through a vacuum. The sun's optical and magnetic radiation is another good example.

Capacitive circuits, including some antennas, do require a "return" path as you said.

Chuck

Roy L. Fuchs wrote:

Interesting, so I have a 120v line to a toaster and it *returns* don a neutral, so I have 120 volts... then I have two 120v lines to my heater but one *returns* down the other but somehow I get 240v ? help a layman understand this concept req

On Tue, 21 Feb 2006 17:16:24 -0500, "reqluq" Gave us:

All of your household 120 volt circuits are one leg or the other of a 240 volt transformer winding with a center tap. THAT center tap is the neutral line. SAo, either side is 120 volts with respect to that center tap. ACROSS the entire winding, however, is 240 volts. That should clarify it for you. The transformer on the pole or in the ground feeds you from a 240 volt winding that has a center tap on it.

" I have a 120v line to a toaster and it *returns* don a neutral, so I have 120 volts... then I have two 120v lines to my heater but one *returns* down the other but somehow I get 240v ? "

I'll start from the start-so to speak.

-Voltage is always measured 'relative' to something. Example- Take 2 9-v batteries, and connect - of one to + of the other, so yoiu have -.....+-.....+ Take a voltmeter (set to DC) and measure across the "-" to the "+-" and you get 9V. meas. "+-" to "+" and you get 9V. measure "-" to "+" and you get 18V. The "+-" is like the center tap of the transformer, so-to-speak.

The (2) 120V legs are AC, in this case each leg swings from +120 (that's actually a little off...) to -120.

If you had 2 legs "in phase", where one leg was at +120 at the same time as the other, you'd be measuring from +120 (ref. to 'ground') to

If you had 2 legs where one leg was at +120 at the same time the other was at -120V (180 degrees out-of-phase), you'd be measuring from +120 (ref. to 'ground') to -120: the meter would read 240V.

Those are the basics-

Dave

Thanks, I'll digest this req