240 w/o a neutral

[mgbinspect]

Well, I'm going to tee this question up and see where it goes.

So far I've exhausted two 2" thick electrical manuals and the Carson Dunlop course manual and no one adresses this phenomenon!?

I've even consulted with two master electricians and even they say basically, "I can't explain how, I just know it works." or "I'll have to get back to you on that one."

I understand that on a 120v circuit the neutral will read the same amps on both black and white as long as current is flowing through a fixture. I also understand that the reason ground wires read no amperage even though they're on the same buss with neutrals is because they provide no path (unless shorted).

So, here's the $64,000.00 question for the braintrust:

In a 220v circuit with no neutral, what path does the current take to return to ground since there is no neutral? Is it traveling the opposite supply wire via the alternating phase? It can't simply be "spent" or vanish into thin air can it?

Naturally, this is nothing that a home inspector need understand, but my curiosity is peaked.

I figure if all else fails, I'm going to stop in at an local power company office and hunt down an electrical engineer. (Maybe there's one among us?)

Inquiring minds want to know!

[charlieb]

Ok,

I'll step out. Let's see how I do.

240 volt current alternat back to the two poles of the transformer.

The coil in the transformer is connected to earth at the center. Does this mean that It returns to earth at this point? I do'nt know. I suppose that is a question for someone with letters after his name.

Shoot away gang[:-party]

[mgbinspect]

I know!

I was originally afraid to ask the question feeling a little bit ignorant or stupid, but it's a difficult concept to express and comprehend.

So, to clarify the question, we know that current goes to a light bulb via the black "hot" wire and returns to ground via the white "neutral" wire. But, in the case of a 240 blower motor or a 240 compressor etc, with two hot wires where does the current go after performing the work? How does it complete the circuit back to the panel and on to the common ground?

Apparently, very few understand what is truly occurring, and I think learning the concept and theory would be challenging and fascinating! So, as you say, Charlie, the lecture hall has grown to at least two...

"Come batter!.. Come batter!... "

[charlieb]

I'll swing again

Let's start with a picture. Lay a barrell on it's side and call it a transformer. Ground to earth at the center. Attact a feeder at both ends. Each supplies 120 volts if connected to ground. 240 if each other. The "ground" only comes into play if the two feeds are supplying differing amounts of amperage. So, If only 1 240 volt appliance is running and no 120 volt no current travels to earth. If one also feeds a 120 volt appliance (the fan assembly on an A/C) then that imbalance if transfered to earth at the transformer. The ground at the house does not transfer to earth unless there is a problem. It is part of the safety system.

OK guys --- anyone else in the room.

[:-wiltel]

[Bob White]

The thing is -- the current will still flow if you remove the center tap ground from the secondary of the transformer ( if you float the 230 (or 240, or whatever) if you're taking the 240 from the secondary of a delta (or single phase, for that matter) transformer. The 240 volt AC load doesn't usually need a common or ground reference to work (though it sometimes needs the ground path for safety).

This is kinda hard to explain with out pictures, so I (or someone else who knows and has training aids availablecan post them immediately) will have to find one of my old books to put up some illustrations. The current that flows through the load also flows through the secondary of the transformer. The ground bond at the center of the secondary is to provide a safety ground and to clamp the relative voltage at the center of the secondary to 0 v --- to establish a common voltage. It is not necessary to complete the electrical circuit.

Clear as mud now, right? I need som diagrams here.

[mgbinspect]

Yup, you're right in that the ground is a fail-safe only protecting a particular unit from shorting. that is why current from the neutral doesn't travel back from the buss up a ground wire to another unit... no path to ground!

Well, we know that current travels back and forth at the speed of light 100s of times per secnond on a 120 even when it is completed to ground via a neutral. (hence alternating current) Adding the two 120s together gives 240, which may not actually be the demand, but handles surges during peak demand... but still... it seems that somewhere along the path of a motor or compressor the energy needed must complete the circuit back to common ground or there would be "no flow"? What is the complete path of the current? That is the elussive question? Current reaching the motor goes where?

According to the master electrician I spoke with, the amps will read the same on both sides of an appliance ( the hot and neutral) although the quality of the current he says is somehow different.

This is not an easy question and I don't have the answer, but someone does...

"Come batter... Come batter..."

[mgbinspect]

Bob, Does this suck or what? Yeah, I need a color coded daigram with arrows etc. It's a mystery to me and obviously most non-electrical engineers. But, I'm chomping at the bit to understand!

[mgbinspect]

Well, Bob, I guess that's the point of my question... and the part that isn't connecting in my pea sized brain... What's the return path with 240 w/o a neutral? Maybe I'm just pitifully stupid... [:-dunce] but, if I am.. I can accept that... [:-party] (When in doubt.. reach for the Redbreast, Johny Walker Black or Eagle Rare)

SAVE ME FROM MYSELF, BOB!... OR SOMEBODY... [:-bigeyes

[:-slaphap

[Bob White]

I used to teach this stuff in a power quality course, but I'm no wordsmith.

I gotta go find my pictures!

[Bob White]

That's OK -- I get pitifully stupid when people try to explain how heat pumps (or any refrigeration system) work.

[mgbinspect]

Oh, cool! Now heat pumps, I get! My HI school teacher used to own a company that actually built them and my dad was an engineer on the staff of the Architect of the Nations Capital providing Heating and Cooling to all the House and Senate office buildings on Capital Hill. I get water cooled and refrigerant systems. But Gas chillers... ugh... that's kinda like 240 w/o a neutral! I just know that propane is a natural refrigerant and once it's done the work it's burned off to complete the flow rather than returned to the tanks which would require a compressor. My travel trailer refrigerator runs off of it automatically when electricity isn't available. I'll trade ya! [:-magnify

[Bob White]

We're gettin' off topic here, but ---

I spent 10 yrs in the USNavy, much of that riding on submarines, In order to not kill everyone on board, us bubbleheads were requred to learn how just about everything on the boat worked --- so we could recognize when it wasn't working properly, and so we could take quick, appropriate action when the equipment or system presented an immediate hazard.

I mostly kept myself clear of the evaps and coolers (that way I would not be the guy that didn't recognize the life threatening situation with them) and stayed with the the sparkies and electronics types (I 'knew' how that stuff worked...)

[Cowboy]

It's called potential difference. For Current to flow all you need is a difference inpotential energy.

[mgbinspect]

Well, first and foremost, I can't possibly thank you enough for your service, Bob!

My son ran a catapult on the USS Stennis and as soon as he got off after an around the world cruise from Norfolk to San Diego to deliver it to the Pacific Fleet, my son-in-law got on the same boat as a navigator on an A-6 Prowler flying over "the sand box" for an extended stay at sea of 9 months. I had the pure pleasure of going out to sea on two Dependants day cruises on the Stennis and taking in two fabulous air shows and I also flew out to Washington State to see my son-in-law bring in his A-6 to be mothballed. Those planes were so tired that Kirk could no longer fly them at full throttle and into heavy g's because they'd come apart. Apparently, they had a lot of stress cracks in them and were pretty much "played out". He was happy to get out of it and go to the dessert in California to test-fly the new stuff for a while.

[Chad Fabry]

Draw two sine waves opposite of each other..look where the difference in potential exisists. It's how I made myself understand 3 phase, but it works here too.

[mgbinspect]

I've seen those sine waves. So, is current fromt the black wire completing the circuit through the backward milli-second surges on the white and the same on the white or is each returning on its own wire?...

I guess I can't get past the flow of water and thinking it must pass through and beyond the unit to actually do "work"..

Not to mention, without real current flow, how does the local power company meter sense that current has been used?

[Chad Fabry]

The sine waves represent the cycle. If the two cycles are out of sync, it allows for a difference in potential where each phase can be used as a "neutral" for the other.

[Jim Katen]

Originally posted by mgbinspect

. . . In a 220v circuit with no neutral, what path does the current take to return to ground since there is no neutral? Is it traveling the opposite supply wire via the alternating phase? It can't simply be "spent" or vanish into thin air can it? . . .

The easiest way to understand it is to remove the neutral from the entire installation (in your mind).

There are two coils in the transformer at the street, a primary and a secondary. Power from the primary coil induces electrons to flow through the secondary coil; that's the one attached to our service panels.

So forget about the neutral. Just pretend it isn't there. The electrons in the secondary coil flow in one direction for a while, then they flow in the other direction for a while -- back & forth, back & forth. That's where our 240v power comes from.

Think of a slinky held between your hands and pulsing back & forth. If you were holding either end of the slinky, your body would be experiencing 240v power. One side pushes electrons while the other pulls, then they switch -- 60 times a second.

- Jim Katen, Oregon

[mgbinspect]

Ok, I think I've got it between Chad and Jim's explanations.

But, it sounds as if my suspicion is correct that the opposite supply, be it black or white serves as the return or functions as a neatral would between waves back and forth so in a way there actually is "flow"? As Chad explained?

[hausdok]

Hi,

I've not wanted to get into this one because, to me, understanding electricity is akin to understanding string theory (or algebra), and therefore undicipherable. I think you're looking for too pat or too simple an explanation. When 240 volt circuit is actually working it expends it's energy. There is no "return" to earth per se. If there were, we wouldn't have to keep purchasing power because it would constantly replenish itself. Just be glad that they've figured out how to make it work to man's advantage and don't sprain your brain trying to figure out intangibles. Einstein used to try and do that and look what it did to his hair.

ONE TEAM - ONE FIGHT!!!

Mike

[mgbinspect]

I think it's already been answered!

I had already reasoned and suspected that the only real possibility that made sense was what Chad has described and Jim has enhanced. I was merely hoping to have someone with complete understanding nail it down.

Thanks to all!

I think I'm good to go.

PS. I do have a call into a local power company electrical engineer and if he offers a really enlightening explanation, I will share it here.

[Rob Amaral]

Jim K is on the simplest path. I too was befuddled by this years ago when I started out. What I did was go to the MIT bookstore and bought an Electrical Engineering 101 type of book. It helped. The book brought me there slowly. This issue you've asked is in the section on power transmission (from high voltage to low) and then on down into a user's place. ("the Load"). What is cool is how electricity in one part of the transformer causes an effect in the other part, and they don't touch. The whole thing is pretty cool anyway. ("Rotating machines" that generate electricity by cutting magnetic fields...). As in most things, it is more complex than usual. My ham-radio brother used to bother me because he always had a hard time explaining radio waves (despite constantly 'being on them'). It took home inspection for me to try and figure it out. Kind of gnawed at me.

I think one of the most important things to 'own' with electricity and home inspection is what can happen 'when things go wrong'. Understanding ground faults, paths of least resistance and short circuit currents is key to understand why things must be installed properly and 'optimally'. Done wrong, a piece of the system can fail before it 'clears' a fault. Then we have the tiger out of the cage. Not cool. A lot of the 'bad things' we see are problems that can occur under specific circumstances that may not be occurring when you look into a system. No matter, you don't mess around with it.

[mgbinspect]

Well, here's a fascinating little bit of food for thought. I had the pleasure of meeting with that master electrician again who said he had pondered my question and soon after I left recalled this interesting phenomenon regarding neutral wires:

He explained that if you were able to turn off everything in a home and merely hook up two 2 amp light bulbs, one to each of the two 120 entry cables and turn on only one of the bulbs you'll read 2 amps at the neutral returning to the power company. However, if you turn on both bulbs, the neutral to the power company will now read "0"! He said that the neutral handles imbalanced load.

That tid bit added with the fact that parallel circuits are said to enjoy decreased resistance and offer multiple paths for current to travel nails down the fact that in a 240 circuit the current may travel or return via it's own cable or the parallel cable and in fact ultimately seeks balance. Interesting!

[hausdok]

My hair's starting to hurt!

OT - OF!!!

M.

[mgbinspect]

Lol, I think this is profound, myself. When it comes to all but the most basic "codes" , to my shame, I'm pretty pitiful, (a code-check aholic) but this fascinates me.