240 AC Stick Some Of These Near Your Electrical Box

You remove 120 volts from a three phase wye transformer and you have two phases of 120 volt left. Take 240 volts from a three phase transformer and you have 120 volts left.

WHADDYA MEAN?

A three phase wye connected transformer has a FOURTH TAP comprende? It is the neutral tap. Any 1-2 1-3 or 2-3 phase to phase connection is a 240 volt connection.

1-2-3 to the transformer neutral tap is a 120 volt connection (still with me)

Many USA transformers ARE NOT WYE WOUND. THEY ARE DELTA WOUND. They are not shaped like a dot with three equally spaced radiating lines.

Their diagram is like a fat christmas tree triangle with a stump sticking out the middle of the horizontal flat line that is the bottom of the tree. The result is 240 three phases plus 277 volts and 208 volts from two of the phases to the stump. From the two opposite ends of that horizontal bottom line to the stump IS TAH DAH! 120 volts. Across the total length of the bottom line is TAH DAH 240 volts.

Why don't they put a stump in the middle of all the flats of the christmas tree and have an orgasm of stump neutrals?

Every neutral has to see an earth ground bond and whoppee wouldn't that be fun?

Residential service drop transformers are simple H1 / H2 & X1 / X2 transformers.

Wye commercial transformers cost about twice as much as Delta commericial christmas tree with a stub transformers.

And WhooWhee when you suck one phase voltage way down, it tends to elevate the one or two remaining phases. So please read a little. It may "Enlighten" you.

Transformer engineering gets esoteric with high Kw units. Ground loops and eddy currents. Subractive and Additive winding concepts. So if you encounter transformer rules and regulations, it may be confusing.

That is exactly why there are strict electrical code.

The word phase seems to have two meanings. There are 3 phases 60 degrees out of phase of a power line into buildings with heavy duty electric motors. Only one of these phases goes to a house or RV. The center tapped transformer on one of these phases provides two 120 volt “legs” which combine to 240 volts, demonstrating that they must be of the same phase.

An apprentice electrician informed me that the word phase is widely used for these 120 volt legs in his classes. I find this very confusing.

Nothing could be easier for posting photos in forums than http://photoposting.is-great.net/?i=1 created by an RV.net member for us. Just drag the photo icon to its box and it uploads and shows a link that can be copied and pasted into a post.

I need "someone" that can accept an email image of a drawing then post it. For whatever reason I have nothing but problems accessing a photo image site then trying to use it as an image base for url based images.

Basically all three meters need tiny wire. Even 25 gauge would do fine but the fat limit would be 22 gauge. Simply strip the end of the wire and stick it into the recessed clamp then tighten the recessed screw (it's recessed for safety)

Each screw terminal can accept 2 wires. So it's Christmas lights series with one black wire for phase and one white wire for neutral. Each module has four wires except the last in line. Being AC polarity is not important.

The frequency meter inductive pickup wires length is too short. Period. It needs to be extended and the extension would require soldering on an extension. If used correctly tiny butt connectors for 22 gauge wire would work if they ended up solidly crimped.

A lot of "capable but not electrical expert" folks here.

It would be helpful if you post an installed wiring diagram ;)

Being aware and taking appropriate action is a large part of vigilance and you can use the following as an example.

Plug in and the A/C acts sluggish. Perhaps it's leg is operating at 103 volts while the other leg is cruising along at 117 volts. Wiring a phase flip flop is not all that hard.

Does the generator sound a little weird? Aha! 67 Hz will do it every time. Or 55 Hz.

These three gauges stop guesswork and the newbies from posting vague symptoms asking for help.

Even if an owner knows squat diddly what he's doing, coming to the forum and posting the readings of the three gauges gives participants half a chance of diagnosing things correctly.

"Gee my lights went out and I hear clicking but the refrigerator works but the toaster doesn't" is a frustrating clue.

People that ATTEMPT to help themselves will get the best results. But vague meandering through a list of symptoms are likely to get ignored or roared at.

MEXICOWANDERER wrote:
Disconnect that phase to neutral paths at the neutral and watch the no-current blue flash?

Up -and- down amplitudes of the sine wave are now filled.

But that isn't the point of meters. Meters are to verify and to alert.

And with twin pathways of 120vac the only way to do it...

Phase to neutral voltage and Phase to neutral current

On each phase.

With 240vac phase to phase no neutral the second set of meters is not necessary.

Diagnosing a center tap transformer is similar

"Theory" in a "perfect world".

The problem with "Theory" is we are not in a "perfect world".

IF you had a home that EXCLUSIVELY uses 240V ONLY appliances (Like European homes) then your "Theory" would hold true and correct.

The problem is we are not in Europe and we do not have 240 only homes.

in our homes we have a MIX of 240V and 120V devices, MOSTLY 120V items too boot.

This causes an imbalance between L1 and L2, the imbalance current then shows up on the Neutral line.

So, in reality the only TRUE way to "monitor" the current is to monitor BOTH L1 and L2.

For that reason I used two separate Ammeters on my home Generator emergency transfer panel to monitor both L1 and L2. This way I can shed some loads or move some loads to balance the generator load.

I must say, those are nice looking small Ammeters you found and could be fit into pretty much any small electrical box with ease..

Mine, I mounted in a 4x4 work box with a blank plate that I cut out openings for the meters.

Disconnect that phase to neutral paths at the neutral and watch the no-current blue flash?

Up -and- down amplitudes of the sine wave are now filled.

But that isn't the point of meters. Meters are to verify and to alert.

And with twin pathways of 120vac the only way to do it...

Phase to neutral voltage and Phase to neutral current

On each phase.

With 240vac phase to phase no neutral the second set of meters is not necessary.

Diagnosing a center tap transformer is similar

"Neutral will show total load of 120 vac."
I am a little confused. If leg 1 has a 30 Amp load and leg 2 has a 30 Amp load what will the neutral current be? 60 Amp? I think 0 Amp, perfect balance.

Neutral will show total load of 120vac. Low amps low volts on leg one or 2 needs to be investigated.

Put a current monitor on the neutral and measure the imbalance.