measuring current in a 220 ac circuit

[Chris Lewis]

According to Tony :

Even after spelling and gramatical corrections, that's linguistically and technically wrong, not to mention just plain silly.

Even if the neutral was carrying current, you're not going to get a shock between the neutral and ground because the voltage difference between the neutral and ground is at most a volt or two[+]. This is true even in a 120V circuit pulling 15A.

Remember, the neutral and ground are connected together in the panel. They're never going to be more than a volt or two different. Unless something goes very wrong.

The neutral in a 3 wire 240V/120V circuit only carries the difference current between the two hots. If it wasn't and currents added on the neutral, then 3 wire 240V/120V circuits would be illegal. I assure you, they're not. In fact, up until a few years ago, they were _mandatory_ in the Canadian electrical code for kitchen counter outlets (and used to be fairly common practise in the US). This has only changed in Canada because of new requirements for GFCIs on kitchen counter outlets, and GFCI'ing split duplex receptacles requires expensive dual GFCI breakers.

If the hots are equal current, the current in the neutral wire is _zero_. Not only that, but the voltage between neutral and ground will also be _zero_[+].

[+] presuming of course that the neutral and ground are properly connected to where they're supposed to be - connected together at the main panel.

[Tony]

Sorry Chris for me it is kind hard to explain because of language barrier I should have said that you open neutral from the source/panel in other words you body would be in series with neutral leg/line That is tied to the load in this case light bulb. look easiest way to solve mystery is hook up one light bulb and measure the current on both wires and you will find that both weirs have same current flow, that's easy enough,

[Chris Friesen]

In a 3-wire circuit you have two hots and a neutral. If you put a light bulb between each of the hots and the neutral, there will be no current flow in the neutral.

In essence, the current flows up one hot, through the bulb, through the other bulb, and back down the other hot. (It's like one hot is positive, the other is negative, and the neutral is zero.)

The neutral is only needed for the case where the load on each of the hot legs is not equal.

Chris

[Tony]

O yes it will and twice the hot legs, as I siad try and do little expirement on your onw and find out for your self Tony

[Zyp]

And here I thought the 3-wire line from the pole was a center tap 220 volt transformer with the load carrying neatrul being the center tap [110 volts.]. Learn something new each day.

[Chris Friesen]

Just to clarify...it is a center-tap 220V (or 240V) transformer. However, the center tap is tied to ground. The two hots alternate positive and negative, but exactly opposite from each other.

Chris

[Chris Friesen]

I honestly can't tell if you're a troll or not.

If the neutral could carry twice the current of the hots in normal use, then it would have to be a larger conductor than the hots.

In reality, the neutral in a feeder line is often *undersized* relative to the hots. This is because it only carries the difference between the two hots, and if you have balanced loads or 240V loads there is no current in the neutral.

If that isn't enough of an explanation, I give up. This thread has gone long enough. Please don't do your own wiring.

Chris

[Tony]

Chris we are not going any way so I am not going to comment however? there is no such thing in AC circuit as positive and negative the on three phase system or single phase, the phases are out of phase by 90 degree that is it! no positive or negative just about 6-7 months ago I had job replacing 25 hp Refrigeration compressor that runs on 480 three phase and guess what one phase was neutral, amazing isn't and you telling me neutral is not carrying current I afraid you will need eat few more Winnies by have nice day Tony

[CJT]

Have YOU tried that experiment?

[CJT]

May I suggest you read this: ?

[Mark H]

sounds like a "b" phase ground a and c phase to ground 480v b phase 0v

In 3 phase panels you can also have a high phase between a and b b and c a and c all 240v a and c to neutral 120v b to neutral 240v

problem is Chris is still right

[George]

He is simply trying to give you a simplified analogy.

The legs on a three phase system are 120 degrees out of phase with each other. On a single phase system the legs are 180 degrees out of phase with each other.

[SRN]

. On a single phase system the legs are 180 degrees out of phase

When you say this you need to add ", referenced to ground (neutral)"

[trader4]

I can't believe you guys have taken this crazy discussi "It is been so long since I stody the basics of Kirechhoffs Law, That I would not atempt to go there Tony "

it became obvious he's totally unqualified to be giving advice or opinions on current flowing in a shared neutral. Kirchoff's Law is quite simple and elementary: The sum of all currents at any node must be zero. Which is to say, current can't pile up, it has to go somewhere. In the case of a 240V shared neutral settup, that means whatever current goes up one hot must either go back on the other hot, which is out of phase or back via the neutral.

And to go back to the example Chris gave earlier, on a shared neutral, if you put a 100W light bulb from one hot to neutral and another 100W light bulb on the other hot to neutral, you will have zero amps flowing in the neutral because the load is balanced. The current flows from one hot, through the first bulb, through the second and back via the other hot.

Now connect another light bulb from one hot to neutral, then you will have current flow in the neutral.

Very basic.

[Doug Miller]

No, you don't. The statement refers solely to the phase difference between the two hot legs, which has absolutely nothing to do with either's potential difference from neutral.

[Zyp]

Hmmm... you're sort of right, they do "alternate" but 60 times a second. What's the frequency of the AC current got to do with it?

[Zyp]

Thank you!

[Thomas Horne]

Tony You are off your soundings there bud. In case your not nautically inclined that means you are out of your depth. If you wire two sixty watt bulbs in series across a two forty volt circuit they will burn just fine. Now connect a neutral to the connection that is between the two bulbs and if the bulbs are truly identical then no current will flow on the neutral.

Here's a little experiment for you to try. You can build an Edison circuit from two twelve volt batteries and two twelve volt lamps. Wire them all in series. The two twelve volt lights will light just fine. connect a volt meter across the connection between the lights and the connection between the batteries. It will measure six volts. Now change the leads and settings on your multimeter from voltage to current and measure across the same two points. Applying the ammeter as a neutral conductor will not change the current significantly. The only current flowing will be caused by the slight differences in manufacture between the two lights and the two batteries.

-- Tom Horne

[Thomas Horne]

Tony wrote: > Chris we are not going any way so I am not going to comment > however? there is no such thing in AC circuit as positive > and negative the on three phase system or single phase, > the phases are out of phase by 90 degree > that is it! no positive or negative > just about 6-7 months ago I had job replacing 25 hp Refrigeration > compressor that runs on 480 three phase and guess what > one phase was neutral, amazing isn't and you telling me > neutral is not carrying current I afraid you will need eat few more > Winnies by have nice day Tony >

Tony If you think all grounded current carrying conductors are neutrals then you are inadequately trained. A corner grounded Delta transformer set, such as the one that probably supplied your refrigeration compressor, cannot supply a neutral. The only time phases will be ninety degrees out of phase is in a Scot T transformer arrangement.

The two hundred and forty volt, single phase, transformers that are used to supply homes in North American practice are supplied from a single phase on the primary side. How can a transformer with only two windings produce a phase difference across it's output winding?

If you have worked with buck boost transformers you know that a single phase transformer can be tapped on it's secondary side to supply several different voltages and although it is rarely done those different voltages can be from the same transformer secondary. I could ground any one of the taps as long as I ground only one without effecting the voltage output available from each portion of the secondary winding. If it produces several voltages on it's output does that make it multi phase? Voltage is usually measured to ground because it is that voltage the insulation must successfully withstand. If you measure the outputs against each other using an oscilloscope you will find that the wave forms are identical in the horizontal or time domain and that they differ only in their amplitude as an expression of their voltage.

-- Tom Horne

[Tony]

RE: to above You right because you have just made artificial neutral your center tap between two light bulbs is acting same as perhaps if you have tied to transformer with center tap. Look in any system if you have two wires going to a load each wire will carry same amount of current it does not matter if is

120 or 220 or 480 if is light to be light or motor to be run both wire/legs will carry identical current regardless if is neutral or hot, the current is equal in both legs, in three phase system current will depend on the balance of electrical components to be powered and voltage supplied this are basics and they do not change

Tony