Hi guys
Been a while since I've been around - got lots to keep me occupied. Got a question about electricity. Want to run some wires in my shop and was wondering... In 110volt you have a live wire and nuetral wire, this is also single phase. In 220volt is there 2 live wires of 110volt each that act as the others nuetral. Or does is it have two 110volt phases running in one wire with a nuetral wire. And are both phases in phase or out of phases.
Thx Mat
120V = 1 hot wire and neutral
240V = 2 hot wires, no neutral, one wire has one phase and the other wire has another phase and its 120 degrees between the two phases
For wiring 220VAC in your shop, I recommend pulling cable with 2 hots, 1 neutral and 1 ground. The motors in your machines don't need the neutral, but it's handy to have there if you need it in the future.
Bernie
Rather than risk a short-circuit between brain and fingers, I'll give a URL.
One minor correction: The hot wires are 180 degrees out of phase.
Bill
That's an excellent diagram. Thanks for posting the link.
Bob
Technically (not that it matters in practice), the hot wires are *in phase* but with opposite polarity voltages. After all, you only have one secondary winding on that transformer; the "neutral" is really a center tap or halfway-voltage.
There is such a thing as two-phase power, where the hots are 90 degrees out of phase (three or four wire systems) but they're obsolete these days.
But those details don't matter for our purposes, I'm just being pedantic.
Pedantic mistakes in that picture:
Worse than nitpicking, actually. What makes you think that, for instance, the mere proximity of the "120V rms" to the primary means it references the primary? It's a case of space, and has no pointer.
It's not meant to instruct you how to wire, they refer you to the NEC for that.
Now go have a nice warm milk to counteract that nervous caffeine energy.
He did say pedantic, and although I can understand that the drawing takes liberties for the sake of readability (like not having bus slots zig-zag) putting a neutral connection on that 240V outlet is just wrong.
-Steve
Thats what I did. 10-3, 30A for my 220 TS and 12-3, 20A for my 220 DC. I then added a few 110 convienience outlets to the DC circuit. I only worry a bit about tripping my breaker if I move my compressor from its dedicated
110v 20A circuit, for convienience sake ;) , to one of the outlets on my DC circuit. If the compressor kicks in while DC is on..... has happened once but never tripped the breaker yet! I'm sure if both were starting at same time that sucker would blow pretty quick.-B
I did say "pedantic".
Er, a degree in electrical and computer engineering? I mean, *I* know it refers to the secondary (which is 240v) but standards for such drawings make it seem to refer to the primary.
I was hoping to make sure everyone else understood that. You never know when someone's going to trust a picture and end up getting hurt.
Breakers tend to be heat-based, so a short pulse of over-current is usually acceptable. The purpose of breakers is to protect the wiring up to the outlet, not to protect the device plugged into it, so they try to simulate how much heat the wiring is generating and shut off the current before the wire's insulation breaks down.
The only time I've seen a breaker blow "pretty quick" was when it was completely shorted.
Accidentally starting my chop-saw while the blade lock was engaged tripped the breaker PDQ...
Breakers are designed with various trip delay curves to suit the intended application. There's a good overview at
"DJ Delorie" wrote: Technically (not that it matters in practice), the hot wires are *in phase* but with opposite polarity voltages. (clip) ^^^^^^^^^^^^^^^ If there is ANY difference between two voltages of opposite polarity, and two voltages 180 degrees out of phase, I can't find it with an oscilloscope or in my mind. I don't think there is any difference, but I may also be a pedant.
You're correct there is no difference in observable characteristics, just a difference in how the two voltages are generated in practice. (That is, the two legs of 240V are generated from a single phase supply.)
The relationship is not symmetrical.
It's relatively easy to generate two signals that are 180 degrees out of phase, each of which can be measured relative to a common ground, but show no voltage difference relative to each other. Think of two relays (or light switches) which take turns turning a circuit on. You can measure the output of either relays' contacts to ground, and see the signal, but if you just connect from one relay to the other, you get nothing.
In the case of a multi-tap transformer, the fact that it's a multi-tap transformer is enough to make it a voltage issue rather than a phase issue. Consider a transformer with ten taps. Are there ten phases? Of course not, but there are ten (er, plus or minus a fence post) voltages, which you can use in any [linear] combination, much like putting batteries in series.
Now, if you had two identical transformers, and wired one backwards,
*then* you'd have a phase issue (still, though, no practical difference). But like I said earlier, there's no practical difference when we're talking about house current.My primary motivation, other than to have some fun on a Friday, is to keep people from confusing single-phase house current with the original two-phase (4 wire, 90 degrees) AC invented by Tesla. This
2-phase was replaced with our current 3-phase (3 wire, 120 degrees) power.
To make it more amusing, we had a tree fall take out the "ground" wire coming to our house, leaving only the Earth ground as a return. We have 7200v service (transformer at the house), so this left us with a single wire coming up the driveway. Power inside the house seemed normal to me, although we weren't using very much of it at the time.
If anyone knows how to get more than one phase out of a single wire (plus return), there's a Nobel prize waiting for you.
After all, you only have
Actually, there are two secondary coils on the transformer, and they're in series in this application. But there are other times when they are in parallel. You can have a look at my website, and see some transformer connections, including phase angles, that I had up for a discussion on another NG. They are the most common three phase connections used today.
There is also a 5 wire. On my web page you can see the Scott connections that require special transformers to serve these obsolete loads from modern three phase power. These are very rare today.
So am I :)
Don
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