What is this motor tag telling me?

[nickel-city-fab]

The 120V legs each provide a ful sine wave when looked at separately, it is just 120V rms.

When looking at both, relative to the neutral, for one half-wave, wire "A" is a positive half sine wave, and wire "B" is a negative half sine wave. But they reverse for the next half wave, so that "A" is negative and "B" is positive.

If you look at just the two wires for 240V, you see an ordinary sine wave of 240V rms.

No net DC. You cannot get DC through a transformer, you have to "reset the core" so the input has to have as many volt-seconds negative as positive. (volt-seconds are the product of the voltage times the length of time it is applied)

I stand corrected and re-educated. It has been a while since the 1980's last I looked at these things.

[J Tiers]

No, it is ordinary AC. The 110v is half of a wave, it could be either the bottom half, or the top half. If you are measuring a 220v line it will be the full wave. One easy way to think about it, is to imagine that the home is connected to a center-tapped transformer. The center tap is neutral, and the 2 outer legs each provide 110v but they are 180 degrees out of phase with each other, because the 110v legs are only providing half wave.

The 120V legs each provide a ful sine wave when looked at separately, it is just 120V rms.

When looking at both, relative to the neutral, for one half-wave, wire "A" is a positive half sine wave, and wire "B" is a negative half sine wave. But they reverse for the next half wave, so that "A" is negative and "B" is positive.

If you look at just the two wires for 240V, you see an ordinary sine wave of 240V rms.

No net DC. You cannot get DC through a transformer, you have to "reset the core" so the input has to have as many volt-seconds negative as positive. (volt-seconds are the product of the voltage times the length of time it is applied)

[nickel-city-fab]

I see, 180 degrees different. From what has been said, am I right in thinking that electrical plugs are not available for the public to buy in the USA?

Electrical plugs are everywhere, and cheap. It's just a matter of using the correct one for the application. Most of the answers are dictated by the building safety codes, and electrical codes. Professional builders and remodelers are required to know these, and adhere to them. Homeowners can do whatever they want but it's not recommended (due to insurance legalities)

You can buy whatever you want, no questions asked (unless your home burns down -- then they will be asking questions)

[nickel-city-fab]

" each 110v leg is 1/2 of a full sine wave ": now you got me confused. is dc comming out of the wall?

No, it is ordinary AC. The 110v is half of a wave, it could be either the bottom half, or the top half. If you are measuring a 220v line it will be the full wave. One easy way to think about it, is to imagine that the home is connected to a center-tapped transformer. The center tap is neutral, and the 2 outer legs each provide 110v but they are 180 degrees out of phase with each other, because the 110v legs are only providing half wave.

[old mart]

I see, 180 degrees different. From what has been said, am I right in thinking that electrical plugs are not available for the public to buy in the USA?

[rdfeil]

That will be fine, until someone comes along and says "my brother in law knows a electrician who...." wires houses and he said.

You are SO right... life will go on in any case.

[wmgeorge]

That will be fine, until someone comes along and says "my brother in law knows a electrician who...." wires houses and he said.

[rdfeil]

No, AC is coming out of the wall. In the US the common wall outlet voltage is 120 volts AC in reference to Neutral. As stated above there are 3 POWER wires, 2 hot and 1 neutral and 1 earth safety ground. This is created by having a 240 volt ac transformer secondary with a center tap. The center tap is the neutral and also earth at the service entrance to the building/home. This is the ONLY place it is legal/allowed/mandated to join the neutral and earth ground together. The difference between neutral and ground it technical only. The neutral is designed to carry the current of the 120 volt AC loads back to the transformer. It is therefore considered a "current carrying conductor". The earth ground wire is for safety only and ONLY carries current if there is a safety fault in proper installations. So to answer your question, with the neutral as a reference the wall outlet is 120 volts AC 60 Hertz Rms sine wave. Now for our 240 volt AC appliances, heaters and single phase machines we simply use the two hot wires without the neutral. plus the earth safety ground This gives us 240 volt AC 60 Hertz Rms sine wave to use for higher voltage equipment. The main reason for this is that we can get twice the power out of the same wire by doubling the voltage and keeping the current the same. This results in smaller wire size for the same load. I hope this clears this a bit 😊

[dian]

Its basically single phase. Sometimes called "split phase" because electrically it looks like a coil tapped in the center. The center is the neutral, each "leg" is (nominal) 110v. Looking on a 'scope, each 110v leg is 1/2 of a full sine wave -- It just gets cut off flat in the middle, or "zero" point. Use the two outside legs to get the full 220v sine wave. Use one leg or the other with the neutral in the center to get the 110v.

There is no problem with running over or under the correct voltage because the outlets are very different for appliances with plugs. And industrial equipment is almost always the higher voltage and amperage. The 110v is normally only for ordinary household outlets and lighting.

" each 110v leg is 1/2 of a full sine wave ": now you got me confused. is dc comming out of the wall?

[J Tiers]

Is that single phase or two phase? Or both? A clever system if you know what you are doing, but it must be prone for stupid people to either run things over or under the correct voltage.

Can be (and commonly is) used by the brainless among us without problems (there are too many of them, and 120/240 has apparently not thinned the herd yet....).

Despite quibbles by some, it is solidly single phase. If the two 120V lines were at 90 degrees phase angle instead of 180, it would indeed be classical 2 phase. But they are not. Too bad, since then we could all have 3 phase.

A mentioned, there are plug types for each, and they are not possible to plug in accidentally, so unless one of the brainless uses the wrong receptacle when they (as they often do) wire a new outlet, all is well.

[nickel-city-fab]

Is that single phase or two phase? Or both? A clever system if you know what you are doing, but it must be prone for stupid people to either run things over or under the correct voltage.

Its basically single phase. Sometimes called "split phase" because electrically it looks like a coil tapped in the center. The center is the neutral, each "leg" is (nominal) 110v. Looking on a 'scope, each 110v leg is 1/2 of a full sine wave -- It just gets cut off flat in the middle, or "zero" point. Use the two outside legs to get the full 220v sine wave. Use one leg or the other with the neutral in the center to get the 110v.

There is no problem with running over or under the correct voltage because the outlets are very different for appliances with plugs. And industrial equipment is almost always the higher voltage and amperage. The 110v is normally only for ordinary household outlets and lighting.

[old mart]

In the States we have three wires. 2 lines and a ground. Line to Line is 220-240, Line to ground is 110-120.

Is that single phase or two phase? Or both? A clever system if you know what you are doing, but it must be prone for stupid people to either run things over or under the correct voltage.

[Captain K]

Anyone who does not get the difference between ground and neutral should not be doing electrical work.

[wmgeorge]

In the States we have three wires. 2 lines and a ground. Line to Line is 220-240, Line to ground is 110-120.

Single phase is as above 2 hot wires and a Neutral wire which is grounded... but not an equipment ground.. His motor which has already been IDed is a 3 phase one. Single phase motors do not need a Neutral.

[rdfeil]

In the States we have three wires. 2 lines and a ground. Line to Line is 220-240, Line to ground is 110-120.

Not to be picky, OK I am being picky, but to make things clear to those that are not familiar with various electrical systems....

In the US there are actually several standard electric systems. The one you mentioned above is the most common SINGLE PHASE system used. There are also 208 volt single phase, 277 volt single phase, 208, 230 and 480 volt three phase. Some of these systems are combined for various reasons. IE: 277 single phase is included in the 480 three phase wye system. I know I am being very picky, but for people to have an understanding they need to know some of the basic differences so they can do research if they want to know more... Not trying to start a fight, just more info 🙂.