I think terminology is what is confusing reading some of these post.
I always referred to individual legs of electricity for incoming power. Two separate legs create single phase 220v power. One leg to neutral or a ground will provide 110v. Three separate legs create three phase.
Often in 220v control circuits one leg is referred to common and the other as signal. All the commons tie together in the circuit.
Maybe I have been wrong all these years but I usually can troubleshoot and fix most electrical issues. :confused3:
Let me ask a series of questions and you answer them.
If you as a person touch the ground connection in the breaker box with your wet finger are you energized?
If you as a person touch the neutral connection in the breaker box with your wet finger are you energized?
If you as a person touch one of the screws of a 240 volt breaker with your wet finder are you energized?
If you as a person touch the other screw of the 240 volt breaker with your wet finger are you energized?
Answers. No, No, Yes, Yes.
So please tell me on any 240 volt circuit which of the two screws is the common and which is the energized? Answer there is NO common and there never was on a 240 volt circuit. BOTH of the legs are energized. They are simply TWO distinct phases. You can be badly shocked if you touch either one and you are energized with either one. You will only be energized to 120 volts respective to ground if you only touch either one of the screws. You will be energized to 240 volts if you touch them both at the same time and it does not matter if you are grounded or NOT. If you take two fingers and touch both screws while you are standing on a rubber mat, you will be badly shocked and burned. You are liable to have finger damage at the least. If you are still standing on that rubber mat and you only touch one screw you will still be energized to 120 volts BUT you won't feel a thing. If you step off of that rubber mat onto a damp concrete floor while barefooted, you WILL feel it. Just how bad you feel it depends on a lot of factors like skin resistance and how damp that concrete floor actually is.
So to recap, across the TWO phases of standard household delivery in most areas anywhere from 220 to more likely 240 volts is developed, and if any part of your body touches both of those phases at the same time you are going to know it. Whether you touch ground or neutral has NO bearing on your getting the hedoublell knocked out of your and possible serious burns and cooked meat to boot. Touching a single phase of this service as long as your are not touching ground will do nothing to you but energize you and you will feel nothing and have no idea you are even energized. There is absolutely no harm in touching a single phase of electrical service even up to several thousand volts as long as you stay with that phase and do not touch any other phase or do not touch ground. At several thousands of volts there will be some corona effects noticed especially around your eyes where ions are bleeding off into the air. But you won't feel a thing at 120 volts.
If you remember nothing else if you are ever energized, remember this: Stay with your phase. Don't touch another phase and don't touch ground. Think of a bird on a high voltage power line. He is energized to the potential of that power line. But he stays with that phase, and doesn't touch another. If he does, he is smoke and feathers. Or a squirrel on a power line. No problem as long as he stays with that phase. Getting on or off of that phase is where the danger is.
Why do some 240 volt appliances have 4 wires you ask? Good question. Here is why. The green wire goes to the case of the appliance for safety ground so that if something happens to one of the phases of the power that makes it touch in some way to the case, we don't want that case to become energized and then have a person touch that case and touch a real ground like possibly plumbing or some other grounded appliance and become energized. We want that energized leg to draw massive current when it touches the appliance case so that the fuse or break will trip out. Safety grounding for the appliance case.
Now for the two different phases of the "legs" of the power that does the work in that appliance. And that leave the other wire. That wire is the neutral wire. What is its purpose you ask? My welder doesn't have a neutral wire, (most don't anyway), why do I need it here? And besides that in many locales the neutral wire and the ground wire are tied together back at the box anyway. What in heck do I need this 4th wire the neutral wire for? You need it if you have something in the appliance that needs to run on 120 volts. For instance maybe a fan or timer motor that needs 120 volts instead of 240 volts. This is the method to use a single phase of the service and run it against the neutral wire. This will provide the 120 volts that the motor or other part of the appliance needs. Could they have made the fan or timer run off of 240 volts instead and not needed this 4th wire? Sure they could have, but there are good and valid reasons for not doing so. Mainly it has to do with sourcing of suitable parts or having those parts a little safer by running off of the lower voltage.
When we run 120 volt circuits in our house, we use ONE of the phases, it doesn't matter which one (except for load balancing, which is another subject entirely) and we use the neutral wire. The neutral wire carries just as much current as the "hot" wire which we now know is a SINGLE phase of the TWO phase power delivered to our homes. Every electron that flow out of the hot wire and goes thru the appliance flows back into the neutral wire .
This is why if you disconnect a neutral wire with a load in series with it, you will see an arc just as if you had disconnected the "hot" single phase wire. Green ground wires do NOT carry any current UNLESS something goes wrong and a phase has shorted to the green ground wire, THEN they carry massive current. Hopefully enough current to trip out the fuse or breaker before the wire bursts into flame. Remember fuses and breakers are sized to protect the WIRING so that it does not become hot enough to burst into flames or cause something it is next to to burst into flames and burn your house down. They sure as heck don't protect people from getting shocked in any way.
It is a good experiment. Note* Most of the outlets in one room will be on a single phase and nothing wlll happen, but watch out other rooms can and likely will be on different phases. 