[Stratmando]

I would avoid disconnecting Neutrals at panel, unless it is positively NOT a Multi circuit. You can burn out some expensive equipment/appliances.

[Marshall132]

Why is that?

[KISS]

Ok, simple one. Your TV. It has a polorized plug. It should rally have a 3 prong plug. It doesn't.

The neutral is connected to the wide prong, which in turn is connected to ground.

Because components aren't 100% isulated, there is a small amount of leahage current present, so now that leakage current and whatever weird waveform that's present is TRYING to power all the other devices connected to the neutral.

Since ground is used for communications in USB and TV coax, raising these groud potentions can evoke damage. There may be some info in the surge supression sticky in the Electrical & Lightng link on the top left of this page.

[Stratmando]

Plus, if you have a circuit drawing 10 amps, and the other multicircuit hot has 1 light bulb on it.
The load being very great compared to the bulb will cause the bulb to blow, can go as high as 240 volts.

[Marshall132]

So you are saying that equipment that creates this stray current is traveling through other equipment that are tied into ground through other means than the neutral thus making it a complete circuit despite the neutral being disconnected.

[Marshall132]

And stratmando, could you contextualize your response a little more. Where does the 240 volts come from?

[Stratmando]

No, only the 2 circuits will be affected, The total voltage of the 2 circuits will equal 240 volts, without the neutral, 1 device could see 80 volts, the other would see 160 volts.
80 + 160 equals 240.
High or low voltages are dangerous.
Nothing should be going through ground.

[Marshall132]

You have completely lost me. The voltage between two different legs could be 240, though I thought it was more like 230, or 220. But you would need a short between two circuits with different legs (or the third if you have three phases, which I believe most residential electrical breakers don't) or a two pole breaker. Right? Is this what you are referring to? Or are you referring to the previously mentioned stray current and voltage?

[KISS]

In the US voltages have been bumped up a bit. The standard single phase distribution is from a 240 volt center tapped transformer. That center tap is the ground neutral bond. Connect both ends of opposite 240 phases together, you'll get zero volts out.

The second distribution that you'd see is 208 both in single and 3 phase. You'll also see 277 as a single phase voltage. 277 is used for lighting loads.

I'm thinking on the second part of the question.

Suppose we had a stove with a 4 wire connection and the sove turned on with the neutral disconnected. That neutral would se 120 V with respect to ground because it's being powered by a say a clock motor winding. Now suppose that there were 120 V outlets that used the neutral that you disconnected, say a convienience outlet. Now that 120 outlet is 240 V and limited in current by the winding of the clock motor.

It's harder to explain the varying differences, but they are caused by RF filters which tend to connect the line to ground through various leaky devices like capacitors. This is where varying voltages come from.

Here is a schematic of a typical filter: EP/VP Series

Note all the interconnections. Note the leakage at 125 V is .73 mA. This low of a current may also a source with a 171K output resistance. This will skew a reading when a certain voltmeters are attached esecially those that have a Z in ohms/volt measured. A 10 Meg ohm resistor (many voltmeters) in series will act as a divider.

The 10 meg ohm input Z meter needs 12 uA to measure 125 V, so weird voltages show. They can't deliver appreciable power, but could spark and could damage connected equipment.

[Stratmando]

I'm not talking about any induced voltages, stray currents or anything, Just basically if 2 circuits sharing a neutral, and the neutral is opened and a Motor was plugged in on 1 circuit(black circuit), and you had a lamp(on red circuit/opposite phase)You can get close to Line Voltage. I see More 240 than the others.
I was also talking about 2 Pole Breaker.

[Stratmando]

Check this out:
Weird Circuit Problem at Home?

[Marshall132]

I get it now, I did not know what you meant by multi circuit.

[Marshall132]

"In the US voltages have been bumped up a bit. The standard single phase distribution is from a 240 volt center tapped transformer. That center tap is the ground neutral bond. Connect both ends of opposite 240 phases together, you'll get zero volts out."

The last sentence is confusing to me. Each phase is 120v to neutral and 240 to each other, right? Where are you getting 0v?

[tkrussell]

The single phase is across the 240 volts, the 120 volt is only a center tap of a transformer, based on ratio and physical location in a coil of wire, to deliver the 120 volts.

I found a couple of interesting diagrams. One new and shows grounding of current systems, and another very old by the verbage and obsolete 220 volts but gets the point across, that it is still only one single phase.

[Stratmando]

You should have 0 Volts between Neutral and Ground.
TK's drawing shows the Ground and Neutral Tied Together.

[KISS]

Zero volts has been defined as the reference. A reference can be anywhere. But it makes sense to make the earth the 0 volt reference point. Earth and neutral is tied to the center tap, hence that is also the zero volt reference.

What should be confusing is that wee call this single phase, because the PRIMARY is fed by a single phase system. The secondary is sort of a two-phase system with the phases tied together. These are just 180 degrees out of phase from each other, so putting the ends of a 240 line together will result in zero volts out.

[Marshall132]

So the two phases have a 240v difference, correct? And each 120v to the neutral/ground. So what do you mean when you say "putting the ends of a 240 line together will result in zero volts out"?

[tkrussell]

The last time I put two ends of a 240 volt circuit together, there was a large flash, melted metal, and a fire, due to what is called a short circuit.

Then there was zero volts.

I am interested in an explanation also.

In addition, what is "sort of a two phase"?

It is single phase, period.

[KISS]

My friend has two phase distribution in Philadelphia.

Two-phase electric power - Wikipedia, the free encyclopedia

My transformer thing was all wromg:

Soldermans Basic Electronics: Transformers Series and Parallel Connections.

Some electronic trabformers are supplied as dual secondaries and dual primaries. The way you iterconnect them determines the voltage of the primary and current that the primary can handle. At the lower voltage it requres twice the curret and the higher voltage half. If you so happen to connect the primary in series the wrong way, you end up with zero volts out of the secondary.

The secondaries can be connected in various ways two. Namely series and parallel. You get an extra wire to deal with when the transformer is not center-tapped.

Connecting the 240's volt legs together 120 with an out of phase 120 V) should give you nearly zero volts. The phases would cancel. One way you would get double the voltage and the other the voltages would subtract.

Making the connections live and unintentensional and not with matched parts could stress out some parts.

120 in parallel with 100 VAC is not the same as 120 in parallel with 120 V.

[EPMiller]

The last time I put two ends of a 240 volt circuit together, there was a large flash, melted metal, and a fire, due to what is called a short circuit.
Then there was zero volts. <snip>

Hahahaha. I love it. Scares the bejeebers out of you too. Best one I ever did was cut into a 20A 120v line with a linesmans pliers. Big hole burned out of the side of it.

EPMiller