[zats]

Hi All,

I have a 110V, 20A household electrical circuit that has current but no voltage. If I shut down the circuit break and no voltage or current is present at a plug (checked with Volt/OHM meter as well as a Voltage/Current tester) and then turn on an overhead light (three-way switch) in the same room, current appears at the plug but still no voltage. If I disconnect the wire carrying the current, the overhead light goes out; if I then turn the circuit breaker on I have a Hot/Neutral Reverse condition at the plug. I am in the process of taking the wall down so I can trace the circuit at that time. I was just curious; I thought you needed voltage to have current. Any ideas as to way this is happening would be appreciated and will help shorten my troubleshooting time.

Thanks,

zats

[donf]

It is a principal of electricity that you cannot have current flow without voltage.

Voltage pushes current through the conductor..

In Ohm's law this is symbolized by the following formula:

E = R/I.

What amount of current are you seeing?

[zats]

Don,

Thanks for the quick reply; I thought that was the case. There is enough current to power the six double fluorescent lights connected to the "other"circuit. I will measure the exact Amperage draw later today and let you know.

Much appreciated,

zats

[Tev]

Neutral carries current but does not have voltage in relation to ground.

The two circuits may be sharing a neutral. Which would explain the current and lack of voltage. It also explains why lights on a different circuit would turn off if a wire at the receptacle is disconnected.

[zats]

Neutral carries current but does not have voltage in relation to ground.

The two circuits may be sharing a neutral. Which would explain the current and lack of voltage. It also explains why lights on a different circuit would turn off if a wire at the receptacle is disconnected.

Tev,

I think you are correct, it is the neutral wire that is carrying the current and that one neutral definitely affects both circuits. Probably why all the radios in the vicinity buzz when the lights are turned on... :( Any reason why this would be done? Could they have been trying to take a short-cut when installing the two-way switch in the room? There is plenty of capacity at the breaker box and it is fairly close.

Thanks for the help, I think I'll split the circuits off and give them both their own neutral.

-Dan-

[donf]

If you are getting that much current, then there has to be a voltage on the line.

Set your meter to AC Voltage say around the 200 VAC range.

Now measure between the Black (red probe) and White (Black probe) I would expect that you see 120 Vac at a minimum.

Neutral is the return leg for current. Black carries the current to the load and white returns it to the electrical system.

Make sure you are measuring the correct black line to the correct white.

We really need much more information regarding what failure you are seeing and how you are testing for current and voltage.

[zats]

If you are getting that much current, then there has to be a voltage on the line.

Set your meter to AC Voltage say around the 200 VAC range.

Now measure between the Black (red probe) and White (Black probe) I would expect that you see 120 Vac at a minimum.

Neutral is the return leg for current. Black carries the current to the load and white returns it to the electrical system.

Make sure you are measuring the correct black line to the correct white.

We really need much more information regarding what failure you are seeing and how you are testing for current and voltage.

Hi Don,

I know what you mean and you would assume voltage on the line, but that is not the case, and what prompted my question.

In fact there must be voltage…as you state…it is just coming from another source/circuit.

I am a little familiar with the use of a Volt/OHM meter in it's testing of both AC and DC circuits for voltage/current/resistance/continuity. My Volt/OHM meter is a SCOPE DVM-632 Digital Multitester, with probes; I supplement my testing with an EXTECT Instruments DVA30 CAT-III Voltage and Current tester, a non-contact type and a GB Electrical Inc. GRT-500 circuit tester, a plug-in type.

All three testers indicate the same thing; no voltage. With the receptacle circuit breaker shut off, the overhead lights shut off at the switch (they are on a different circuit remember), and my SCOPE tester set in the 200V range, I get; .78V (less than 1V) using any combination of white (neutral) and black (hot) wires, and .00V (none) on white to white or black to black combinations. There are only two black Hot and two white Neutral wires at the outlet so it is easy to test all combinations; I can also see the cable so I am sure of which two go together. There is no amperage draw at that time (yes, I broke the circuit and used my probes for testing), the EXTECT confirms this. When I turn on the overhead lights the voltage does not change at the receptacle; no voltage, but the amperage draw changes to 14A on my SCOPE and the EXTECT goes nuts. Again no volts, lots of current.

Some additional information; the two-way switch the activates the overhead lights seem normal in all conditions of on or off, with the exception of a voltage drop when the lights are powered on; from 124V in the off position to 94V in the on position.

I do think Tev is onto something with his “shared neutral” theory and would indeed be the reason I see no voltage but current at the receptacle.

I hope this helps, please let me know what you think, any assistance is appreciated.

-Dan-

[Tev]

The voltage is there, so current can flow. It's just a matter of which ungrounded wire you use to measure it. Use the ungrounded that has the breaker off and the voltage will read near zero. Use the ungrounded that has the breaker turned on and you'll read normal voltage.

Do yourself a favor when working on either of these circuits, turn both breakers off. With one on you could have the white wire running to the panel in one hand and the white wire running to the light in the other and the circuit becomes complete through you. If I were you I'd put these two breakers next to each other and use handle ties so they must be operated together. Or preferably since you are opening the wall anyway, get rid of the shared neutral so the circuits are completely separate.

[KISS]

Donf:

In post #2 you state that E=R/I; That's a big OOPS. V=IR or E=IR for the old folks who use Electromotiveforce rather than Voltage.

[zats]

The voltage is there, so current can flow. It's just a matter of which ungrounded wire you use to measure it. Use the ungrounded that has the breaker off and the voltage will read near zero. Use the ungrounded that has the breaker turned on and you'll read normal voltage.

Do yourself a favor when working on either of these circuits, turn both breakers off. With one on you could have the white wire running to the panel in one hand and the white wire running to the light in the other and the circuit becomes complete through you. If I were you I'd put these two breakers next to each other and use handle ties so they must be operated together. Or preferably since you are opening the wall anyway, get rid of the shared neutral so the circuits are completely separate.

Thanks Tev,

I guess it doesn't matter why it was done but it's not good. I never handle electrical wiring with both hands, in fact I wear rubber insulated gloves just to prevent any problems, but I'll gladly take your advice. Connecting both breakers together is a good idea but won't be necessary, as I mentioned earlier and you eluded too in your last post; I will be totally separating the two circuits. I knew this was a problem and would not have proceeded until I corrected it, and I appreciate your help in identifying the problem.

Thanks everyone and have a Merry Christmas and a safe and Happy New Year!

-zats-

[zats]

Donf:

In post #2 you state that E=R/I; That's a big OOPS. V=IR or E=IR for the old folks who use Electromotiveforce rather than Voltage.

As you already know; you are correct Sir, thanks.

-zats-

[EPMiller]

<snip>In post #2 you state that E=R/I; That's a big OOPS. V=IR or E=IR for the old folks who use Electromotiveforce rather than Voltage.

Hey! I resemble... err... resent that. I don't consider myself old, but I use E for voltage. Learned it that way in school back in the 70's. Well.. maybe to some I would qualify. :p

EPM

[tkrussell]

I would not necessarily say big oops,

Donf:

In post #2 you state that E=R/I; That's a big OOPS. V=IR or E=IR for the old folks who use Electromotiveforce rather than Voltage.

Since E=IR is the basis of the formal Ohm's Law expression, and Don may be showing his seniority.

However, I would agree not to use E when explaining theory to laypeople, and stick with Voltage.

I would also like to add that Resistance is seldom used by electricians in everyday Power, or should I say Watts, calculations.

And what about Intensity that means Amperes?


I don't want to bring up Volt-Amps here. May just confuse the issue.

[KISS]

tk:
You needed to put your glasses on. The operator used by don was divide, rather than multiply and the quantity solved for was E. e.g E = R divided by I. That is a BIG oops.

We always talk about and IR drop, so that should be easy to pick up. But, we all have bad days, including me.

[tkrussell]

Jeez Kiss, I just saw my mistake, but your too fast for me.

Your right, the " / " did not jump out at me.

I thought you were on Don for E and V substitution.

I came back to to retract my statement, as of course I did not see it at first, only after open mouth insert foot, and damn your quick.

Ok I deserve it.

[donf]

Forgive the typo, for that was actually a typo. The point is that regardless of what is being said by the poster, you cannot have a current flow without Voltage (EMF) pushing the current.

Either this is a multiwire circuit or the circuit he is testing is being backfed.

[KISS]

Strictly speaking the "you cannot have current without voltage" is true 99.9% of the time and is true here.

The short circuit current parameter of a solar cell is indeed the current when the voltage is zero. It can be forced to operate there. The voltage is zero and the current is negative.

[EPMiller]

Somebody said "you cannot have a current flow without Voltage (EMF) pushing the current". What about the panel grounding conductor for the electrical service in my house? I've measured over 5 amps on it, but there is no voltage there. Now I know, it is the low side of a circuit, but it seems that the above quote should be qualified.

[donf]

OK,

Set up an ohms law equasion with 0 volts and demonstrate for me a greater than 0 amperage, please.

I does not matter if there is even a trace of voltage, there still needs to be voltage to push a current through resistance.

[tkrussell]

Don, the calculations will be irrelevant in dealing with AC power that is using a grounded conductor (AKA Neutral).

This is why standard theory and troubleshooting will only be on the Hot conductor.

There will always be measurable current in a Neutral conductor of an operating circuit in use, same as measured in the Hot conductor.

This is why a Neutral is considered as a Current Carrying Conductor by the National Electric Code.

However, since this is a Grounded conductor,there will not be, or should not be in a properly grounded/wired system with no wiring faults, any measurable voltage.

This wire has been grounded to insure the voltage in this conductor has been brought to Zero or Earth Potential, but still will have current flowing, as it the return for the circuit.


Once an open neutral develops, all bets are off, as the circuit is now operating abnormally, and troubleshooting methods need to change to the condition.

Troubleshooting AC circuits with a grounded conductor requires the knowledge of how and why the system is wired.

I still am not sure if I am explaining this sufficiently to help understand the why's and wherefores of current but no voltage in a Neutral, and why it is so important to have this understanding in giving advice on troubleshooting and theory.

An electrician understands without going into some much detail, it is something we just not accept but get, but so hard for us explain to laypeople without just saying Because We Say So.

We all got enough of that comment from our parents growing up.

This may help a bit:

May-June 2006: Current in the Grounded Conductor