Finding a neutral with a multimeter

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160218-1106 EST

Roger:

From your post #16
Of course bringing other items or methods into the scenario changes things but with nothing more than a voltmeter it can't be done.
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With a voltmeter you can as I described in my post #12. The word "voltmeter" puts no restrictions on what a voltmeter is, the voltmeter's lead lengths, or the shape of a probe tip. Nor does the word voltmeter mean that it can not measure phase angle, or direction of an electric field flux line.

The field map of the electric field around a pair of wires relative to a reference conductive area, where the two wires are at different potentials relative to the reference, can identify which wire is at the higher potential. A voltmeter of the correct design can provide a means to study this field map.

More than 50 years ago electrostatic voltmeters existed. These required no DC steady state current to function, and have very high input impedances. They did have shunt capacitance.

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160218-1142 EST

Roger:

The word "voltmeter" was used, post #16. The word "wiggy" was not in the statement of the problem.

You did not originally specify in your statement of the 40 year old problem that a wiggy was the voltmeter. But let us assume that was part of the problem statement, then was there a restriction on the wiggy's lead lengths and whether or not you could contact the actual conductor in each of the two black wires?

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gar said:
160218-1142 EST

Roger:

The word "voltmeter" was used, post #16. The word "wiggy" was not in the statement of the problem.
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And given it was 40 years ago I'd say it is a safe bet that my wording of the question is probably missing some pertinent details, note I said "It went something along the lines of"


gar said:
You did not originally specify in your statement of the 40 year old problem that a wiggy was the voltmeter.
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Correct, I did not, but by saying ""It went something along the lines of" it should have been evident that I was not trying to be accurate in the wording of the question.

Forty years ago we carried hacksaws, wooden folding rules, yankee or swivel screwdrivers, scratch awls, and wiggins type testers as standard tools.

gar said:
But let us assume that was part of the problem statement, then was there a restriction on the wiggy's lead lengths and whether or not you could contact the actual conductor in each of the two black wires?
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I didn't write the test but, for the answer to have been impossible what do you think?

Roger
 
If you are not sure you can ring them out, then mark all the wire in the 1900 box
go to the panel feeding this conduit and turn all the breakers on that enter this conduit.

Go back to the 1900 box and see which wires do not read 120 to ground. That should
be your neutrals and grounds. :)
 
160218-1231 EST

Roger:

If the given answer to the question was the word "impossible", then the given answer was wrong.

What is a correct answer to the question --- what is the maximum phase shift of a resistance-capacitance network?

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gar said:
160218-1231 EST

Roger:

If the given answer to the question was the word "impossible", then the given answer was wrong.

What is a correct answer to the question --- what is the maximum phase shift of a resistance-capacitance network?

.
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Gar, I wouldn't worry to much about it, it was a question (and we don't even know what the exact wording was) on an apprentice exam from the 70's.

I just brought it up because the OP's situation reminded me of it.


Roger
 
160218-1547 EST

GoldDigger:

i would expect that you would know the answer.

But it is supprising how many senior level EE students don't closely read or understand the question and answer 90 degrees. This was a stock question that A. D. Moore would ask his senior level class. Also Moore would usually call on students by name to answer a question, and those that did not pay attention were usually called.

.
 
Along similar lines:
If you have an unlimited supply of dominos and start from a single domino resting at the edge of a flat level table, how far beyond the edge can you extend a tower of dominos which rests entirely on that one domino.
Consider for simplicity that you can only lay each additional domino flat on the one immediately beneath it.
No glue, of course. :)
 
GoldDigger said:
Along similar lines:
If you have an unlimited supply of dominos and start from a single domino resting at the edge of a flat level table, how far beyond the edge can you extend a tower of dominos which rests entirely on that one domino.
Consider for simplicity that you can only lay each additional domino flat on the one immediately beneath it.
No glue, of course. :)
Click to expand...

Might want to assume a very stable table as well, or you won't build very far;)
 
Sparkyboy71 said:
Good day everyone. I am a first year apprentice with a quick troubleshooting question. I notice sometimes things will not be what they should so I open a 1900 box and all 12awg conductors are black. Using my DMM can someone please tell me how to find my neutral for the circuit? Any help would be greatly appreciated guys!! Thanks in advance!!
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If this isnt a test question... ALL wires (even grounds) are black? If so, can we assume that all connections are proper, i.e., no paralleled neutrals between circuits, grounded and grounding conductors separated? Box is bonded? Are there any loads on the circuit? Is it energized? Wired in MC or conduit? Is there a device in the box or is it just a j-box? Tho all relevant questions in practice, for a test I'm guessing that info is n/a or they want a method of determining the neutral that doesnt involve any of that..So...

The wires that are twisted together and tailed to a screw on the box would be the grounding conductors. Remove a wirenut from one of the other connections, measure voltage from it to the box. If you have none, or continuity, those are you neutrals. You will have continuity as the grounded and grounding conductors are tied together in the panel. If you have 120V (or 277V), those are your ungrounded (hot) conductors, and the neutral is what is still capped.

It's also possible to have no neutral, such as a 240V feed to an air handler. and it's possible to have 2+ circuits (and 2+ neutrals) in a box
 
Sparkyboy71 said:
Good day everyone. I am a first year apprentice with a quick troubleshooting question. I notice sometimes things will not be what they should so I open a 1900 box and all 12awg conductors are black. Using my DMM can someone please tell me how to find my neutral for the circuit? Any help would be greatly appreciated guys!! Thanks in advance!!
Click to expand...

Two pieces of wire each one attached to a fuse holder. Several fuses. Attach one wire to ground.

Insert fuse.

Take the un attached wire and shove it up into wire nut connection ( or what ever is needed to get to the bare conductor) ( turn your head close your eyes).
If it blows the fuse it's a hot. Replace with new fuse and try again. When the fuse doesn't blow it's a neutral

Not a recommended test but ...
 
ritelec said:
Two pieces of wire each one attached to a fuse holder. Several fuses. Attach one wire to ground.

Insert fuse.

Take the un attached wire and shove it up into wire nut connection ( or what ever is needed to get to the bare conductor) ( turn your head close your eyes).
If it blows the fuse it's a hot. Replace with new fuse and try again. When the fuse doesn't blow it's a neutral

Not a recommended test but ...
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If the fuse blows, there will be full voltage across the ends, which can be verified using a meter. If the fuse doesn't blow, there won't be full voltage.

Why not skip the fuse part and just use the meter?
 
K8MHZ said:
If the fuse blows, there will be full voltage across the ends, which can be verified using a meter. If the fuse doesn't blow, there won't be full voltage.

Why not skip the fuse part and just use the meter?
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Electricity 101 ??

Wow you're right.

I just plugged a pigtail light socket into a cut extension chord.

At the pigtail hot to Grd at receptacle 120v
At the pigtail neutral to Grd at receptacle 0v

Shouldn't there be some type of voltage thru the filiment neutral side to Grd ??

Guess not as I'm not getting any , but why?

Wow. Good thing I do this for a living :- 0
 
Ok. Removed the neutral splice at the pigtail and get voltage thru the filament to ground.

When the neutral is spliced Why/How is all that energy eaten up that there is no voltage to ground ?

I mean, if I spliced another wire also to that neutral connection and went to ground with that conductor, wouldn't that be running parallel neutral and ground for the return ??
 
ritelec said:
Electricity 101 ??

Wow you're right.

I just plugged a pigtail light socket into a cut extension chord.

At the pigtail hot to Grd at receptacle 120v
At the pigtail neutral to Grd at receptacle 0v

Shouldn't there be some type of voltage thru the filiment neutral side to Grd ??

Guess not as I'm not getting any , but why?

Wow. Good thing I do this for a living :- 0
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Electricity 101:
When you put current into the neutral (via, say, a light bulb) that does not mean that the neutral goes up to the hot voltage. All you see is the voltage developed across the small resistance of the neutral wire back to the utility transformer.
If you did not have close to line voltage across the filament it would not light up properly.
:)
 
GoldDigger said:
Along similar lines:
If you have an unlimited supply of dominos and start from a single domino resting at the edge of a flat level table, how far beyond the edge can you extend a tower of dominos which rests entirely on that one domino.
Consider for simplicity that you can only lay each additional domino flat on the one immediately beneath it.
No glue, of course. :)
Click to expand...

1 micron or so less than the length of a domino

Hovevere, if you stack lots..
 
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