Is there voltage on the neutral?

Status
Not open for further replies.
M

monkey

Senior Member
Location
Arizona
I am having this discussion with a co worker. He argues that there is no voltage on the neutral side of a 120 load, that it is all used up by the load. I say there is voltage present on the neutral side, we just can't measure it because it is at ground potential. If we put an amp clamp on the neutral, we can see current, so why wouldn't there be voltage?
 
He can feel it if he touches the copper in between the two neutrals. It will use his finger for a path over to the other neutral. He should to be on a fiberglass ladder. The neutral can be dangerous. So don't try this.
 
Voltage is measured as the potential between two points. What that voltage is depends on how you measure it. Measuring from neutral to ground should show a voltage near 0 volts because they are connected together at some point.
 
Certainly can be voltage on the neutral. As stated it depends on where you measure it and the amound of load current flowing. IF you are down stream from the main panel that contains the N-G bond and current is flowing you darn well better be able to measure voltage between N-G or something is wrong. Depending on length and the amount of current flowing it can be as high as 5 to 8 volts.
 
Your coworker may not understand the physics, so here is a way to illustrate it for him. Take an Amp reading around just an ungrounded conductor (hot). Let's say it reads 5.72 amps. Test just the grounded conductor (neutral). Wow, there is that same 5.72 amps.

Ohms law says Amps multiplied by Resistance equals Volts. If the Black and White wires have the same Amps, and we can assume that they have the same resistance... then there must be the same voltage.

Okay, that might be over simplified, but sometimes that's what it takes.
 
monkey said:
I am having this discussion with a co worker. He argues that there is no voltage on the neutral side of a 120 load, that it is all used up by the load. I say there is voltage present on the neutral side, we just can't measure it because it is at ground potential. If we put an amp clamp on the neutral, we can see current, so why wouldn't there be voltage?
Click to expand...


I would say "used up by the load" is certainly an inadequate expression, and incorrect.

Between infinity and minuteman, I'd say they got it covered.. plus I like minuteman's explaination very much.
 
The more correct term for voltage is difference of potential. It depends where you are measuring. From neutral to ground there should be no difference of potential. From neutral to phase you should read the phase voltage. So the short answer is yes there is voltage on the neutral. The important thing for us that there is no ddifference of potential to ground wich we are all usualy hooked to.
 
Monkey, in theory, there is no voltage difference between an intact grounded conductor and ground. In the real world, there is the distinct possibility of voltage for various reasons.

Presuming an intact system with no unintentional resistances, for every drop of voltage measured on the hot wire at the load end of a supply circuit, there will be the same amount of voltage rise (relative to ground) on the load end of the grounded conductor.

In other words, for the total circuit voltage drop, half is seen over each wire. If the hot is dropping 2.5v, the neutral is also. With 120v at the source and 115v at the load, the hot would measure 117.5v to ground, and the grounded condictor would measyre 2.5v.

According to your friends theory, it would be perfectly safe to use the grounded conductor as a grounding conductor (and vice versa), which is clearly not the case. Unintentional resistances or breaks increase the potential (sorry :cool:) danger of his assumption.
 
monkey said:
I am having this discussion with a co worker. He argues that there is no voltage on the neutral side of a 120 load, that it is all used up by the load. I say there is voltage present on the neutral side, we just can't measure it because it is at ground potential. If we put an amp clamp on the neutral, we can see current, so why wouldn't there be voltage?
Click to expand...

There is voltage if current exists, current is the flow of voltage (EMF).
 
LarryFine said:
You can have voltage without current, but you cannot have current without voltage.
Click to expand...
unless you keep a slight downhill slope on the circuit like how plumbing drains are arranged to drain, then a small amount of current can flow without voltage being applied. It's my favorite way to get free elecricity. Using this gravity current generating technique, I can power up some of my smaller loads for free. :)
 
Minuteman said:
.

Ohms law says Amps multiplied by Resistance equals Volts. QUOTE]Actualy thats not quite true.I hate to nit pick,but what Mr. Ohms law realy says is that the current in a circuit is a function of the pressure(EMF) and the resistence. While true that an algebraic relationship exists between all three circuit variables, I think that a failure to understand the fundamental relationship between potential, resistence and current flow leads to a lot of misunderstanding as to how things realy work.
Click to expand...
 
I like to say that Ohm's Law states that one volt will push one amp through one ohm.

iaov said:
While true that an algebraic relationship exists between all three circuit variables, I think that a failure to understand the fundamental relationship between potential, resistence and current flow leads to a lot of misunderstanding as to how things realy work.
Click to expand...
Agreed. It's easy to forget what the variables really are and are not in a given situation.

Mathemtaically, it can be correct to say that, when the voltage doubles, the currect doubles. But, that's mostly true for a load with a fixed impedance. Not all loads do.

Mathematically, it can be correct to say that, when the voltage doubles, the current halves. But, in the real world, an equipment change is required for that to happen.

In most cases, the equipment can be considered a constant, and the current will vary with the applied voltage. The variables are the applied voltage and the resultant current.
 
I think your coworker understands what he is talking about.
Obviously, voltage is measured between two points. When he refers to the voltage, as a single point,
he obviously means with respect to ground and must mean ?essentially? zero.
Of course there is a few volts in reality. because of the resistance of the neutral wire.
If the neutral wire were a superconductor, current would still flow with exactly zero volts to ground.
 
If Monkey's coworker understands or not, we don't know. Point is, he could make a fatal mistake of breaking a neutral and making contact with himself and the upstream side and ground.
 
LarryFine said:
Mathemtaically, it can be correct to say that, when the voltage doubles, the currect doubles. But, that's mostly true for a load with a fixed impedance. Not all loads do.

Mathematically, it can be correct to say that, when the voltage doubles, the current halves. But, in the real world, an equipment change is required for that to happen.

In most cases, the equipment can be considered a constant, and the current will vary with the applied voltage. The variables are the applied voltage and the resultant current.
Click to expand...

I used to think that for a long circuit that it was important to upsize the conductors to reduce voltage drop so that the circuit didn't draw too many amps. Because I used to think that when the voltage goes down that the current goes up, which is true if the load changes accordingly, but for a given load if the voltage drops then the current will also drop.

This now makes me wonder why is it important to upsize for voltage drop? I can understand you don't want your equipment operating on too small a voltage but is that the only reason?
 
Status
Not open for further replies.
Top