Resistance in a Volt meter

[timberfinn]

Most meters today I understand are multimeters but I am only interested in the volt meter circuitry. The reason I am asking this is because the volt meter seems to only register voltage across a load and not on a plain conductor such as the neutral circuit. In my limited experience and according to my instructor, the volt meter reads zero if you try to get a reading anywhere along the neutral circuit for one of two reasons: 1. "the voltage has been used up at the end of the last load" or
2. the "potential difference (difference in potential?) in the current in the neutral wire between the two leads of the voltmeter is zero". I argued that neither of these can correct because there are always amps in the neutral circuit and you cannot have amps without volts to push the electrons along. I argue that maybe it is possible that the resistance in the neutral circuit is lower (.005 ohms/ft for 12ga. copper wire) than the resistance in the internal circuitry of the volt meter itself since the circuitry wires are obviously going to be smaller in diameter than 12 ga. and thus of higher resistance. The current therefore takes the path of least resistance and by-passes the volt meter. Thus a zero reading in the neutral circuit. I am talking about a single phase 120v residential wiring system, although the principle is the same in any circumstance I would think. So what is the resistance in the internal circuitry of a standard analog voltmeter? Digital voltmeter?

 

[w0z]

The current doesn't "bypass" the voltmeter although I know what you are trying to say, it just may be too small to measure. Current will always favour the path of least resistance, but that doesn't mean none will flow where the resistance is higher.

Typically a decent analogue meter moving coil may have a resistance of 20kΩ/V DC and 1kΩ/V AC. Digital multimeters can (note can) have higher figures (some are selectable hi z lo z for AC that's a whole topic in itself) but for example 10 or 20MΩ/V DC, 1M or 10MΩ/V AC is typical.
Also you should be talking about impedance not resistance for AC

Across a long length of neutral passing a current you certainly would be able to measure a voltage, but then you'd have to allow for your very long test leads.

 

[EricMark]

We years ago had two types on volt meter, one had an ohms to volt rating the other the valve volt meter in essence generated a voltage and when the voltage measured equals the voltage generated then zero flows between the two circuits.

So on the typical voltmeter we would measure on two scales, if both readings were similar then the volt meter was not causing a volt drop, if they were not you knew the volt meter was causing an error.

 

[Bobster]

1. "the voltage has been used up at the end of the last load"

Please, please tell me that tutors are not teaching this?

 

[oracle]

Please, please tell me that tutors are not teaching this?

Met one guy who did 5 day Part P course and without working a day on site became a college tutor so what can we expect?

 

[Pete999]

Depends

Met one guy who did 5 day Part P course and without working a day on site became a college tutor so what can we expect?

Angry not at you Oracle at the thought of the outcome or what you said in your post

 

[oracle]

Depends

Angry not at you Oracle at the thought of the outcome or what you said in your post

Pete, colleges sell courses first and then look for tutors, I can accept guys coming off the tools to teach after years of experience but that one beggars belief.

The reason why they’re always short of trainers is the kids on funded courses often have floated through school and expect to float through college and life.

The colleges get about £3500 for each bum on a seat in the classroom and the poor sod teaching is personally responsible for attendance, achievement, timekeeping etc. Would you like to do that?

 

[Pete999]

Pete, colleges sell courses first and then look for tutors, I can accept guys coming off the tools to teach after years of experience but that one beggars belief.

The reason why they’re always short of trainers is the kids on funded courses often have floated through school and expect to float through college and life.

The colleges get about £3500 for each bum on a seat in the classroom and the poor sod teaching is personally responsible for attendance, achievement, timekeeping etc. Would you like to do that?

No not really no patience for time wasters, or any wasters come to that.

 

[static zap]

My thoughts are that a meter safe for use at line voltage , will not be sensitive enough for the test you want ,unless extreme loads are present.
( Anything more sensitive needs to be used with great care -as it may not be designed with the correct level of Safety/Failsafe == Not beginner territory )

 

[Pete999]

Pete, colleges sell courses first and then look for tutors, I can accept guys coming off the tools to teach after years of experience but that one beggars belief.

The reason why they’re always short of trainers is the kids on funded courses often have floated through school and expect to float through college and life.

The colleges get about £3500 for each bum on a seat in the classroom and the poor sod teaching is personally responsible for attendance, achievement, timekeeping etc. Would you like to do that?

Yes it does Mate, and that's the worrying part, trouble is all these providers just think of tick sheets and of course bank statements, a sad reflection on training.

 

[static zap]

Pete,
..... colleges sell courses first and then look for tutors....

This does explain alot of my sons "Dissapointments" ,and "Moans about instability & lacking consistency "
for a slightly more distant Local college - allegedly better.

 

[dmxtothemax]

QUOTE -
2. the "potential difference (difference in potential?) in the current in the neutral wire between the two leads of the voltmeter is zero".


The second statement is equally as preposterous !
A little knowledge is a dangerous thing
And he is teaching his nonsense to others !