If I put the measuring probe of a voltmeter between the positive terminal of a DC 24V source voltage and earth ground, will I get any voltage reading on the voltmeter?

 

It depends on whether the source is grounded.

 

As Dick said.
Any electrical circuit requires a complete circuit to operate.
You can't measure a voltage between two points if they are isolated.

 

If you do happen to see a voltage reading, either AC or DC using a modern high impedance VOM, it is usually due to this high impedance of the meter that is reading stray currents due to capacitive/inductive coupling of the circuit that may otherwise be Galvanically isolated.
In this case it will not support any significant current.
Max.

 

Most likely not. If you connect an identical voltmeter between the negative terminal (positive probe) and ground (negative probe), the first will read 12 V and the second will read -12 V. Since no two voltmeters are truly identical, all you can really count on is that the first reading minus the second reading will be 24 V -- and they probably won't change even if you disconnect the meters from ground, but keep the two negative probes of the meters together.

 

As Dick said.
Any electrical circuit requires a complete circuit to operate.
You can't measure a voltage between two points if they are isolated.

As Dick said.
Any electrical circuit requires a complete circuit to operate.
You can't measure a voltage between two points if they are isolated.

So am I right to say that theoretically there is voltage difference exist between the DC source and earth ground but practicaly speaking we are unable to measure the voltage difference using a VOM ?

 

So am I right to say that theoretically there is voltage difference exist between the DC source and earth ground but practicaly speaking we are unable to measure the voltage difference using a VOM ?

I have had readings per post #4. Especially if of mains origin.
If it is not previously intentionally referenced then it is of high impedance.
Max.

 

So am I right to say that theoretically there is voltage difference exist between the DC source and earth ground but practicaly speaking we are unable to measure the voltage difference using a VOM ?

No, you are not correct to say that. The voltage between ground and any point not connected to it is the path integral of the electric field in the direction of the path between ground and that point. That is the definition of the voltage between two points. But the electric fields between ground and some point that is not ground-referred are very malleable. All you know is that the voltage from the point in space infinitesimally close to the positive terminal of the source is 24 V higher than the voltage at the point in space infinitesimally close to the negative terminal. But you have no idea, whatsoever, what the voltage is between ground and either of those points. If the battery as a whole has a bunch of excess electrons because whoever hung it out there off the ground on this wonderful insulating shelf walked across the carpet, then the voltage on the positive terminal might be -1234 V relative to ground (and the voltage on the negative terminal would then be -1258 V).

In practice you have a lot of poorly defined capacitors from everything to everything and how the stray charges are distributed on them will determine these voltages relative to ground -- and as anything changes, from someone walking by up to and including moving the probes of the voltmeter toward where you want to connect them, will change this.

 

Bow Meiler.....I believe there most certainly is a voltage potential there. There just isn't a conductive path. You may see it with an electroscope. If you increase the potential enough........it will make a path.

 

There's definitely "A" voltage potential there -- but it is ill-defined. The chances of it being 24 V is vanishingly small. It also changes with the tiniest change in the surrounding environment.