Question about voltage Reading

[Adrian Francis]

Good day, Question I want to ask. is that I know when you are measuring voltage between neutral and ground, there should be zero potential. However, why it is when you are measuring voltage between hot and ground you are getting a reading?

 

[bwat]

That's the case whenever the ground is bonded to the neutral. Reading "hot" to "ground" is effectively the same thing as reading "hot" to "neutral", and you shouldn't be surprised by reading a voltage there..

(ground meaning EGC here)

 

[don_resqcapt19]

If you are measuring between the neural conductor and the EGC at any point other than in the panel with the main bonding jumper you will not read zero volts if there is current flow on the neutral. You are actually measuring the voltage drop on the neutral between the location of the main bonding jumper and the point at where you are taking your voltage reading.

As far as reading hot to the EGC, the EGC and the neutral are bonded together at the service equipment or the first disconnect of a Separately Derived System, and you will see the full line to neutral voltage between the hot and the EGC.

 

[hbiss]

when you are measuring voltage between neutral and ground, there should be zero potential. However, why it is when you are measuring voltage between hot and ground you are getting a reading?

Neutral and ground are tied together (at the service) hence there should be no voltage between them.

Therefore hot to either neutral or ground will result in a voltage reading. Neutral to ground will result in a zero voltage reading.

-Hal

 

[ptonsparky]

Neutral and ground are tied together (at the service) hence there should be no voltage between them. At that point.

Therefore hot to either neutral or ground will result in a voltage reading. Neutral to ground will result in a zero voltage reading.

-Hal

 

[hbiss]

At that point.

He asked a basic question, trying to give a basic answer. Once he understands that we can go on to what can really happen.

-Hal

 

[ptonsparky]

More than one tech has told me the building steel was energized because they measured voltage from the Neutral to EG, or Neutral to building steel at the end of a loaded branch circuit.

 

[JimmySparks]

when you are measuring voltage between neutral and ground, there should be zero potential.

As others have pointed out, when you measure voltage Neutral to Ground, you will see some voltage (just a volt or 3 hopefully) if the circuit is under load. This reading will be half the total voltage drop at that point on the circuit, assuming a number of conditions: the hot and neutral are the same length, there are no bad connections upstream of that point, the neutral is not shared with another circuit, the neutral is not touching the ground downstream of the MBJ, etc. Under load, the hot to ground voltage will be a little higher than the hot to neutral voltage, assuming the above conditions.

 

[paulengr]

As others have pointed out, when you measure voltage Neutral to Ground, you will see some voltage (just a volt or 3 hopefully) if the circuit is under load. This reading will be half the total voltage drop at that point on the circuit, assuming a number of conditions: the hot and neutral are the same length, there are no bad connections upstream of that point, the neutral is not shared with another circuit, the neutral is not touching the ground downstream of the MBJ, etc. Under load, the hot to ground voltage will be a little higher than the hot to neutral voltage, assuming the above conditions.

Except at the main bonding jumper (if it is grounded), the ground and phase conductors (including neutral) are insulated from one another. The definition of a capacitor is two conductors separated by a ground. Capacitors pass AC but block DC. It should thus not be a surprise that the ground to neutral voltage is not zero.

Nothing to do with voltage drop. Voltage drop is due mostly to series impedance. Shunt capacitance has an effect too but it is dominated by line impedance.

 

[gar]

210621-0730 EDT

paulengr:

Your post makes no sense.

The definition of a capacitor is not ---- "two conductors separated by a ground."

Whereas JimmySparks gave a rather clear description. If no current is flowing in an EGC wire, then the voltage at any point along the EGC wire will be very close to the voltage of the EGC wire at the main panel. Likely in the millivolt range. There are a lot of factors that can determine this small voltage. Capacitive coupling is not likely one.

It is true that there is capacitance between the EGC wire and the low potential current carrying conductor, possibly called a neutral wire, which is connected to the EGC at the main panel, about 20 pfd per foot, or on a 50 foot run about 1000 pfd. 1000 pfd has a capacitance reactance of about 2,650,000 ohms at 60 Hz.

Most voltage drop seen between the EGC and the low potential current carrying wire is the result of resistive, and inductive voltage drop on the current carrying wire. Roughly the same amount of capacitance exists between the hot wire and the EGC, and therefore a much larger current would flow from hot to EGC because of the higher voltage difference from hot to EGC, but still insignificent.

.