Testing ground for voltage

[The electron man]

Let's say I working on some electrical and I'm testing for voltage

From
Ground to black I should get 120v
Ground to red I should get 120v
Ground to neutral I should get 0v
Since ground and neutral are at the same potential

But there are times the ground can be energized because there is a problem in the system

How would I test the ground to make sure its not energized ??

 

[BillyMac59]

If everything is wired properly, an energized ground should be momentary. The ground would offer virtually no resistance causing the upstream OCD to trip/blow.

 

[ActionDave]

Let's say I working on some electrical and I'm testing for voltage

From
Ground to black I should get 120v
Ground to red I should get 120v
Ground to neutral I should get 0v
Since ground and neutral are at the same potential

But there are times the ground can be energized because there is a problem in the system

How would I test the ground to make sure its not energized ??

Ground is too vague of a term for an in depth discussion on electrical. Start using Ground only when referring to a connection to the earth.

1) Ground = Earth
2) Grounded = Intentionally connected to the earth
3) Equipment Ground, Equipment Grounding, Equipment Grounding Conductor = A path to clear a fault

 

[LarryFine]

My #1 tester is a Knopp K60 solenoid tester. I only use a voltmeter when I need to know the voltage.

A non-contact tester can be handy for finding voltage relative to the earth or the local ground plane.

Maybe you mean what do you test against; i.e., what you use as a reference, like neutral vs electrodes.

 

[The electron man]

If everything is wired properly, an energized ground should be momentary. The ground would offer virtually no resistance causing the upstream OCD to trip/blow.

Yes I understand that, I was talking in about a scenario were there is a wiring issue and the ocpd doesn't trip

Would it not be a good safety measure to test the ground as well just to make sure it not energized even tho 99.9 % of the time it won't be

 

[The electron man]

Ground is too vague of a term for an in depth discussion on electrical. Start using Ground only when referring to a connection to the earth.

1) Ground = Earth
2) Grounded = Intentionally connected to the earth
3) Equipment Ground, Equipment Grounding, Equipment Grounding Conductor = A path to clear a fault

So egc to black 120v like that

 

[The electron man]

My #1 tester is a Knopp K60 solenoid tester. I only use a voltmeter when I need to know the voltage.

A non-contact tester can be handy for finding voltage relative to the earth or the local ground plane.

Maybe you mean what do you test against; i.e., what you use as a reference, like neutral vs electrodes.

Exactly what would be my reference point

 

[LarryFine]

Exactly what would be my reference point

Okay. You try them all. You look for power between every pair of points where there should be power, and for no power between points that should be at the same voltage. What you stated in your OP.

You also want to make sure you have (practically) no voltage between points along a current-carrying pathway (while under load), like between the service neutral and the neutral in downstream panels.

When doing a troubleshoot, I sometimes plug an extension cord into a known-properly-working (non-GFCI) receptacle, and carry around the female end with a reference hot, neutral, and EGC to test against.

 

[The electron man]

Okay. You try them all. You look for power between every pair of points where there should be power, and for no power between points that should be at the same voltage. What you stated in your OP.

You also want to make sure you have (practically) no voltage between points along a current-carrying pathway (while under load), like between the service neutral and the neutral in downstream panels.

When doing a troubleshoot, I sometimes plug an extension cord into a known-properly-working (non-GFCI) receptacle, and carry around the female end with a reference hot, neutral, and EGC to test against.

Got it , question regarding reference point

If I have a transformer coil testing from one end to the neutral point I'll get 120v and testing from the other end I get 120v since the neutral is grounded and at zero volt

So why do I get 220v from side to side if its at the same potential

Voltage is the difference in potential of to points ?

 

[ActionDave]

So egc to black 120v like that

Yes. It will help keep the discussion clear for everyone.

 

[LarryFine]

Got it , question regarding reference point

If I have a transformer coil testing from one end to the neutral point I'll get 120v and testing from the other end I get 120v since the neutral is grounded and at zero volt

So why do I get 220v from side to side if its at the same potential

Voltage is the difference in potential of to points ?

Again, reference the two batteries in series.

When you test from the center tap, you're reading two points of opposing polarity; the voltages add.

When you test from one line to the other, you're adding the two voltages (240, not 220,by the way).

 

[electrofelon]

Got it , question regarding reference point

If I have a transformer coil testing from one end to the neutral point I'll get 120v and testing from the other end I get 120v since the neutral is grounded and at zero volt

So why do I get 220v from side to side if its at the same potential

Voltage is the difference in potential of to points ?

You can make as many taps as you want on a transformer coil. You could have 240 taps along the length so you have a volt between two adjacent ones, or any voltage you want depending on which taps you measure from. Grounding one of the taps doesnt change any of the voltages between the taps. All grounding does is make whatever tap you chose to be at the same potential as what ever you connected ("Grounded") the tap to. IT could be a pipe or conduit system, building steel, or physical earth, but it really should be all of them connected together and acting as one.

 

[LarryFine]

If you were to flip only one of the two batteries, you'd still read 1.5v across either one, but 0.0v across the pair, because they would be subtractive, not additive.

Likewise, if you mis-wired the two secondaries of a 120/240v dual-secondary (as opposed to one with a 120/240v center tap), you would have two x 120v but no 240v.

 

[ActionDave]

Got it , question regarding reference point

If I have a transformer coil testing from one end to the neutral point I'll get 120v and testing from the other end I get 120v since the neutral is grounded and at zero volt

So why do I get 220v from side to side if its at the same potential

Voltage is the difference in potential of to points ?

Here's a good video.

 

[LarryFine]

That's an excellent video. It's almost a visual representation of my batteries and neutral explanation.

I remember a long debate about polarity vs phase/timing with a center-tapped or a dual secondary.

His explanation of moving one probe vs moving both shows it's about polarity and being in-phase.

 

[The electron man]

Here's a good video.

Got it so the reason I can test line to line is one side is in the + and one side it in the - so there is a difference in potential

Only in 3 phase the phases are out of phase ??

 

[LarryFine]

Only in 3 phase the phases are out of phase ??

With 3ph, there is a genuine phase difference. The alternator has three sets of coils that are physically offset by (360/3) 120 degrees, so their outputs are electrically 120 degrees apart.

When one phase is at its positive peak, the second phase is approaching its negative peak, and the third has passed its negative peak. The three chase each other 'round and 'round.

 

[TwoBlocked]

Yes I understand that, I was talking in about a scenario were there is a wiring issue and the ocpd doesn't trip

Would it not be a good safety measure to test the ground as well just to make sure it not energized even tho 99.9 % of the time it won't be

Hope I don't confuse things or get things off track. You can have a partial ground and not trip a breaker. This can be tested with a clamp-on meter, especially one specifically made for ground fault detection. It can be clamped around the ground and should read 0 amps. Or you can clamp it around both the hot and neutral of an energized circuit, and it should also read 0 amps.

Another scenario is having a high resistance ground conductor, where even though one end is a dead ground to a voltage source, somewhere in the current path, there is a poor ground connection, limiting the current going back to the neutral and not allowing the breaker to trip. This can be detected by measuring from hot to ground, and from neutral to ground. Hot to ground should be full voltage, neutral to ground should be 0 volts.