Grounded conductor (neutral) and earth voltage

[Bro8898]

Yeah the neutral on the dryer was loose, but the neutral lead of the 120V motor was bonded to the frame of the dryer, since the heating elements are 240V somehow the 120V dryer motor was able to run without a neutral. It was a mystery to me, perhaps one of the people smarter than me on here can explain it.
Years back my boss measured about 5 amps flowing on a gas pipe, it was a fancy combo gas / electric range on one of those special old 3-wire circuits and the neutral pin was broke off and stuck in the receptacle, so the neutral path for the range was via the gas pipe.

That’s very interesting. And the type of things you come across in piping systems. It’s been good learning more about it here.

 

[PWR_ENG]

Thank you for the quick response. Bonding neutral and earth together sounds to me like a ground rod making contact with the earth, so there would be 0 volts between the rod and the earth at that point.

But as you get farther from the rod will you read a higher potential if you were to touch the rod with one lead and stick the other lead in the earth a few feet away? If I’m on the right track, why does that difference exist? Is there a potential difference there because there is another ground rod located farther away at the transformer that the current is trying to flow to?

You also make me think of equipotential bonding around a pool. Sounds like the goal is to make all of the earth in the area as close to the same potential as neutral as possible. But in the case of a pool the connection to ground is much more sophisticated than a single ground rod connection.

Thanks

Here is a good article from Mike Holt in the early 2k's. It is focused on step and touch potential but provides some details on the fundamentals you are asking about.

Mike Holt Enterprises - the Leader in Electrical Training.

Mike Holt worked his way up through the electrical trade from apprentice electrician through electrical contractor, to become one of the most recognized experts in the world as it relates to electrical power installations. He was a Journeyman Electrician, Master Electrician, and Electrical...

www.mikeholt.com

 

[kwired]

I did not read all the post carefully so may repeat something already said. I will primarily try to address the questions asked in the OP here.

Earth is a good low resistance conductor, however earth is somewhat difficult to make a low resistance connection to, which is why you see voltage gradients around electrodes, some cases is more some is less, all depends on the particular application. The more contact with the soil by the electrode the lower the resistance the earthing connection generally will be. Some soils will have more conductivity than others, and is usually impacted by moisture level of the soil as well.

A basic stand alone source with a ground rod or two as an earth reference typically will not have as stable of a voltage reference to earth as a utility system that has thousands of electrodes all bonded together through the grounded conductor network of that system. That said if they use that grounded conductor as a current carrying conductor for portions of the system it still will have voltage rise on it due to voltage drop - that's natural. This will still result in locations that have a somewhat low voltage between the grounded conductor and true earth, most the time just a volt or two is deemed "normal" though there are certain situations that is not acceptable and further methods beyond basic code installation allowances are needed to eliminate that problem.

 

[Bro8898]

Here is a good article from Mike Holt in the early 2k's. It is focused on step and touch potential but provides some details on the fundamentals you are asking about.

Mike Holt Enterprises - the Leader in Electrical Training.

Mike Holt worked his way up through the electrical trade from apprentice electrician through electrical contractor, to become one of the most recognized experts in the world as it relates to electrical power installations. He was a Journeyman Electrician, Master Electrician, and Electrical...

www.mikeholt.com

I’ll read up on it. Thank you. I read and watch everything I can by Mike Holt. That’s what got me started. I appreciate it very much

 

[Bro8898]

This will still result in locations that have a somewhat low voltage between the grounded conductor and true earth

The more contact with the soil by the electrode the lower the resistance the earthing connection generally will be.

Is the purpose of a low resistance connection with earth to keep neutral and the earth at as close to zero potential between them as possible? I know you might have explained it before but what are the advantages of this method/idea?

I keep thinking of equipotential bonding around a pool area as a way to minimize potential voltage difference between earth and neutral so that a breaker will trip if current flows somewhere that it shouldn’t like the water or the area around the pool.

 

[wwhitney]

Is the purpose of a low resistance connection with earth to keep neutral and the earth at as close to zero potential between them as possible? I know you might have explained it before but what are the advantages of this method/idea?

The purpose of a low resistance connection between the earth and one of the conductors from the power source is to provide for stable voltages between earth and the various conductors from the power source.

The purpose of bonding (via the EGC) one of the conductors from the power source to all the various metal objects related to the electrical installation that aren't supposed to be carrying current (and which a person can easily touch, like the metal chassis of equipment) is to cause the circuit breaker to trip if one of the other conductors from the power source should happen to fault to one of those metal objects. With no EGC and no such bond, one power source conductor could fault to one metal chassis; another power source conductor could fault to another chassis; and you come along and touch them both and get shocked.

Given that we are going to make both of the above bonds, we choose the same power source conductor for each bond. Otherwise our metal objects would end up with a voltage difference to earth, and we could get a shock touching earth and a metal object.

When the power source is a configuration that has a neutral (like the 120/240V split single phase we find in US residences), the power source conductor we choose to bond is the neutral, because that choice minimizes the voltage to earth/metal objects from the other power source conductors.

I keep thinking of equipotential bonding around a pool area as a way to minimize potential voltage difference between earth and neutral so that a breaker will trip if current flows somewhere that it shouldn’t like the water or the area around the pool.

It is not that, and the equipotential bonding around a pool could in theory have no connection to the electrical system. [In practice, with an electrically powered pool pump, I believe it will have a connection to the electrical system.] The purpose of the equipotential bonding is, as the name implies, simply to help ensure that the water and any metal objects around the pool are all at the same potential, so you don't get a shock by touching two of them at once.

Cheers, Wayne

 

[Fred B]

I keep thinking of equipotential bonding around a pool area as a way to minimize potential voltage difference between earth and neutral so that a breaker will trip if current flows somewhere that it shouldn’t like the water or the area around the pool.

Creates a bird on a wire effect. If the pool was to become energized even at a higher voltage level the Equipotential Bonding would prevent electrocution if done correctly. The electrical source could be from any source not necessarily one of the pool circuits or even related to the service that the pool is associated with. As Wayne above indicated everything that is potentially conductive should be bonded together to eliminate or limit the difference of potential between two points of contact.

 

[Bro8898]

Given that we are going to make both of the above bonds, we choose the same power source conductor for each bond. Otherwise our metal objects would end up with a voltage difference to earth, and we could get a shock touching earth and a metal object.

This is good information. Very helpful. Thank you so much

the power source conductor we choose to bond is the neutral, because that choice minimizes the voltage to earth/metal objects from the other power source conductors.

Wouldn’t it be a benefit and a positive thing if there were a voltage potential between a hot conductor and something bonded to neutral like the case of an appliance? Would you want a higher voltage potential between the two to flow enough current to trip the breaker?

 

[Bro8898]

The electrical source could be from any source not necessarily one of the pool circuits or even related to the service that the pool is associated with.

Is there a chance that neutral current flowing through the earth could be an electrical source?

 

[wwhitney]

Wouldn’t it be a benefit and a positive thing if there were a voltage potential between a hot conductor and something bonded to neutral like the case of an appliance?

There is, because there is 120V between hot and neutral.

Would you want a higher voltage potential between the two to flow enough current to trip the breaker?

120V is enough voltage to flow enough current to trip the breaker for a decent fault between a "hot" conductor and the metal case bonded to the EGC (and ultimately to the neutral via the MBJ).

As to whether more voltage would be better, I don't know enough to comment. It would perhaps be more dangerous in some situations if the breaker doesn't trip.

But another reason to use the neutral as our conductor bonded to earth and bonded to non-current carrying components is that most 120V equipment is designed with the expectation that one conductor is grounded. For example, if you change a light bulb that uses a normal Edison style screw-in socket while the light switch is on, and the light fixture is properly installed, the screw shell is the circuit conductor that is grounded, and if you touch it you shouldn't get shocked. The "hot" or ungrounded conductor is connected to the little button at the very bottom of the socket, which is harder to reach.

So if we instead bonded one side of 120V/240V supply to earth, we could only use that leg and the neutral (now at 120V to earth) for our 120V loads. The other leg would be at 240V to earth; we couldn't use the neutral and that leg for 120V loads, as both conductors are ungrounded. The utility power source would be utilized in a less balanced and less efficient way.

Cheers, Wayne

 

[ActionDave]

Is the purpose of a low resistance connection with earth to keep neutral and the earth at as close to zero potential between them as possible? I know you might have explained it before but what are the advantages of this method/idea?

Neutral and earth at zero volts is a byproduct. I think of it more as everybody doing the same thing because it helps make the electrical world work together easier. Lets say you lived out in the country and you bond A phase to ground at your house. The guy a mile down the country road could bond B phase, and somebody else another mile away could bond N. At some point in the evolution of life though, there are going to be more houses and more buildings and there is going to need to be some standardization. We all drive on the right side of the road. We all stick out our right hand to shake. We all bond the Neutral to earth.

I keep thinking of equipotential bonding around a pool area as a way to minimize potential voltage difference between earth and neutral so that a breaker will trip if current flows somewhere that it shouldn’t like the water or the area around the pool.

No. Pool bonding is not the same and has nothing to do with tripping a breaker.

Inside the house we have an Equipment Grounding Conductor to make sure the breaker trips if something gets energized that is not supposed to be energized.

Outside at the pool we establish an equi-potential ground system. We bond all the rebar in the pool shell and all the metal parts of the pool to each other, we put metal mesh in the concrete around the pool and we make sure it is bonded to all the same stuff so if the pool water gets energized nobody gets shocked even if the breaker never trips.

 

[Bro8898]

another reason to use the neutral as our conductor bonded to earth and bonded to non-current carrying components is that most 120V equipment is designed with the expectation that one conductor is grounded.

This is something that I had never thought of. Makes a lot of sense. Appreciate you pointing that out.

The utility power source would be utilized in a less balanced and less efficient way.

This as well. It seems like from what I’m learning here that things have always been done a certain way and efficiency is an important reason that things are the way they are.

 

[Bro8898]

if the pool water gets energized nobody gets shocked even if the breaker never trips.

Thanks for your response. How can that happen exactly? If something energized touches something else then there is a path for current to flow right? What equal potential is everything being bonded together at the pool to be made equal to? Is it the 120v circuit so that there is no difference if there is a fault? If that makes sense.

 

[wwhitney]

Thanks for your response. How can that happen exactly? If something energized touches something else then there is a path for current to flow right? What equal potential is everything being bonded together at the pool to be made equal to? Is it the 120v circuit so that there is no difference if there is a fault? If that makes sense.

Everything is just bonded together so that if anything gets energized (relative to some source), it all gets energized equally.

Current flow requires a difference in potential (=voltage); if everything is at the same potential, there will be no current flow.

Of course, everything has limits; if a big enough voltage source were applied to opposite sides of the pool, the equipotential bonding might not be enough to ensure safety. E.g. if an overhead power line broke and the two ends landed on opposite sides of the pool (probably why IIRC the overhead power line is prohibited).

Cheers, Wayne

 

[ActionDave]

Thanks for your response. How can that happen exactly? If something energized touches something else then there is a path for current to flow right?

In order for current to flow there has to be a difference in potential between two points.

What equal potential is everything being bonded together at the pool to be made equal to? Is it the 120v circuit so that there is no difference if there is a fault? If that makes sense.

Energize the pool to 120V, or 240V or as little as 50V and as long as the water and everything in reach is at the same potential you won't get shocked. Bird on a wire.

 

[Bro8898]

Everything is just bonded together so that if anything gets energized (relative to some source), it all gets energized equally.

This makes sense. I’m going to study it again and knowing this will help.

If you were to place many ground rods in succession and maybe create some sort of bonding of the entire earth from the rod at the house all the way to the rod at the transformer, then you couldn’t get a difference in potential between a hot conductor shorted to the ground rod and ground surrounding it, right? Would that be comparable to equipotential bonding by eliminating touch potential of the ground rod?

 

[Bro8898]

Energize the pool to 120V, or 240V or as little as 50V and as long as the water and everything in reach is at the same potential you won't get shocked. Bird on a wire.

Thank you. I’m going to read back over it with this knowledge. I’m starting to get it. Appreciate this response.

 

[wwhitney]

If you were to place many ground rods in succession and maybe create some sort of bonding of the entire earth from the rod at the house all the way to the rod at the transformer, then you couldn’t get a difference in potential between a hot conductor shorted to the ground rod and ground surrounding it, right? Would that be comparable to equipotential bonding by eliminating touch potential of the ground rod?

Any time current is flowing through a regular (not super-) conductor, the conductor has resistance, and the resistance of the conductor means there will be a voltage difference between the two ends of the conductor. Via V = I * R (Ohm's Law), where R is the resistance of the conductor. So if the conductor is 100' and has a resistance 0.2 ohms (i.e. #12 copper), that would make the voltage difference 2 volts (10 amps * 0.2 ohms).

In your example, you've actually created a circuit that doesn't require any path through earth. The ground rod at the transformer will be bonded to the secondary neutral, I believe, and since you've bonded all the ground rods together, and you shorted the ungrounded (hot) conductor to one of those ground rods, there's a wire path to create a circuit. You've just referenced that wire to earth in many places. [And so to the extent that the path from ground rod to ground through earth is viable, it will carry some current in parallel with the wire path, in proportion to its resistance vs the wire's resistance. If that resistance is say 200 ohms, then it will carry 1/1000 of the current, or 10 milliamps when the bonding conductor is carrying 10 amps.]

A more interesting example is to not have the bonding conductor present, so the earth path is the only path. With 200 ohms for the earth path, and if we ignore the resistance of the wires, and we impose 120V from the house ground rod to the transformer ground rod, we should get a current of 0.6A amps. If we hook a voltmeter up between the two ground rods, we'll get a measurement of 120V. [If those other wires we ignore had a resistance of 1 ohm, then we'd really get (200/201) * 120V, which is basically 120V, which is why I'm ignoring the wires here.]

But what if we check the voltage between the ground rod 1/4 of the way between the house and the transformer? If the resistance from the ground path is primarily due to the earth itself, and not the resistance of the interface between the earth and the rod, we'd get a measurement of 30V (or 90V, depending on which end rod you measure against). While if the resistance is primarily between each rod and "bulk earth", with bulk earth having very low resistance (once you get away from the rod, there are many, many different paths available for current through the volume of earth separating the rods), then you'd expect to get around 60V (assuming each rod has about the same resistance to bulk earth).

I am fairly sure, but not certain, that the latter is typical.

Cheers, Wayne

 

[Bro8898]

If that resistance is say 200 ohms, then it will carry 1/1000 of the current, or 10 milliamps when the bonding conductor is carrying 10 amps.

That sounds like a lot although the conductor is still the lowest resistance path. But this reminds me of my original question where we are in parallel with the circuit and not in series.

A more interesting example is to not have the bonding conductor present, so the earth path is the only path. With 200 ohms for the earth path, and if we ignore the resistance of the wires, and we impose 120V from the house ground rod to the transformer ground rod, we should get a current of 0.6A amps.

Is this the same idea behind utility companies making many connections to the earth around high voltage lines and power stations? If a line were to touch the ground they would want enough current to flow to trip the breaker, right?

you'd expect to get around 60V (assuming each rod has about the same resistance to bulk earth).

I’m starting to see how I was off regarding equipotential bonding. I need to study in that area. How do we reduce touch potential and step potential? Is equipotential bonding even related to reducing or eliminating touch potential?

Thank you so much Wayne.

 

[ActionDave]

That sounds like a lot although the conductor is still the lowest resistance path. But this reminds me of my original question where we are in parallel with the circuit and not in series.

Is this the same idea behind utility companies making many connections to the earth around high voltage lines and power stations? If a line were to touch the ground they would want enough current to flow to trip the breaker, right?

We bond one conductor to earth because everybody has access to earth and it gives a zero volt reference point. We bond the neutral most of the time because that is the most sensible point on the system to bond. There are buildings that have a corner grounded system so instead of bonding a neutral B phase is bonded. There are delta utility power systems and customer power systems that are ungrounded, none of the power lines are bonded to the earth, but these have issues that make their use rare.

I’m starting to see how I was off regarding equipotential bonding. I need to study in that area. How do we reduce touch potential and step potential? Is equipotential bonding even related to reducing or eliminating touch potential?

Equipotential bonding is all about reducing touch potential. If everything is at the same potential no current can flow. That's why a bird can sit on an uninsulated power wire that is 12,000 volts and not get shocked. Pools are one place that uses equipotential bonding, agriculture facilities that house livestock are another. You can do it in someone's backyard or around a barn but you can't make the whole 500 square mile county an equi-potential plane.