lets say you have a 200a breaker under a meter on a utility pole.the 200 amp breaker is the first disconnecting means and the neutral is bonded to the ground wire going down the pole.the code states that if the neutral is sized properly from this disconnect to the main lug subpanel located in the garage,and there are no metallic objects connecting the two, a grounding conductor need not be pulled.the neutral is bonded to the subpanel once again at the garage and a ground rod driven at the garage.why then would anyone pull a grounding conductor in with the service feeders if they didn't need to? to me it would be a waste of money.
GROUNDING A SERVICE
- Thread starter jap2525
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luke warmwater
Senior Member
Re: GROUNDING A SERVICE
So when the owner decides to install a phone and/or a tv line, you're covered.
So when the owner decides to install a phone and/or a tv line, you're covered.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Re: GROUNDING A SERVICE
Jap2525, Some jurisdictions do not allow this method, Washington State for example, dont know of any others though. Luke, can you elaborate?
~Electro
Jap2525, Some jurisdictions do not allow this method, Washington State for example, dont know of any others though. Luke, can you elaborate?
~Electro
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: GROUNDING A SERVICE
Jap2525
First if you have the 200 amp main service breaker/disconnect at the pole and a main lug panel at the garage this panel at the garage would have to have the rating of the circuit feeding it. 408.16(A) exception 1. It would also have to have a disconnect or a main breaker if it has more than 6 breaker handles. 225.33(A)
And now for your question 250.32(B)(2) does allow 1. where there is no EGC ran with the supply conductors, and
2. where there is no other metallic paths bonded to the grounding system in both buildings or structures involved.
You can be allowed to bond the grounding electrode conductor, the Equipment grounding conductors, to the grounded neutral conductor.
The problem with this method is:
1. the problem with what Luke said: future installs of metallic paths.
2. If there is a great distance between the service and this building there could be a voltage drop on the neutral conductor and this voltage could be imposed upon all the grounding to earth. This could pose a shock hazard especially if there was a ground fault or hot to neutral short while someone was touching something that is bonded to this neutral and standing bare foot on the Earth or the concrete floor of the building.
Jap2525
First if you have the 200 amp main service breaker/disconnect at the pole and a main lug panel at the garage this panel at the garage would have to have the rating of the circuit feeding it. 408.16(A) exception 1. It would also have to have a disconnect or a main breaker if it has more than 6 breaker handles. 225.33(A)
And now for your question 250.32(B)(2) does allow 1. where there is no EGC ran with the supply conductors, and
2. where there is no other metallic paths bonded to the grounding system in both buildings or structures involved.
You can be allowed to bond the grounding electrode conductor, the Equipment grounding conductors, to the grounded neutral conductor.
The problem with this method is:
1. the problem with what Luke said: future installs of metallic paths.
2. If there is a great distance between the service and this building there could be a voltage drop on the neutral conductor and this voltage could be imposed upon all the grounding to earth. This could pose a shock hazard especially if there was a ground fault or hot to neutral short while someone was touching something that is bonded to this neutral and standing bare foot on the Earth or the concrete floor of the building.
- Location
- Illinois
- Occupation
- retired electrician
Re: GROUNDING A SERVICE
See 225.31 and .32
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: GROUNDING A SERVICE
The phone and TV systems are bonded to the neutral at both ends, street and house, creating a smaller parallel path to neutral. My question: if this occurs, and the neutral opens, then your phone/TV conductors will be damaged. How do people get injured from this scenario? The redundant bonding of the phone/TV's spelled their demise, but that path to neutral will likely open as well.
I'm not fluent in voltage drop, so I really can't visualize what you're saying, Wayne.
Re: GROUNDING A SERVICE
Its not a failure of the wire doing its job -- the 4th grounding wire is doing a different job.
If a 100A 3-wire feeder has 4 volts of drop along its neutral (which is bonded to the ground electrodes at each end), then there will be current flowing through the earth as the 4 volts also finds it way back to the service neutral through the dirt. This won't hurt you or me, but can bother animals. A broken/open/corroded feeder neutral wire will also energize the dirt around the ground electrode at 120V, which would be bad.
If you have the same feeder, but with a 4th separate grounding wire, then there is no voltage difference between the service and the remote building ground electrode systems, and no current flows. The voltage drop in the neutral is isolated from the grounding system. If the neutral breaks, the neutral return path voltage is not imposed on the earth.
Its not a failure of the wire doing its job -- the 4th grounding wire is doing a different job.
If a 100A 3-wire feeder has 4 volts of drop along its neutral (which is bonded to the ground electrodes at each end), then there will be current flowing through the earth as the 4 volts also finds it way back to the service neutral through the dirt. This won't hurt you or me, but can bother animals. A broken/open/corroded feeder neutral wire will also energize the dirt around the ground electrode at 120V, which would be bad.
If you have the same feeder, but with a 4th separate grounding wire, then there is no voltage difference between the service and the remote building ground electrode systems, and no current flows. The voltage drop in the neutral is isolated from the grounding system. If the neutral breaks, the neutral return path voltage is not imposed on the earth.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: GROUNDING A SERVICE
Thank's Mark that was a good response. George a conductor has to have current on it to have a voltage drop and If the 4th grounding conductor is not carrying any current as it's not suppose to it should be at the same potential that the main grounding electrode at the service is at. And yes the same apply's for the service between the pole transformer and the house but the utility's don't want to run a 4th conductor and they have more power to say NO!
well they do have more power.
Megawatts of Megawatts of it.
Most phone lines don't have a bonded conductor unless they install a shielded cable.
Thank's Mark that was a good response. George a conductor has to have current on it to have a voltage drop and If the 4th grounding conductor is not carrying any current as it's not suppose to it should be at the same potential that the main grounding electrode at the service is at. And yes the same apply's for the service between the pole transformer and the house but the utility's don't want to run a 4th conductor and they have more power to say NO!
well they do have more power.
Megawatts of Megawatts of it.
Most phone lines don't have a bonded conductor unless they install a shielded cable.
paul
Senior Member
- Location
- Snohomish, WA
Re: GROUNDING A SERVICE
Nobody has yet addressed the situation that I have in my own neighborhood. Code requires that all houses bond to the metal water pipe system. My development was built around 1972 and all the houses here are galvanized pipe and each house is fed with galvanized pipe to the house. So...if all the houses that are on the same transformer I'm on, of which there are four, then we have parallel paths back to the transformer should a neutral break. If we follow the logic for separate neutral and grounds, then the POCO should be grounding their transformers and supplying all services with a separate ground. This way we would never have any stray neutral current finding alternate paths back to their source, because the neuts would all be isolated.
But there is also another problem. The 7200/12470 primary that serves the residential areas uses a neutral. This neutral is grounded at each pole by the bare #6 that runs to the copper plate at the bottom of the pole. It's also used on all the transformers that reduce your power down to 120/240. I now have another source of stray voltage. The phone and cable company can also be seen using the ground at the pole, hence another source back.
Anybody ever been inside a telephone CO? They ground to the AC neutral at the main and run it to their MGB (Master Ground Bar) in the office. They also grab building steel and water. Now we have even more parallel paths.
So I sit here and wonder how running separate grounds is going to work if you only use it in one small part of electrical distribution, when the industry doesn't adopt the same standards across the board. Either allow it, or don't allow it.
Nobody has yet addressed the situation that I have in my own neighborhood. Code requires that all houses bond to the metal water pipe system. My development was built around 1972 and all the houses here are galvanized pipe and each house is fed with galvanized pipe to the house. So...if all the houses that are on the same transformer I'm on, of which there are four, then we have parallel paths back to the transformer should a neutral break. If we follow the logic for separate neutral and grounds, then the POCO should be grounding their transformers and supplying all services with a separate ground. This way we would never have any stray neutral current finding alternate paths back to their source, because the neuts would all be isolated.
But there is also another problem. The 7200/12470 primary that serves the residential areas uses a neutral. This neutral is grounded at each pole by the bare #6 that runs to the copper plate at the bottom of the pole. It's also used on all the transformers that reduce your power down to 120/240. I now have another source of stray voltage. The phone and cable company can also be seen using the ground at the pole, hence another source back.
Anybody ever been inside a telephone CO? They ground to the AC neutral at the main and run it to their MGB (Master Ground Bar) in the office. They also grab building steel and water. Now we have even more parallel paths.
So I sit here and wonder how running separate grounds is going to work if you only use it in one small part of electrical distribution, when the industry doesn't adopt the same standards across the board. Either allow it, or don't allow it.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: GROUNDING A SERVICE
Mark, Wayne, thanks. That's a little clearer.
The part that leaves me confused is, how does that four volts magically find the ground without us intentionally grounding the system? If the neutrals and grounds were seperate in a subpanel, without grounding electrodes installed, what happens to the four volts?
This concept is new to me.
Mark, Wayne, thanks. That's a little clearer.
The part that leaves me confused is, how does that four volts magically find the ground without us intentionally grounding the system? If the neutrals and grounds were seperate in a subpanel, without grounding electrodes installed, what happens to the four volts?
This concept is new to me.
Re: GROUNDING A SERVICE
With a separate grounding wire (4 wire feeder), the 4 volts is only on the neutral which is isolated from the grounding system. Nothing happens to it, it is just a side effect of the resistance of the neutral. Its the same reason you may only get 117V from a power outlet whereas the supply is 125V -- it is lost as heat in wire resistance and this costs you some voltage. So now you're probably wondering why we ground things at all, since it is a parallel conductor that seems to always be around.
If we didn't ground our house main service equipment or the subpanel, then this voltage drop on a 3-wire feeder neutral wouldn't take a path through the earth. I believe most electrical systems would be safer (from a shock point of view) if they weren't grounded at all. But that would make them more susceptable to lightning and the degradation that causes.
Since the grid distribution system is grounded, it makes things safer for you and I to have our houses regrounded too. However, I can't think of a good example of why its bad to have the distribution grounded but not your house. Perhaps houses (structures) are grounded too solely for lightning protection, as the transformer earth ground is probably too far away to do you much good for lightning protection.
[ April 26, 2005, 04:47 PM: Message edited by: suemarkp ]
With a separate grounding wire (4 wire feeder), the 4 volts is only on the neutral which is isolated from the grounding system. Nothing happens to it, it is just a side effect of the resistance of the neutral. Its the same reason you may only get 117V from a power outlet whereas the supply is 125V -- it is lost as heat in wire resistance and this costs you some voltage. So now you're probably wondering why we ground things at all, since it is a parallel conductor that seems to always be around.
If we didn't ground our house main service equipment or the subpanel, then this voltage drop on a 3-wire feeder neutral wouldn't take a path through the earth. I believe most electrical systems would be safer (from a shock point of view) if they weren't grounded at all. But that would make them more susceptable to lightning and the degradation that causes.
Since the grid distribution system is grounded, it makes things safer for you and I to have our houses regrounded too. However, I can't think of a good example of why its bad to have the distribution grounded but not your house. Perhaps houses (structures) are grounded too solely for lightning protection, as the transformer earth ground is probably too far away to do you much good for lightning protection.
[ April 26, 2005, 04:47 PM: Message edited by: suemarkp ]
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Re: GROUNDING A SERVICE
That's kinda shaky, but I understand. Thanks for your help!
That's kinda shaky, but I understand. Thanks for your help!
Re: GROUNDING A SERVICE
There is so much talk now about eliminating parallel ground paths,yet most specs in our area require a ground wire to be pulled in and bonded to each box with a device in it even though emt conduit is being ran.Is this not creating a parallel ground path in a sense,the conduit being one and the ground wire being the second.
There is so much talk now about eliminating parallel ground paths,yet most specs in our area require a ground wire to be pulled in and bonded to each box with a device in it even though emt conduit is being ran.Is this not creating a parallel ground path in a sense,the conduit being one and the ground wire being the second.
Re: GROUNDING A SERVICE
The terminologies must be used correctly.
Of course the EMT with redundant green/bare conductor is a parallel equipment ground path.
That is all well & good & NEC complient.
Your original question is actually dealing with a separate issue,IMO.
Unless it is right there at the POCO service & the service equipment, then an equipment ground path (other than the grounded conductor) should be installed.
Now I'm starting to question how I worded that.
The terminologies must be used correctly.
Of course the EMT with redundant green/bare conductor is a parallel equipment ground path.
That is all well & good & NEC complient.
Your original question is actually dealing with a separate issue,IMO.
Unless it is right there at the POCO service & the service equipment, then an equipment ground path (other than the grounded conductor) should be installed.
Now I'm starting to question how I worded that.
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