grounding grid calculations
- Thread starter alberto
- Start date
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- Location
- Massachusetts
Re: grounding grid calculations
The power companies in this area will typically ask for one 3/4" x 10' copper clad ground rod about 18" off of each corner of the pad.
These 4 rods will be connected in a loop with 4/0 bare cad welded to the rods.
Then a 4/0 bare will be cad welded from the right and left sides of the 4/0 loop and brought into the wiring compartment of the transformer.
This is pretty much standard in this area.
The power company?
The power companies in this area will typically ask for one 3/4" x 10' copper clad ground rod about 18" off of each corner of the pad.
These 4 rods will be connected in a loop with 4/0 bare cad welded to the rods.
Then a 4/0 bare will be cad welded from the right and left sides of the 4/0 loop and brought into the wiring compartment of the transformer.
This is pretty much standard in this area.
peter d
Senior Member
- Location
- New England
Re: grounding grid calculations
Why do utilities spec such massive copper and ground rods? Lightning protection?
I'm assuming here (bad idea), but wouldn't a single ground rod and smaller conductor be enough to blow a cutout, assuming a high side to ground or high to low side fault?
Why do utilities spec such massive copper and ground rods? Lightning protection?
I'm assuming here (bad idea), but wouldn't a single ground rod and smaller conductor be enough to blow a cutout, assuming a high side to ground or high to low side fault?
- Location
- Massachusetts
Re: grounding grid calculations
Maybe Charlie can answer, I always assumed it was for durability.
It is hard to damage a 4/0 bare that is cad welded to a 3/4 rod.
It is also likely to get low resistance as without having to dig up the surrounding area.
Maybe Charlie can answer, I always assumed it was for durability.
It is hard to damage a 4/0 bare that is cad welded to a 3/4 rod.
It is also likely to get low resistance as without having to dig up the surrounding area.
Re: grounding grid calculations
1.Step rise potential differences. The grid forms an equipotential ground plane in which all equipment in the sub/gen yard is bonded too. The step potential (distance between you feet) difference is enough to kill during a high voltage fault
2. Utilities uses earth as a return conductor.
Two reason.
1.Step rise potential differences. The grid forms an equipotential ground plane in which all equipment in the sub/gen yard is bonded too. The step potential (distance between you feet) difference is enough to kill during a high voltage fault
2. Utilities uses earth as a return conductor.
peter d
Senior Member
- Location
- New England
Re: grounding grid calculations
Thanks Dereck. I learn something new every day.
Thanks Dereck. I learn something new every day.
Could you elaborate on this some more?
- Location
- Massachusetts
Re: grounding grid calculations
Here is a site that explains using the earth as a conductor, however I do know if this is used at all in the US.
SWER
I think dereckbc may have been taking about using the earth as fault clearing conductor.
This works at the voltage levels the POCO runs, it will not work for us at our voltages.
Here is a site that explains using the earth as a conductor, however I do know if this is used at all in the US.
SWER
I think dereckbc may have been taking about using the earth as fault clearing conductor.
This works at the voltage levels the POCO runs, it will not work for us at our voltages.
Re: grounding grid calculations
Alberto, have you tried IEEE Green Book for a start. The application you are working with is more in line with NESC rather than NEC. All the info I have on grids is from A utility engineering practices and not availible to the public. Hopefully Charlie E will pick up and offer some more info.
Alberto, have you tried IEEE Green Book for a start. The application you are working with is more in line with NESC rather than NEC. All the info I have on grids is from A utility engineering practices and not availible to the public. Hopefully Charlie E will pick up and offer some more info.
Re: grounding grid calculations
PeterD & Kiloamp7, all primary and secondary distribution systems in the US to my knowledge use a mutli-grounded neutral (MGN), there may be exceptions, and perhaps Charlie can elaborate.
IMO one of the main purpose of the MGN is to carry a portion of neutral load current, as a cost saving measure. You do not have to run a full size conductor. Fairly simple ohm's law if you think about it. What would the impedance of several thousand feet of isolated cable compaired to an paralleled earth return path. The parallel resistance of the MGN is much lower than say an isolated neutral conductor.
There are of course other reasons to MGN such as minimizing voltage drop along the length for safety of utility personnel, lightning protection if ran above phase conductors, etc. Finally earth is used as a fault clearing path @ HV and the MGN aids in this function.
As Bob mentioned there are systems in the US, Utah and Alaska to my knowledge, that uses earth as the only return path called SWER. In that system there is no neutral conductor for a return, only earth. The only purpose of SWER is to eliminate the cost of the neutral conductor all together. SWER is used in remote sparsly populated areas where cost are prohibitive otherwise.
Sorry for the hyjack Alberto
PeterD & Kiloamp7, all primary and secondary distribution systems in the US to my knowledge use a mutli-grounded neutral (MGN), there may be exceptions, and perhaps Charlie can elaborate.
IMO one of the main purpose of the MGN is to carry a portion of neutral load current, as a cost saving measure. You do not have to run a full size conductor. Fairly simple ohm's law if you think about it. What would the impedance of several thousand feet of isolated cable compaired to an paralleled earth return path. The parallel resistance of the MGN is much lower than say an isolated neutral conductor.
There are of course other reasons to MGN such as minimizing voltage drop along the length for safety of utility personnel, lightning protection if ran above phase conductors, etc. Finally earth is used as a fault clearing path @ HV and the MGN aids in this function.
As Bob mentioned there are systems in the US, Utah and Alaska to my knowledge, that uses earth as the only return path called SWER. In that system there is no neutral conductor for a return, only earth. The only purpose of SWER is to eliminate the cost of the neutral conductor all together. SWER is used in remote sparsly populated areas where cost are prohibitive otherwise.
Sorry for the hyjack Alberto
charlie
Senior Member
- Location
- Indianapolis
Re: grounding grid calculations
Don't you realize that approximately 90% of the "dirty power" is caused by improper grounding on the customer side of the meter? Anyway, the SWER system (as bad as it is) doesn't cause dirty power but is does increase the stray voltage since the return current path is through the earth. HMMM . . . I wonder why it is not called stray current? I know, it is noticed by using volt meters.
I have tried to stay away from this one ever since the SWER distribution method was mentioned. I absolutely detest that method of service to the public especially in the rural areas where stray voltage is a real problem. The problem is that I couldn't let that comment go.
Don't you realize that approximately 90% of the "dirty power" is caused by improper grounding on the customer side of the meter? Anyway, the SWER system (as bad as it is) doesn't cause dirty power but is does increase the stray voltage since the return current path is through the earth. HMMM . . . I wonder why it is not called stray current? I know, it is noticed by using volt meters.
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