ground rods
- Thread starter mjmelect
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russ
Senior Member
- Location
- Burbank IL
Re: ground rods
He must be reading 250.24(A)(2).
I don't see any explanation as to what kind of transformer it refers to. If you take it one way, you could say every service needs an outside ground rod, because it is fed by a poco transformer that is outside.
He must be reading 250.24(A)(2).
I don't see any explanation as to what kind of transformer it refers to. If you take it one way, you could say every service needs an outside ground rod, because it is fed by a poco transformer that is outside.
friebel
Senior Member
- Location
- Pennsville, N.J.
Re: ground rods
The main purpose of a driven ground-rod at the main service is for lightning protection, and for high voltage surges.With that said, I would not want my grounding electrode inside of a building.
I have never seen a driven ground-rod inside of a building. It does state in Section 250.24(A)(2) Outdoor Transformer, to install the rod outside the building.
The main purpose of a driven ground-rod at the main service is for lightning protection, and for high voltage surges.With that said, I would not want my grounding electrode inside of a building.
I have never seen a driven ground-rod inside of a building. It does state in Section 250.24(A)(2) Outdoor Transformer, to install the rod outside the building.
russ
Senior Member
- Location
- Burbank IL
Re: ground rods
I took this rod to be the supplemental electrode.
I took this rod to be the supplemental electrode.
Re: ground rods
Looking at the 2002 NEC Hard cover Illustration... It seems to me that they are calling for the "additional grounding electrode" to be connected outside the bldg some where near the transformer. The supplemental grounding electrode at the service is also shown outside but the NEC IS NOT SAYING that the supplemental grounding electrode MUST be placed outside of the building. NEC 250.24(2) Exhibit 250.9
So, What I'm reading, allows one to place the ground rod inside the building as long as the transformer is also grounded on the secondary side outside of the building.
Looking at the 2002 NEC Hard cover Illustration... It seems to me that they are calling for the "additional grounding electrode" to be connected outside the bldg some where near the transformer. The supplemental grounding electrode at the service is also shown outside but the NEC IS NOT SAYING that the supplemental grounding electrode MUST be placed outside of the building. NEC 250.24(2) Exhibit 250.9
So, What I'm reading, allows one to place the ground rod inside the building as long as the transformer is also grounded on the secondary side outside of the building.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: ground rods
For best performance the ground rods should be outside the building, away from the roof line, to be in a wet area. But in the basement is OK, I don't see how 250.24 applies to your installation, assuming this is a electrical service fed from a poco transformer.
For best performance the ground rods should be outside the building, away from the roof line, to be in a wet area. But in the basement is OK, I don't see how 250.24 applies to your installation, assuming this is a electrical service fed from a poco transformer.
Re: ground rods
250.53 Grounding Electrode System Installation.
(A) Rod, Pipe, and Plate Electrodes. Where practicable, rod, pipe, and plate electrodes shall be embedded below permanent moisture level. Rod, pipe, and plate electrodes shall be free from nonconductive coatings such as paint or enamel.
IOW the deeper the rod is driven the better. Starting below ground level is one way to get the rod to be "below permanent moisture level".
The providing utilities transformer is not governed by the NEC. Only a customer owned transformer on the customers side of the demarcation point would require a ground rod to be provided outside the building. The grounding of the utilities transformer is the exclusive province of the Authority Having Jurisdiction for the enforcement of the National Electrical Safety Code. YMMV
--
Tom Horne
Actually I think you will get better performance by driving the rod inside the basement. I base that belief on the language in
250.53 Grounding Electrode System Installation.
(A) Rod, Pipe, and Plate Electrodes. Where practicable, rod, pipe, and plate electrodes shall be embedded below permanent moisture level. Rod, pipe, and plate electrodes shall be free from nonconductive coatings such as paint or enamel.
IOW the deeper the rod is driven the better. Starting below ground level is one way to get the rod to be "below permanent moisture level".
The providing utilities transformer is not governed by the NEC. Only a customer owned transformer on the customers side of the demarcation point would require a ground rod to be provided outside the building. The grounding of the utilities transformer is the exclusive province of the Authority Having Jurisdiction for the enforcement of the National Electrical Safety Code. YMMV
--
Tom Horne
grandpapastu
Member
Re: ground rods
Ground rods may provide and effective fault current path
Hello,
I have a subject of interest that I would like to address please. Pertaining to Mike Holt's Video & Graphics site: 'Ground Rod Does Not Provide Any Protection From Electric Shock (2 of 2), the statement made under this site: ?Electrons do not take path of least resistance and a ground rod does not provide an effective fault current path,? is questionable to me.
Does this statement imply that it is believed that some understand electric current to take the path of least resistance only and therefore leave them unaffected if they get into the circuit?
(1) If this were true, then why does a 100 watt light bulb draw more current (but not the only current) than a 60 watt light bulb when it is connected in parallel with the 60 watt light bulb in a 120 volt two-wire single-phase circuit?
(2) Why then, in a parallel circuit:
Et=E1=E2=E3=En
It=I1+I2+I3+In
Rt=1/(1/R1+1/R2)
Electric current (the flow of electrons) generated by an electromotive force seeks the path of least resistance to ground, not the path of least resistance only. In fact, electric current seeks any conductive path to ground that may turn out to be a designed or accidental parallel, series, or parallel-series path of electron flow.
A dishwasher homerun circuit at an emergency residential service call, Peachtree City, GA assigned to me started an attic fire.
A very high impedance - nearly open - public utility provided underground service lateral grounded conductor (R3) caused system operating current to seek a ground return path by means of and through the 12 AWG equipment grounding conductor of the 20A dishwasher branch circuit homerun (R2) from the 150A 120/240volt main breaker panel ground buss to the bonded frame of the dishwasher and it's connected copper plumbing to earth ground.
A single ground rod and it?s GEC (R1) tapped to the service grounded conductor at the meter base-service point was the systems only grounding electrode.
The metal plumbing of the house was not bonded as part of the grounding electrode system.
The three wire SEU service entrance grounded conductor connected from the MBO panel to the grounding electrode (R1) at the service point, and the dishwasher circuit equipment grounding conductor from the MBO panel to the underground water plumbing (R2) formed a parallel path for current flow to ground that was in series with the service lateral grounded conductor (R3).
(4) In this case could not two ground rods (R1) driven with 8' earth contact driven no less than 8' apart provide significantly lower impedance to ground than the single existing ground rod which was driven more than 20' away from the service point? Without a doubt the existing grounding electrode was also providing only a very high impedance to ground, as they usually will in time, because of changing soil conditions, ground rod corrosion, oxidation of GEC connections, etc.
(5) With a low impedance path provided by a repaired service lateral grounded conductor (R3) back to the transformer pad, would not the majority of the system operating current be on that conductor and any other current reduced to zero or a negligible value? E/R=I
(6) Bonding the water pipes correctly from the service point with a correctly sized GEC would have reduced the current that was present over the dishwasher circuit equipment grounding conductor and connected plumbing to a smaller value right?
Concerning your Video & Graphics site here considered that pictures a man getting shocked by an energized light pole, I calculated that he would realize about 80mA across his heart. The 80mA would be sufficient to prove fatal. If a ground rod were not used to ground the light pole, then the man would have been the only available path to ground and the current felt across his heart would have been much greater increasing the probability of death.
Stuart.
Ground rods may provide and effective fault current path
Hello,
I have a subject of interest that I would like to address please. Pertaining to Mike Holt's Video & Graphics site: 'Ground Rod Does Not Provide Any Protection From Electric Shock (2 of 2), the statement made under this site: ?Electrons do not take path of least resistance and a ground rod does not provide an effective fault current path,? is questionable to me.
Does this statement imply that it is believed that some understand electric current to take the path of least resistance only and therefore leave them unaffected if they get into the circuit?
(1) If this were true, then why does a 100 watt light bulb draw more current (but not the only current) than a 60 watt light bulb when it is connected in parallel with the 60 watt light bulb in a 120 volt two-wire single-phase circuit?
(2) Why then, in a parallel circuit:
Et=E1=E2=E3=En
It=I1+I2+I3+In
Rt=1/(1/R1+1/R2)
Electric current (the flow of electrons) generated by an electromotive force seeks the path of least resistance to ground, not the path of least resistance only. In fact, electric current seeks any conductive path to ground that may turn out to be a designed or accidental parallel, series, or parallel-series path of electron flow.
A dishwasher homerun circuit at an emergency residential service call, Peachtree City, GA assigned to me started an attic fire.
A very high impedance - nearly open - public utility provided underground service lateral grounded conductor (R3) caused system operating current to seek a ground return path by means of and through the 12 AWG equipment grounding conductor of the 20A dishwasher branch circuit homerun (R2) from the 150A 120/240volt main breaker panel ground buss to the bonded frame of the dishwasher and it's connected copper plumbing to earth ground.
A single ground rod and it?s GEC (R1) tapped to the service grounded conductor at the meter base-service point was the systems only grounding electrode.
The metal plumbing of the house was not bonded as part of the grounding electrode system.
The three wire SEU service entrance grounded conductor connected from the MBO panel to the grounding electrode (R1) at the service point, and the dishwasher circuit equipment grounding conductor from the MBO panel to the underground water plumbing (R2) formed a parallel path for current flow to ground that was in series with the service lateral grounded conductor (R3).
(4) In this case could not two ground rods (R1) driven with 8' earth contact driven no less than 8' apart provide significantly lower impedance to ground than the single existing ground rod which was driven more than 20' away from the service point? Without a doubt the existing grounding electrode was also providing only a very high impedance to ground, as they usually will in time, because of changing soil conditions, ground rod corrosion, oxidation of GEC connections, etc.
(5) With a low impedance path provided by a repaired service lateral grounded conductor (R3) back to the transformer pad, would not the majority of the system operating current be on that conductor and any other current reduced to zero or a negligible value? E/R=I
(6) Bonding the water pipes correctly from the service point with a correctly sized GEC would have reduced the current that was present over the dishwasher circuit equipment grounding conductor and connected plumbing to a smaller value right?
Concerning your Video & Graphics site here considered that pictures a man getting shocked by an energized light pole, I calculated that he would realize about 80mA across his heart. The 80mA would be sufficient to prove fatal. If a ground rod were not used to ground the light pole, then the man would have been the only available path to ground and the current felt across his heart would have been much greater increasing the probability of death.
Stuart.
Re: ground rods
Q1. Does this statement imply that it is believed that some understand electric current to take the path of least resistance only and therefore leave them unaffected if they get into the circuit?
A1. Some do belive current only takes the path of least resistance. Truth is current takes all paths availible to it. That is what Mike is trying to point out.
Q2. If this were true, then why does a 100 watt light bulb draw more current (but not the only current) than a 60 watt light bulb when it is connected in parallel with the 60 watt light bulb in a 120 volt two-wire single-phase circuit?
A2. Because current equals the voltage applied acrross the load divided by the resistance of the load.
Q3. Electric current (the flow of electrons) generated by an electromotive force seeks the path of least resistance to ground, not the path of least resistance only. In fact, electric current seeks any conductive path to ground that may turn out to be a designed or accidental parallel, series, or parallel-series path of electron flow.
A3. Inaccurate statement. current only seeks a path back to the source, not ground. For NEC compliant systems ground has nothing to do with any circuit or fault operation. It is forbidden to use earth as a planned fault or circuit path.
Q4. In this case could not two ground rods (R1) driven with 8' earth contact driven no less than 8' apart provide significantly lower impedance to ground than the single existing ground rod which was driven more than 20' away from the service point?
A4. Doubtfull, that is not it's purpose. You would have to have an GES impedance less than one ohm to replace the grounded conductor circuit conductor.
[ May 10, 2004, 06:44 PM: Message edited by: dereckbc ]
Q1. Does this statement imply that it is believed that some understand electric current to take the path of least resistance only and therefore leave them unaffected if they get into the circuit?
A1. Some do belive current only takes the path of least resistance. Truth is current takes all paths availible to it. That is what Mike is trying to point out.
Q2. If this were true, then why does a 100 watt light bulb draw more current (but not the only current) than a 60 watt light bulb when it is connected in parallel with the 60 watt light bulb in a 120 volt two-wire single-phase circuit?
A2. Because current equals the voltage applied acrross the load divided by the resistance of the load.
Q3. Electric current (the flow of electrons) generated by an electromotive force seeks the path of least resistance to ground, not the path of least resistance only. In fact, electric current seeks any conductive path to ground that may turn out to be a designed or accidental parallel, series, or parallel-series path of electron flow.
A3. Inaccurate statement. current only seeks a path back to the source, not ground. For NEC compliant systems ground has nothing to do with any circuit or fault operation. It is forbidden to use earth as a planned fault or circuit path.
Q4. In this case could not two ground rods (R1) driven with 8' earth contact driven no less than 8' apart provide significantly lower impedance to ground than the single existing ground rod which was driven more than 20' away from the service point?
A4. Doubtfull, that is not it's purpose. You would have to have an GES impedance less than one ohm to replace the grounded conductor circuit conductor.
[ May 10, 2004, 06:44 PM: Message edited by: dereckbc ]
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