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Old 2-Dec-2013, 9:45 PM   #21
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changing methods

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The changing thinking and information and the "Correctness" of grounding.

There is and was a time when separate ground rods were the Correct action.

There is and was a time when cold water pipes were the correct action to take.

There is and was a time when connecting to the electric service ground was a Big No , do not do it.

The Correct thinking changes over time.
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Old 2-Dec-2013, 10:38 PM   #22
GroundUrMast
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There is and was a time when separate ground rods were the Correct action.
Yes, then it was realized that fault current flowing in one grounding system could raise the voltage to dangerous levels relative to the separate ground system. So the current codes call for bonding to prevent dangerous voltage differences from occurring.

Examples:
Quote:
250.4 General Requirements for Grounding and Bonding.
The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.
(A) Grounded Systems.
(1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

FPN: An important consideration for limiting the imposed voltage is the routing of bonding and grounding conductors so that they are not any longer than necessary to complete the connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops are avoided

250.50 Grounding Electrode System. All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used.

(NEC - 2008 edition)
Quote:
There is and was a time when cold water pipes were the correct action to take.
Yes, and in the case of metal pipe that is buried in earth for 10' or more, that is still a grounding electrode and needs to be bonded to any other grounding electrodes.

Example:
Quote:
250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
(1) Metal Underground Water Pipe. A metal underground water pipe in direct contact with the earth for 3.0 m (10 ft) or more (including any metal well casing bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joints or insulating pipe) to the points of connection of the grounding electrode conductor and the bonding conductors. Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall not be used as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system.

(NEC - 2008 edition)
Quote:
There is and was a time when connecting to the electric service ground was a Big No , do not do it.
Perhaps you can cite examples of that... was that an old version of the NEC, a local interpretation/modification by a city or state or a lay persons opinion?
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Old Today, 2:20 AM   #23
OTAFAN
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Do not neglect the part about connecting the new ground rod to your service entrance ground. That insures that the two ground rods maintain the same electric potential and prevents some serious issues from occurring with voltage differentials that could cause significant problems.

Please explain specifically what "some serious issues" could be. And what you mean by "electric potential." Any past examples of what has gone wrong when you don't follow your recommendations above that you could think of, would be helpful too.

I think this would help many people understand better in "real time" what issues you are raising concern about here. It would help translate code issues into everyday life.

Thanks Tim and GroundUrMast for your input!

(The above quote was from a current thread on reception issues and I was directed by Moderator GroundUrMast to post it here along with my questions.)
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Old Today, 4:47 AM   #24
GroundUrMast
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OTAFAN, Thanks for inviting more discussion about this...

Electrical potential is simply the voltage difference between two objects or points in an electrical circuit.

The purpose of grounding is to provide a conductive path for current between the ‘grounded’ object and earth. In the early history of electrical distribution systems, grounding was not common. As a result, those early systems experienced problems with static build up and so would experience insulation break-down and the subsequent damage to distribution equipment and/or customer equipment when the static voltage rose too high. By connecting one of the distribution conductors to earth, the voltage difference can not rise to damaging levels on the rest of the system. An antenna system would be at similar risk if it's not grounded. The modern day electrical distribution systems in most parts of North America use the multi-grounded-neutral method which has a connection to earth at most if not every distribution station, pole, transformer and customer service entrance. This assures that even if there is a poor connection to earth at one or even many points in the system, overall, the system neutral conductor has a very low resistance (impedance) connection to the earth. As a result, there is very high confidence that static build up and the damaging effects of it can be prevented.

Bonding is not the same thing as grounding and grounding is not the same thing as bonding. However, they work together to reduce hazards. Bonding is simply connecting two or more conductive items with a conductor that has low resistance and that can safely carry current if one of the objects becomes energized through some fault or accident. If the source of fault current is from a circuit conductor, you would want the use a bonding conductor that could safely carry the current until the circuit breaker trips. This serves two purposes during the fault… First, the voltage difference between all the items bonded together remains very close to zero so if you were touching two bonded items during the fault, you wont experience a shock. Two, the fault condition generates enough current flow so as to ensure the breaker will trip and thereby disconcerting what would have been a hazardous voltage on the item had it not been bonded.

The earth is a rather poor (high resistance) conductor in many areas. Here in the Northwest, we commonly encounter glacial-till (the deposits left by glaciers grinding mountains into sand and gravel). My property is pretty much glacial-till with a small amount of clay. The last time I drove a ground rod here, I applied 120 AC to it (before connecting it to any part of my existing electrical service) and then measured the current… and calculated the resistance of the rod. As I expected, that 5/8ths inch by 8 foot copper clad rod had about 1500 ohms of resistance. Pretty typical for this part of the country. That means that I would have to apply 1500 volts to that ground rod in order to make one amp of current flow.

If I were to rely on a ground rod with any significant resistance to protect my antenna system I would almost always have confidence that I was protected from static build up on the antenna system. Great… But if a nail of screw happened to be driven through a a power cable and my coax, the 120 volts shorted to my coax would not be able to force enough current into the earth to cause a fuse or circuit breaker to open… I could have 120 volts standing on the exposed part of my antenna system, including the TV connected to it. That would be an obvious shock hazard and it could remain there for an indefinite period of time.

By bonding my antenna system to the electrical service grounding system (which in turn bonds to the rest of the electrical system on my property), I can have high confidence that damaged Christmas lights or errant nails and screws can’t apply hazardous voltage to my antenna system.

For what it's worth, in my work over the years, I have encountered improperly boned/grounded systems in homes and businesses. One was a dentists office where an outlet receptacle had an open circuit neutral inside... rather than replace it, someone had connected the downstream receptacles to the the conduit in order to return circuit current to the panel. I found out when I was holding onto both sides of a loose conduit connection. Current traveled through both arms and my chest. I've also come across appliances that were wet inside and as a result, had enough leakage current through the wet insulation to make me 'wakeup'. Both examples demonstrated the danger of improper bond/ground connections. I would not have been shocked if the appliance ground had not been defected or the conduit had not been used as a circuit conductor.
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Last edited by GroundUrMast; Today at 4:56 AM. Reason: sp.
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