Just for my own information, and so I can explain when clients ask -- what is the danger (if any) if 2 separate grounding systems are not bonded together? I am thinking specifically of a residence where there is a ground rod for the telephone system driven on one side of the house, about 125 ft. from the electrical system ground rod. They are not bonded together. I know they should be bonded together, but I am just wondering why. Thank you for any explanations you can give.
Why bond telephone ground rod to electrical ground rod?
- Thread starter joemly
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ptonsparky
Tom
- Occupation
- EC - retired
Lighting is the first of my thoughts and the difference of potential between those two rods when it strikes. Doesn't mean much unless you have a wire hooked to each then bring them close to one another. Could be one hell of a flash between those wires when lightning strikes. You may be part of the path or just the couch.
When I was a kid it used to be interesting to watch the balls of lightning bounce around during thunder storms. Just don't see it as much anymore & I would venture to guess grounding (bonding to earth) has had a lot to do with it.
When I was a kid it used to be interesting to watch the balls of lightning bounce around during thunder storms. Just don't see it as much anymore & I would venture to guess grounding (bonding to earth) has had a lot to do with it.
Cavie
Senior Member
- Location
- SW Florida
My faverite answer...."Cause the book says"
StephenSDH
Senior Member
- Location
- Allentown, PA
With a lightning strike you can get a large potental differnce between the two system grounds. If the are bonded together it removes the potental difference between the two grounds. If they are unbonded then you risk frying equipment that is plugged into both systems at the same time. Laptops with modems, Answering Machines, and Phones. Insulatation failure of wires, circuit boards.
Think about it this way. If you don't bond them together, they are still electrically connected, it is just through their laptop computer.
Steve
Think about it this way. If you don't bond them together, they are still electrically connected, it is just through their laptop computer.
Steve
weressl
Esteemed Member
To equalize any potential difference. That is one provision that bonding all equipment that may become energized. It also assures that insulation is subject to equal voltage stresses throughout the system. One of the harmful effects of non-bonded different grounding system is that when potential difference exist between the two grounding system and equalizing current will flow on some indeterminable path that could be detrimental to electronic equipment, namely phone service in this case.
Lightning and other over-voltages are the most extreme conditions of the above.
bphgravity
Senior Member
- Location
- Florida
The best explanation of bonding principles for protection against potential differences can be found in Annex C of the NFPA 780. While this document deals with lightning protection systems, the concepts are the same for general NEC grounding and bonding requirements.
Go here to view the NFPA 780:
http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=780
Go here to view the NFPA 780:
http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=780
ceb58
Senior Member
- Location
- Raeford, NC
A little off topic but it still relates. Saw an episode of Myth Busters once that talked about being electrocuted in the shower during a lightning storm. They set up a room in a lab that had a generator that could simulate lightning. The shower was plumbed in plastic water and drain lines and the tub was fiberglass. They set up monitors in the shower and started the generator causing lightning to hit the room. No electrical charge was found. Then they set up the room with a corded telephone and did the same thing. The high voltage traveled through the line to the phone causing it to fry. Their point was that you could be killed talking on a corded phone if the house took a lightning hit.
K8MHZ
Senior Member
- Occupation
- Electrician
T
The average bolt of lighting is 30,000 amperes and can be as much as 300,000 amps at a voltage of over 10 million volts.
They may have made a bunch of electricity, but I doubt they came anything close to the trillion watts the average bolt of lighting carries.
The average bolt of lighting is 30,000 amperes and can be as much as 300,000 amps at a voltage of over 10 million volts.
They may have made a bunch of electricity, but I doubt they came anything close to the trillion watts the average bolt of lighting carries.
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