BobAccount deleted
join:2012-07-22
New Jersey Reviews:
 ·Optimum Online
| reply to 49528867
Re: Surge Protection Residential Whole House quote:
These shunting devices are most often installed from each data line to the local earth ground, and should be selected to begin conducting current at a voltage as close as possible above the system's normal communications level. For RS-422 and RS-485 systems, the voltage rating selected is typically 5 - 7 volts, in RS-232 systems 12 - 15 volt devices are appropriate.
The voltage spec for RS-232C is -15V to +15V. So by choosing a MOV in the 12 to 15 V range, you'd be shunting signals within the RS-232C spec.
RS-232C devices are required to withstand connection to any voltage in the -25V to +25V range for an indefinite amount of time. (Yes, you can take an RS-232C output pin at +15V and connect it directly to a -25V power supply and let it run all day without damage!)
So a more appropriate MOV device for RS-232C would be in the 20 to 22 V range, not 12 to 15 V as suggested by the author. |
|
 49528867Premium
join:2010-04-16
Fort Lauderdale, FL
kudos:3 | Ok that makes sense.
Thanks
Wayne |
|
| Where I live it is common to have the "service entrance" on an outdoor pole, and from there to extend underground to multiple buildings and in different directions from the pole, resulting in sub-panels in each building that are hundreds of feet apart from one another. The only ground rod is at the pole itself, meaning afaict that a lightning strike at any one of these buildings, that finds the wiring therein, only finds ground after traversing say 200 feet to the ground rod at the pole.
Conversely, if a surge event occurs in the overhead wiring and gets through the main panel all-the-way to the remote buildings, then even if you have surge protectors, the excess voltage you need to shunt to ground has to go all-the-way out to the pole again.
Do I have this right, and if yes, how can surge protectors work effectively given the distances to ground? I suppose the answer is: I could add ground rods at each of my buildings and then trench/wire these together between each other and the main service pole/ground. Is this ultimately the right way to do it? Is 6ga enough for a 250' distance?
 |
|
|
|
iknowPremium
join:2012-03-25 | said by laserfan:Where I live it is common to have the "service entrance" on an outdoor pole, and from there to extend underground to multiple buildings and in different directions from the pole, resulting in sub-panels in each building that are hundreds of feet apart from one another. The only ground rod is at the pole itself, meaning afaict that a lightning strike at any one of these buildings, that finds the wiring therein, only finds ground after traversing say 200 feet to the ground rod at the pole.
Conversely, if a surge event occurs in the overhead wiring and gets through the main panel all-the-way to the remote buildings, then even if you have surge protectors, the excess voltage you need to shunt to ground has to go all-the-way out to the pole again.
Do I have this right, and if yes, how can surge protectors work effectively given the distances to ground? I suppose the answer is: I could add ground rods at each of my buildings and then trench/wire these together between each other and the main service pole/ground. Is this ultimately the right way to do it? Is 6ga enough for a 250' distance?
you should have about 1.024M ohms impedance at 1 ghz with that 6ga 250F wire, so that's not good. |
|
49528867Premium
join:2010-04-16
Fort Lauderdale, FL
kudos:3 | reply to laserfan
said by laserfan:Do I have this right, and if yes, how can surge protectors work effectively given the distances to ground? I suppose the answer is: I could add ground rods at each of my buildings and then trench/wire these together between each other and the main service pole/ground. Is this ultimately the right way to do it? Is 6ga enough for a 250' distance? If it where my buildings I would do just that.
Wayne
--
Madness takes its toll, please have exact change ready… |
|
 Jack_in_VAPremium
join:2007-11-26
Mathews, VA
kudos:1 | reply to laserfan
said by laserfan:Where I live it is common to have the "service entrance" on an outdoor pole, and from there to extend underground to multiple buildings and in different directions from the pole, resulting in sub-panels in each building that are hundreds of feet apart from one another. The only ground rod is at the pole itself, meaning afaict that a lightning strike at any one of these buildings, that finds the wiring therein, only finds ground after traversing say 200 feet to the ground rod at the pole.
Conversely, if a surge event occurs in the overhead wiring and gets through the main panel all-the-way to the remote buildings, then even if you have surge protectors, the excess voltage you need to shunt to ground has to go all-the-way out to the pole again.
Do I have this right, and if yes, how can surge protectors work effectively given the distances to ground? I suppose the answer is: I could add ground rods at each of my buildings and then trench/wire these together between each other and the main service pole/ground. Is this ultimately the right way to do it? Is 6ga enough for a 250' distance? I have a detached garage with a 100 amp panel fed by a 100 amp breaker off the meter base. The contractor/electrician installed a ground rod for the panel. The inspector made him remove the ground wire and run a #6 back to the the main ground rod for the service. He stated only one ground point is permitted.
He did however make us install a second ground rod 5 foot from the existing rod and tie them together with #6 bare copper.
Be careful with advice and the best thing is to consult with your local electrical inspector. You can't go wrong doing that regardless of what you may see here. |
|
nonymousPremium
join:2003-09-08
Glendale, AZ Reviews:
 ·Callcentric
| said by Jack_in_VA:said by laserfan:Where I live it is common to have the "service entrance" on an outdoor pole, and from there to extend underground to multiple buildings and in different directions from the pole, resulting in sub-panels in each building that are hundreds of feet apart from one another. The only ground rod is at the pole itself, meaning afaict that a lightning strike at any one of these buildings, that finds the wiring therein, only finds ground after traversing say 200 feet to the ground rod at the pole.
Conversely, if a surge event occurs in the overhead wiring and gets through the main panel all-the-way to the remote buildings, then even if you have surge protectors, the excess voltage you need to shunt to ground has to go all-the-way out to the pole again.
Do I have this right, and if yes, how can surge protectors work effectively given the distances to ground? I suppose the answer is: I could add ground rods at each of my buildings and then trench/wire these together between each other and the main service pole/ground. Is this ultimately the right way to do it? Is 6ga enough for a 250' distance? I have a detached garage with a 100 amp panel fed by a 100 amp breaker off the meter base. The contractor/electrician installed a ground rod for the panel. The inspector made him remove the ground wire and run a #6 back to the the main ground rod for the service. He stated only one ground point is permitted. He did however make us install a second ground rod 5 foot from the existing rod and tie them together with #6 bare copper. Be careful with advice and the best thing is to consult with your local electrical inspector. You can't go wrong doing that regardless of what you may see here. I understand tieing them together with #6 or whatever code requires. The removal of the ground rod after they are tied together? |
|
iknowPremium
join:2012-03-25
1 edit | reply to 49528867
said by 49528867:said by laserfan:Do I have this right, and if yes, how can surge protectors work effectively given the distances to ground? I suppose the answer is: I could add ground rods at each of my buildings and then trench/wire these together between each other and the main service pole/ground. Is this ultimately the right way to do it? Is 6ga enough for a 250' distance? If it where my buildings I would do just that. Wayne it's about 1.024M ohms impedance at 1 ghz with that 6ga 250F wire, so that's good for 60hz, but not lightning, in combination with rods at each building with short heavy connections would take care of that. so this looks good. research lightning protection, sometimes a proper job according to an inspector can conflict with what should be done for lightning protection. the bottom line is, you can't protect from a lightning strike with small, long wires at one point, even if it's nec compliant. research this. there's a license for lightning protection installers, and they do a proper job. |
|
robbinPremium,MVM
join:2000-09-21
Leander, TX
kudos:1 | said by iknow:research lightning protection, sometimes a proper job according to an inspector can conflict with what should be done for lightning protection.
That shouldn't be a problem if the installation is done according to proper code. |
|
iknowPremium
join:2012-03-25 | said by robbin:said by iknow:research lightning protection, sometimes a proper job according to an inspector can conflict with what should be done for lightning protection.
That shouldn't be a problem if the installation is done according to proper code. you would need a huge cable to have one ground 250 feet long, and have low impedance at 1ghz, which lightning contains. so if electrical code calls for one ground only, that would be very expensive. 1/0 welding cable gets fried by lightning because the individual conductors are too small!. |
|
robbinPremium,MVM
join:2000-09-21
Leander, TX
kudos:1 | Code for Lightning Protection Systems is NFPA 780. Are you saying that it conflicts with NFPA 70 (NEC)? |
|
49528867Premium
join:2010-04-16
Fort Lauderdale, FL
kudos:3 | reply to Jack_in_VA
said by Jack_in_VA:He did however make us install a second ground rod 5 foot from the existing rod and tie them together with #6 bare copper.
Be careful with advice and the best thing is to consult with your local electrical inspector. You can't go wrong doing that regardless of what you may see here.
That depends on the inspector, for example when the AHJ required you to install an additional ground rod at five feet from the existing ground rod he had you violate NEC 250.53(B).
Rule of thumb when installing additional ground rods they should be spaced at least the length of one (10 feet).
Wayne
--
Madness takes its toll, please have exact change ready… |
|
49528867Premium
join:2010-04-16
Fort Lauderdale, FL
kudos:3 | reply to Jack_in_VA
said by Jack_in_VA:The contractor/electrician installed a ground rod for the panel. The inspector made him remove the ground wire and run a #6 back to the the main ground rod for the service. He stated only one ground point is permitted. What a shame he didn't know better.
From my grounding manual published by RO Associates a leader in designing ground systems whose grounding and bonding for communications facilities course I attended a few years back.
»www.protectiongroup.com/Ro-Associates
Wayne
--
Madness takes its toll, please have exact change ready… |
|
49528867Premium
join:2010-04-16
Fort Lauderdale, FL
kudos:3 | reply to iknow
said by iknow:it's about 1.024M ohms impedance at 1 ghz with that 6ga 250F wire. Your calculations are way off for a bare direct buried bonding conductor.
Wayne
--
Madness takes its toll, please have exact change ready… |
|
iknowPremium
join:2012-03-25 | reply to robbin
said by robbin:Code for Lightning Protection Systems is NFPA 780. Are you saying that it conflicts with NFPA 70 (NEC)?
here's a good example of proper protection. »www.tchams.org/FILES/Grounding.pdf |
|
iknowPremium
join:2012-03-25 | reply to 49528867
said by 49528867:said by iknow:it's about 1.024M ohms impedance at 1 ghz with that 6ga 250F wire. Your calculations are way off for a bare direct buried bonding conductor. Wayne that was for free air, assuming a .125" conductor 250 FT long. |
|
nonymousPremium
join:2003-09-08
Glendale, AZ Reviews:
·Callcentric
| reply to 49528867
That is what i am thinking. The one common grounding point should not preclude additional ground rods at the other building. Just the one common point is still needed. Plus I always learned in most basic setups you need a ground rod at both ends of a cable outside. Then on top of that a common ground in most setups even if it is just say a continuous cable sheath. |
|
| reply to Jack_in_VA
said by Jack_in_VA:I have a detached garage with a 100 amp panel fed by a 100 amp breaker off the meter base. The contractor/electrician installed a ground rod for the panel. The inspector made him remove the ground wire and run a #6 back to the the main ground rod for the service. He stated only one ground point is permitted.
He did however make us install a second ground rod 5 foot from the existing rod and tie them together with #6 bare copper.
Be careful with advice and the best thing is to consult with your local electrical inspector. You can't go wrong doing that regardless of what you may see here. Jack that's exactly what I have to my garage--100amp breaker at the pole, with garage about 200 feet away. And no ground rod at the garage panel, but a big honkin' wire (stranded) for ground, back to the pole, no markings on it but it's a quarter inch across. So I guess our electrician did it right.
What's a "local electrical inspector"? Oh, I remember, yeah we had those up north, but not here in Texas! 
So I guess my buildings were done right by the elect contractor, who installed to one common ground point. But then our pool contractor wired the swimming pool and broke the rule by grounding the pool panel (also wired a couple hundred feet back to the pole) to the pool grid, which was really extensive.
So an inspector that looks at my pool panel would make me remove the local ground (there is already a separate ground wire going back to the pole).
I am now sufficiently dizzy that I'm frozen to inaction. We in fact just had a few lightning bolts hit here within the last hour (no rain of course, just friggin' lightning) and all is good, as it has been for 9 years here, through some of the fiercest lightning I have ever witnessed in my 60 years on this planet. I'm inclined at this point to leave well enough alone and thank my lucky stars.
This has been very interesting discussion fellas, thanks. |
|
 nunyaWho is John Galt?Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:8
·Charter
 ·surpasshosting
·voip.ms
| That's incorrect. I drive a rod on every pool with a sub-panel. As long as it is bonded back to the main with a #6 or greater, it's perfectly compliant. It's not required, but it's not a violation.
A grounding electrode IS required on a building or structure supplied by a feeder or branch circuit (other than a single branch circuit). The ground wire is also required.
The inspector who demanded the removal of the rod was dead wrong.
--
If someone refers to herself / himself as a "guru", they probably aren't. |
|
49528867Premium
join:2010-04-16
Fort Lauderdale, FL
kudos:3 | reply to nonymous
said by nonymous:The one common grounding point should not preclude additional ground rods at the other building. The confusion many people have with grounding is the neutral bond to ground which the code restricts to only one, that aside there is no restriction or prohibition under the NEC which would stop a person from connecting additional earth grounds to the existing ground system as long as those additional grounds are all boned to the “existing and required by code” service ground.
Wayne
--
Madness takes its toll, please have exact change ready… |
|
