Author Topic: bonding wire  (Read 3541 times)

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pellets4fuel

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bonding wire
« on: August 24, 2016, 01:33:06 PM »
Been doing a lot of reading and looking at different tower install manuals, what others have done, wiring diagrams, etc.  I know I need to ground my guy wires, and tower.  Also am pretty certain then that I also need bonding wire back to other areas on my property like from the turbine back to the house.  At the tower I was going to ground at each of the 4 sets of guy wires.  Was also going to do a perimeter ground around the tower base, with probably at least 3 rods (halo concept).  Would it be good to tie the 4 guy wire grounds into center as well?  The turbine site is 450ish from the house.  So I am pretty certain from what I have read that this needs to be bonded back to like the house for example.  So bare copper wire 8 to 18in below ground back to house.  I have read that it is not a good idea to have this in the same trench as the 3-power wires as you can create like a transformer effect.  At least 3ft away is what I read.  Does that apply if your power wires are in PVC conduit?  Then also how do you go about sizing this whole thing?  I have read that surface area is important.  With many HAM radio apps I have read about they use flat copper strips rather than wire.  I can't see doing that for 450ft. So is the next best option solid copper or stranded?  And then like I mentioned what size?  If lightning is "mucho" power, and we are just doing the best we can is it a matter of the biggest wire your budget will allow, and you get what you get against lightning?
One other question, with the 3-power wires do you also need a lighter weight ground to tie metal equipment together at tower base (example junction box with kill switch and lightning arrestors,etc) to metal equipment together at the house or wherever your rectifier and inverter stuff is?
Like I said I have done a lot of reading and have some things figured out (I think)  I know I need to go by my local codes, and what the NEC laws are, but some input from some of you would be highly appreciated.
Thanks,
David

joestue

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Re: bonding wire
« Reply #1 on: August 25, 2016, 08:25:15 PM »
I don't think its practical to protect against a direct lightning strike, and you don't have to worry about the transformer effect because the currents are not significant.


If you put gas discharge and mov's between the 3 phases (or after the rectifier, so two wires) between the line and the ground, you have to put them on both ends of the tower. if they are at the base of the tower, you could still potentially have enough difference in voltage at the top of the tower to puncture the wire insulation.

If you run the ground wire with the transmission line back to the house, then when the voltage at the tower's ground rods reach 30,000 volts (30,000 amps through 1 ohm ground resistance) well, now you have that much more current flowing into your house's grounding system.

theoretically if you coil your transmission line into a big enough inductor, you can install the lightning arrestors at both ends of the transmission line.

problem being, that might be practical if you run a 480v wind turbine. also the voltage across the inductor will be as high as say, the 30,000 volts i mentioned. PEX tubing would probably work for that.

it could be broken up into a number of inductors, with gas discharge between each one, connected to their own ground rods.
My wife says I'm not just a different colored rubik's cube, i am a rubik's knot in a cage.

Mary B

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Re: bonding wire
« Reply #2 on: August 26, 2016, 06:28:25 PM »
On that long of a run you do not ground it back to the house. The tower should have its own ground system of multiple ground rods in a star pattern.

pellets4fuel

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Re: bonding wire
« Reply #3 on: August 28, 2016, 01:20:28 PM »
So in doing some additional reading, (trying to find copies of NEC 250 and 694), but of just excerpts from these two articles printed in partial in various articles and websites, I am reading that lighting protection grounding is to be carried back to the house grounding to keep everything at the same potential.  solarcity.com has some good reading on bonding (though they are Canadian based I think) But they too show a good/proper grounding system for a tower.
I know that nothing else around my door yard is "bonded" together.  I have a separate service entrance for my shop and for my house.  The grounds there are not connected.  I have lightning rods on my shed roof with a cable down the side connected to a ground rod, again not connected to any other grounding system.  Both my services were put in by electricians (years ago mind you).  This "bonding" concept seems to be new to the small wind in the NEC since 2014 perhaps.
Are there any small wind installers out there (or others) that can perhaps clear up what is a "must" according to the NEC?
Maybe I will just hear that I should hire a professional, and then I wouldn't have to worry about it. ;)

Mary B

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Re: bonding wire
« Reply #4 on: August 28, 2016, 06:31:08 PM »
on a 450 foot run you will not maintain the same potential is the problem. That length becomes an inductor and that can actually cause damage. My solar panels are 80 feet behind the house, they have their own ground and I have the main entrance ground at the other end.

pellets4fuel

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Re: bonding wire
« Reply #5 on: August 29, 2016, 12:09:53 PM »
I here you Mary, and I get it for the most part :o.  It's a long wire run.  There is going to be losses/differences over that wire and I will just be introducing voltage to the house that I don't want.
Just trying to read and understand what the NEC stuff says.  I guess I will have to pick through section 250 some more.  694 though seems to make it clear to bond to other grounds.
Curious...was your solar installed by a "professional" installer, or did you do it yourself?

Mary B

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Re: bonding wire
« Reply #6 on: August 29, 2016, 05:22:31 PM »
Myself but my dad was a state electrical inspector and I picked his brain on grounding.

pellets4fuel

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Re: bonding wire
« Reply #7 on: August 29, 2016, 10:42:20 PM »
Mary,
Thanks.  Helps to know your Dad is an inspector, and knows.
Did some searching on some other forums as well.  Most are saying the same thing you are.  I have decided to go the route you and others have mentioned.  The bonding wire can always be added later if need be.  Besides conduit is in the trench and covered already.  :)

Mary B

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Re: bonding wire
« Reply #8 on: August 30, 2016, 03:23:10 PM »
I use an X ground comprised of 5 ground rods. One in the center then the other 4 are 16 feet away and bonded to the center with #6 solid copper. the 4 rods on the tips and the wires are buried, the center rod is just above ground level for access in case I add something.

The main house ground is comprised of 6 ground rods across the back and west side of my house and shed where the towers are. All are 8-16 feet apart and all are bonded together with the wire buried a couple inches. I could probably take a direct hit with little damage in the house. I need to add 1 more ground rod but right now the garden is in the way.