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Author Topic: Question on Tower Ground  (Read 4204 times)
KB4MB
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« on: June 14, 2011, 08:36:43 AM »

I feel stupid that I don't know this, but... on my tower, I have three ground rods, one for each leg.  Wire attaching the legs to the rods.  The third rod, I have attached back to my ground rods that comprise my grounding system for the shack (3 rods, and includes the service ground rod).

However, do I need to connect the other two ground rods together to the third rod?  Or does the tower take care or that?

If I do, can I use one wire underground to connect the tower rods together?

Right now, I think I have it ok, but I want to make sure.
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K1CJS
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« Reply #1 on: June 14, 2011, 10:03:08 AM »

Yes, all the ground rods HAVE TO BE bonded together.  The connection through the tower just will not do.  Once more, those ground rods have to be connected to any other ground rod that is driven in around your house--your shack ground AND the AC main service ground.  That is according to the National Electrical Code.
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KB9CRY
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« Reply #2 on: June 16, 2011, 09:41:43 AM »

I feel stupid that I don't know this, but... on my tower, I have three ground rods, one for each leg.  Wire attaching the legs to the rods.  The third rod, I have attached back to my ground rods that comprise my grounding system for the shack (3 rods, and includes the service ground rod).

However, do I need to connect the other two ground rods together to the third rod?  Or does the tower take care or that?

If I do, can I use one wire underground to connect the tower rods together?

Right now, I think I have it ok, but I want to make sure.


The tower takes care of that; even Polyphaser does not recommend additional bonding of the leg grounds to each other besides thruogh the tower.....

now on that subject....Polyphaser recommends 75 ft of ground wire, with ground rods every 16X their height for each leg.  So you need more rods per leg.....but the bonding to the SPG ground and that to the service entrance is a big big step in the right direction.
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W6RMK
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« Reply #3 on: June 16, 2011, 05:08:00 PM »

Yes, all the ground rods HAVE TO BE bonded together.  The connection through the tower just will not do.  Once more, those ground rods have to be connected to any other ground rod that is driven in around your house--your shack ground AND the AC main service ground.  That is according to the National Electrical Code.

I'm not sure about the first part.  I think that one could consider this as similar to having a metal framed building.  Bonding separate ground rods to the building without a separate bonding conductor is allowed at least by NEC, not sure about NFPA780 for lightning.

Think of this as similar to the situation where a separate conductor isn't required when you have your bonding through the conduit. (not that I'm wild about using the conduit as a bonding conductor, particularly if it's flex conduit, but it meets code.. notwithstanding the MGM fire disaster)

The second part.. everything has to be bonded.. Totally in agreement.
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K1CJS
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« Reply #4 on: June 16, 2011, 05:53:03 PM »

The comparing to a metal framed building aside, I once thought so too.

I helped in putting up an 'erector set' tower one summer.  All the pieces marked, crossbraces having to be bolted to the tower legs, etc.  The town electrical inspector arrived for the inspection and told the owner to bond the tower leg ground rods together with cables.  He was informed that the tower company said it wasn't necessary.  He said that according to the NEC it was and would only issue a final inspection certificate if it were done.

Maybe he was mistaken or misinterpreted the code, I don't know.  But that is where I got the info.  If I'm wrong--if inspectors will allow the tower to become the bond, then I apologize--but my statement was made from that experience.



 
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W6RMK
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« Reply #5 on: June 17, 2011, 10:07:38 AM »

Probably more the "AHJ" issue.. any given inspector, on any given day, can ask you to do something that's not in the code, directly contradicts the code, etc.  been there, done that, pounded in the second ground rod a foot from the existing ground because that's what made him happy.

I can see the inspector being a bit skeezy about a "bolted together" tower (I was thinking welded sections, like Rohn 25/45, etc.).  They would see all the bolted joints and wonder if they're going to hold up.

Different from a bolted together steel frame building: there's a lot more bolts, and there's just a general impression that it's less likely to become disconnected.

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K1CJS
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« Reply #6 on: June 19, 2011, 08:29:56 AM »

After thinking a bit about it, it could be also a case of local code being a bit more stringent than the NEC.  Remember that local code cannot undercut the NEC, but it CAN and sometimes does specify conditions and precautions that can be greater than what the NEC does specify.
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KI4SDY
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« Reply #7 on: June 19, 2011, 08:35:38 AM »

It is probably best not to take advise from someone who has never owned a tower, especially on a subject as serious as grounding!  Wink
« Last Edit: June 20, 2011, 06:22:03 AM by KI4SDY » Logged
KD5FX
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« Reply #8 on: July 03, 2011, 06:39:58 PM »

Yes, all the ground rods HAVE TO BE bonded together.  The connection through the tower just will not do.  Once more, those ground rods have to be connected to any other ground rod that is driven in around your house--your shack ground AND the AC main service ground.  That is according to the National Electrical Code.
This IS what the National Electrical Code says. There was a recent article in QST all about this! Check it out....
See page 53 of the Jan. 2011 QST...
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W8JI
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« Reply #9 on: July 04, 2011, 02:56:26 PM »

Yes, all the ground rods HAVE TO BE bonded together.  The connection through the tower just will not do.  Once more, those ground rods have to be connected to any other ground rod that is driven in around your house--your shack ground AND the AC main service ground.  That is according to the National Electrical Code.
This IS what the National Electrical Code says. There was a recent article in QST all about this! Check it out....
See page 53 of the Jan. 2011 QST...

All grounds for things entering a dwelling like feedline, CATV cables, electrical lines MUST be bonded together. That has been a requirement for as long as I can recall reading NEC and NFPA codes.

It not only is code, it is common sense.

However, this does NOT mean the tower ground has to be bonded to the house. None of my towers are grounded to the house, and I would never dream of that. That is because my towers are a good distance from the house. The TV tower right next to the house is tied in.

By far the single most important thing is bonding all wires and cables entering the house and any station ground to the mains ground. That is FAR more important than the tower ground, ground rods, or any lightning suppressors. Having an entrance ground bonded to the mains ground is the bulk of house protection. That is why code requires all CATV, telco, and power to be connected to one point, even if that point is a crummy single ground rod.

My system takes a few dozen hits a year. Last Sunday my 318 foot tower was hit twice! My DSL modem stays plugged in, my antenna cables are connected, and despite not having any polyphaser protection on the 10-20 cables entering the direct hit does nothing inside the house or barns.

http://www.w8ji.com/ground_systems.htm


73 Tom

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KB4MB
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« Reply #10 on: July 04, 2011, 03:40:09 PM »

Tom,

Hi, originator of the thread.  My tower is 30 ft away from the station.  So I figure that is close enough where bonding the tower to the ground system makes sense.  I have three ground rods, one for each leg, and the third leg is 16 ft away from the last station ground rod, so I clipped on there.  I also have all wires in and out attached to the SPG (which happens to be right at the shack entrance, so I lucked out there).

I will most likely add another four rods - two each for the other two legs, to help dissipate any charge; my tower is only 30ft, and there are 60ft trees only 20 ft away on either side. 

I am planning for a strike, but I think the odds just aren't there.  Hopefully I have done enough; I think I have.
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W8JI
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« Reply #11 on: July 04, 2011, 06:51:34 PM »

If it all comes up together at the same potential and similar rate, then you won't likely have damage.

My 318 foot tower gets whacked about every lightning storm at least once. Just last Sunday it was hit twice in a row by "sizzlers". Those are the nasty things, not the normal little snaps that look like gian spark plug arcs. :-)

I don't disconnect modems, TV's, computers, or my radios and I don't have any polyphasers, and my stuff just never breaks. About the most that happens is a coax shield melts, a connector blows apart, or an antenna blows up. :-)

How things are routed and bonded are more important than anything else. Sounds like you are OK.

By the way, I do have large DX Engineering antenna switches. They do disconnect the center conductors on my HF antennas and gear, but other cables come right in.
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KB4MB
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« Reply #12 on: July 05, 2011, 05:22:29 AM »

One more question, what do you do for your rotator cables?

I still disconnect everything when not in use - why invite trouble - easy for me, since I am a small station.
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KI4SDY
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« Reply #13 on: July 05, 2011, 06:20:36 AM »

"... my stuff just never breaks. About the most that happens is a coax shield melts, a connector blows apart or an antenna blows up."

You are wise to disconnect everything when not in use! Wink
« Last Edit: July 05, 2011, 06:33:35 AM by KI4SDY » Logged
KB9CRY
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« Reply #14 on: July 05, 2011, 10:20:18 AM »

One more question, what do you do for your rotator cables?

I still disconnect everything when not in use - why invite trouble - easy for me, since I am a small station.


If you disconnect outdoors, then you're fine.  If you do it indoors, you could be playing with fire...literally.

I use lightning arrestors on my rotator cables also...ICE make them, others do too.
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