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Grounding Repeater Antenna?

WRZM243

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SteveShannon Grand Master

SteveShannon

Posted
Posted
8 hours ago, WRZM243 said:

Affixing 5' fiberglass repeater antenna with base of antenna 18' off ground on stainless steel L type pole mount affixed just to the 2X6 framing board.  Grounding needed or not... thanks, Steve

Amazon.com: ANNTLENT Antenna Pole Mount L-Type for Outdoor Antenna - Universal 12" Length Outside Antenna Mounting Pole for Cell Phone Signal Booster Antenna-Pole Mount Bracket : Cell Phones & Accessories

Here’s a pretty good document that describes what the National Electrical Code requires:

https://reeve.com/Documents/Articles Papers/Reeve_AntennaSystemGroundingRequirements.pdf

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SteveShannon Grand Master

SteveShannon

Posted
Posted
3 hours ago, Surfer59840 said:

After being a rigger aboard ships in the US Navy, we had static suppressors to keep the St Elmo's Fire effect from occurring on the masts and antennas all over the ship ... 

BUT - a lightning arrester is kinda a hoax in that you have a bolt of electricity that has traveled miles to your antenna and has a gazillion volts in it and a small spark-gap device is going to take that charge away from your equipment?! No way! 

 

If you get hit by lightning, I don't really think any of your gear - let alone the place where it sits - is going to survive. 

 

Your results may differ - but don't count on it.

So how did the static suppressors work on the masts and antennas on the ship and why wouldn’t that work on land?

A direct strike to your antenna probably would be a very bad day, but a properly grounded gas tube surge suppressor near your entry point, as well as other measures, such as single point grounding of devices that are connected along the coax, adequately grounding your tower, and placing lightning rods higher on your tower than your antenna, can help prevent a direct strike in the first place.  Before lightning strikes, a static charge often begins building up.  A gas tube surge arrester can help avert the conditions that can lead to a “direct strike” by allowing that static electricity to dissipate more easily to ground rather than building up.  I suspect the static suppression on-ship worked similarly.  

No single measure is perfect, but many thousands of professionally designed repeater installations survive storms annually (and some die).

Of course you folks in Hamilton never get storms, right?

Welcome to the forum!

Steve, in Butte, where gallows frames serve as lightning rods.

 

 

 

 

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WRKC935 Mentor

WRKC935

Posted
Posted

Grounding bonding and the like are NOT to deal with a direct strike. 

The first and foremost reason to ground and bond is safety for the operator.  And that is where the bonding part comes in.  If you install a tower, toss a couple ground rods in the ground and connect them to the tower and do NOTHING else you create a bigger issue than if you just did nothing.  And here's why. 

Your house, building or whatever has an electrical service connected to it.  Part of the code for that service being connected is there is a safety ground.  So that service has one or two ground rods connected to it (newer builds require 2 rods).  You radios are plugged into that service and that ground.  That ground is connected to the case of your radio and then the antenna is ALSO connected.  That antenna is connected to the tower and the tower is grounded with a second set of ground rods.  A ground strike that hits neither the tower or the electrical service will induce a pulse that will spread out across the ground as it disperses.  Since the two different grounds are at different places, they are at different voltage potentials as the strike disperses in the ground.  But you have connected them together with your radio being the fuse in the middle.  So it goes poof.

If the radio is NOT connected to the electrical ground, but is connected to the tower, but other equipment is sitting there on the desk that is connected to the electrical ground, then it will arc across from one device to the other, OR if the radio is connected to a computer or some other device that is on the electrical ground via data cables, then one device has a different voltage potential than the other across the data cable,,, again POOF. 

None of these are 'direct hits'  They are all ground strikes that fry your gear due to lack of proper bonding between the different pieces of equipment connected to the different grounds.

 

Specific to tower grounding.

For a small tower for GMRS / HAM radio use, and NOT a big commercial tower, the reason for grounding the tower is NOT to deal with a direct hit, it's more to prevent the hit from coming at all.  As we have all been told over and over.  Lightning will take the path of least resistance.  If you have an ungrounded tower, that tower can build a static charge on it with reference to ground.  The tower is more conductive than the tree's around it, and it's now at a higher potential due to the static charge.  That makes it the path of least resistance and therefore the most likely target for a strike.  Anything connected to that tower is going to become part of the dispersion of that strike.  So you ground it.  Grounding the tower brings the entire tower back to the same voltage potential as the rest of the surrounding earth and therefor makes it no more of a target than anything else there because the grounding pulls the static charge off the tower, and in reality will not let it build up to begin with.

Lightning suppressors.

Lightning suppressors perform two different tasks when they are properly installed, and don't do anything if they are not installed correctly.  They first and foremost need to be grounded.  That ground needs to be right at the entry point where the cable enters the building.  But the shield of the cable needs to be grounded on the outside of the building just before it enters the building as well.  The surge suppression part of the device is to short down any voltage higher than the trigger voltage of the suppressor in use.  This is typically about 100 volts.  If any part of the tower is hit, every part of that tower and anything connected to it will have a voltage induced on it.  That induced voltage will create a magnetic field (like a transformer) that will induce voltages on any other conductor near it including the center conductor of any coax on the tower.  The suppression is to short that to the shield of the cable and then to the grounding system it's connected to.  It's NOT to deal with a singular hit on a specific antenna on the tower.  If that happens, the radio connected to that antenna will go POOF.  BUT if the grounding is done correctly and the bonding is right, that will be the only radio damaged.  If not, then the lightning will come down and tear up lots of stuff. 

 

  • 1
WRKC935 Mentor

WRKC935

Posted
Posted
On 12/22/2023 at 12:59 AM, Surfer59840 said:

After being a rigger aboard ships in the US Navy, we had static suppressors to keep the St Elmo's Fire effect from occurring on the masts and antennas all over the ship ... 

BUT - a lightning arrester is kinda a hoax in that you have a bolt of electricity that has traveled miles to your antenna and has a gazillion volts in it and a small spark-gap device is going to take that charge away from your equipment?! No way! 

 

If you get hit by lightning, I don't really think any of your gear - let alone the place where it sits - is going to survive. 

 

Your results may differ - but don't count on it.

A lot of that is going to depend on the bonding more than the surge suppressor.  As mentioned elsewhere, the BONDING is done for safety reasons and to keep all the equipment at the same voltage potential.  So single point grounding of all equipment on the operator position is KEY in keeping the equipment running after a strike.  If you have a strike hit any piece of the equipment , it should ALL jump to the same potential as the gear next to it.  If that happens, you stand a better chance of it surviving.  If one piece of gear jumps to 10KV and the rest stays at 0 volts,  POOF.  And you get a big fireworks show on your desk to boot. 

And one of the things that I had a hard time with when discussing grounding was how does a number 2 or number 6 wire really deal with a hit.  It's tens of thousands of amps and millions of volts.  But what was explained to me is there really is no way that you could pass that amount of current across a conductor that size for any length of time.  But if the time was short enough, it would hold that sort of current.  The other part was once you are in the structure, and the site has proper grounding, those smaller conductors are NOT exposed to those sorts of currents and voltages.  If a single DC floating antenna takes a direct strike, the maximum voltage across the cable from center conductor to ground is the breakdown voltage of the cable.  You can't put 100KV across two terminals that are 1 inch apart.  The voltage will arc over and limit due to the arc, and that arc will short the rest of the voltage to ground.  And that breakdown voltage is only present until the arc starts.  Once an arc starts, it's no longer an open circuit.  You have current flow and therefore a load against the potential. 

Welders will recognize this with simple stick welding.  You have to fight to get the arc to establish.  And a typical stick welder open circuit is about 60 to 80 volts.  Once the arc is established, the welding voltage drops down to about 20 volts.  And you can pull up several inches from the welded material and maintain the arc, still having a really low voltage present between the welding electrode and the material.  Same thing with a coax cable on a tower that is hit.  The center will arc over to the shield and  the voltage gets limited between the shield and the center conductor.  Of course the shield is grounded to the tower at the base of the antenna, where it transitions off the tower to the structure, at the entry point of the structure on the outside and then at the surge suppressor just inside the structure.  At least that's the way it's done on commercial towers.  In addition, it's grounded not less than every 100 feet coming down the tower. 

Back to the number 2 wire and the 100K amps and a gazillion volts. 

Lightning is swift.  It's a LOT of power being dispersed very quickly.  So the wire will heat up, but it's not an instantaneous thing.  And since the duration of the voltage drop across the conductor (which is the actual voltage across the wire and NOT the total voltage present during the strike) is so quick, the relatively meager conductor size in actually ample to pass the voltage across it and into the ground.  Now, something else that's NOT being considered.  Since the cables are all grounded to the tower and everything else and all that is bonded together, the tower carry's a LOT of the power to ground via the metal structure and the metal in the concrete base of the tower.  In other words, the single antenna cable of the antenna that gets hit, never really see's the entire blast of lightning, it's spread across a number of other conductors to ground.

 

  • -1
Surfer59840 Newbie

Surfer59840

Posted
Posted

After being a rigger aboard ships in the US Navy, we had static suppressors to keep the St Elmo's Fire effect from occurring on the masts and antennas all over the ship ... 

BUT - a lightning arrester is kinda a hoax in that you have a bolt of electricity that has traveled miles to your antenna and has a gazillion volts in it and a small spark-gap device is going to take that charge away from your equipment?! No way! 

 

If you get hit by lightning, I don't really think any of your gear - let alone the place where it sits - is going to survive. 

 

Your results may differ - but don't count on it.

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