Grounding Radios

[wuzafuzz]

CUL's and other radio heads:  The most recent issue of The Sentinel described an incident in which a cadet was zapped (not injured) while working in a comm trailer, and blamed a lack of proper grounding.

Given that our SAREX's and events are usually in borrowed buildings, I'm not about to pound an 8 foot grounding rod into the ground (or a parking lot.)  I'm curious what others typically do to ground radios and antennas in a temporary install.

[Airrace]

If you can place something into the ground purchase the following items from your local hardware store:

10 feet piece of 3/4 " copper plumbing pipe
Electrical pipe ground connector
#10 electrical wire (length depends on how far your trench is from the radio)

Attach the electrical connector and wire to the 3/4 " copper pipe.
Dig a trench at least six inches deep and place the copper pipe in the ground and cover over with dirt. Make sure to frimly place all the dirt back over the 3/4" copper pipe. You will also need to wet and tamp the ground over the copper pipe.

Then hook up the wire to your radio.

[Airrace]

You can also place rock salt over the pipe prior to placing the dirt on top. This will help!

[Airrace]

I have a three foot ground rod that I attach to my power source (generator). You don't need to drive a ten foot rod into the ground.

[wuzafuzz]

Thanks for the info Airrace. 

What if you can't find a place to drive a ground rod?  I'm thinking of scenarios where I'm setup in an FBO surrounding by asphalt and concrete, or in a trailer in a parking lot.

[Thom]

Thanks for the info Airrace. 

What if you can't find a place to drive a ground rod?  I'm thinking of scenarios where I'm setup in an FBO surrounding by asphalt and concrete, or in a trailer in a parking lot.

You know, someone here might know a good answer, but I know where I'd start asking, and it isn't CAPTalk...

http://www.usraces.org/

http://www.ares.org/

http://www.arrl.org/

Surely the guys at those places have experience with running radios in 'inhospitable' environments.  Probably much more so than CAP, though I bet we are right behind them and ahead of a lot of other organizations/agencies.

Thom Hamilton

[Al Sayre]

Clamp to a Pad Eye on the ramp.  They are usually connected to a huge mesh of steel screen embedde in the concrete...

[Airrace]

If you have a metal building nearby that also can used as a good ground. Just place a clamp to the metal building.

[RADIOMAN015]

The best grounding in the world isn't going to stop the radio or the operator from getting fried if there's a near miss or direct hit by lightening.  This might add a false sense of security    Perhaps when there's thunder it's time to disconnect the antenna from the equipment and turn off the radio!

When we are using the radios & have cadets & seniors out in the field durint squadron ES training night on our reserve base, I make sure if there's even a slight chance of bad weather that our simulated mission base (squadron radio base station) call base weather for an initial report & depending upon that report (probability of lightening) will get 1/2 hour updates.  Good practice for the comm team.

RM   

[Major Lord]

To say that the Cadet was shocked due a a ground problem does not really address the root problem. Does this mean that the cadet was shocked because a piece of equipment that he touched was hot in relation to ground, due to an internal power supply problem ( or design problem) or because he touched a wire that was hot while at the same time being in contact electrically with ground? If the Com Trailer was set up properly with a shore-power plug, then there should not be a "ground" problem. Not all conditions causing electrical shocks are due to ground problems, and of the few that are, copper ground spikes are not likely to be the cure. If you need to physically mount radios and antennae in a temporary install, You should be able to grab a perfectly good AC ground from the AC plug, or if not available ( Its hard to believe that there are some places in the US old enough to have AC outlets without ground tabs!) grab a ground from a cold water pipe or water spigot.

An RF ground is a different animal entirely. HF antennas may require an enhanced ground, usually at the antenna site, especially for vertical antennae not having sufficient radials. Keep your cotton picken hands of RF radiators! These can shock and burn you , and unlike Gamma radiation, you won't develop superpowers as a result of exposure.

I can just imagine my local FBO as I whip out the old sledge hammer and start driving spikes into the tarmac......

Major Lord

[wuzafuzz]

Thanks for all the ideas!  Contacting ARES/RACES types is a good idea since they do this stuff all the time.  I'm under no illusions grounding a mast and coax will prevent all damage from a direct lightning hit, but do want to try to be safer and comply with regs.  Unfortunately the regs don't seem to anticipate setting up a comm shack in anything other than a permanent installation.

Mobile radios are so much easier...

[Airrace]

The only way to prevent damage from lighting is to install a surge arrestor. I recomend them on any tower due to a lighting strike. You can purchase them at any wholesale electrical supply dealer.

[RiverAux]

For those who didn't go read the Sentinel referred to in the original post (SHAME ON YOU!):

At a wing encampment this year, lightning struck a communications
antenna mounted on a trailer parked adjacent to the building being
used as the encampment headquarters. The strike damaged several
pieces of equipment. A cadet was using a laptop at the encampment
headquarters and experienced an electrical shock. Luckily the cadet
suffered no lasting side effects, complications or restrictions to duty.
The investigation revealed neither the antenna nor the trailer was
grounded. According to CAPR 100-1, Communications, paragraph 7-1b,
Equipment Grounding: "All communications equipment not in motion
will be adequately grounded at all times." Paragraph 7-1e states,
"Lightning arrestors or grounding switches should be installed on all
antennas."

[desertengineer1]

I share the same basic concern as Major.  Instructing someone to pick the nearest metal pipe can be more dangerous than having no ground at all - for reasons that are more complicated than I have time to explain here.

The key word is SINGLE POINT GROUND when dealing with power.

ANY grounding of electrical equipment should be done with guidance by properly trained and qualified individuals.

Grounding is NOT a catch-all solution to electrocution hazards, and in most cases of injury, a ground would have not prevented the incident.

Most electrocution cases result from multiple failures of improperly installed or modified equipment (Hot/Neutral wires swapped or open cabinets), or by use of equipment not designed for electrical safety or not compliant with UL/NEC/NFPT. 

I am not happy to see this Safety entry.  It could propigate a false assumption that (1) Grounding of equipment is all that is required, and (2) propigate misinformation that can be more unsafe as no ground at all.

Earth ground, if not tied to a single point ground, can be very dangerous to personnel and equipment if a lightning strike or major power event occurs.  Resistance of earthen ground is high between two points.

I think I'll be sending an email up the chain on this one.

To say that the Cadet was shocked due a a ground problem does not really address the root problem. Does this mean that the cadet was shocked because a piece of equipment that he touched was hot in relation to ground, due to an internal power supply problem ( or design problem) or because he touched a wire that was hot while at the same time being in contact electrically with ground? If the Com Trailer was set up properly with a shore-power plug, then there should not be a "ground" problem. Not all conditions causing electrical shocks are due to ground problems, and of the few that are, copper ground spikes are not likely to be the cure. If you need to physically mount radios and antennae in a temporary install, You should be able to grab a perfectly good AC ground from the AC plug, or if not available ( Its hard to believe that there are some places in the US old enough to have AC outlets without ground tabs!) grab a ground from a cold water pipe or water spigot.

An RF ground is a different animal entirely. HF antennas may require an enhanced ground, usually at the antenna site, especially for vertical antennae not having sufficient radials. Keep your cotton picken hands of RF radiators! These can shock and burn you , and unlike Gamma radiation, you won't develop superpowers as a result of exposure.

I can just imagine my local FBO as I whip out the old sledge hammer and start driving spikes into the tarmac......

Major Lord

[desertengineer1]

The only way to prevent damage from lighting is to install a surge arrestor. I recomend them on any tower due to a lighting strike. You can purchase them at any wholesale electrical supply dealer.

NEGATIVE.  The only way to prevent damage is to not have electrical equipment at all.

The most efficient, risk reduced, methods are to follow NEC and NFTP procedures and codes when equipment is installed.  Again, lots of details here I can't go into fully.

This includes, but is not limited to:

1.  Single point ground to get as close to equal potential as possible.  Refer to NEC or NFTP.

2.  Grounding of antenna and transmission line at points specified in code.  This varies depending on structure and EES characteristics.  Again, ask someone who is trained and qualified.

3.  Yes, use of a surge arrestor is one link - but remember those ONLY protect from transient events that are nearby.  THEY DO NOT protect the system from a direct strike.  See #2 above.

4.  FOLLOWING ALL PROCEDURES FOR LIGHTINING HAZARDS.  This should be addressed in your communications or safety plan (Hopefully both and they are the same).

[desertengineer1]

We do the following when lightening is estimated within 10 miles or thunderstorms are immenant:

1.  Disconnection of all coaxial cable from radio equipment not installed in a mobile configuration.

2.  If installed in a communication trailer or temporarily running into a window, cable is removed and laid near the antenna.  This reduces the potential of a strike path entering into the structure.  If a direct strike occurs (especially in the case of a tactical antenna in a tree or temporary pole), the energy is most likely to stay in the antenna structure/line area.  This will melt the cable, but less likely to take the equipment or personnel with it, or set fire to the building.

3.  Personnel are removed from the radio equipment area and sheltered accordingly, if able.

You don't want to be anywhere near radio systems if theya re connected to tall metal objects.  Best to go inside the FBO or hangar and drink coffee until the storm is over.

[Al Sayre]

Most hangars are tall metal objects, so stay away from the walls and supports if you use one for shelter...

[desertengineer1]

OOKKK.

1.  Grounding of the trailer with a copperweld rod may have had little effect on the hazard.  Note my use of the word MAY.  If the ground rod and item connected to the rod is not tied to the single point ground of the 120 VAC system per NEC, the hazard is increased.  You now have a big resistor between the rod and the single ground point.  A direct or nearby strike can result in thousands of volts of potential between the ground rod and the electrical ground or neutral line.  Again, consult someone qualified and trained!!!

2.  Direct strike of an antenna has a HIGH probability of damaging equipment regardless ground or surge arrestor installation.  In the case of #1 above, a floating ground rod can actually increase the chance of damage, and injury to other personnel elsewhere.

3.  "Adequitely Grounded" should be clarified.  What defined adequite?  I would give a resounding NO to using the nearest water pipe!  Now you have possibly the same situation I described in #1.  If the building plumbing entry point is not tied to the equal potential ground point, you could have immense potential between the plumbing and any nearby electrical equipment.

TO ME, "adequitely grounded" means connection from ground lugs on the equipment to the single ground point of the structure or trailer.  In the case of a comm trailer, there should be a location marked as such.  The ground rod and all equipment goes there.

Second - why were personnel in the trailer using electrical equipment tied to AC power to begin with?  This should be a lesson to everyone.  Stay away from AC fed equipment, wired phones, and plumbing during a storm!!

For those who didn't go read the Sentinel referred to in the original post (SHAME ON YOU!):

At a wing encampment this year, lightning struck a communications
antenna mounted on a trailer parked adjacent to the building being
used as the encampment headquarters. The strike damaged several
pieces of equipment. A cadet was using a laptop at the encampment
headquarters and experienced an electrical shock. Luckily the cadet
suffered no lasting side effects, complications or restrictions to duty.
The investigation revealed neither the antenna nor the trailer was
grounded. According to CAPR 100-1, Communications, paragraph 7-1b,
Equipment Grounding: "All communications equipment not in motion
will be adequately grounded at all times." Paragraph 7-1e states,
"Lightning arrestors or grounding switches should be installed on all
antennas."

[desertengineer1]

Hey Mike - I vote this thread be moved over to Safety.

[desertengineer1]

Negative.

Connect the ground to the single point ground lug of the comm trailer.

Connect radios to the single point ground lug.  Recommend daisy chain them (all on one single line) using #6 stranded, non-insulated, or green color if insulated.

If you can place something into the ground purchase the following items from your local hardware store:

10 feet piece of 3/4 " copper plumbing pipe
Electrical pipe ground connector
#10 electrical wire (length depends on how far your trench is from the radio)

Attach the electrical connector and wire to the 3/4 " copper pipe.
Dig a trench at least six inches deep and place the copper pipe in the ground and cover over with dirt. Make sure to frimly place all the dirt back over the 3/4" copper pipe. You will also need to wet and tamp the ground over the copper pipe.

Then hook up the wire to your radio.

[desertengineer1]

An RF ground is a different animal entirely. HF antennas may require an enhanced ground, usually at the antenna site, especially for vertical antennae not having sufficient radials. Keep your cotton picken hands of RF radiators! These can shock and burn you , and unlike Gamma radiation, you won't develop superpowers as a result of exposure.

Major Lord

In this case, you become the ground.  RF burns are NOT fun. 

[arajca]

I've read the item a few times. I presume the strike was probably within 15'-20' of the cadet. Even if the antenna and trailer were properly grounded, if the cadet was by an open window (the article states the cadet was inside the encampment hq), he probably would have still received a minor shock just from proximity. The limited description indicates to me that the cadet did not receive the shock through the power system.

As for the equipment that was being used, remember, he was inside a building, not a trailer.

[desertengineer1]

CUL's and other radio heads:  The most recent issue of The Sentinel described an incident in which a cadet was zapped (not injured) while working in a comm trailer, and blamed a lack of proper grounding.

Given that our SAREX's and events are usually in borrowed buildings, I'm not about to pound an 8 foot grounding rod into the ground (or a parking lot.)  I'm curious what others typically do to ground radios and antennas in a temporary install.

If in a parking lot or concrete pad, the RIGHT thing to do is tie the trailer to the single point ground (or Earth Electrode System - EES) of the structure feeding it power.

If you are using a generator, it can get a little more complicated.  The simplest answer is to tie the generator and radio ground point to the single point ground of the structure (Radio --> Generator --> building EES) and KEEP power isolated as much as possible.  i.e. try to keep everything in the trailer on the generator and everything in the building on building power. 

Yeah, that's hard to do, but will lower your risk of damage/injury if there is a ground fault somewhere. 

[arajca]

If you can place something into the ground purchase the following items from your local hardware store:

10 feet piece of 3/4 " copper plumbing pipe
Electrical pipe ground connector
#10 electrical wire (length depends on how far your trench is from the radio)

Attach the electrical connector and wire to the 3/4 " copper pipe.
Dig a trench at least six inches deep and place the copper pipe in the ground and cover over with dirt. Make sure to frimly place all the dirt back over the 3/4" copper pipe. You will also need to wet and tamp the ground over the copper pipe.

Then hook up the wire to your radio.

I take it you are running the pipe horizontal, instead of vertical?

[desertengineer1]

Clamp to a Pad Eye on the ramp.  They are usually connected to a huge mesh of steel screen embedde in the concrete...

NO!

You do not have guarantee the pad and the power feeding structure are equal potential. 

Only if you used a ground continuity meter to verify NEC (10 Ohms, I think) can this be trusted.

[desertengineer1]

OK, here's a good place to start...

www.tscm.com/MIL-HDBK-419A.PDF

[arajca]

OK, here's a good place to start...

www.tscm.com/MIL-HDBK-419A.PDF

Nothing like a little light reading before bed. j/k

Thanks for the link.

[desertengineer1]

Nothing like a little light reading before bed. j/k

Thanks for the link.

NO KIDDING!  Yeah, it's one of the driest documents I've ever worked with - but good info.  Handbooks are intended to be guides for design and in this case, give you the info to keep risks as minimal as possible within your design constraints.

It ties well with what we do.  No, I don't have 200' of #6 AWG stranded laying around to ground everything to NEC.  But..  I can take steps to avoid the bigger landmines.

During our SAREX this weekend, I had minimal grounding resources and a single comm trailer provided by the local Emergency Management folk - generator fed and on concrete.  The only option was to either tell the IC can't do it, I'm going home, or lean into available options.  We leaned to procedure.  I briefed to the Safety officer, IC, and MRO's that under no condition will the trailer be operational in lightning hazards.  our procedure was to disconnect the antenna cables, pull them out away from the trailer and go in the hangar office.

[SarDragon]

Most hangars are tall metal objects, so stay away from the walls and supports if you use one for shelter...

Watch out for the same thing in concrete block structures. The walls retain enough moisture to give you at least a small zing if lightning strikes the building or nearby. BTDT. Not fun. No interest in a second experience.

[Airrace]

If you can place something into the ground purchase the following items from your local hardware store:

10 feet piece of 3/4 " copper plumbing pipe
Electrical pipe ground connector
#10 electrical wire (length depends on how far your trench is from the radio)

Attach the electrical connector and wire to the 3/4 " copper pipe.
Dig a trench at least six inches deep and place the copper pipe in the ground and cover over with dirt. Make sure to frimly place all the dirt back over the 3/4" copper pipe. You will also need to wet and tamp the ground over the copper pipe.

Then hook up the wire to your radio.

I take it you are running the pipe horizontal, instead of vertical?

Yes the pipe is horizontal.

[Airrace]

Try to remember that electricty or lighting will always follow the shortest path to ground.

If you are woried about lighting strikes then you will need to install a lighting sure protector. This will prevent the lighting from traveling past the surge protector.

If you have a generator or other power source make sure it is adequitely grounded which means connection from ground lugs on the equipment to the single ground point of a ground rod or metal structure. 

[desertengineer1]

Try to remember that electricty or lighting will always follow the shortest path to ground.

If you are woried about lighting strikes then you will need to install a lighting sure protector. This will prevent the lighting from traveling past the surge protector.

If you have a generator or other power source make sure it is adequitely grounded which means connection from ground lugs on the equipment to the single ground point of a ground rod or metal structure.

This is not correct.

The main lightning (return stroke) will follow the path established by stepped leader ionization paths, and is commonly NOT the shortest path.

Lightning strikes don't follow the same physics as we're used to with batteries and AC voltages.

When two opposing charges approach each other, an electric field is present.  The strength of the electric field is a product of the charge magnitude difference and the distance between them.  It has units of volts/meter.  Air at sea level pressure ionizes at around 10,000 V per centimeter.  The initial magnitude of stepped leaders can peak in the millions if the timing is fast enough.

Depending on the substance between the charges, at a certain field magnitude, electrons will begin to come out of their orbits and the material will ionize.  Free electrons means it is now conductive like a metal (factoid - metals conduct electricity because their electrons are freely moving to begin with).

Although metal objects are common targets of lightning strikes, they are not all the time.

The bottom line is this...  Anything will conduct electricity given a high enough electric field - and lightning paths are established by fields of enourmous magnitude.  Just prior to lightning strikes, charges move, the field adjusts, the charge moves again, and so on.  The magnitude of the electric field follows a 1/R^2 behaviour, which means extreme magitude at small distances.

Anything is a target in a thunderstorm if exposed to the electric field between terrain and cloud, and will happily conduct the return stroke if ionized.  This includes the wood in your house, fiberglass flagpoles, even the rubber of your tires.

My point is DO NOT ASSUME lightning will strike only metal objects.  We get at least one house fire per storm here due to the above mentioned physics.  And most of them are right next to a tree or grounded metal telephone pole.

Second serious misconception - SURGE ARRESTORS WILL NOT PROTECT YOU FROM A DIRECT STRIKE!!!!!!!!  THESE DEVICES ARE TO PROTECT THE EQUIPMENT FROM TRANSIENT VOLTAGES OF NEARBY STRIKES OR CONTACT WITH LOW VOTLAGE POWER LINES, ECT..

Surge arrestors are designed to connect the inner and ourter conductors of transmission line when the potential between them exceeds a certain magnitude, usually 300 volts.  They are usually electrodes mounted in a gas like zenon or argon, that ionizes (conducts) when a certain field strength is reached.  It will short the coax line, preventing distructive current between the center conductor and shield in the front end of the radio. 

If an antenna is struck directly, the initial potential can be in the hundreds of thousands of volts, with a peak current of hundreds of thousands of amperes.  There is enough energy in the larger strikes to explode trees, brick walls, and rocks. 

If your antenna line takes a direct strike, it, along with your equipment, has a survivability of about 0.01%.

Again SURGE ARRESTORS WILL NOT PROTECT FROM DIRECT STRIKES.

[desertengineer1]

I need to also throw out a disclaimer...

Commercially installed antenna systems have several required actions to prevent return stroke currents.  These are required by BCSI, NEC, and other similar standards...

Towers (depending on the type) usually have one or sometimes two large copper conductors from the top to the bottom.  This prevents excessive currents in the steel structure which can damage joining sections and reduce the operational lifetime.

Antenna mounts are metal and are bolted directly to the steel frame, as well as grounded to the ESS wire or bonded directly to the structure with a lightning down conductor.

The coaxial feedline shield also grounded directly to the structure or ground wire within a few feet of the antenna, immediately before the bend away from the antenna structure at the bottom, and (depending on run distance) grounded to the structure EES before entering the building.  Some codes require intermediate grounds between the antenna and the tower bottom.

Thirdly, surge supressors are installed before the coax enters the equipment.  Equipment racks are grounded to the EES as well - usually with #6 stranded copper or copper strips.

Altogether, these minimize voltage differentials to the coax cable and the radio.  remember it's a function of ohms law.  Even if the resistance is small, a current of 100,000 amperes can do some damage.