Non conductive ham masts

[daveleonard]

I have heard it said recently that under no circumstances should a ham use non-conductive materials like pvc to make a ham mast for his antenna. Why is this? If the vertical antenna atop the mast is securely and deeply grounded with deep sunk rods, The lightening arrestor is also grounded, the coax cable is ground also, and every piece of equipment in the shack is ground to deep sunk copper coated rods and all appliances in the shack are grounded to a common plate and cross ground to the antenna ground, why is it not good to use PVC? Pvc is lite, strong and easy to put up and take down especially on a tilting mast.

 

[n5ims]

Could it be that the wire(s) used to ground the antenna just might act as a fuse and open up due to the high current and voltage from a lightning strike while the metal mast that's several hundred times larger may be enough to handle that load from the antenna to the ground?

Could it be that PVC is quite weak compared to a metal mast? How about that PVC may weaken due to the UV bombardment from the sun while a metal mast won't. How about a PVC pipe will flex in strong winds while a metal mast will need much stronger winds to do so. PVC can break if something mounted on it is over tightened while metal may bend a bit, but provide a lot more feedback to the "over tightener" so they stop prior to doing any real damage.

Could it be that PVC will help generate static while a metal mast will help dissipate it? There may be other reasons, but I can't think of them at this point.

 

[prcguy]

An antenna mast or tower is not considered a ground conductor for lightning no matter how large or thick or even if its made of solid copper. An antenna ground is always run separate from the mast and tower and bypasses all mast mounting points, tower leg junctions, etc. This is not my opinion, its the electrical code in the US.

Otherwise like n5ims says, PVC is not the strongest and the white stuff doesn't last very long outside if not painted due to UV. If you have a lightweight antenna and PVC will hold it up and its not going to be outside till eternity then why not use it?
prcguy

 

[n5ims]

While neither the mast nor tower should be considered the main ground conductor, they will indeed conduct during a large direct lightning strike. If not, the typical ground wire used will not handle but a small fraction of the 45,000 amps from a strong strike. A separate ground is necessary both to meet code and to ensure that the current flow from static and indirect strikes have a direct and low resistance path.

 

[daveleonard]

Learning a lot.

I guess the consensus then is to use a metal mast of some sort grounded by itself, the antenna and coax also having their own ground. The issue here is I am to darn old and creaky to climb a tower so I am limited in the length of the mast in height and weight. I plan to use a "tilting" mast which I can walk down when I need to work on it. I think that will be fine for my hf vertical. I simply do not have the room necessary for a horizontal dipole. I think for my 2 meter antenna I will get some young and foolish kid to climb a tree and place it as high as possible since this a "line of sight" antenna. I don't care so much if I lose the tree or antenna to a lightening strike as the antenna is not all that expensive. I just don't want the surge coming into the ham shack. So if I ground out the coax line to a good deep ground, would that be enough to be safe inside the shack? Thanks

 

[WA0CBW]

As long as you have a ground wire (#6 or larger) connected to the metal mast or the ground part of the antenna, ground the braid of the coax before it enters the house, and use a surge arrestor on the coax grounded to your ground rod you are good to go. As stated for all the reasons above a PVC mast is really not suitable for the application. Don't forget that the NEC requires ALL grounds be connected to your Electrical entrance panel ground. All grounds (water pipe, CATV, satellite, phone, etc) should be "home runs" to your main single point ground (no daisy chains).
BB

 

[LtDoc]

Is there any particular benefit from using PVC as a mast? Not really. PVC has some draw-backs. If those draw-backs make it unreasonable to use then don't use it. If they aren't particularly a problem for you, then why not?
A non-conductive mast can certainly be a benefit, but you really need to evaluate how much benefit it will be before changing everything. Any 'benefit' has to be weighed against it's practicallity(?). Would it be worth the time/effort/expense??
- 'Doc

 

[daveleonard]

A shock

I am a retired American living in the Philippines on a small island in the Pacific. This may come as a shock, I know I was shocked, the electrician I used to install my electric when I built the house did not connect the system to ground! Over here it is 220 as opposed to 110 in the States. I asked him about this and he said it was not necessary and hardly ever done. It passed the electrical inspection under the permit. Since I was afraid to run a ground wire myself as I did not know that much about the box installed, I let it go. So far no problems. But, having learned what I have about ham radio I see I need to have that done. I know I'm going to ground out all of my ham components correctly and if I can get the house grounded I will ground to that also.
Thanks for all the info, I will put it to good use. Dave

 

[wbswetnam]

I am a retired American living in the Philippines on a small island in the Pacific. This may come as a shock, I know I was shocked, the electrician I used to install my electric when I built the house did not connect the system to ground!

I have lived in Latin America (more specifically, Nicaragua) and I have seen some very questionable electrical house wiring jobs, too... especially those electric showerhead water heaters, jerryrigged to 220V and no ground! Yipes!

Back to the subject of mast grounding - I was at a local monthly ham meeting just last night, and I also asked about masting with fiberglass masts and what kind of ground I needed. One guy (an Extra class) told me that for several years he has had a 40' mast for a 2m J-pole in his back yard and he has never bothered to ground it, and he's never had a problem... ???

 

[LtDoc]

I can honestly say that over 40 some years I haven't grounded any antenna. None of them have been particularly high, and we don't get a huge amount of lightning strikes. I may be 'pushing' my luck, but I've never had equipment damaged by a lightning strike or even a close one.
A really adequate electrical safety ground system is NOT a simple thing at all. One or two ground rods are worthless as a safety ground. If grounding an antenna makes you feel better then do it.
- 'Doc

 

[daveleonard]

I plan to use four ground elements for the antenna, either four cold water pipes or rods driven six or eight feet in the ground. I plan to connect all four points to a metal plate like tin and then ground the mast into that with braid. I will ground the coax braid into the shack equipment plate and into rods once again. I hope that is enough, nothing fancy but a good ground.

 

[PrimeNumber]

I have lived in Latin America (more specifically, Nicaragua) and I have seen some very questionable electrical house wiring jobs, too... especially those electric showerhead water heaters, jerryrigged to 220V and no ground! Yipes!

Aieee! Wonder what they look like? I'll just mosey over to the Darwin Awards site and look up a few pics of these devices in action....

Back to the subject of mast grounding - I was at a local monthly ham meeting just last night, and I also asked about masting with fiberglass masts and what kind of ground I needed. One guy (an Extra class) told me that for several years he has had a 40' mast for a 2m J-pole in his back yard and he has never bothered to ground it, and he's never had a problem... ???

The problem with directly grounding at the antenna and at the shack is that it sets up a ground loop. How significant this is will be extremely situation-dependent, I am sure.

 

[prcguy]

Do a search on "NEC article 810 antenna grounding" to find out what meets code. You may be wasting your time with grounding that will not survive anything in a lightning storm and also not meet code.
prcguy

I plan to use four ground elements for the antenna, either four cold water pipes or rods driven six or eight feet in the ground. I plan to connect all four points to a metal plate like tin and then ground the mast into that with braid. I will ground the coax braid into the shack equipment plate and into rods once again. I hope that is enough, nothing fancy but a good ground.

 

[wbswetnam]

Aieee! Wonder what they look like? I'll just mosey over to the Darwin Awards site and look up a few pics of these devices in action....

They look something like this:

http://mojotrotters.com/wp-content/uploads/2009/07/DSC06629-1024x768.jpg

Welcome to third-world wiring standards!

 

[davenlr]

I had a 70' tower struck by lightning. It vaporized the 2" wide ground strap from the tower base to the ground rods. Luckily, no equipment was damaged at all. That said, Ive never used inline coax ground devices or grounded the equipment past using the ground prong on the power cords, except for my HF rig, which runs on 12V.

 

[daveleonard]

Mast and ground.

My mast will be 30' at most and will likely be a verticle hf rig. I know that some antennas do not need grounding, I just don't know yet which ones. I don't believe I will ground the antenna at the bottom of the mast but will ground the coax to the common plate before it enters the shack. The metal mast I will ground.
By the way, the common ground plate, is it best to put it near the rods outside the shack or can it be in the shack itself. I used a ply board one half inch to place my grounding circuit on and all equipment will be coming off that to the ground rods. I used brass strap to attach my various equipment grounds and will connect that to deep ground rods. I know copper is better but its very hard to find here.

 

[WA0CBW]

The ground bus should be mounted on insulated standoffs. Ground rods should be no closer than 2 times their length. An 8-foot ground rod should be 16 feet from the next 8-foot rod. Placing them closer does not increase their effectiveness.

 

[daveleonard]

Thanks WA0CBW for the reply. I think I got it. This is my set up: the equipment will be located on a long table in front of a window. I plan to drill a hole in the wall under the table for access of my cables. The ground set up will be directly outside, maybe four or five feet from my equipment directly to ground. If I can place my insulated stand off under the table it will be very convenient for me to access. Putting the plate outside would require me to build some sort of support or cabinet off the ground for it. I just want to work with the situation I have but at the same time I want to be safe. Thanks.