Ground rods and exothermic welding

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AC0GV, Mar 26, 2020 at 4:47 PM.

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  1. AC0GV

    AC0GV Ham Member QRZ Page

    I mentioned cad welding in a post a few days ago and today found my pictures. They are a permanent joint and will not corrode. I used the Cadweld one shots but they also come in other forms. They must be the correct size for your ground rod and wire size, or the molten metal will run out like mercury.
    cadweld 2.JPG Cadweld1.JPG
     
    KK4NSF likes this.
  2. KK4NSF

    KK4NSF Ham Member QRZ Page

    Cad Welding is the best possible joint for bonding grounding rods to grounding cables. That is why they are required by many building codes for commercial lightning protection. I shot a few thousand of them back when I was a lowly Engineer-in-Training. Then later when I got my license, I had the job of supervising all the new EIT's. That was a lot more fun!

    As you pointed out, you must have the right mold and shots for the size of bar, and the cable. For a typical ham it can get pricey unless you have a whole bunch of cables to shoot. I do know however of one club that all went in together, bought the molds, and shot everybody's grounding system as a club project.
     
    W1TRY likes this.
  3. NG1H

    NG1H Ham Member QRZ Page

    A Cadweld connection is not just for the ground rod. You can also use it to attach the cable to the tower, make splices in cables and ground rods, all sorts of things. The hard part is finding someone with all the molds because as KK4NSF mentioned they can get pricey. The cost of the "shot" isn't too bad, though.

    As others have mentioned it is the best system I've seen for attaching ground cable.
     
  4. W9KEY

    W9KEY XML Subscriber QRZ Page

    I used some expensive Burndy GAR644C clamps to build my perimeter ground system, but in hindsight now wish I'd gone the cadweld route. Wasn't able to find any local hams with direct experience, which contributed to my choice of the Burndy clamps (designed to connect a bare #4 stranded ground wire to the rod at right angles - thus allowing one continuous run of wire across multiple rods).

    One question I had - how often does the cadweld process "screw up"? I realize you must use the proper cup size for the rod and number & size of the wires, plus special clay to seal the gap area. But even with care, there must be a few joints that end up with problems? How are "mistakes" fixed? Can you "reshoot" a joint that doesn't look right, or is the wire sometimes burned away and thus not repairable?

    Maybe there are "never" any problems or misfires, but back when I was considering them, worried that as a new inexperienced installer, I might have more problems than I wanted to deal with. So for those that have only done this for one installation, how many joints had a "problem"? And were those repairable / salvageable?
     
  5. AC0GV

    AC0GV Ham Member QRZ Page

    I've done a lot of them over the years and screwed up my share. I have found that it helped me if I got the mold in place, heated it with a torch to dry it out and then filled it and set it off. Even then the finish is not perfect, as you can see in the picture.
     
  6. KB8VUL

    KB8VUL Ham Member QRZ Page

    Couple things.
    First is never try to cad weld to Rohn 24 or 45 legs. Wall thickness is not large enough and you will burn a hole in your tower.
    If you really want to cad weld to a 25G tower, get the correct clamp on mold and weld to a rung.

    Second, there are two secrets to cad welding and getting it right.
    The first is it HAS to be clean. Bare metal, clean copper wire. Anything less will not work well or not at all.
    Second is preheat.
    If you are going on heavier material, it should be preheated. Get it up to 400 degrees before welding it if it's anything more than a wire to wire or wire to ground rod connection.
    There are molds for flat bar, pipe from 1/2 inch to 12 inch, stranded to solid wire of all the larger gauges of wire. To find what you need go to the CADWeld web site and look at what's available.
    Molds are not cheap. It's best to get a group together if you are needing molds outside of the basic ground rod molds. Rod molds are called ONE SHOTs. the mold is ceramic and sets down on the top of the ground rod and the wire goes through it. THey are good for a single shot, and are then broken off.
    Multishot molds are graphite blocks machined for specific wire sizes and surfaces. These HAVE TO BE DRY when you use them. Once you have preheated your surfaces, preheat the molds. The molds are rated to take a shot at over 5000 degrees. No propane torch can even approach that. You can't get them too hot with a propane torch. But if they are wet and you fire them, they WILL explode. You are bringing them from air temperature to over 2000 degrees in a matter of a second or two.
    If you are going to get molds,,, find others that also are needing them and split the cost. Or do it as a club thing where the club owns the molds. Another option is call a commercial electrician and see if they have the molds you need and will come out and make your connections. It may be cheaper than buying a mold for two connections.

    If you are CADwelding to galvanized, it has to be ground off and clean. If not the weld will fail. Also, ANY time you are welding galvanized clean it, weld it, and then get a can of COLD GALVANIZE paint and paint the surface while it is still warm (NOT HOT). This will seal the area where you did the grinding and welding and protect it from rust.

    Lastly, there are some tools and tips.
    The spark ignitor for doing CADwelds is a must. The sparks are hot enough to get he magnesium powder going, a lighter, or even a propane torch is NOT hot enough.
    The shots are made of two materials. THe main shot material is basically thermite. The second part is magnesium powder. The powder is in the bottom of the shot. You will put it in last and save a bit to put on top of the mold you are using to get the main charge burning. Nothing short of an oxy/acetylene torch will light the main charge if you don't get the magnesium in there right.
    NEVER double charge a mold. If you get a charge missing the magnesium powder with get a magnesium fire starter block and scrape off a pile of it from that, or dump it out and put in a full fresh charge. Double charging will get you liquid metal going everywhere, will burn holes in things and just generally be a bad scene with lots of fire added.
    Speaking of fire,, you are dealing with stuff that will burn through most anything. Having flammable stuff around is a really bad idea.
    If you have a fire,,, do NOT spray water on the mold for at least two minutes. Get back and let it start cooling. Flash cooling a mold will burst it, throwing molten metal all over the place, more fire more burns and more bad stuff.

    If you haven't figures out... its' hot... damn hot... and angry... angry like your wife gets when you tell her you bought a new radio.
    Wear safety glasses or a face shield... or both and a GOOD pair of WELDING gloves when doing shots. Honestly, wearing leather, or a welding coat, is of little use... it will burn right through it. But protect your eyes and hands. and at least wear long sleeve shirts and long pants.
     
    W9KEY and KK4NSF like this.
  7. K4SAV

    K4SAV Ham Member QRZ Page

    Be sure you use gloves and eye protection. See all those sparks in the air when this is first ignited. Welding gloves would be better than the ones I am wearing.

    Jerry, K4SAV

    one shot.jpg
     
  8. N1LOU

    N1LOU XML Subscriber QRZ Page

    I think before I go the CADWELD route, I'd probably try to save money and just drag my TIG welder out to the location.
     
  9. N5TJD

    N5TJD XML Subscriber QRZ Page

    While not ideal you CAN use a propane torch to light the starter. It's not something I enjoy doing but it works. Also depending on mold sizes, you can use duct seal to plug gaps between a conductor and the graphite mold, if you use the correct size mold it isn't much of an issue but at around $10-13 a shot it is cheap insurance. This becomes less effective though if you are making multiple connections as the mold get hotter, the duct seal doesn't like to adhere as well but it works great for one offs.
     
  10. KB8VUL

    KB8VUL Ham Member QRZ Page

    One other thing I will say here... NEVER UNDER ANY CIRCUMSTANCE should you SOLDER ground connections. EVER!!
    If you don't want to CADweld them, braze them with bronze rod, but NEVER solder them.
    Solder has a low melting temperature. If it takes a strike, the solder will melt and then vaporize and be gone.
    The next hit will find ground through the ground prong on your $2000 radio. And it's not gonna like it.

    Motorola, and several cell carriers, use an install standard called R-56.
    https://www.blm.gov/sites/blm.gov/files/Lands_ROW_Motorola_R56_2005_manual.pdf
    The class for learning to be an R56 installed is a week. You renew it every 4 years. And are required to retake the training every 8 years.
    They give 2 ways of joining ground cables.
    First is Exothermic welding or CADweld
    Second is a irreversible crimp with a compression force not less than 15 tons.
    So the split nuts, and those bolt on things for ground rods are out.

    Why the crazy stuff and 518 pages of installation standards?
    Because at a dispatch center with a transmission tower located at the center, there is a DIRECT WIRED path between the top of said tower and the headset that the dispatcher has on their head.
    Now there are all sorts of things the standard spells out. Down to the distance between the lights in the room and the cable tray. But the grounding part is worth sitting down and reading.
    Should you as a ham build to that level? For ham operation, it's really not necessary to put a halo around your ham shack. Or to install a ground ring around your whole house and tower installing dozens of ground rods.
    But relying on one ground rod that would only go in 6 feet because you got lazy, and didn't finish driving. And then didn't want to run the ground system over to the electrical panel because 2 gauge wire is too expensive. Well having two building grounds is terrible idea because it becomes a really good setup for a voltage differential to occur. Meaning it the right side of the house has a strike near it. The lightning will come IN on the ground rod because the panel is over there, and then traverse the grounds in the house via the wire in the walls, into your radio and out your better constructed ground system on the left side of your house. Any guesses what happens to your radio when that happens? Run the extra wire from your master ground bar ( main ground bar fed from your ham ground rods) over and into the electrical panel and to the ground bar in the panel. It's just better that way
     

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