For a number of years, I’ve had reason to suspect my house’s ground isn’t what it should be. Then, again, recent events may have just made me paranoid. But I think I’m right….
I went on a energy conservation binge several years ago, and bought a TED 1002 to help understand where my power was going. But I had quite a bit of trouble with it, and it is clear from reading its support forums that its Achilles heel is susceptibility to electrical noise. In particular, if my well pump went on, its display would stop hearing the MTU’s; as we have geothermal heat pump, this is most of the time I’m using most of my power. Adding a filter on the well pump circuit reduced, but did not eliminate the problem. I was able to get it to work just well enough to debug a number of problems in the house’s energy consumption, but never well enough to really reply on it overall. I’ll try to see if it works properly sometime soon (but I think one of it’s MTU’s was damaged by lightning as well). The one working MTU now seems to signal fine even when the heat pump and well pumps are running, so I’m hopeful I’ve also cured my electrical noise problems.
The existing ground for the entire house had been solely a thumb sized piece of stranded copper cable, that runs entirely across the house to the well located on the far side of the house from the power panels, in parallel to other circuits in the house. This is far from desirable for a lightning ground, though clearly meeting code requirements, even if well bonded to the well casing well; and I have no good way to inspect that bond regularly. Some of the reading I had done indicated you may have noise in your house wiring if your grounds are not well bonded to ground.
We have a iron fence (with normally closed gate) that runs a long way from the house under several more oak trees; I was concerned about ground bounce if one of the trees were hit, and you should always bond any metal objects within 4 feet of a ground system (for safety in a storm).
I decided to install a much better ground for the house, and for it to be located on the side of the house nearest the power/cable/telephone entrance. Additionally, the pool pump had failed this time, which was probably caused by a poor neutral bond in the pool shed (which has its own ground, as it should; but I’ll probably add a fresh ground rod to it sometime soon).
As part of relocating my Comcast cable, they had to trench along the side of the house; I asked the Comcast contractors who did the work not to fill this trench, just to save effort.
If you read the ARRL documents, you may have learned that copper strap is much better than wire or cable per pound of copper. This is due to the skin effect of conductors, and the fact that lightning occurs so fast it behaves as RF energy, rather than DC current. Big copper cables like the existing house ground are also a PITA to deal with, being very hard to bend. So I decided to do this right, and use 2″ copper strap rather than wire or cable to connect my single point ground system to the new ground rods I had installed.
While doing my homework, I learned that exothermic welding of the strap to the ground rods is much better than the typical mechanical bonds generally used. Exothermic welding is exactly like thermite: it is a chemical reaction that rather than resulting in molten iron, results in molten copper. This is sometimes called “cadwelding” after the name of one of the companies that supplies the molds and “shots”. I don’t want the ground rods sticking out above ground just to be able to inspect the bonds; if exothermically welded, there is no possibility of corrosion at that joint, since it is an actual weld, and I could then bury the ground rods and forget about them forever more.
Additionally, the copper ground rod clamps to properly mechanically bond copper strap to the ground rod turn out to be expensive (something like $31 a piece; versus $16 for a “shot” when exothermically welding), and the clamps take time to clean and assemble. So there is a break-even point where connecting the straps “right” via welding is cheaper than doing it with mechanical bonds.
And I’ve always liked fireworks :-).
So I decided to exothermically weld the strap to the ground rods despite the marginally higher cost for five ground rods. Ding so was much simpler said than done: finding the right mold to order and where to order it was very time consuming, but in the end I succeeded. And it worked like an amazing champ! The 2″ copper strap was solidly welded to each ground rod really quickly and easily. No possibility of any problems, and it was much faster than assembling mechanical clamps.
Erico CADWELD® is the well known guys on the block. But I couldn’t figure out for the life of me if Erico sold molds for strap to ground rod. The other guys who sell exothermic weld molds are Harger: the Harger Ultraweld, and they indeed do make molds for copper strap. The handles for the molds are usually interchangeable between vendors, I gather. You have to buy both a mold and a clamp handle. So I went with the Harger mold. I probably should have video’ed the process, but it would have been completely redundant to the existing videos, such as this YouTube video, one of many.
Feeling too poor after this event to immediately install a perimeter ground system all the way around the house, I decided to put in five ground rods on two straps. Each segment of the iron fence is also bonded to the straps, using special stainless steel pipe clamps (the clams have an extra piece of stainless steel tack welded to them, so that the copper does not bond directly to the steel; you’d have electrolytic corrosion if you don’t take that precaution).
You need to space the ground rods at about twice their length apart to dissipate the energy (about 16 feet, given these were 8 foot ground rods. With only modest additional digging beyond what Comcast had done for me, we were able to get the strap from the house to the five ground rods using a bit under 100′ of copper strap. Thankfully, we were able to get all five ground rods almost completely driven without excessive effort; I had worried about hitting ledge or a big rock (this is New England, after all). The tradesman I used was a local guy; your conventional electrician will almost certainly charge much more and be just as clueless, so you might as well work with someone who can take direction and do what you ask. Even with a snafu about having the right tool for pounding in the ground rods, we finished up all five including reburial and cleanup in one day, so I got away with only about $400 for labor. It was probably 10 hours actual work to do all this (but my bad back would not have dealt with driving the ground rod, so I had to hire the hard pounding and digging).
I’ve updated the picture on the previous blog post with the finished work (though I just added the last bolt after I took that picture today).
After properly cleaning the straps, applying the copper joint compound and bonding them to the fence, and doing likewise on the single point ground system, and all the cleanup, I’m done! This time, I used a little copper plate over the ends of the straps and bolted that to the SPG panel; I’m much happier with that solution than the bolts I used directly when bonding the strap from the SPG panel to the existing house ground cable.
Someday I might like to install a perimeter ground; who knows if I’ll ever do so. I definitely want to redo the ground rod at the pool shed, as it is old enough to possibly need replacement.
And, of course, I’ll never know if I’ve done all this effort right, statistics being what they are. But mother nature will tell me if I’ve overlooked anything sometime, I expect. Such is life…..
To save others who want to exothermically weld strap to their ground rods, I include here exactly what I ordered via my local electrical supply company (Harger will happily tell you who acts as distributors for them in your area). I found it really hard to track this information down, and was unable to find anyone stocking molds for strap online; Harger’s part numbering system for molds is pretty inscrutable and I finally confirmed the numbers with a call to Harger. I suspect a lot of ham operators give up and order ground rod clamps and/or use ground wire/cable in disgust, despite it being better and possibly cheaper to exothermically weld strap. It took less than a week for the order from Harger to be fulfilled, even via my local distributor. The part number below is for 2″ x .022″ copper strap (Harger says the molds aren’t very sensitive to the thickness of the copper strap).
1 HGR GVSO582016K 166.86 166.86 10 HGR UWM200 WELD METAL 16.08 E 160.80 1 HGR MH1 MOLD HNDL CLMP 77.84 E 77.84 1 HAR MCBRSH1 LRG MOLD CLEANING BRUSH 8.08 E 8.08
As noted before, I could have lived without the clamp with some metal clamps of the right size, though the mold handle is certainly very convenient; and the mold cleaning brush can be almost any small stiff bristle brush (though probably not a wire brush; the molds are made out of graphite). Keep the mold bone dry.