Acorn Ground Rod Clamp Sizes Question

Discussion in 'General Technical Questions and Answers' started by N0TZU, Jun 27, 2020.

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  1. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    A practical question for the electricians here -

    Is it allowed to use a 5/8” clamp on a 1/2” copper clad rod with a slight mushroom head? Obviously I don’t want it to loosen over time.

    Some retailers show “G5” types as separate models for 1/2” and for 5/8“, but then some show the very same 5/8” part number as applicable to both diameters. Looking at some spec sheets from the manufacturers, I seem to see similar confusion.

    The “universal” acorn clamps are clearly for 1/2 through 3/4” diameter rods and their shape is obviously made for that purpose, but they are larger and cost more of course. Then there are rebar clamps which are larger for the same nominal size and would go over the mushroom, but I’m not sure if they are compatible with copper rod.

  2. WA4SIX

    WA4SIX Ham Member QRZ Page

    Always put the clamp on before pounding it in.
    Yes, it will clamp just fine.

  3. WB5THT

    WB5THT XML Subscriber QRZ Page

    Use a hacksaw or reciprocating saw to cut the mushroom head off.
  4. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Thanks. Yes I put them on first but in this case the rod is already in the ground. Not so easy to file or cut.

    Today I went to the box store to look at them and readily found an acorn clamp listed for 1/2 and 5/8 rod plus 3/8 and 1/2 rebar. The write up for the same item on their website listed only the 5/8 rod.o_O
  5. W9KEY

    W9KEY XML Subscriber QRZ Page

    One of the things I don't like about those acorn clamps -- I read somewhere that typical stranded #4 copper ground wire should be installed with a minimum 8" bend radius (presumably to minimize inductance in the event of a large current surge).

    Assuming that's true, it's really hard to run a wire from rod to rod without digging up a huge deep area for those two 8" 90 degree bends. Only clamps I could find that allowed the wire to run perpendicular to the rod (versus acorn clamps where the wire runs parallel) were made by Burndy and they are expensive at >$50 each. Guess that's another reason to Cad-Weld the wire to the rods when interconnecting them. But even then, it might be handy to first put a couple acorn clamps on each rod, just in case you want to hook something to it later (after the wire has been welded across the top).
    KB0MNM likes this.
  6. KB0MNM

    KB0MNM Ham Member QRZ Page

    If you have a few extra dollars and want a more permanent bond, I would have to agree with W9KEY that a Cad-weld would be a better solution than an acorn clamp. There are new Cad-weld 'shots', made by a company called Erico. Where the old ones required a very expensive 'graphite block' mold, the new shots are ceramic and require a lot less of someone who has not done the work before. I highly recommend the training video before attempting the work, and appropriate protection regarding eyes, face, hands, and general fire protection for any thermo-chemical welding ( irregardless of old or new system- the video should be seen first ). I have no financial stake in Erico(mfr) nor Cad-welding (tm possible).
    W6KCS likes this.
  7. W9KEY

    W9KEY XML Subscriber QRZ Page

    I did some searching last summer, and recall Cad-Weld "shots" were about $12 - $15 each which is less expensive than the Burndy clamps I used. But there are a number of options available, so you have to pick exactly what you want to do at each ground rod (for example the rod diameter, and number of wires to be attached - 1, 2, 3, or 4). Each option requires a different ceramic "cup". You need to also use their "clay" material to seal the holes (for sure the bottom one) to prevent powder from leaking out, and you must use their "igniter" gadget (or something similar) to light the charge.

    In hindsight, wish I'd gone that route instead of the mechanical clamps. But worried at the time if I screwed up one of the welds in the middle of my perimeter ground that it might be hard to "re-try" a second time with a partially burned rod and ground wire. Would be nice to help someone else first to get the hang of it - but the videos look easy enough.
    KB0MNM likes this.
  8. KB0MNM

    KB0MNM Ham Member QRZ Page

    I seem to remember that some companies which sell ground rods ( maybe Harger ) also sell an adapter coupling for a hammer drill which is supposed to keep the top of the rod from 'mushrooming' in the first place. I did hear that it can get 'stuck' to the rod in certain cases. Others have said that getting the ground wet in advance of 'pounding', or using an adapter for a garden hose that 'sleeves' the rod with a 'tee connection on top', will speed the installation and avoid the distorted 'mushroom top' on your ground rods.
    Yes, regarding the Cadweld shots- their 'clay' contains no water ( that would produce a sudden burst of steam ) unless pieces sit in a wet toolbox for a month. The material is a mixture of ground-up metals, and so a very high temperature is needed to start the reaction. Most mistakes in this involve the distinction between the main material and the igniter powder- it is a very similar color and found only in the bottom of conventional ( graphite mold ) shots. The material needed is finely powdered magnesium or similar- such as would be made by a 'metal match' found in the camping section of many larger stores. Electric igniters, sold with some 'shots', are somewhat similar to those used in model rocketry. A fine wire inside will glow like a filament in a light bulb, which gets another group of chemicals 'started' for a hotter fire.

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