At 12:25 AM 1/29/2006, Dick Green WC1M wrote:
>
>The note said all rebar must be bonded to the ground grid, and inspection
>will be required prior to backfill. My plan showed a ground system with 36'
>radials made of 1/0 wire Cadwelded to ground rods every 12 feet, and I have
>no problem installing a Ufer ground connecting the rebar cage in the pier to
>the radial system. I was thinking about doing that anyway, but hadn't done
>the research on it yet. I'm a bit surprised because our town is very small
>and has traditionally not had stringent building codes. Last time I put in a
>tower (1997), they didn't have any engineering requirements at all (they
>still don't require loading calculations, wet stamps, etc.)
The times they are a changin'
Many jurisdictions require UFER (or, in "code speak": Concrete encased
grounding electrode) these days, with no real exceptions. If they
periodically adopt the revised electrical codes, that would do it.
The interesting question is why they're requiring the rebar to be bonded to
your UFER ground. That's a pain, because it means the cage has to be
welded. Much easier to do the 20 feet of copper wire in the concrete thing.
>
>First questions: Are Ufer grounds commonly required by code these days? Have
>any of you out there in TT Land been required to install a Ufer ground?
>What's the best way to bond the pigtails to the rebar?
>
>A bigger concern is that I was going to try to dig the 2.5' x 2.5' x 4' hole
>by hand in order to get a nice square hole exactly to the required
>dimensions and pour the concrete against undisturbed soil. An excavator will
>be faster, but past experience leads me to believe the hole dimensions won't
>be perfect and I would end up needing a wooden form.
You'd only need a form at the top, right? (so that you have a surface that
is level to smooth the concrete to) You don't care if the excavator makes
the hole a bit bigger, and you just wind up buying a few more yards of
concrete to fill the hole. There's nothing requiring the base to be a
perfect square.
>Besides, the Foundation
>Notes in the Rohn catalog say that, except for pier-and-pad installations,
>the concrete must be poured against undisturbed soil. That's what I've
>always heard one should do. So, I'm planning on telling the building
>inspector that the manufacturer's specifications call for doing the pour in
>undisturbed soil and that they need to inspect the Ufer ground before the
>pour (i.e., there won't be any form and there won't be any backfilling
>unless I can't dig the hole by hand and have to use an excavator.)
>
>Second questions: Is it really better to pour against undisturbed soil
>rather than using a form? Would a form for a padless pier be a bad violation
>of Rohn's specs?
Yes, it really is better to pour against undisturbed soil. Unless you want
to spend a LOT of time and effort doing backfilling and compacting to get
the soil back to undisturbed condition.
>
>Further, it's not clear from the note whether the electrical inspector wants
>the anchor footing rebar to be bonded to the ground system, too. I don't
>want to do that for several reasons.
Might be too late, but perhaps your ground radials shouldn't be in the
plans to be approved? You're going to install them later, after all the
structural work is done.
You could point out to the electrical guy that those radials are purely for
RF grounding, and don't form part of the electrical or lightning protection
grounding system.
>First, I'd have to make the radials at
>least 80 feet long with a lot more ground rods. Second, the guy anchors
>won't be electrically connected to the tower because I'm planning on using
>phyllistran guys, so there should be little danger of a lightning strike
>compromising the anchor concrete.
Point that out to the plan checker. However, bear in mind that you'll
probably have some number of feet of steel guy attached to the anchor
before going to the synthetic.
> Third, as recent posts suggest, anchor rod
>corrosion can be accelerated if they are connected to the ground system.
>That's another area I haven't researched yet (i.e., whether to spend $1,500
>to protect my anchors from the battery effect.) I would think that
>connecting the rebar to ground would have the same effect.
>
>Third question: Has anyone out there been required to connect the rebar in
>the anchor pads to the ground system?
>
>Finally, the note (which I haven't seen yet) says something about conduit
>for electrical, radio and control wire routing to the tower (the run will be
>a little over 200'.) My plan shows "conduits" (I used the plural) for AC and
>other cables to the tower. My guess is the guy just wants to make sure I'm
>not running AC in the same conduit with the other cables and/or wants to
>make sure I know the code requires electrical conduit to be buried at least
>4' deep.
Or, you can bury it less deep and cover it with concrete, if that's an issue.
> But since filing the application I'm reconsidering whether I want
>to run conduit to the tower. I know the code would require me to do that if
>I run AC, and if I run one conduit I might as well run several. But AC isn't
>required -- it's just a nice-to-have, handy for rotor testing, plugging in a
>rig, power tools, etc. The decision will rest on just how expensive it will
>be to run the conduit. I haven't gotten quotes yet, but I know it isn't
>cheap to dig a 200' long 4' deep trench. But the real issue is whether
>there's ledge in the way. There was ledge when we dug the trench for my
>first tower (a motorized crankup that required AC), and it was *really*
>expensive to pound through it. Bottom line, if there's ledge in the way or
>the cost is otherwise too high, I don't want to run conduit to the tower. In
>that case, I would forego the AC and just direct bury the hardline and
>control cables in a shallow trench. My worry is that the electrical
>inspector wants me to use conduit even if I don't run AC.
>
>Fourth questions: Do building codes address non-AC cable runs? Has anyone
>out there been required to install conduit just for coax/hardline and
>low-voltage control cables?
yes, the electrical code DOES address low voltage cabling AND also coax and
antennas. Go to the Mike Holt website (http://www.mikeholt.com/) and
download his lowvoltage handbook (it's free). It covers most of the code
issues around low voltage control, coax, phone, etc. along with grounding.
By the way, there's a big difference between "power limited" low voltage
(called Class 2) and non-power limited. Low Voltage just means <50 Volts
(e.g. no shock hazard). Power limited means it's not likely to start a
fire. I know someone who got wrapped around the axle with the code
compliance folks with a high power low voltage system (battery banks) (for
which conduit IS required).
The code term for conduit, by the way, is "raceway"
>
>Our town has issued very few amateur tower permits (maybe four since the
>late 80s), so they don't have a lot of experience with it. I think our local
>inspectors are probably pretty reasonable people and if I can show them that
>common practice is otherwise, they'll accept it. But if it's in the code,
>then I may have to do it.
>
>Would appreciate any knowledgeable comments on the subject.
>
>73, Dick WC1M
>
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