>Of the catalogs cited, I'm aware of only one clamped connection
>(Burndy) that is specifically rated for direct burial (and
>certified by the NRC for that purpose). That clamped connection
>requires a hydraulic press for installation and is for copper to
>copper only - not for dissimilar materials. I'm not saying
>others don't exist. just that I'm not aware of them.
Blackburn, Burndy, Teledyne, and Thomas & Betts have several different
products for bonding / grounding purposes. Each of them has some products
U.L. approved for direct burial without the need for a crimper. Ideal, and
Ilsco both make aluminum alloy clamps for attaching either copper, or
aluminum wire to either copper tubing, or galvanized pipe.
>>Some of them are specifically rated for direct burial when
>>connected to steel, and for use in corrosive environments.
>
>I am very interested in this area. Can you point me to a specific
>clamp rated for this purpose? I am aware of several that are
>rated for application within a concrete pour. But I don't know
>of any that claim to be survivable long term in soil.
I'm speaking of a variety of clamps for different purposes. If you give
me a very specific application, I can see what would work best. For example,
the Thomas & Betts cat.# 3849 is a clamp U.L. approved for attaching copper
or aluminum wire to copper tubing, galvanized pipe, or ground rods in
corrosive environments, and is also U.L. approved for direct burial. I
believe that every acorn clamp I've ever seen for attaching to ground rods
was rated for direct burial. Enclosing them in an underground junction box
is not "direct burial", or "direct soil burial" as the NEC calls it.
>What caused the soil surrounding these clamps to be removed so
>that you could observe them? Most of the connections we bury
>stay buried until there is an observable problem or they find ore
>under the radio site.
I was referring to exposed connections, since that's what the original
post was referring to, but now that you mention it I have had many
opportunities to examine buried connections as well. I too, like Nate, am an
electrical contractor. I've done extensive grounding work at cell phone
repeater sites, and factories that manufacture explosive gases. The example
I'll use though is a military contractor that handles many types of
explosives. They take their grounding seriously. I've done many jobs for
them, installing many miles of underground conduit, and many miles of copper
cable in their ground grid. Each building would get bonded to two rings
around it, which in turn were bonded to the next building. Ground cables
were taken to any kind of metal object, or structure with metal. Every
trench would have a ground cable run through it, attached every so often to
a ground rod before the conduit was placed in. You can't dig through this
maze with a backhoe without locating many of the splices in the grid.
>I have a bronze clamp for connection of the power system ground
>at the service entry point to my house to a galvanized cold water
>pipe. This clamp is above grade in a very dry climate. The
>house was built in 1983. I go out annually and inspect this
>clamp. In the 4 years that I have been doing this, I have been
>forced to reposition the clamp twice. I have been required to
>tighten the screw that clamps the conductor every time I
>inspected the clamp. There is obvious degradation of the zinc
>galvanic coating where the clamp touches the pipe. I suppose I
>might be forced to replace this pipe in 20 years or so. But I
>would be replacing it now if it was a structural member of my
>tower.
A customer asked me to look at a problem today at a location that had a
history of abuse long ago. It's been over 30 years since any electrical work
has been done. I wasn't about to leave without taking the opportunity to
check the water bond. After cleaning off all the crud concealing it, I found
a perfect, solid electrical connection with no trace of corrosion. The
screws used on the clamp were rusted, but not the clamp or pipe. In fact, I
sometimes have to replace clamps because of rusted screws after disturbing
them, but I put them in the same spot because it's the cleanest place I can
find.
>But I have already had to replace two galvanized steel pipes at
>this house which were in the soil and had corroded enough to leak
>water. No clamp of any kind was necessary for them to fail.
Working for the military contractor mentioned above, I've dug up
galvanized conduits that were almost completely eaten away after long term
exposure to corrosive chemicals, but I don't often see corrosion in our area
under normal conditions. There must be some unusual factor involved in your
area if the pipes can't last 15 years.
>>Certainly, U.L. is concerned with electrical safety. If the
>>connection corrodes, the ground path is lost, creating a life
>>threatening hazard. The connection has to be good for the life
>>of the installation.
>
>That is why the codes specify a regular inspection routine for
>clamped connections which are critical to safety. If they are in
>a benign environment, then inspection is all that is usually
>necessary. In harsher environments, some maintenance is required
>from time to time.
>
>73, Eric N7CL
I've never seen this inspection requirement before, or any type of
maintenance requirement in the NEC. Can you point me to it? Perhaps it's a
local requirement due to unusual conditions in your area.
Many people due not realize the NEC has no authority in, and of itself.
The authority belongs to your local building department which will adopt
portions, or all of the NEC with their own amendments to it to suit the
particular needs of the local community. For example, both the city, and
county here have not allowed ground rods for grounding electrodes in the
past due to the unreliable results in our soil, but they are very common in
surrounding areas.
Jim Smith
KQ6UV
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