I've looked through several of my catalogs including Blackburn, Burndy,
Ideal, Ilsco, Teledyne, and Thomas & Betts. They manufacture a variety of
clamps using a variety of alloys, and platings for use in different
installations with the specific intent to avoid a problem with dissimilar
metals. Bronze clamps are made for the purpose of bonding directly to
copper, and galvanized steel. Some of them are specifically rated for direct
burial when connected to steel, and for use in corrosive environments. I've
seen lots of these clamps in old installations on galvanized pipe, and
bronze hubs on galvanized conduit, but never any corrosion.
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.
You're not likely to improve the products by modifying them, and voiding
the U.L. listing. There's no need to reinvent something that's already been
engineered, tested, and proven millions of times over.
Jim Smith
KQ6UV
>I'm sure that the UL is referring to the electrical safety of the
>bronze to galvanized connection and not necessarily certifying
>that there will not be corrosion of the galvanized participant.
>The connection will remain safe for UL purposes as long as there
>is significantly more material making up the galvanized conductor
>than the bronze clamp.
>
>It is no skin off the UL's nose if the galvanized coating on the
>pipe is degraded in small areas over the years. They (or the
>NEC) specify that the connection must be regularly inspected. It
>can be slightly relocated and retightened occasionally to restore
>the connection's effectiveness. The galvanized pipe is generally
>not a thin wall load bearing structural member.
>
>
>Using stainless steel shim as an intermediate material in a
>clamped connection between either bronze or copper and zinc will
>reduce the galvanic potential difference across the physically
>connected materials to approximately half of what it would be if
>the copper or bronze were directly connected to the zinc. So
>the corrosion process will be approximately half as rapid as it
>would be without the stainless.
>
>Whether this is an important consideration depends entirely on
>the environment the tower is exposed to. In an arid climate far
>from industrial or metropolitan sources of atmospheric
>contamination, it is probably not an important consideration.
>
>In a climate that frequently wets the connection, or exoses it to
>acid rain or is near salt water, it might be a very important
>consideration. In such an environment, unless the connection can
>be completely protected from its immediate environment by a
>durable moisture barier, a stainless intermediate material should
>probably be used. Corrosion can't happen if the electrolyte
>can't touch both sides of the connection. And it will happen
>only half as fast with the stainless intermediate material.
>
>Of course this or any other kind of clamped connection between
>dissimilar materials should never be used below grade where it is
>continuously in contact with an electrolyte solution.
>
>73, Eric N7CL
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|