I think it's because in our area there can be massive frost heaves in the
frost zone. If the ground deforms enough, the constant expansion and
contraction can crack or crush the conduits and/or tear them apart. I
believe the worry is that this could result in a high voltage cable breaking
and a live end being thrust above the surface by a frost heave.
At least, that's what I've always thought. One clue is that there's an
exception if you bury at least two feet down and use a concrete cap on the
trench (can be very expensive for a long run.) In that case, the conduit and
its contents can't penetrate the surface.
73, Dick WC1M
> -----Original Message-----
> From: john@kk9a.com [mailto:john@kk9a.com]
> Sent: Wednesday, November 12, 2014 10:57 AM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] Schedule 40 or 80 PVC Conduit Underground
>
> Why would tower/antenna control lines and coax need to be buried below
> the frost line?
>
> John KK9A
>
> To: "'Allen Brier N5XZ'" <n5xz@earthlink.net>,
> <towertalk@contesting.com>
> Subject: Re: [TowerTalk] Schedule 40 or 80 PVC Conduit Underground
> From: "Dick Green WC1M" <wc1m73@gmail.com>
> Reply-to: wc1m73@gmail.com
> Date: Wed, 12 Nov 2014 07:02:29 -0500
>
> <snip> Where I live, Schedule 80 is
> always used for buried conduit runs, but that's probably because the frost
> line goes down four feet and the conduit has to be buried at least that
deep.
> Could be a different story in your area.
>
> 73, Dick WC1M
>
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