In New England, we get a phenomenon called "frost heaves". It happens when
the ground freezes, melts, and refreezes in late winter. It causes the
ground to heave and buckle, often as much as a foot or more. This causes the
pavement to crack and the roads to become very bumpy. When the weather warms
up in the spring, the ground relaxes to roughly the shape it had the year
before (leaving a lot of broken pavement and potholes.) The heaving and
relaxing can put a lot of stress on buried wires and conduit, certainly
enough to cause breaks in even the most rugged copper wires, steel pipes or
PVC conduit. Also, the heaving process tends to make rocks "boil up" and
move around, potentially crushing or breaking wires and pipes.
Good builders around here always always bury service pipes at least four
feet down. Some will lay sheets of building insulation on top of the pipes
before refilling. Concrete footings and piers are dug that deep as well. If
you don't sink the footings for a porch or the piers for a deck that deep,
the frost heaves will push them up, making the porch or deck buckle and
Someone else suggested that ground wire needs to be below the frost line to
remain in contact with moist soil for less resistance to ground. I think
that's correct as well. I've even heard that, if possible, the wire should
be deep enough to contact the water table.
73, Dick, WC1M
From: Pete Smith <email@example.com>
To: Dick Green <firstname.lastname@example.org>; email@example.com
Date: Thursday, June 11, 1998 10:51 AM
Subject: Re: [TowerTalk] Peripheral ground system
>At 10:12 AM 6/11/98 -0400, Dick Green wrote:
>>>> I'm going to do the full peripheral
>>>> ground system per the PolyPhaser books. Question (the answer to which
>>>> cannot find in the book): Should the ground wire be at the French
>>>> level, just below ground level, or does it matter at all?
>>> It should be below the frost line. About 2 feet is a good depth as
>>>it satisfies the preceeding condition.
>>>Cheers, Steve K7LXC
>>Probably OK for Western Washington, but here in the frozen tundra of the
>>Northeast, four feet deep is the standard for getting under the frost
>More to the point, what does the frost line have to do with buried wire,
>anyway? If you don't bury radials that deep, why would you have to do so
>with a perimeter ground wire? For that matter, all of my feed and control
>lines come across the lawn in two runs of PVC conduit, which is buried only
>about 3 inches deep, and it has stayed put so far through one very hard
>winter and two average ones.
>Am I missing something?
>73, Pete Smith N4ZR
>In wild, wonderful, fairly rare WEST Virginia
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