[TowerTalk] [Grounding of tower

[K8RI]

On 5/11/2013 5:43 PM, K8RI wrote:
> On 5/11/2013 9:10 AM, W2RU - Bud Hippisley wrote:
>>
>> On May 11, 2013, at 7:51 41AM, "K1TTT" <K1TTT at ARRL.NET> wrote:
>>
>>> Consider this example... my neighbor had a broken ground in the wire
>>> overhead from the transformer to his entrance panel.  There are
>>> ground rods
>>> at the pole and at his entrance as required.  When a big load on one
>>> side of
>>> the line started, like a refrigerator, that leg browned out but the
>>> other
>>> leg of the 220 would get up to about 200v and blow out stuff on that
>>> circuit
>>> due to the overvoltage.  Obviously there wasn't enough return current
>>> through the ground, even over that relatively short distance, to keep
>>> the
>>> supply balanced.
>>
>> This can happen in an _underground_ distribution system, as well.  Our
>> home -- originally a seasonal summer camp -- was first electrified in
>> the '50s with an underground single-phase 110-0-110 3-wire feed from a
>> shared distribution transformer to the entrance panel.  The shortest
>> path from the distribution wires and transformer to the camp was
>> diagonally across the dirt driveway and part of my parking area.
>>
>
> I had this happen this week.
>
> About 1:30 AM I sat here listening to 40 and surfing the internet.
> There was a tremendous bang, but more of a "Boom" through the headset.
> It was loud enough I was reaching to grab the headset off, but
> immediately following the boom, it got real dark in here.
>
> Still I saw light coming from the hall.
>
> Troubleshooting a panel with one hand is... well... exasperating and I
> was getting strange readings with my DVM and they were unstable.
> It appeared the one line was low and varying
>
> So it was out to the shop to get the Simpson 250.
> Now that line was dead.  I said, This can't be good.
>
> Consumers made it out in the morning, said the problem was underground
> and somebody would be out to fix it soon.
>
> They made it at 1:00 PM.


Hmmmm...A little comma mahes such a difference


  This: The one hot feed that wasn't broke at the base of the pole 
(underground)
Should be:The one hot feed that wasn't, broke at the base of the pole

<sigh>

73

Roger (K8RI)

> where it turns 90 deg to enter the conduit.
> Around here they figure the frost line is 3 feet.  Last winter it was
> less than a foot.
>
> 73
>
> Roger (K8RI)
>
>> It's well known by contractors and life-long residents here in the
>> frozen north that snow-plowing a driveway and driving on it all winter
>> long "drives the frost line deeper into the ground", but back in the
>> '50s all the properties in our neighborhood were seasonal so
>> underground utilities were seldom more than a foot or two below the
>> surface.  (Our present building codes assume a frost depth of at least
>> 4.5 feet.)  By 2000, probably half of the dwellings, including ours,
>> had become year-round.
>>
>> And so, about five years ago, we experienced the same fate as Dave's
>> neighbor.  In our case, the constant shifting of the driveway frost
>> line eventually caused the buried neutral to break in half.
>> (According to the power company crew, the shifting frost line causes
>> rocks and gravel beneath the surface to move enough to repetitively
>> stress the wire until it snaps.)  As Dave noted, if the ground
>> characteristics at 60 Hz are high-resistance, a big load (in our case,
>> probably either our refrigerator compressor or our well pump turning
>> on) on one side of the line will cause the other leg to rise to nearly
>> the full 220 volts of the single-phase feed.   We lost a microwave and
>> a bunch of other household items in that little "event".
>>
>> Once the power company located the problem, I immediately hired an
>> excavation contractor and an electrician to re-route my entrance cable
>> so it skirted my entire driveway and parking area.  They were required
>> to coordinate with someone from the power company who had to be
>> on-site for the re-connection to the distribution transformer and
>> back-filling of the trench.  My difficulties in getting all three
>> people to show up at the same time were seemingly never-ending.  Let
>> me simply say that scheduling that meeting was the most difficult part
>> of the process (other than ponying up "mucho" dollars), but I have
>> never regretted having the power line installation finally done right.
>>
>> Bud, W2RU
>>
>>
>>
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