Re: Ultrasonic Sensors

["Stanley Barthfarkle" <sbarth@xxxxxxxxx>]

>>> There are companies that will do the locates for you...
>
> They're called utilities, as in electric power, CATV and telephone
> companies.  They don't charge for coming out to locate their wires for
> you. There's a page in the front of most phone books with the heading,
> "Call Before You Dig".
>
>> Unless you hit an a/c svc line with a walk-behind
>> trencher....
>
> Found a lot of high power cables less than 36" below grade, have you?
> Power companies lay their lines deeper than the trencher can reach.



Not only is it illegal to machine trench over or within 3 feet of a locate
mark, it is considered incredibly stupid. There are very few utilities that
are precisely the correct depth. We've found electric svc drops at 12",
phone at 3". CATV and sprinklers are sure to get cut regardless. And you
DON'T want to know what a cut gas or water line will do to a house if you
damage it closeby. Most utilities are the right depth or deeper, but you
really don't want to gamble with that kind of liability. Also, any svc
utilities on one's property were likely put in by the contractor or subs,
and are less likely to be at proper, uniform depth.

Some things are difficult or impossible to locate properly, such as PVC
drain cleanouts, (a common thing in the yards of newer homes) gutter drain
lines, sprinkler pipes, low voltage lighting wire, outbuilding a/c circuits,
etc etc. Takes a trained eye to spot these things reliably, and a liability
policy to ensure that they're fixed properly if damaged.

Even found a 3-phase subdivision feeder coming off a pole, down a riser, and
UG, ostensibly 4' deep, which was located by hand at about 2 INCHES, in PVC
conduit, in a road right-of-way about 30' from the riser, less than 5' from
the first house's property line. The bozos couldn't figure out how to
jackhammer through a boulder, I guess. Could have killed our shovel guy, and
almost certainly would have killed the crew coming in to install the lighted
rock wall and landscaping for the subdivision entrance the next week.

Another horror story- fiberoptic telecom cable. While this is usually found
elsewhere, there ARE places where a right-of-way cuts through or between or
abuts someone's property. This stuff is INCREDIBLY expensive to repair- it
has to be spliced in a "clean-room" environment with a very expensive mobile
setup. Cut a 1000 conductor fiber and you'll soon appreciate just how cheap
professional liability insurance is. I knew of a contractor that did this in
the late 80's, and they were fighting with the ins. co to determine the
liability for a very long time.

Anyway, point is it isn't wise to tell folks to "go for it" until providing
full, appopriate info and professional guidance. Even then, they should be
aware that there ARE risks, both physical and financial. This is NOT like
running a door sensor wire and hitting a 110V A/C circuit...