"guest987" wrote in message
news:uWuyd.546239$Pl.492525@pd7tw1no...
"Duane Bozarth" wrote in message
...
[...]
Despite your best attempts, eventually there virtually
surely will be
a leak and water will find a way in. Only
underground-rated cable
should be used in an underground run despite the conduit.
Normally
(unless there is an access tunnel in an industrial site,
for example)
conduit is used to protect the cable from the above ground
junction to
the required depth then the cable is laid in a trench. A
protective
barrier is sometimes used over the cable, but not normally
full run
buried in conduit. It's not an immediate danger, but
eventually it is
virtually certain to get water...

I see. So conduit was never meant to be a substitute for
rubber-sheathed
underground-rated cable in the first place. And here people
were conveying
to me that rubber-sheathed underground-cable was something
new in that it
didn't require conduit underground!

Close but no cigar just yet. You do need underground
rated cable for UG locations...but you do not have to use
conduit beyond a certain depth...usually 32"..

You can go shallower if you have a concrete pour over it, or
if it is in conduit of various sorts...the *minimum depths are
all called out in the NEC... but that doesnt mean a persons
particular job is safe or right, depends on how soft the
ground is in worst case conditions (muddy etc, with heavy
vehicles over the top).. salt water infiltration as we have at
low levels near the coast in many regions.

and of course no J Boxes underground at all (unless they are
in a manhole etc)....

Then there is fudging... say for instance you had an oversized
plastic J box underground with very carefully bolted
connections, then those painted with insulating sealant, say 3
or 4 coats, then that wrapped in rubber tape about 1/8"
thick... then the J box filled with urethane roof sealant
(dries like tire rubber), then the water tight lid applied...
cement bulkheads poured at each side of the box so it couldnt
move or break at the conduit connections... well some guys
might call that safe enough for govt work. But it wouldn't
be legal. A short though would go directly to ground in
virtually all cases...so there are much worse actual hazards
in the world... a red head could move in next door for
instance.

If it were in well drained ground, not prone to getting muddy
it might be a lot closer to OK.. If it were in muddy ground
with loads driving over it... it would not be ones slickest
move.

You have to scratch your ass and figure these things out....
sometimes I burp too. that helps.

The NEC code is part of the fire code... over heated wire,
shorts where they can cause a fire or go to ground though a
person are the primary issues... When you are underground
the fire hazard all but dissapears, same with the shock
hazard...unless someone digs into it etc.

In your case, and wire being relatively cheap, Id install
separate runs on your job... if the ground is muddy or
freezes, Id go deeper than the NEC requires, Id use schedule
80 pvc conduit regardless. put a few long radius glued bends
in it so it can expand and contract without stress, be sure
its in sand on the bottom and a few inches of sand on top,
40 years down the road the next owner is going to love you for
it. To make it easier on yourself, go one size larger on the
conduit than required as well....so the wire will pull easier.
Or you can bury the cable direct with no conduit below 32
inches... some people then lay redwood boards over the top and
yellow plastic marking tape so that if anyone digs there later
they will hit the boards and the tape as a warning. That
saves you the work of putting in the conduit and a long wire
pull. If the wire goes under a drive way or road you may
want to slide a schedule 80 pvc section of pipe over that part
of the run... bury it a little deeper there as well...and
maybe even pour some concrete over the top, 3" or so with a
little rebar in it. All that exceeds the NEC...but remember
the NEC and all of these codes are *minumum requirements and
are sure not best practice in all cases.


As I get older, I find that doing a job to world class
standards or better gives me a warm fuzzy feeling inside.
...its satisfying... Im also finding that it doesnt take much
more effort in most cases.






Phil Scott








So I chose conduit thinking that was
the 'tried-and-proven' standard method of laying underground
cable. I now
see I got it wrong. Well, the cable hasn't been tied in to
the power yet
(decided to wait until I can get the cash to hire a licensed
electrician for
the inside-of-house wiring --mainly for insurance reasons).
Guess I'll be
pulling out all the romex (as well as the
single-strand-wires) from the
conduit and replacing with underground-rated cable then. I
have junction
boxes underground too where power gets split to serve two
separate
destinations. (The rubber-sealed junction box covers, I had
reinforced with
silicone sealant --but come to think of it, silicone does in
time lose some
of its effectiveness), Guess I'll have to modify the cable
layout scheme,
in order to serve all of the separate power destinations,
without those
junctions...


Danger, fogey story...

Used to work w/ online coal analyzers at mines, prep
plants, etc. Had
location at mine in KY where they pulled the high voltage
signal power
cable (2.4kV) and had to go from the control shack where
the
electronics/computer were housed across a truck crossing
to the analyzer
mounted on the beltline. That installation was the mine's
responsibility, wasn't around when they did it. Installed
the unit,
brought it up, calibrated it, watched for a few hours,
went home...two
weeks later, get call...it's not operating. Drive up,
discover HV cable
shorted. Hood up the spare (we did require a spare be
pulled in the
specs), it worked, calibrated, watched, went home. Within
six months
second failed...turned out they had buried the cables in
conduit and it
filled w/ water. HV instrumentation cable isn't designed
for water
immersion and water also got inside the insulation.
Didn't help they
had pulled the cable through the conduit by hooking it to
a front end
loader when they couldn't pull it by hand , but that was
secondary...

They pulled with wire through with a front loader?! LOL!
Now that's a case
of applying too much 'brawn', as it were, and not enough
brain. Why didn't
they just use an approved lubricant and avoid stretching (if
not the risk of
breaking) the cable? (Don't try to answer. I'm sure you
wondered the same
thing.)


Thanks,

Guest987