I am planning on running underground electric to my garage.
First off, let me tell you how it is configured now. There is 10/3
romex running along the side of the house and then suspended until it
reaches the garage. This romex is run out of a 30 amp double
breaker. There is no breaker in the garage just a master power switch
where the branch circuits run out of.
I would like to run an underground feeder to the garage so I can
get rid of this eyesore. My ground is very rocky so I will only dig a
trench about 12' deep. I understand that this would require a
conduit. My main question is can I run regular romex through the
conduit or do I need to buy UF/B 10/3 since overtime I assume the
conduit will fill with water. What other wiring options do I have?
Single strand like what is run to my well? Also should I install a
GFCI breaker for the underground feeder? What size conduit should I
use? Any answers would be appreciated. I am not concerned about
following code but do want the finished work to be as safe and
reliable as possible.
Far and away your best bet is local building codes and your power
company. An example, in our locale underground service up to 100 A
takes 1 1/4" conduit at a burial depth of 2'. In rocky ground conduit
is a common sense requirement. Our power company will pull Type UF
separate wires through the conduit, Al for service entrance. In your
case you'll want Cu Type UF and a small service panel with main
breaker in the garage. Use GFCI's where needed in the branch circuits.
Nothing wrong with using good techniques and foloowing codes. It beats
standing in the ashes of your dwelling and arguing with an insurance
adjuster about what happened. HTH
You do want to use either UF cable or THWN conductors in the pipe. Romex
would not meet NEC for underground, even in a conduit. Personally I'd sleeve
10/3 UF in a 1" conduit. You will want a double pole 30 amp breaker in the
main building and a small panel in the garage. You can install a six circuit
panel without a main breaker, or a larger panel, with a main breaker. You
will have to drive ground rods at the garage and run a grounding conductor
from them to the garage panel. I would not use a GFCI at the house, as there
is no need to gfci protect the underground line, but any outlets at the
garage will have to be gfci protected
If the trench is not at least 18 inches deep to the top of the conduit
then you do have to use a GFCI breaker to protect the feeder or branch
circuit. The only code compliant alternative is to pour two inches of
concrete over the conduit.
"This alternating current stuff is just a fad. It is much too dangerous
After reading all the posts. I have decided on running UF 10/3 from a
30 amp GFI breaker through 1" conduit covering a length of 70 feet
buried approximately 12" deep (there is really no good way to dig a
deeper trench as I live on the side of a mountain with very rocky
ground). Once inside the garage I will install a subpanel where I
will have three circuits; indoor outlets, indoor lights and outdoor
lights. My last remaining questions are
1. What is the proper subpanel to buy for this setup?
2. I am still not entirely sure why direct burial cable is encouraged
over the individual wires (THHN I believe) when the cost is more?
3. Are there any concerns with the setup as described?
On May 6, 4:42 pm, rodney firstname.lastname@example.org wrote:
You're burying it aren't you? And it isn't "encouraged", it's
A non-U rated cable or wire insulation is not designed for direct
burial and the insulation will not stand up for the long haul.
dpb, what I am referring to is the type of wiring that runs a well
pump (THHN or THWN I believe it is called). Perhaps my house is
different as well as most others I have seen around here but if you
look in my basement or under the cap of my well shaft there are
individual wires not one cable.
You can run four individual #10 THWN or similar conductors in a continuous
PVC. NEC requires it to be minimum 18 inches deep, (with exceptions). You
say you're only going down 12 inches. My opinion is that a direct burial
cable sleeved in PVC, under those circumstances, affords the most protection
I agree w/ your recommendation and in fact thought it was required --
that conduit underground was considered the same as direct burial
rather than wet environment. But, I'm pretty sure on thinking about
it that it's lore I've inherited, so might, in fact not be Code. As
noted in other response, couldn't find it in a quick hunt...
It's not clear the multiple individual wire will be any cheaper than
the cable in small quantity, but if you're running conduit it may be
more convenient. For underground it would definitely be considered a
wet environment and THHN is only rated for dry so at a minimum it
would have to have the "W".
I'm not positive whether it meets NEC for burial even in conduit--was
always told it was considered the same as direct burial and couldn't
find a direct reference for absolute confirmation.
You would have a hard time finding THHN that wasn't dual rated THWN.
Just remember that is still THWN when derating. It is THWN (75c)
whenever it is used in a wet location. As long as you use 240.4(D)
rules (the good old 14gaa, 12ga a) it won't come up.
Hmmmm...maybe on the dual rating, I've not really checked much lately,
used to be pretty common to not be wet-rated, but high temp (what
commonly knew as "appliance wire")....
But doesn't address directly the question of whether "wet location" is
synonymous w/ "underground" -- I didn't think it was/is and that
should still be U rather than W.
OK, I looked at Southwire site and their designations -- I guess
probably in conduit the "W" rating is equivalent and the "U" would be
only a real difference for direct burial for the extra protection
against physical damage (abrasion, nick, etc.).
They're not synonymous; however, "underground" is a subset of "wet". All
underground locations are by definition wet, but not all wet locations are
"Location, Wet. Installations underground or in concrete slabs or masonry in
direct contact with the earth; in locations subject to saturation with water
or other liquids, such as vehicle washing areas; and in unprotected locations
exposed to weather." [2005 NEC, Article 100]
Doug Miller (alphageek at milmac dot com)
After reading all that information about THHN versus THWN It turns out
I will not be using either anyhow. I went to Home Depot last night to
buy some trim for a new door and decided to take a closer look at
their prices of wire. It turns out that I can buy UF 10/3 for $1.61 a
linear foot. Somehow I got it in my head that the price was much
higher then that. It is actually cheaper by .03 a foot to run the UF
10/3 then the individual wires. Also after closely examining the
width of the cable I understand why it was recommended to me to buy
1.25" conduit. The 10/3 is actually about 3/4" wide if not more, so
there would be a lot of resistance to pulling the cable through 1"
conduit. Sorry about questioning all the advice earlier I am just a
curious person by nature.
In that case, go with the individual wires.
1) It will be *much* easier to pull four stranded AWG10 THWN wires than one
10-3 UF cable composed of four AWG10 *solid* conductors.
2) Stripping the individual conductors out of UF cable (which you need to do
everywhere you make a junction) is a PITA.
IMO it's not worth the hassle of using UF cable just to save three cents a
Doug Miller (alphageek at milmac dot com)
I thought I posted this but it didnt come up so here it goes again.
Last night I went to Home Depot to buy casing for a new door and
thought I would take a look at their cable pricing. It turned out
that UF 10/3 is only $1.61 a foot. Somehow I thought it was $2.50 a
foot, so I am much relieved. It is actually cheaper to run UF then
THWN by about .03 a foot. Also after examining the UF cable I
realized how big it was and now understand why I was encouraged to run
it through 1.25" conduit. Thanks all for the help!
UF wire doesn't "need" to be installed in conduit at all, it is made for
Still conduit is a small expense that would let you easily upgrade the
cable to something larger in the future if needed (10/3 wire will only
carry 30amps max, less if you have a long distance to run). It also
provides an extra layer of protection from shovels and whatnot.
I don't know about UF cable, but generally it's against code to run
sheathed cables inside conduit. The concern is heat build-up from the wires
being so close together. Individual wires have more airspace to dissipate
From a practical standpoint, the individual wires will be easier to fish
through the conduit, especially if there are any bends along the way. But
it probably wouldn't be a big deal to fish UF cable through a straight
section of conduit, especially if you have 1.25".
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