Hopefully, this is a simple question that someone can answer. I'm
looking for the type/size cable to run (inside conduit) from my house
underground to my new shop.
I am building an unattached workshop in my backyard. I am planning on
running my electrical off of my house's panel. I am going to install
an auxuillary panel in the workshop (100 Amp). I'm planning on two 15
Amp circuits for outlets, One 220V circuit, and 1 circuit for
lighting. The distance between the house and the shop will be about a
I know I'll have to have an electrician come out and finish the work,
but I want to purchase the correct size wire when I purchase my
You'll get as many opinions as responses. Just suffice to say, that we
ran a detached garage for over 30 years , 300 feet from the house, on
an underground direct burial 10/3 . Yes, we had lights, fans, forced
air heat, welder, grinders, air compressor, stereo, the whole gammut of
equipment you'd find in the average home fabricators shop. Never once
in 30 years, did we trip the 30A breaker in the house. YMMV.
Let me go on to say, if _I_ were doing what you're doing today, I'd
probably run a 6/3 with ground and hook it to a 50A breaker. That's
going to be more than plenty for a home shop. That's what I plan to do
for the feed to my current 30x40 that is about 400' away. The size of
the sub panel can be dictated by how many breakers you want to break it
down into. A 100A sub is a bit of an overkill in my opinion. An eight
breaker panel would probably be enough, unless you plan to have more
than one 220V outlet, or device.
I hear ya, but as i stated before, we ran a shop 300 feet away for 30
years on a 10ga. The barn i have now, will probably never see a welder,
and if it does, it'll be seldom used. Right now, it's been run on a 12
ga. NM-b laying on top the ground for two years. Lights and door
openers are all that i have in regular use.
A quick google for "voltage drop calculator" gave me a web site which
claimed that for 30 amps on #6 Cu for 400 feet (one-way), the voltage
drop for a 240 volt circuit would be 4.8%. So go ahead and use your
#6 Cu, but put it on a 30 amp circuit breaker instead of a 50 amp
I'll do what works. The #6 is actually good for about 70A. The 50 will
be fine. Right now, i'm running a refrigerator, lights, two door
openers and two 1000 W. tank heaters on a 12-2 NM-b laying on the
ground. The #6 will be WAY WAY overkill, but that's what I'll do. I'll
never pull anywhere nears 30A anyway.
Don' believe you. Make sure it's actually on, not just turned on. In
other words both your tank heats are putting out heat. Two 1000 watt
tank heats are about 16 amps. There's no way you're running 16 amps
over 400 feet of 12/2 and not seeing a voltage drop. Nevermind the
refer and the lights which have to be pushing you up to 20 amps total
if they kick in while both tank heaters are on. I'd consider a
lockout circuit so that only one tank heater can be on at a time if
you want to keep the wire size down.
email@example.com babbled some shit he knew nothing about:
Not hard on it 'cause the voltage is always around 115 - 118. YOU seem
to have a problem with comprehension. You don't seem to understand what
you've been told. So, here's the deal. I'll drop the thread, and you
can fuck off.
A 400 ft run of 12 AWG, at 120 volts, a 15 amp load, will drop 23.7
volts, giving a terminal voltage of about 96.3 volts. The power lost
will be 355 watts over the run. Power available at terminal will be
Real world results do vary a bit from the calculations because of
quality control of the wire. But apparently some of us live in a
magical 5th dimension where the normal laws of physics do not apply.
No inspector in the country would let that go. I'm no particular fan
of building inspectors but there is nothing wrong with complying with
the code. If for no other reason than to avoid complications when you
sell the property.
*For 100 amps a 1 1/2" PVC conduit will suffice using 2 -#1s, 1 -#4, and 1
#6 aluminum single conductors such as THWN. There is no reason to spend the
extra money for cable in a conduit. You could use copper conductors as the
price has gone down quite a bit. For copper you can use one size smaller
for each conductor.
Something else to consider is a conduit for a telephone or TV line. A 1"
PVC conduit should suffice for that.
I wouldn't purchase any wire until you are ready to install it. It could
get damaged or stolen and you don't know what the final length will be until
everything is in place. No sense paying for waste.
You may want to consult with your electrician ahead of time so that your
work will be to code and that he has no problem finishing the job that you
For the circuits that you have planned, 100 amps sounds like overkill unless
you have plans to add more down the road.
For more info on this topic you can do a search of the newsgroup
alt.home.repair on Google. This subject has been covered a lot there.
As the originator ofthis thread, let me say thanks for all of the
posts. I decided my 100 Amp panel was overkill and decided to go with
50 amp panel instead. I purchased 50' of 6/3 w.Grnd at Lowes and ran
it inside 1.5" conduit. When the inspector came out, he said that
the cabling was not "W" weather-rated, such as TNHW rating.
Apparently, it was for inside work and labeled NM-B. I went back to
lowes and talk to the older guy who I had previously worked with. He
was surprised and then said that they sell this for that exact
purpose. Well, I then bought 3 sections of #6(Blk,Wht,Red) and 1
section of #10 for ground.
But Lowes did take the cut wire back and give me a refund, so I
commend them on that.
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