Our new house has a 1/2" conduit from the main panel to our unfinished
basement. Yes, I requested a 3/4" minimum but the contractor knows
much more than I do! :(
I want to run a sub panel using this conduit. The total distance may
be about 100'. I plan on running at least 4 circuits off this panel
ie. 20A for plugs, 15A for lights etc...
What size wire should I run in the 1/2" conduit for this subpanel?
Is there a special type of wire for this application (stranded vs.
I would like to run #8 but not sure if it will fit. What configuration
would be best. 120V only no dryers or any need for 240V.
Get a copy of "Wiring Simplified." Understand what you're proposing,
and decide for yourself whether or not it's over your abilities.
There are bigger and more expensive books, but that one's a pretty good,
"Do I feel up to this" kind of book, filled with lots of warnings about
how not to kill yourself.
IF you still feel up to it, make sure that in Yakima, it's not required
to have a liscensed electrician do the work.
You still with me? Okay. Head to the library reference room with a big
1. Using a good electricians reference or electrical engineering
handbook, calculate the size wire you need for 2% voltage drop on your
2. Check against the NEC. If what you calculate is smaller than their
requirement, follow the NEC. They're the law, not you.
3. Using the ampacity figure from step 1, look up in the NEC how big a
grounding wire you need.
4. Using the tables in the NEC, calculate the total area of your wire
for all the conductors you specified in steps 1-3. Remember that you'll
have THREE conductors to carry current, plus a (probably) smaller
5. ESPECIALLY if you've not pulled wire before, multiply that by 4.
That gives you the minimum conduit area for 25% fill. Why? Feel free
to use 40%, but I wouldn't want to do it.
6. Find the cross sectional area of your intended type of conduit in
the appropriate NEC table and find the smallest trade size that's larger
than the number you've just calculated.
7. Double and triple check all your calculations. Now do it again.
8. If this seems too involved, hire a professional. Not to be flippant,
but what you're proposing is nontrivial, and there are a lot of details
you want to get right.
Use THHN stranded.
Although you are allowed 3 #8 in 1/2", as the other poster said
it will be a really tough pull. Unless...you can insert one
or more pull boxes along the way.
If the inspector will require a separate equip grounding conductor,
you'll be out of luck on fill capacity.
#10 stranded THHN sounds like a better way to go, giving you
a 30 Amp subpanel, probably plenty (compute the loads).
<< Our new house has a 1/2" conduit from the main panel >>
Save yourself all the grief now and especially in the future by simply
replacing the conduit. Sure it might be a little hard to do, but no reason it
would be impossible.unless it was buried beneath some priceless paneling. The
more creative pros I've seen have done some astonishing things with "old work"
updates. Good luck.
Did you specify the 3/4" in writing? If so, put it on the punch list to be
fixed BEFORE he gets final payment on the construction. Especially if he
charged extra for the 3/4" that he didn't install.
Thanks for all the replies.
I had a licensed electrician come to take a look at the problem.
Currently, there is only about 60' of 1/2" metal conduit and from
there to were I would place a sub panel is about 20 - 30' max. He has
told me that code will not allow 3 #8 conductors in a 1/2" conduit and
has suggested running a new conduit to supply the sub-panel. This
would involve #6 wire for a 60A sub-panel. The total cost of about
He mentioned that I could get 3-20A circuits or 4-15A circuits in the
1/2" conduit without adding a sub-panel. I may opt for the 3-20A
approach since I am looking at plugs and lights mostly.
Is there any way to get 4-20A circuits in that 1/2" or even 2-20A and
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