On Wed, 20 Nov 2019 01:35:30 -0600, Jim Joyce
wrote:
There are a few things here you may have heard about that are wrong.
First the 3% is just a recommendation now a real rule and that would
be based on you actually using all of that 20a at one time. 16a is a
more realistic max design load (80% of your 20a). At 16a your #10 will
drop 4.64v or 3.8%. Bear in mind that is a max continuous load for a
20 a circuit.
If you want to use the "dwelling" exception to the 18" deep for
conduit and 24" deep for UF rule, the GFCI protection needs to be at
the house end of the circuit. If you are burying this 18" or 24"
anyway that might not be important.
You can get THHN/THWN conductors in 500' spools at home depot or they
will sell it to you by the foot. The same "by the foot" is true of UF.
If you would never use the left over, that premium they charge by the
foot will come out cheaper. Just be sure you buy enough so you don't
come up short. If you up size the current carrying conductors, you
also need to up size the ground so it will end up the same size on a
20a circuit. (not #12). Code wise, you would be in violation with most
UF cable since the ground for a #8 is typically #10 unless you
specifically get the style with an 8ga ground. That will not be at
Home Depot. For that reason alone, #10 would be a better choice.
The reality is you would have a hard time finding a piece of cord and
plug connected equipment that pulls more than 1440 watts. (12 amps).
You have to seriously ask, "what are you really going to be doing out
there"?
If this is just a shed with a light, a receptacle for yard equipment
and maybe a 1440w heater now and then. I bet #12 would be OK and #10
should be perfect.
If you go much beyond that, like a sub panel, you will be driving
ground rods, installing disconnects etc and this gets a tad more
complicated.
The simple answer is #10/2 for the underground. GFCI at the house so
you can bury 12". They may want a local disconnect depending on your
AHJ but it can just be a 20a rated snap switch and I would do the rest
of the distribution in the shed with #12.
If you really think you might change your mind and want a shop or
something out there use conduit but if this is one and done, UF is
fine. Personally I like wire in pipe but I also change my mind about
things. If you do decide #8 is for you, it will be wire in pipe anyway
unless you go to a real electrical supply and get 8/8/8 UF. Legally
you can run 3 # 8s in a 1/2 inch but I would never try to actually
pull that 120'. 3/4 or even 1' is a better choice and buy a bottle of
lube. If I have a long run like that I squirt a little in the pipe
every couple of sticks as I am putting it together, particularly in
elbows. The pull goes a lot easier.
On Tue, 19 Nov 2019 20:10:58 -0800 (PST), trader_4
wrote:
On Tuesday, November 19, 2019 at 10:33:25 PM UTC-5, Jim Joyce wrote:
Hi folks,
I'm planning to run a new electrical circuit out to a storage shed in my
back yard and I'd like some help with the details. I'm the homeowner and
I'll be doing most of the work myself, but I want it to be safe and up to
code.
1. I have called 811 - Call before you dig. They'll be coming out on
Thursday of this week to locate and mark all of the underground utilities.
2. I will be using a licensed electrician to connect the new service to the
existing service, but other than that final step everything else is on me.
I have experience with switches and fixtures, but not with the other
aspects of the project.
Permit? If you're going to get an electrician out there anyway, might
be easier and not much more for you to just dig the trench, let them
do the rest.
A permit is a good idea. I got one for building the shed, so I know the
procedure now.
3. The rest of the 120VAC circuits in my home are 20A circuits, so by
default I'm planning to make this new circuit 20A as well. I believe a
single 120VAC circuit should be fine for both lights and receptacles out
there. The biggest load I can envision is possibly running a miter saw,
which is rated at 12A. Just in case I take that saw out there, I think a
15A circuit might be stretching it thin.
Having extra capacity isn't a bad idea. Any chance you;d need 240V
for anything?
I really doubt it. I've never needed 240V anywhere else in all these years.
Q: Any issues with a single new 20A circuit for both lights and
receptacles?
Not that I'm aware of. Make sure it's on a GFCI. Probably best
to put a GFCI receptacle as the first point in the shed. That way if it
trips, you can reset it there.
Good point.
4. Web calculators say I should use 8AWG wire for this circuit because the
run is about 120 feet, from the exterior of the house to the exterior of
the shed. I'm planning to buy 3 solid copper wires, 8AWG, in colors white
(neutral), black (hot), and green (ground). This is instead of a packaged
cable such as Romex because I think it will be less expensive to buy
individual wires and because it might be easier to pull 3 wires through
conduit than to pull Romex.
8 sounds like over kill to me, don't know what calculator you're using.
Generally, 12g is used for 20A. Since it's a 125 ft run, I'd go down to 10g.
You can run individual conductors, but you can just use UF cable and it
will be easier/cheaper.
I used the calculators he
https://www.southwire.com/calculator-vdrop
and
http://www.paigewire.com/pumpWireCal...ookieSupport=1
My inputs were 120v, 120 feet, 3% voltage drop, conduit. Both came up with
8ga wire.
Looking at Home Depot's selection of UF cable from Southwire, it looks like
it comes in lengths of 100 and 250 feet. Crap, I'd need the 250 and I'd
have a bunch left over.
Q: Any issues so far? I know the black and white wires need to be 8AWG, but
does the green (ground) also need to be 8AWG? Am I looking for wire labeled
THHN or is it something different? I'm buying everything at the local Home
Depot.
THHN is not rated for wet locations. You need THWN. The minimum ground
size for 20A is 12g.
I only see 2000ft rolls of THWN. I'm not the intended customer for a roll
that size, especially since I'd need 3 rolls to get 3 jacket colors.
5. I'm planning to use conduit versus direct-bury wire. Web calculators
seem to indicate that 1/2 inch conduit is fine, but I was thinking about
using 1 inch to make pulling the wires easier. I'm also open to using 3/4
inch conduit.
Use UF, skip the conduit.
I see this 150ft roll of 10/2 on Amazon:
https://www.amazon.com/Wire-Underground-Feeder-Direct-Burial/dp/B077XM19M5/ref=sr_1_5?crid=4ZPN9M8W4FWZ&keywords=uf+cable+10% 2F3&qid=1574234435&sprefix=uf+cable%2Caps%2C144&sr =8-5
Is that what you're recommending?
Q: Does code mandate a minimum conduit size? (Conduit fill) Does common
sense suggest a different (larger) size? Also, does conduit get assembled
as dry press fit, or does it get glued, section by section?
Yes, yes. If you use conduit, I'd go with 3/4". It gets glued together.
6. The house has a 240VAC breaker box on the exterior wall, with no room
for an additional breaker, so I'm planning to buy a small 2-circuit
sub-panel that I'd attach to the house, right next to the existing 240VAC
panel. I would ask the electrician to connect the sub-panel to the existing
240VAC panel.
Q: I assume the electrician can create a new circuit from the 240VAC panel.
Are there any issues with that plan?
Should be OK, depending of course on what other loads are on the existing
panel.
That panel is dedicated to the kitchen range, the clothes dryer, and the
HVAC.
7. The conduit will be buried by using a trencher. My understanding is that
electrical conduit needs to be buried at least 18 inches deep, whereas if I
went with direct bury I'd have to go 24 inches deep.
That's correct.
Q: Any advice on the use of conduit versus direct bury cable?
***
Once I get power to the shed, I'm good with the project after that. I
appreciate any help I can get with the questions above or anything I might
be overlooking.
If you have to pull a permit and have it inspected, which would be the case
in most locations, I would consider doing the trenching and having the
electrician do the rest. He has to come out and do a subpanel anyway,
installing a couple receptacles and light isn't that much more and you know
it will pass. Or at least get it quoted that way before deciding.
Excellent, thanks. I appreciate the info.