My wife and I won an auction over the weekend for a house, shop and property.
While the shop is currently wired, I'll be adding more lights, outlets and specialty wiring (exhaust fan, air compressor etc.) to it as I go along.
OK, first things first... Congratulations on the new (to you) property. I'm guessing that you're pretty excited about the possibilities it provides, and are champing at the bit to dive in and start work. HOWEVER... I would suggest that the more you can resist that urge, the better off you will be in the long run.
NOW is the time to plan EVERYTHING out, down to the last gory detail, even if you don't intend to implement everything immediately (or even "ever" in the case of some of the more ambitious items, such as full air-conditioning, or in-floor heat, or whatever your "Dream Shop" might comprise -- plan for it anyway, and it won't be a problem if/when you change your mind). This includes not only the electrical (tho' that is of course a major part of it); but also your general layout of the shop (i.e., exactly where your workbench and any major stationary tools will be located, etc.), plumbing, HVAC, insulation (in Alabama -- even "northern" Alabama -- you are DEFINITELY going to need all the insulation you can get), whatever you're going to do in terms of surface treatments (floor, walls, ceiling if any, etc.), cabinetry and other storage facilities, and so on. The point here is, you want to do each of these things ONCE, and not have to tear out or modify one thing when you get around to doing the next thing. So...
Here's a pic of the shop from the mezzanine, you can see the 200 amp CB box right behind the tractor.
That's already some good news. Most "home" shops don't have the luxury of such a large/high-capacity panel. You may not (probably won't) ever use anything like 200A in there; but it's still really nice to have breaker slots to burn, when it comes time to start adding things. Is it a sub-panel fed from the house's main service panel, or an independently metered service direct from the PoCo? If the former, what sort of service capacity does the main panel have, and what size breaker is protecting the feeder to the shop?
Please ignore the mess, that's the current owner's stuff, it's all moved out now.
Actually, some of that "mess" looks like it could be some interesting/useful stuff. But if it's gone, it's gone; and at least that gives you a relatively clean slate to work with.
So, my first question is: what kind of wiring can I use to wire this shop. I *assume* I can use this Indoor non-metallic wire from Lowe's or it's equivalent:
http://www.lowes.com/pd_70114-295-28829055_4294722493__?productId=3129313&Ns=p_product_price|1 If not, what can I/should I use?
Yes, you can use "NM-x" cable indoors. The particular stuff you pointed to is AWG 10, which may be (probably is) overkill for at least some things. But see below regarding Voltage Drop. Also, if you're going to install as much stuff as I suspect you're planning on, you would probably be better off buying the wire in larger (say, 1,000-ft. spool) quantities.
2nd question: The shop dimensions are approximately 36'x76'. When I string the wire, I'll have to go about 20' for so up to clear the doors and then come back down again.
Twenty feet? Really? Offhand, that seems excessive. Just how tall are those doors, anyway? (I'm betting no more than about twelve feet, even for the larger one.) And besides, it would at least appear that you would not need to go all the way up for any runs which lead back along the left-hand (as viewed from the camera position) side wall.
For typical 20 amp outlets, should I use 10 ga wire or is 12 ga good enough for the longer wiring distances inside this shop?
Most folks will tell you that AWG 12 is fine for "20A" outlets, and leave it at that. And in MOST cases, they'd even be right. However, if the wiring runs are especially long, going to a heavier wire (such as AWG 10) CAN be beneficial, even if not strictly "required". The reason for this is, ALL wire, no matter how heavy or how short, will exhibit SOME resistance; and in turn, that resistance will impose SOME voltage drop along the way. The question becomes, how much is "too much"? AFAIK, there is no "official" hard-and-fast limit on allowable voltage drop dictated by the NEC or similar. But that doesn't mean this isn't an important consideration. IMCO, a good rule of thumb is to allow no more than 3.0% voltage drop at the full rated load on any circuit (and ideally, some sensitive equipment really shouldn't see even that much). This translates to a 3.6V maximum loss on a 120V branch circuit, or a 7.2V maximum loss on a 240V circuit -- and less is ALWAYS better.
Now, you may be thinking, "Wonderful. So how do I determine how much voltage drop a given circuit will impose?" The answer is, you need to map out each and every wiring run, to determine it's total effective length, then calculate the required wire size needed to limit the V.D. at full load to your desired target over that length. (As a practical matter, you only need to calculate this for your LONGEST run of a given type of circuit & wiring, such as 120V branch circuits for general purpose 20A outlets. Whatever AWG is "good enough" for that one longest run, will be more than good enough for all the shorter ones.)
There is a formula you can use to fairly precisely calculate the voltage drop over a given length of wire of a given size, with a given current flowing through it:
CM = K x I x L / E
where:
CM = Circular Mil area of Conductors
K = 10.75 (Constant representing the approximate mil-foot resistance of copper)
I = Current (Maximum), in Amperes
L = Length, ROUND TRIP to the source, in feet
E = Voltage drop at load (in volts)
This will determine the MINIMUM cross-sectional area for each current-carrying conductor in your cable. As noted above, you typically want to limit the allowable voltage drop to no more than 3% of the nominal input voltage (i.e., 3.6V for a "120V" circuit). And note, that "ROUND TRIP" qualifier on the run length is vitally important; so given "normal" wiring techniques, such as using NM-x cable or similar, you MUST double the actual run length before plugging that value into the formula. I would also suggest that you arbitrarily add at least 10 feet (maybe more) to your calculated/measured run length for each splice in the line between source and ultimate destination (and yes, splicing both the Hot and the Neutral conductors, as would normally be the case when daisy-chaining from one outlet box to the next, counts as TWO splices). Now, before folks start arguing with me, I have to point out that this is by no means a precise value (because it's next to impossible to be precise here); but the point is, all splices, no matter how skillfully done, WILL impose significantly more resistance than an unmolested run of wire, and you should take that into consideration when calculating maximum voltage drop.
So... With all that in mind, solve for "CM". Then consult the chart at
http://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes (note that they list cross-sectional area it in KILO-circular mils ("kcmil"); so multiply by 1,000 for use with the above-cited formula) to find the smallest standard AWG which will provide AT LEAST that much cross-sectional area. Voilà!
Here's a sample calculation for that prototypical "20A outlet" circuit, with the last box 50 feet away from the panel (as the wire flies), and splices in two intermediate boxes along the way:
CM = K x I x L / E
CM = 10.75 x 20 x 140 / 3.6
CM = 30,100 / 3.6
CM = 8,361.11
Referring to the above-cited chart, we find that AWG 12 provides only 6,530 CM; so yes, you'd want to use AWG 10 (at 10,400 CM) for this circuit. Could you "get away with" AWG 12? Very probably yes. But your tools and such (particularly those with motors in them) won't run as well or last as long.
Also, obviously, one way to mitigate this problem is to avoid splices at almost all costs. In the above example, we would have been just fine with AWG 12, if there were no splices in the line. One way to do this, WITHOUT requiring separate runs to (and concomitantly, a separate breaker for) each and every outlet, is to NOT actually cut & splice the wire when installing outlets and such "in the middle" of a run. Instead, loop the unbroken cable into and back out of the box, then strip off a short chunk of the jacket and insulation only as/where needed to make the connections to the screw terminals on the outlet. You probably ought to also run an extra pigtail of bare copper from the green screw to the inside of the box itself, if it is a metal box (which it probably ought to be, in this application). Note that some nit-pickers MIGHT have a problem with this technique from a code point of view (I recall seeing an argument over this point awhile back, but I don't remember which way was considered preferable by the code); but in practice, it's done all the time without issue -- MANY of the outlets in both of my homes were installed this way (yes, by "licensed professional" electricians).
Obviously, this just scratches the surface of all the things you will no doubt be dealing with as you move in and start to upgrade that shop. But I hope it at least answers your immediate questions. In any event, good luck with your new (and, I suspect, to become never-ending) project!
)
I knew about vapor barrier, but had never heard of a vapor pan for electrical boxes. GJ must be THE MOST educational site on the web!
, and the third link has to do with boat wiring, a completely different animal!
