Have heat in the new workshop, so now I’ve got to update the electrical. The shop is drywalled, so it’ll be surface run.
I’m going to have an electrician run a subpanel out to the garage, the I’ll probably finish off the rest myself. In the last shop I had an electrician do it all. He ran the armored BX(?) cable. Which for the most part was tidy as I had 3 circuits running down my shop wall. The cables were low enough that the did not interfere with anything on the wall. You can see it in the pictures of my bench. (If the pictures attach). Getting the electrician to run conduit was very expensive.
Since I’m going to finish it off myself I was considering using conduit for a cleaner look. I’ll be running multiple circuits down the wall, I assume that it’s one circuit per conduit. So I’ll need three conduit runs running down the wall… Will this look as clean?
Is there any real advantage to running conduit over the armored cable? Is the conduit as easy to run as I imagine it to be (I wont need to make an of my own bends…).
Replies
Buster,
Conduit is cheap, gets the job done neatly, and is easy to run. Get yourself a bender and with a little practice you will be turning out professional looking work. There are a number of web sites that can give you information on angles, etc.
Happy wiring!
-Nazard
Not an electrician, but here's my $.02.
Conduit isn't that hard to work with, once you get the hang of bending it so you actually get what you started out to achieve. (You need to learn how to work with the offest the bends make so the conduit ends up at the correct overall length.)
But, conduit has it's own set of concerns and code issues. You have a choice of metal or plastic. You can run more than one circuit per conduit, if everything's correctly sized. You need to plan on adequate cable pulling access and not exceed limits on the number and amount of bends in any one run. You may or may not be able to run Romex in the conduit -- I've seen opinions on that both ways -- and, if you do run Romex, that may be an element to consider when calculating fill.
I'd post this Q over on Breaktime and see what you get. There are a bunch of very knowledgable posters there.
As for advantages of conduit over armored cable, all I can say is that if your current setup was in my shop, I'd have snagged those cable loops about a million times just moving wood around.
Mike Hennessy
Pittsburgh, PA
Conduit will be neater in appearance, if that is your concern. Conduit allows you to pull wire for additional/future circuits when needed. Working with conduit is pretty easy to learn. Most benders have a small book that will cover things like offsets and shortening. But generally you can make the bend that is needed and cut the straight run to length as needed until you get the hang of it. You will need to learn to bend slight offsets in your pipe near each box to get a properly anchored and neat appearing job. This one of those skills that practice will make you better, so don't get frustrated if the first one or two don't quite look like the picture in your head. Recommend that you also pay attention to max recommended capacities for each size conduit that you use. If in doubt, go bigger or plan on another run. And remember to never have more then 360 degrees of bend in any one run.
Another good thing about running conduit is that when you run your wires, make sure you run "stranded" wire vs. "solid wires". "Stranded" wire carries more voltage than "solid" wire.
???
The voltage rating of insulated wire depends solely on the insulation. Solid vs. stranded makes no difference.
-Steve
I stand corrected. I meant amperage.
Thanks,
This is one of those legends that's based on a kernel of truth and a whole bunch of misunderstanding. (WARNING: Geeky details below--click "Next message" if you're not interested.)
There is a genuine physical phenomenon called the "skin effect." Because of the skin effect, an alternating current will travel mostly along the surface (skin) of a conductor, in a sense "wasting" the material that's in the central core of the conductor. Since stranded wire of a given gauge has more surface area and less core than solid wire of the same gauge, the reasoning goes, the wire can carry more current.
There are two problems with this reasoning. The first problem is that the "skin depth" (the thickness of the region where most of the current flows) is inversely proportional to the frequency of the current. The higher the frequency, the thinner the skin and the more pronounced the effect. When we look at the actual numbers, we find that for the sizes of wires used in typical AC power wiring, and for the frequencies involved, the difference is so small as to be unmeasurable. At 60Hz, as long as the conductor diameter is less than about 1/4", the skin effect is negligible.
People who design power stations and transmission lines have to be aware of the skin effect, since the wires they use are so big. (In power stations, the current is carried in flat copper bus bars that are no more than 3/8" to 1/2" thick, to mitigate the skin effect.) And people who work with radio frequency equipment (hundreds of kHz and above, such as cable TV and satellite wiring) have to be aware of it as well, since the skin depth at those frequencies is measured in millions of an inch. (And, of course, audiophiles worry about the skin effect because they think they have to worry about anything that might add 0.0000001% distortion to their precious signals.)
The second problem is that the arguments in favor of using stranded wire to combat the skin effect are completely wrong! If you bundle a bunch of smaller-diameter wires into a single cable, the inner wires will act just like the core of a larger solid wire--they won't carry their share of the current. Solid vs. stranded doesn't matter; what matters is the physical geometry of where the copper is located within the overall cross-section of the wire. (For high-frequency applications, there is a type of stranded wire called litz wire, where the strands are insulated from each other and woven in a carefully designed pattern so that each strand moves in and out of the bundle, and all of the strands share the load equally.)
-Steve
A huge advantage for stranded over solid, which nobody has mentioned, is that stranded is a helluva lot easier to pull through conduit, especially if you're running 12 guage.
Jeff
"A huge advantage for stranded over solid, which nobody has mentioned, is that stranded is a helluva lot easier to pull through conduit..."
That's actually it's only real advantage: It's just plain easier to work with. The flip side is that it costs more, and it's slightly larger and heavier overall than the equivalent solid wire. So you have to balance the trade-offs.
-Steve
The corrections are quite right. In my old tube-driven amateur radio days (where my tech skill started and stopped) we worried about skin affect with VHF and UHF frequencies, and used tubing instead of wires for some purposes. Doubtless that is still done. For household and workshop wiring, read the ratings and apply the wire accordingly. If you try draw excessive amperage through wires because they are stranded, you are in for a hot time. You should also be aware that running multiple circuits through the same conduit causes wire to be "de-rated," that is, the current judge safe is lowered because all of the circuits are emitting some heat,and the combined buildup from multiple circuits can hit dangerous levels at lower amperages (same is true of ganged switches, BTW).Provided that the insulation is good, this is all about heat and not starting fires in your walls.Another critical factor though, is voltage drop over distance. You should look this up or better still, consult with an electrician. Basically, though, your voltage drops proportionately to the distance of the wire run. The drop is smaller in larger wire sizes. You start measuring at the panel. So, you need to figure your power needs in amps (with some allowance for the heavy load of motor starting if you have big motors), and then consult the voltage drop charts to be sure your wire is sized not only for the amps, but also to deliver an acceptable voltage at the receptacle into which you plug your tool. Low voltages can rob performance, or even wreck your motors.Another factor you need to take into account is proper grounding. Few legacy systems are very well grounded. Grounding is important both for reasons of safety (to protect you from electrocution) and also as the very basis of all your efforts to protect your gear against surges and transient voltages. This becomes more and more important as microprocessors are added to about everything. Cheers!Joe
To Joe and All,
I am fairly certain that voltage drop generally does not become a factor until a circuit run exceeds something like 120'. Since circuits are supposed to be sized at 125% of anticapated load, does not that factor then allow a little "wiggle room" per se?
Yes, there's plenty of wiggle room. The NEC gives guidelines for derating wires in very long runs: for most applications, the acceptable voltage drop is 5%. (The NEC doesn't say that much about voltage drop, because it's a performance issue rather than a safety issue, and the NEC is concerned primarily about safety.)
For whatever reason, people really enjoy overthinking electrical stuff. I guess it's the audiophile tendency that's in all of us. Just follow the NEC recommendations (they already did the hard thinking for you), and you'll be fine--your shop won't burn down, and your machines won't be starved for power. It's not until you get to the really big stuff that there's any point in worrying about the minutiae.
-Steve
I'm not an electrician or expert on the NEC, but I was under the impression that it gives a maximim allowable drop. Still, even if it doesn't, voltage drop is hard on your power tools, and it creeps in on shorter lengths that you might think. Here are some examples for 12 awg copper under normal conditions:
60 ft run (60 feet from the main service panel to the outlets in your workshop:
20 amp load = 4.6 volt or 3.8% drop
30 amp load = 6.9 volt or 5.8% drop
40 amp load = 9.2 volt or 7.7% drop
120 foot run
20 amp load = 9.2 volt or 7,7% drop
30 amp = 13.8 volt or 11.5% drop
40 amp = 18.4 volt or 15.3%
As you can see, the drop becomes material with the heavier loads.
Now, a 60' run is not unusual. If your workshop is on the opposite side of a normal house from the service panel, and you go up a few feet to get into the attic, and then down a few feet to get to the recepticles and have them placed around a decent-sized workshop, you have 60' or more easy. With a big house, it adds up quickly.
In my case, my workshop is in the same building as a detached garage. Bringing the power off of the main house service panel gives me a run of 145'. Then to take it on out to the barn adds another 100'. So, to avoid problems in the future, I have run 50 amps of 240 on 3 awg wire. That gives me only a 2.4% drop at the end of the run.
I use a four-wire system (2 legs hot, neutral, and equipment ground). That comes to a fair investment in wire, but together with a better than code grounding array, and in-panel surge and transient suppression it yields good power quality. Power quality is an issue growing in importance and recognition.
I well understand that many people run big shops without the quality of wiring that I use. However, power tools and electronic devices are expensive, and when they fail it is not only expensive but also a major nuisence. As long as I had to run new wiring (and I had no choice), might as well do it right. Code and the NEC is only a minimum safety guide.
Now, for most people in most set ups with the shop attached to the house, the wiring might only need to be upgraded from 14 awg to 12 awg, or perhaps 10awg. A really good grounding system is not expensive. I panel suppression protects the ehole house and only costs about $75. if you are going to invest in power tools, why not sink $150 in a good wiring system to support them?
Cheers!
J
Edited 1/19/2008 8:05 pm ET by Joe Sullivan
Edited 1/19/2008 8:07 pm ET by Joe Sullivan
Whoa, let's back up a second. If you run 30 or 40 amps on 12 gauge wiring, you're not following the NEC, and that's why you would have excessive voltage drops.
As I mentioned, the NEC guideline for voltage drop is a maximum of 5% (and that's for the complete circuit, including both branch and feeder, so it would be measured using the ratio of the voltage at the receptacle to the voltage at the service entrance--at the meter, essentially). In your examples, then, the 60-ft run should be fine, the 120-ft run is not (using just the 20A numbers, since the higher ones are ruled out from the outset).
The NEC guideline is just a guideline, not a requirement. If a given wiring situation results in a greater voltage drop, it's not an NEC violation (although apparently some local jurisdictions do consider it a code violation). The NEC guideline value of 5% was chosen because most equipment can handle an input voltage of 90% of nominal just fine, so setting the threshold at 95% means that you're unlikely to get into a situation where equipment damage, excessive flickering of lights, etc. could occur.
If you do find yourself in a situation where you'll exceed the voltage drop because your branch lines (the wiring from the circuit breakers to the receptacles) are too long, your best bet is to install a subpanel, as it's usually more cost-effective (not to mention performance-effective) to do that rather than increase the size of the branch wiring. (Although you didn't say so explicitly, it sounds like this is what you did with your shop.)
So, to make a long story short, it rarely makes sense to increase the size of your branch wiring. The standard rules (14 gauge/15A, 12 gauge/20A and 10 gauge/30A) should suffice. If they don't, then it's time for a subpanel.
-Steve
Ah, well, you are absolutely right about the higher amperages. I got caught up in the drop calculations and forgot myself. How embarrassing.
Indeed we did install subpanels.
And, you are right about the 60' run. I guess my original point was that significant drop can occur over runs that can be found in normal housing situations, and that the OP shold be sure about the length of his run before he sizes his wire.
Interestingly, the original 140 ft. run to my detached shop/garage building was #10 for a five circuit subpanel totalling 70 amps. Of course, nowhere near the 70 amps was ever used or the building might have lit up, but that 's how it was.
SO, it pays to look.
J
Folks,Would reading a wiring/code book be really an overkill? Such books typically eliminate any need for guessing. There is much physics/engineering going into them - all converted from theoretical to usable. Even a small job can compensate for one of them those books. Oops, did I say 'reading a book'?Best wishes,
Metod
The code books are thick, dense, and hard to follow if you are not already trained in electricity. However, there is a set called "Code Check" or something like that that covers the key elements in an easy-to-follow way.Also, remember that the code just specifies minimum compliance for safety. If you read some of the published master electricians, like Rex Caldwell. you will find various instances where better than code is the best way to go. For example, grounding can be tricky and it often pays to improve from code.Joe
Joe,
You have a good point about the 'real' code book(s). I meant the code 'embedded' in various wiring books. I have done some wiring around the house - and all in the basement workshop (110V and 220 V). When I began, I had zero clue about anything (different too from what I remembered as a kid growing up in Slovenia). I bought a couple of books, wandered the isles of few stores to match the stuff on the shelves with the pictures/text in the books - and have been enjoying the results for many years.
What irritates me (should be more charitable right after returning from church...) that many folks constantly radiate an aversion to READING. Yup, my professional sensitivity of an educator.
Best wishes,
Metod
I like Rex Cauldwell's Wiring a House. He covers a broader range of topics (including the service entrance) and goes into more of the "why" then most books, which makes it easier to extrapolate. Some of the other books are fine, too, but can leave you hanging out to dry when you need to do something that isn't explicitly covered. Creative Homeowner's Ultimate Guide to Wiring looks pretty good, although I haven't gone over it in detail.
As with woodworking books, you can never have too many....
-Steve
Steve,What you wrote is music to my ears. Thanks for 'moral' support. <g>Yes, all books are not equal, but they do have much to offer. Even a short glance at only a few of them can lead you to what you need at a particular instance.Best wishes,
Metod
I, too like Caldwell's Wiring a House. Excellent, practical book. I am a seruious book junkie, FWIW. We have somewhere between 1500 and 2000 in the house. I am building a catalogue in MS Access, but have only gott to about 870. It is a long-term project like everything else, it would seem.
J
Joe,
Here's a site you might like, http://www.librarything.com. It allows you to catalogue your books online, and to get in touch with collectors with similar interests. You can take a tour of the site, and it's not such a chore as using Access. I did a database for some research once that entailed making over 12,000 entries in Access. I still have nightmares about it.
Jim
WATCH OUT FOR STRANDED WIRE IN CRIMP FITTINGS!
I had a shop burn down two years after a licensed electrician made an inadequate crimp on a tongue fitting to stranded wire to a screw terminal on a fan switch. The stranded wire slipped out of the crimp, shorted to the box and overheated the conduit leading to it, starting the fire.
Personally I would have soldered the strands together before making the crimp but that's probably not it the electrician's book of practice.
Respectfully, Pete
"Personally I would have soldered the strands together before making the crimp but that's probably not it the electrician's book of practice."
That used to be a fairly standard practice, especially in low-power circuitry (e.g., electronics). But it's now known to be the cause of many failed crimped connections. The reason is that solder will "cold flow," which means that the compressive pressure that was exerted during the formation of the crimp can drop as the solder slowly deforms over time, possibly going all the way to zero and allowing the wire to fall out.
Various studies have been done on crimped connections, and it seems that the most important factors in getting a good connection are (a) use high-quality connectors, and (b) use a high-quality crimping tool. The difference in pull-out force between a connection made using a good crimping tool with good connectors and one made using a poor crimping tool with poor connectors can easily be 10 to 1 or more.
Moral: Don't waste your money on bargain-basement crimp connectors or crimping tools.
-Steve
Amen to that. In fact, it seems as though many of the "easy" ways to connect wire have turned out to have problems. Back-stab devices can cause big problems under the right (wrong?) conditions as well.
You know, when setting up something as small as a single shop or home addition, the added cost of commercial spec grade devices is pretty small, especially compared to the upgrade in quality and safety. I would second your comments about bargain basement cripm connectors et al, and would add that it is really a bad idea to use any of the low end electrical devices.
Joe
"Stranded" wire carries more voltage than "solid" wire.
For the record, instead of "voltage", I think you mean "amperage" or you could say "current."
Thanks, I stand corrected. You are exactly right.
1) It is my understanding that the NEC does not allow uncovered MC conductor (flex, or what you are incorrectly refering to as BX) withing eight feet of the floor. It is legal at lower heights if covered with wall, or protected in various other ways
2) That being said, in a private shop, surface MC does not seem like anything to worry about
3) No one worries about stranded vs solid vis-a-vis amperage. The NEC counts all smaller sized conductors as equal. You guys are geeking out too much
4) There is no such thing as "tidy" looking surface mounted MC. I would rip it all out. If you can use woodworking tools, you can run conduit. Then have your sparky run the wires, and hit the panel
1) It is my understanding that the NEC does not allow uncovered MC conductor (flex, or what you are incorrectly refering to as BX) withing eight feet of the floor. It is legal at lower heights if covered with wall, or protected in various other ways
I was just calling it armoured cable, until someone 'corrected' me. I'm in Canada, so we'll have different codes. In my last shop the cable was run on the surface, it was installed by an electrician and inspected. So here at least the cable can be installed on teh surface (at keast in a garage).
4) There is no such thing as "tidy" looking surface mounted MC. I would rip it all out. If you can use woodworking tools, you can run conduit. Then have your sparky run the wires, and hit the panel
I was never really happy with the look, and doubted the safety... when I thought about it. For the most part I didn't. The cable was run low on the wall, so it was behind my bench or tools for the most part, then just popped up to the plugs. Looking back now, it actually wasn't that bad. However the new shop is a different beast. I have more space to use as a shop and I have more electrical concerns to take care of.
The last shop was two car garage. I had the machine side, which had the bulk of the power tools and the bench side... I just ran a cord if I needed a tool. Lighting was so-so. The new shop is a three car, with the bulk of it dedicated to my workshop. The homes cement foundation is esposed on most walls, in particular the back wall which is 14' high (4 feet of foundation exposed).
If you don't want to bend offsets close to the box (this takes a little practice), there are offsets available that you attach to the box and run the straight conduit into.
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