New Shop Wiring Plan

Gents:
Thanks to advice I've received here, I'm ready to proceed with getting my permit and wiring my new (and final) detached workshop at our cottage/retirement home site. It's a detached 2000 sq. ft. two-story frame structure on a concrete slab on grade. My plan is to add a sub-panel as follows: from the 200A service entrance panel on the first floor of the cottage, I'll add a 240V 100A 2-pole breaker feeding three 2-AWG type THWN conductors (2 black, one white) and one 6-AWG (green) grounding conductor. This will be pulled through schedule 80 pvc conduit in a trench 18-24 inches below ground. At the shop, I'll have a 100A-rated service entrance panel with another 100A main breaker (service shutoff) and floating neutral buss. An isolated ground buss bonded to the box will be connected to two grounding stakes (6 ft apart)with 6AWG bare wire. OK so far? If so, I'd like to describe my internal wiring plans. Thanks for your consideration.
Tom Carter

 

Tom, sounds like a plan and that you did your research.

Good Luck

Wg

 

Walt,
Thanks for the quick up-check. Now comes the judgment part: interior wiring and lighting. I'll be putting in as many as six general purpose circuits for both stationary and portable power tools of the 110V variety: they'll be 20A using 12 AWG conductors. Also, I'll have a couple of dedicated 220V circuits for heavier (3-5hp) woodshop tools, plus a welder circuit and possibly a dedicated circuit for a three-phase rotary converter. The building is progressing only slowly, and I probably won't install sheetrock soon if ever. Should I bite the bullet and use armored cable? I've never done muchwith AC/BX than the occasional repair. Are there many special tools needed? Any difficult techniques? I plan to use steel circuit boxes in any event, and I realize they'll have to be grounded. It seems to me that for the interim period before I get the shop completely finished the AC running through the 2x6 studs would provide better protection than NMC would.

Second question: what kind of general lighting would be best for a shop 18 ft by 40 ft with open gambrel-roof trusses 18 ft high at the peak? Flourescent, metal halide, or other? Considering cost, durability and light quality. I will put in task-specific lights where needed (I have two salvaged swing-arm reflector lights from a surgery in a hospital--they're neat!) Would appreciate your insights.
Tom Carter

 

Tom, now you are in an area of design that has some codes to consider but you also have a whole lot of differing opinions, personal tastes, type work being done design charicteristics to consider. You should be getting quite a few different thought on your questions most being personal experience and taste being involved in your replies. Maybe they will all be right but different from others way of thinking. Read them all and then make up your mind after you have researched all our ideas. Have fun!

YOU SAID;
I'll be putting in as many as six general purpose circuits for both stationary and portable power tools of the 110V variety: they'll be 20A using 12 AWG conductors.

REPLY;

If you think ahead you probably can do the same thing with about 3 branch circuits 20 amp rated. Lets talk about where and how you will be working in that structure. If you are working alone you will only be using one of two electric tools at the same time that are manually operated. Any auto operated pieces of equipment probably should be on dedicated circuits only serving that machine to avoid your manual machines running when that auto start equipment such as air compressors etc. starts up causing a breaker to trip.

Then think about where you will place your stationary equipment. If you are one person working in that structure you would most likely be working in a concentrated area around a work bench etc. If you keep this in mind and keep in mind that you are working alone with possibly one person working with you, about three branch circuits in that certain work area could serve all you need. With that in mind try the following suggestions in branch circuit design. If you installed all the general use receptacles all the way around the inside of your building then run circuit A 120 volt 20 amp 12/2wGRnd cable from the panel to recept one then daisy chain to recept 4 then to recept 7 etc. Then install a second branch circuit B from panel to recept 2 then daisy chain to recept 5 then to recept 8. Then install a third branch circuit C to recept 3 then daisy chain to recept 6 then to recept 9. You would have 60 amps worth of general use receptacles in any area around the entire structure. Shouldn't that be enough to serve your hand tool or drill press etc. loads remembering you or possibly one other person will be using those receptacles in any given location throughout the entire structure?

YOU SAID;
Also, I'll have a couple of dedicated 220V circuits for heavier (3-5hp) woodshop tools, plus a welder circuit and possibly a dedicated circuit for a three-phase rotary converter.

REPLY;
Boy you jumped from circuit to circuit quickly in that statement involving a few potent decesions. You welder can take up a statement of two. Remember the rule of noncoincendental loads. If you ran a 6 awg copper branch circuit black red and bare for an arc welder you could daisy chain two or three welder receptacles off the same branch circuit allowing your welder to be plugged in to different locations including by your overhead door allowing welding to be done even outside and use the same branch circuit for welding to all these welding receptacles if you only have one arc welder. If you have a wire welder you may only need a 20 amp 220 volt circuit again you could daisy chain that welder circuit to different locations allowing receptacles to serve your wire welder close to where you are working again only if you have one wire welder.

Then you mentioned some pretty large motors that could be less expensive motors if they were three phase motors. You also mentioned a rotophase. Rotophase generators are often rated for the largest motor yet allowing serveral of those same motors to run at the same time if started at different times. With this in mind and the fact you mentioned a rotophase you may be better served to install a three phase panel to serve your structure with 100 amp single phase serving factory power for line one and three and your generated leg from the rotophase connected to the center lug of that three phase 100 amp panel serving that rotophase. This way you can wire single phase or three phase out to your three phase or single phase motors directly from the panel serving that structure. Then if this panel is in sight of and within 50 feet of those motors you could elminate any need for disconnect forms to meet the Code. The breakers in that panel serving that structure could serve as your motor disconnect form.

Remember that a rotophase whether serving a single branch circuit or a main panel serving the entire structure you must have a time delay sequence to prohibit those three phase motors from starting while the roto phase is starting up. Also you will need a main relay that will kill the power to any or all three phase motors that are running off that rotophase to prohibit those motors from single phasing if you loose the generated leg. Also remember any three phase motor normally do not have overload protection. This means you will need motor control boxes with over load or overload components to protect those motors that are without overload protection built into the motors.

Just a few concerns mentioned for your branch circcuit motor design activities.


YOU SAID;
The building is progressing only slowly, and I probably won't install sheetrock soon if ever. Should I bite the bullet and use armored cable? I've never done muchwith AC/BX than the occasional repair. Are there many special tools needed? Any difficult techniques?

REPLY;
I plan to answer this set of statements with questions in an attempt to get you to consider you plan by using your thoughts against you. Don't take these questions personal. However your statements make it sound like you already have made up you mind on your wiring style yet I have doubt your statements are based on facts per the NEC and logical thinking. Lets try to rethink what you said.

Not installing sheet rock is not a problem that can be done at anytime. Although you will have a problem fitting the holes in the sheetrock after your recepts and switches have been installed already. To solve that problem of fitting tight to your device boxes when you do drywall you can turn off all your branch circut and unscrew the recepts and switches. Then pull them out leaving them connected to your de-energized wires. Then shove your recepts and switches end ways into their device box. Once you drywall then you can reinstall your switches properly onto the new drywalled wall finish. Just remember to shut off your branch circuits so you don't get shocked when installing your tape and bedding on your drywalled joints.

I am wondering why did you pick metal clad or a/c cable. If you are installing your wires through the studs instead of on the edges of those studs then your wire is not normally exposed to physical damage. Romex is allowed even in commercial buildings with wood stud construction methods. Wouldn't the wood studs burn before the romex melted. I am curious why you felt a metal wiring method should be used when the building is built by a non fire rated construction method using wood. If you were concerned of fire risk then why not steel studs instead of wood studs. Even steel studs allow for Romex to be installed. Not trying to be detrimental, just trying to spur thought in your decesion contrary to what you suggest that you are thinking. Personally I see no advantage of metal clad wiring over nonmetallic sheathed cable wiring styles [Romex] in a wood construction setting.

YOU SAID;
I plan to use steel circuit boxes in any event, and I realize they'll have to be grounded. It seems to me that for the interim period before I get the shop completely finished the AC running through the 2x6 studs would provide better protection than NMC would.

REPLY;
Before you commit to steel boxes why not try to tear apart, mash or otherwise damage a plastic device box. I suspect you will find these plastic boxes will take much more abuse than a steel box. Take a hammer and hit a steel box hard. Then take a hammer and hit that plastic box twice as hard. I think you will find that plastic box will survive and still be good for use, yet the steel box will be wasted. See what you think.

Also keep in mind that plastic boxes are nonconductive protecting that circuit from short circuits, yet the metal boxes are conductors of electricity inviting short circuits increasing shock hazards.

YOU SAID;
Second question: what kind of general lighting would be best for a shop 18 ft by 40 ft with open gambrel-roof trusses 18 ft high at the peak? Flourescent, metal halide, or other? Considering cost, durability and light quality. I will put in task-specific lights where needed (I have two salvaged swing-arm reflector lights from a surgery in a hospital--they're neat!) Would appreciate your insights.

REPLY;

Flourescent fixtures if your garage is not heated should be high output fixtures that will still work in cold weather yet these flourescent fixtures are the most common choice in a garage or shop setting due to their high light output with a ballasted bulb saving on electricity and cost effective compared to other lights that you mentioned. These flourescent lights also would not take long to light to full value eliminating a walk through light waiting on other lights you mentioned taking a long time to warm up and light to full value.

I would suggest rapid start flourescent fixtures in a heated building or HO flourescent fixtures where cold is a factor.

Placement of hte fixtures are a strong subject to consider. If you are working on a large product such as a pickup or car. YOur lighting would be better placed with a row of lights along the walls and one row of lights between vehicles. This way the roof of that large product is not blocking your light output and allow you to see to work better.

Hope this helps

Remember the above are mostly opinions and others will most likely use their experiences to provide other thoughts. Concerning the subject you posted there are many many right answers as to design specs.

Wg

 

Walt,
That's a lot of great insight, and I don't mind having my thinking challenged a bit!
I especially like your approach of daisy-chaining the working outlets in a staggered fashion--should save a couple of circuits there.
I understand about the dedicated circuits for larger auto-start loads.
The welder is a bit of a dilemma: my current box is an AC-only stick welder that draws 50 amps. Perjaps I should put on my wish-list a MIG welder that is much easier to use--I don't often need to weld the thick materials that the stick welder is better at.
I believe I'll go with the HO flourescents, as even with heat, shops stay pretty cool in the winter. I find it very irritating to have dim, flickering lights until the space is warmed up.

My original reason for thinking I might need BX or AC was that, in the period before I get the sheetrock up (which, according to my wife, could be a VERY long time ) the armor would provide better physical protection for the wires. I gather from your post that that's not the primary purpose of AC, but fire protection is. So I'll happily go with romex.

Thanks again for youyr advice--superior as usual!
TC

 

Tom

The wiring design is up to you as long as you meet the minimum safety standards set by the NEC. It was not my intent to challenge but to spur your own thoughts on the subject. Hope some of what I had to say helped. By the way you picked up the wrong name as my first name. My first name is Warren. Walt is ok though if you wish.

Wg

 

Gents,
I thought I'd stop by and give a bit of update on my project.

I had terrible luck trying to get any response from the inspector in my rural county. I suspect he's been overwhelmed by a relative boom in building in our county and didn't see a workshop wiring project as very high priority.

So I'm proceeding extra cautiously and have gotten the underground service installed (along with an extra conduit in the same trench for telephone, TV, etc. in the future). The panel is a type QO 40-space breaker box with 100A service cutoff.

I went with 8-foot twin-tube HO flourescent lights on the high ceiling, and they provide more than adequate light at night.

As I install the general purpose circuits, I'm wondering what the preferred technique is for wiring the outlets: to daisy-chain each pair of duplex outlets in each 22 cubic inch plastic box, or to pigtail each fixture. I understand either method will meet NEC requirements. I'd appreciate your thoughts.
Tom

 

I like to pigtail to receptacles and tie the wires. not much danger of them coming out of the box but plastic boxes dont really have clamps so tying them is better? its also easier to push the wiring back, be sure to leave long pigtails so you can get all your wires way in the back, then simply fold the pigtailed ends off the receptacle into it. easier than folding 4 12 guage and a ground all at once. nice choice on the 22cus. They are much easier to work with. Just my .02-Josh

 

Tom,

I recently went thru the same process that you are going through. After a bunch of plotting in my mind i decided to surface mount my electrical in conduit after i sheeted my walls with OSB which I painted.

I wasnt looking for anything domestically pleasing, just purely functional. The OSB allows me to hang tools etc virtually anywhere without wall anchors or locating a stud.

I surface mounted electrical allows me to change without tearing up the walls. I have always found my shop to be a continuous state of work in process because of new tools, different sized projects whatever.

This may not suit your preferences, but it already has paid dividends for me. I recently had to move some electrical outlets because I rearranged my shop to finally utilize my dust collector. It was really easy to do.

Good luck,

John