Detached Garage/Shop wiring WA

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Old 10-27-08, 01:26 PM
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Detached Garage/Shop wiring WA

I'm near completion on my 1000sq/ft detached garage/shop building. I live in a small city in washington state and the city itself didn't require anything regarding electrical to get the building permit. Most of the shop is for vehicle storage, with only one bay being open for a work area. When I excavated the site, I buried a empty 2-1/2" pvc conduit from my house panel to the garage. Before I moved in my workbenchs, I roughed in 6 double outlet boxes with wires on the one wall. 3 outlet boxes each on what will be 2 circuits. I drilled 5/8" holes for each wire thru the 2x6 studs in the center. Then I insulated and sheathed the wall with plywood. I have been told by some that I need a permit, others have said because I am building my shop on my own I can wire everything up and just have the inspector check it? I have used screws on the plywood if necessary it can be removed for inspection if needed.
My other question regards the feed from the house. I am going to be taking 100 amps( I have a millermatic 250 mig welder) from the 200A panel. I am understanding that I will need a sub-panel with 100A main breaker, and isolated neutral bar. I assume I will also have to have a separate ground rod for this building. I will be running a 4 conductor #2 copper wire thru the conduit ~100ft run- from the house to shop, and leaving the neutral un-used in case the code should flip on us again. I am also assuming that the ground ran thru the conduit should connect the sub-panel ground to the main panel ground, effectively allowing the house to ground thru the shops ground rod or vice versa should one ground fail.
This all sound up to par?
 
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Old 10-27-08, 01:33 PM
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Only your inspection authorities can answer if you can close in your work without inspection. Check with them.

The 2008 Code requires a 4 wire feed to detached structures so I am confused when you say you will leave the neutral unconnected. You will not be able to have any 120 loads without the neutral. You will also need a separate ground bar.

I am not sure about your wire sizes without checking my book. I am sure Ben or Marc will add to this.
 
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Old 10-27-08, 01:48 PM
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If your city/county doesn't enforce the NEC then you are required to obtain an electrical permit from Washington state. Because the garage is on the same property as your primary residence, you are allowed to do the electrical work. Contact the your local Wa St. Labor & Industries electrical division.

Inspection is good for insurance purposes, too.

#2 AWG copper is rated for 115 amps.
 
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Old 10-27-08, 03:01 PM
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Originally Posted by rkcarguy View Post
I will be running a 4 conductor #2 copper wire thru the conduit ~100ft run- from the house to shop,
For 100A, I would actually recommend that you install #3 copper THWN for hot, hot and neutral and #8 copper THWN green for ground. Using the #2 copper won't hurt anything except your pocketbook; if you do upsize to #2 copper hots, the ground has to upsize to #6 copper.

You could alternatively use #1 aluminum for the hots and neutral and #6 aluminum for the ground.

and leaving the neutral un-used in case the code should flip on us again.
Both the neutral and ground wires are used; neutral wire connects to the isolated subpanel neutral bar. The ground wire connects to the subpanel ground bar.

shops ground rod or vice versa should one ground fail.
This all sound up to par?
The shop ground rod(s) should be connected to the subpanel ground bar using an acorn clamp on the rod and #6 copper wire from the rod to the panel. Note: Aluminum wire cannot be used here.
 
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Old 10-27-08, 03:23 PM
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Originally Posted by rkcarguy View Post
Then I insulated and sheathed the wall with plywood. I have been told by some that I need a permit, others have said because I am building my shop on my own I can wire everything up and just have the inspector check it? I have used screws on the plywood if necessary it can be removed for inspection if needed.

The plywood will have to removed. The inspector will want to see all of the wiring. They can be pretty stringent with DIY'ers.

I'm trying to decide if the interior plywood is acceptable as non-rated construction material. You may want to ask the inspector about that.
 
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Old 10-27-08, 03:58 PM
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I was told that using plywood on the interior was ok being it's not a residence. Our attached garage doesn't have anything just exposed studs and wires. If the detached garage is closer to the house than 3' I would be required to have a firewall(drywall) installed all across that side of the shop even up into the truss's.
I hate working with drywall, it stains, cracks, and is heavy and hard to work with. The plywood also gives me double the shear strength being my shop is exposed to the nasty northeast winds.

Regarding the neutral and ground- so basically the neutral will be wired commonly between the shop and house, however isolated at the detached garage from the panel?
And the ground is connected to ground rods at both buildings and the buried cable connects both grounds all common?
 
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Old 10-29-08, 03:24 PM
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Originally Posted by rkcarguy View Post
Regarding the neutral and ground- so basically the neutral will be wired commonly between the shop and house, however isolated at the detached garage from the panel?

That is correct. The electrical term for isolating the grounded (neutral) conductor in a sub panel is called "floating the neutral."


Originally Posted by rkcarguy View Post
And the ground is connected to ground rods at both buildings and the buried cable connects both grounds all common?

The wire to the ground rods is called a grounding electrode conductor. The GEC connects the ground rod to the service panel and subpanel. The garages subpanel GEC and ground rod are terminated to the equipment grounding bar in the subpanel.


The 4th wire ran to the detached garage is called the equipment grounding conductor. It connects to the grounded (neutral) bar in the service panel and the equipment grounding bar in the subpanel.

Terminate all equipment grounding conductors to the equipment grounding bar and all neutrals (grounded) to neutral bar in the subpanel.
 
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Old 03-19-09, 10:39 AM
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UPDATE:

I picked up a Siemens 100A main panel kit and installed it in the shop last week. The conduit is extended up into both the garage and shop and punched thru the walls. I have a rope pulled thru to use for pulling the cable in.
The panel had a big copper jump bar in it which I removed according to the instructions which should be "floating the neutral" as required.
All I have left to do is purchase/install the cable and install the shops ground rod.
My last few questions involve the cable type and my conduit terminations. The conduit runs up the side of both the shop and house where I have a 90* junction box installed and hole punched thru inside.
There isn't a bend tight enough to do a 90* down into the panels, is there a certain kind of cable or jacketing I need to buy that can be exposed for the few inches as it comes out of the conduit/flare and into both panels?
 
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Old 03-19-09, 12:13 PM
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Originally Posted by rkcarguy View Post
My last few questions involve the cable type
Through the conduit you don't actually want a cable, you want individual wires. Go to the electrical supply house and ask for THWN in the appropriate sizes and they will get what you need. If you get copper wire use #3 for the hots and neutral and #8 (bare or green) for the ground. If you get aluminum wire get #1 for the hots and neutral and #6 for the ground. Type XHHW wire is okay too depending on what the supply house has in stock.

and my conduit terminations.is there a certain kind of cable or jacketing I need to buy that can be exposed for the few inches as it comes out of the conduit/flare and into both panels?
No, the conduit has to be continuous from panel to panel. Have you looked at conduit body fittings (LB,LL,LR)?




Those are designed for making sharp 90s, just make sure to keep them accessible. Do you have a picture of the panel you could link to? I could probably come up with some other ideas if I saw it. Perhaps a short piece of flex conduit?
 
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Old 03-19-09, 12:22 PM
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I have one of these on the outside of both structures. One comes out directly above the center of the panel in the shop about a foot higher, the other one is off to the side to clear the meter box. I guess I could use these on the inside and outside for lack of something better...
I didn't glue my flares on yet because I was wondering about that....
 
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Old 03-19-09, 12:49 PM
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Yes you can use one on the inside too, but you can't cover it with drywall. Another option is to cut your outdoor conduit shorter so the conduit enters into a knockout in the back of the panel.
 
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Old 03-19-09, 01:01 PM
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Thats fine I am leaving the panel area unsheathed on the inside between the two studs. I'll have a big hole to fill if I try to move the 90* box's down now.
I just called the electric supply house which quoted THHN #2(I have a 110'+ run) copper at $.74 a foot, and a 1-3 SER #1 aluminum w/ground at $1.75/ft.
Obviously the alum is almost 1/2 price, would there be any code problems with this type of wire in a conduit?
 
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Old 03-19-09, 02:14 PM
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sound's like your getting good advice, just a FYI get some lube or pulling soap #3 wire can get tight in conduct and hard to pull thru 90 degree elbows, also when you are pulling wire have someone pushing at the other end, it will help
 
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Old 03-19-09, 02:57 PM
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Originally Posted by rkcarguy View Post
I just called the electric supply house which quoted THHN #2(I have a 110'+ run) copper at $.74 a foot, and a 1-3 SER #1 aluminum w/ground at $1.75/ft.
Obviously the alum is almost 1/2 price, would there be any code problems with this type of wire in a conduit?
You can't use type SER underground -- check to see if they have any aluminum USE-2 instead. The price should be similar. Sometimes it's sold as a twisted assembly, sometimes as individual conductors.

Pick up a bottle of conduit pulling lube while you're at the supply house and a tube of no-ox grease for the aluminum wire. The only issue with aluminum wire is that you'll have to use the no-ox grease on the stripped wire to prevent oxidation, but that's no big deal.
 
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Old 03-19-09, 03:22 PM
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I've pulled enough fat comm cables that I know the wire lube comes in handy for it. The no ox is an anti-corrosion item for the different metals at connection points?
I've used a pretty good size conduit planning on running a larger wire, I'd say 2" or 2-1/2" I'll have to look when I'm home. The 90* bends are all nice radius's I'm hoping they will pull ok because there are 3 of them...
 

Last edited by pcboss; 03-19-09 at 08:01 PM. Reason: terminology clarification
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Old 03-19-09, 03:57 PM
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Originally Posted by rkcarguy View Post
The no ox is an anti-corrosion item for the different metals at connection points?
Yes, the aluminum is more susceptible to corrosion than copper is so the grease is required to get a solid connection that will last.

I've used a pretty good size conduit planning on running a larger wire, I'd say 2" or 2-1/2" I'll have to look when I'm home. The 90* bends are all nice radius's I'm hoping they will pull ok because there are 3 of them...
2" conduit will pull just fine for your conductor size.
 
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Old 03-19-09, 04:11 PM
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Ok great, thank's everyone for all the help!
I will post up some results when it's all done.
 
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Old 03-19-09, 07:30 PM
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#3 in my area is priced higher do to must people use #2 more so the dealers get a better cost on it. So I would use 2-#2 copper (Hots) 1-#4copper (Neutral) & 1-#8 copper ( Ground). You will be able to use 1 1/4" pipe for this. Again, the forum has you going in the right direction but I thought I would throw my 2 cents in the thread. Good luck!

Jim Beer 4U2
 
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Old 06-01-09, 01:28 PM
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I passed my structural final so I'm down to getting this wiring done. I priced some wire over the weekend at Home Depoo, it was USE-2 aluminum 1-1-1-2 twisted together.
$2.49 per foot. I know the #2 is overkill for the ground but it gets them all in there in one pull and gets the job done..just wondering if I can do better on price?
 
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Old 06-01-09, 01:31 PM
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The price sounds appropriate for the #1 USE. You could call around to local supply houses, but they usually can't really compete with the big boxes on per-foot wire.
 
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Old 06-01-09, 01:42 PM
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Or I just got a quote of about $160 for XHHW aluminum individual wires 1-1-2-4......
Thinking that sounds pretty good.
 
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Old 06-08-09, 10:05 AM
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I picked up my cable friday and got it pulled thru the conduit over the weekend.
One of my bars, on the right side looking at the panel, has a green screw in it which grounds it to the box itself. I'm assuming this must be the ground bar. The bar to the left has no continuity to the panel box and I'm assuming is the "floated neutral" ?
Just wanted to make sure before I start cutting and stripping....
Any ground rod information would also be helpful, buried length, overall length, diameter, etc.
Thank you for helping me come this far.
 
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