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Old 06-13-2010, 02:59 PM   #1
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PDX Garage Workshop questions


Let me first thank everyone who has posted here helping others - I have been reading posts for the past few weeks and it has been invaluable to me.

Even so, I haven't found one single post that answers all my questions, and I want to be sure my cobbling together of other answers works as a whole.

I am planning on setting up a wood shop in my detached garage, and I would like to install a subpanel. Main service is a 200 amp Cutler Hammer panel installed by an electrician in 2003. I figure a 60 amp panel would probably be more than adequate for my anticipated needs, but I think I would like to bump the subpanel up to 100 amp just so I never have to revisit this again. I would MUCH rather have a great deal of overcapacity than have to re-dig or re-wire.

The garage is 71 feet away from the house. I intend to dig a trench 24" deep and run gray PVC pipe with at least 24" sweeps on the corners. I was figuring on 1.5" PVC - is this sufficient, or is going to 2" a good idea?

Since I will have 220 volt outlets and 120 volt outlets, I am planning on running 4 wires of THWN : Red, Black, White, Green. The various online wire calculators I've used give different numbers for what gauge wire to use - #6, #4, #3. This makes me nervous enough to think I should just run #2 to be sure, but I would appreciate hearing informed opinions. Again, I emphatically do not mind spending a bit extra to be sure that I am well within, even over the requirements for a 100 amp panel.

I will keep ground and neutral separate and drive two grounding bars at the garage.

I am in Portland, Oregon. I have just called 811 and am in the process of marking where I intend to dig. I have an electrical permit for the work.

To summarize my questions:

- Does my overall plan sound reasonable? Any red flags?
- What gauge of THWN wire do I need to run to support a 100 amp 240/120 panel at 71' feet? (Or should I run another type of wire?)
- What diameter PVC pipe?

Thanks very much.

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Old 06-13-2010, 05:28 PM   #2
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When I was in the planning process for wiring my garage four years ago, I happened see the electrical inspector drive by while I was out for a morning walk. I flagged him down and asked a couple of questions about the project. He came down to the house and gave me a quick overview. He also said I could run a service lateral - tap right into meter with the other panel. All I would need is a main disconnect or no more than 6 individual disconnects, two ground rods, and 2-2-4 aluminum. I went with a 100 Main with a breaker. Passed the inspection a few weeks later with "nice work" written on the sheet. BTW, he said I could clip the meter seal and he would reseal it.
I don't see anyone on this forum ever mention a service lateral instead of a sub panel. Is there a reason?

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Old 06-13-2010, 06:12 PM   #3
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For 100a using THWN copper use #3 wire
You can buy all black wire for hots & neutrals & remark
2" conduit is not that much more & I might go that route for an easy pull

Many meters are not setup for a service lateral
And as a DIY you are not supposed to pull the meter...arc flash can kill
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Old 06-14-2010, 09:11 AM   #4
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Looks like you have it pretty well laid out. I would be sure to use expansion fittings on the vertical runs at either end where they enter the house and the garage. One thing that I always recommend is running a couple of more pipes while the trench is open for low voltage, alarm, cable, phone, etc. It need not be the full 2" size but 1.5" or 1" would be good.
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Old 06-14-2010, 10:54 AM   #5
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Scuba Dave:

Thanks for the advice. Is #3 wire is not made colored, or is it going to be some custom order hassle if I try to find it? I had noticed that Home Depot only carries black for the thicker gauges. I would like to get colored wire, but if it is impractical I'm glad to know I can remark. (With colored tape I assume?)

Teamo:

I was figuring on running additional conduit for just that.
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Old 06-14-2010, 09:47 PM   #6
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Quote:
Originally Posted by stewlg View Post
Scuba Dave:

Thanks for the advice. Is #3 wire is not made colored, or is it going to be some custom order hassle if I try to find it? I had noticed that Home Depot only carries black for the thicker gauges. I would like to get colored wire, but if it is impractical I'm glad to know I can remark. (With colored tape I assume?)

Teamo:

I was figuring on running additional conduit for just that.
They have it colored here:
http://www.wesbellwireandcable.com/E...icalwire3.html
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Old 06-16-2010, 11:15 PM   #7
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First off ill suggest to get to your local supply house dont deal with the summer help at Lowes or Home Depot. A good supply house that does residential and new construction sales will take care of you.

Now. Here comes the tricky part.

Question for you:

Have you asked the inspector if he requires Direct Burial INSIDE of Conduit?
If he requires this then the type of wire youll need is called URD with 1 USE wire added to it. (Total of 4)


Now ill point you in a relatively cheap direction.

For your service you will need.

1.25 or 1.5" PVC. You dont need 2"......

For your wire ill suggest this: Make it an 80 Amp service from the start.....80A Cutler hammer breakers are a bit cheaper than 100A......Unless you have alot of resistive heating out in the subfeed area this will be sufficient.

Use #2 Alum Reduced Ground (2-2-2-4) SER cable for your 80A service. If you are intent on 100 A, then consider #1 or even 1/0 Alum SER. These may be harder to find/more expensive. Dont waste your time and money with colored THWN or THHN. Just get SER. Its easier to work with and its way cheaper. (I looked at the cost....I sell SER for about 1 buck a foot.......THWN is about 4-8 times the cost....)


If you run 4 wires, Im fairly sure you do not need 2 ground rods for subpanels...This would need to be confirmed by your inspector or someone with an intimate knowledge of the NEC. I Know you need 2 for main panels that have well water.

As for ground wire, get #6 bare copper.

As for your Panel, get a "Main Lug" panel. Not a "Main Breaker"
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Old 06-17-2010, 03:57 AM   #8
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Quote:
Originally Posted by LyonsElecSupply View Post
First off ill suggest to get to your local supply house dont deal with the summer help at Lowes or Home Depot. A good supply house that does residential and new construction sales will take care of you.

Now. Here comes the tricky part.

Question for you:

Have you asked the inspector if he requires Direct Burial INSIDE of Conduit?
If he requires this then the type of wire youll need is called URD with 1 USE wire added to it. (Total of 4)


Now ill point you in a relatively cheap direction.

For your service you will need.

1.25 or 1.5" PVC. You dont need 2"......

For your wire ill suggest this: Make it an 80 Amp service from the start.....80A Cutler hammer breakers are a bit cheaper than 100A......Unless you have alot of resistive heating out in the subfeed area this will be sufficient.

Use #2 Alum Reduced Ground (2-2-2-4) SER cable for your 80A service. If you are intent on 100 A, then consider #1 or even 1/0 Alum SER. These may be harder to find/more expensive. Dont waste your time and money with colored THWN or THHN. Just get SER. Its easier to work with and its way cheaper. (I looked at the cost....I sell SER for about 1 buck a foot.......THWN is about 4-8 times the cost....)


If you run 4 wires, Im fairly sure you do not need 2 ground rods for subpanels...This would need to be confirmed by your inspector or someone with an intimate knowledge of the NEC. I Know you need 2 for main panels that have well water.

As for ground wire, get #6 bare copper.

As for your Panel, get a "Main Lug" panel. Not a "Main Breaker"
SER is NOT RATED for underground use even when used in conduiit. 2008 NEC 338.12(A)(2).

Last edited by brric; 06-17-2010 at 04:03 AM.
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Old 06-17-2010, 09:33 AM   #9
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LyonsElecSupply:

I have ordered colored #3 THWN to go in conduit (from the vendor suggested above - thanks plumbvoltage!); from what I could figure out about code and reading around the web this seemed to be an acceptable answer.

I sincerely appreciate your efforts to save me money, but I'm not doing this myself to save money, at least not as a primary requirement. What I do not want to do is cut a $300-$800 corner only to have to rip something out to please an inspector. What I want is something that any inspector is going to sign off on readily, and nobody would argue a corner has been cut on.

More questions soon I'm sure. Thanks again to everyone who has taken the time to reply so far.
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Old 08-14-2010, 08:31 PM   #10
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The trench is laid in with the PVC pipes, and the wires put through. Now I am working on putting the wire through the walls of the house & garage and getting them back to the panel.

Here's the entry point to the garage:



I started first with the garage, but I got stymied by the interior wiring for the 4 wires from the main panel. These do need to be enclosed in some way, correct? I started with that assumption, and tried to rough in a PVC solution:





I am not sure this is the right way to go. I"m afraid the right-angle box shown is too deep, and that I'll have trouble getting drywall over the joists. I'd prefer to go with a flexible conduit here, if that were possible. I looked in the aisles at Lowes and could not find anything that seemed right.

I considered going down to something narrower in flex conduits, but wasn't sure that was legal or appropriate. I also wasn't sure how to reduce from 2" to something like 3/4".

Suggestions? Help?
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Old 08-14-2010, 10:20 PM   #11
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You can not bury that LB inside the wall. If your wire is long enough I would suggest cutting your pipe outside the garage, add a couple of couplings with a length of pipe and install the LB directly into the panel higher up on the wall...

Last edited by brric; 08-14-2010 at 10:26 PM.
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Old 08-14-2010, 11:01 PM   #12
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Garage Entry:

Quote:
Originally Posted by brric View Post
You can not bury that LB inside the wall. If your wire is long enough I would suggest cutting your pipe outside the garage, add a couple of couplings with a length of pipe and install the LB directly into the panel higher up on the wall...
This is definitely an option for the entry into the garage - the wire is long enough. (Is there a tool for cutting PVC pipe without risking the wires inside? I have been using a hacksaw so far, but only for empty pipe.) If there are other options that make sense I'd like to hear about them, but if this is the clear winner I will take your advice.

House Entry:

I do still face this general issue, though: the planned entry to the house is a good 25' horizontally from my main panel. (The logical entry point was a mess of blazes on the grass after I did a call-before-you-dig and I just didn't want to chance hitting something my first time running a ditch witch.)

So - as a separate problem, looking ahead a bit - I would like to know what to do to get four runs of #3 THHN running horizontally exposed in my basement. Here's a picture to give you an idea:



Am I looking at solid metal conduit? Flexible metal conduit? 4 parallel runs? One run? What diameter? Etc.
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Old 08-14-2010, 11:29 PM   #13
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Bring your conduit into the house to a 6" x 6" pvc j-box and transition to NM cable or SER and use that to go to your house panel.
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Old 08-14-2010, 11:30 PM   #14
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Quote:
Originally Posted by stewlg View Post
Garage Entry:

(Is there a tool for cutting PVC pipe without risking the wires inside? I have been using a hacksaw so far, but only for empty pipe.)
There are different methods. Some people use masons string and pull it around the pipe, some people cut around the pipe with a hacksaw 90% thru the PVC, then snap it off.

To protect the conductors inside, you can get a smaller piece of pipe to slide down inside the pipe you want to cut, the conductors would be protected inside this piece.
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Old 08-15-2010, 01:21 AM   #15
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Quote:
Originally Posted by brric View Post
Bring your conduit into the house to a 6" x 6" pvc j-box and transition to NM cable or SER and use that to go to your house panel.
So, SER would mean I don't have to be in conduit? If so, that'd be terrific! The junction box would go on the outside of the house, correct?

If anyone has suggestions for where to buy a length of 4 conductor #3 copper SER I'd appreciate it. Doesn't seem like a Lowes/Home Depot item, but I haven't checked there.

Can anyone else second this as a sound idea?

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