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Old 05-24-2009, 10:29 AM   #1
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Looking for some wiring verification


After reading a bunch of posts on sub-panels to garages and outbuildings, I have formed a plan of attack. In that I am not an electrician by any stretch of the term, I would appreciate a little validation or correction before I buy materials and pull wires ( I will have a licensed electrician do the actual connection, I think). So:

Distance from my outbuilding subpanel to main 200 amp panel in house is a total of 150'

Wires to go through 2" diam underground PVC conduit with large diam. bends each end (It already exists and feeding a fish tape was a piece of cake!)

Outbuilding to be a "typical" small workshop, with table saws, band saw, drum sander, of which only one tool would be on at one time. Maybe 8 additional GFCI outlets and assorted lighting to be powered her as well.

Will install 100 amp sub-panel in outbuilding, controlled by 60 amp breaker at main panel power feed.

I believe that pulling 3 #4 copper wires and one #8 copper ground, all in exterior weatherproof casing will be the right mix of wires (THIS is what I am most uncertain about!! - Comments??)

I believe that the neutral and ground bar need to be disconnected at the sub-panel and it should be connected to two 8' grounding rods sunk into the ground outside the building

I want the sub panel needs to have a main disconnect switch right there in the outbuilding, and I believe the panel/disconnect needs to be located within 6' of the outbuilding entrance (Is that right??).

So that's the plan. ANY comments are very welcome, and thanks in advance for sitting through another "dumb sub-panel question"!

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Old 05-24-2009, 11:23 AM   #2
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Looking for some wiring verification


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Originally Posted by tpagel View Post
After reading a bunch of posts on sub-panels to garages and outbuildings, I have formed a plan of attack. In that I am not an electrician by any stretch of the term, I would appreciate a little validation or correction before I buy materials and pull wires ( I will have a licensed electrician do the actual connection, I think). So:

Distance from my outbuilding subpanel to main 200 amp panel in house is a total of 150'

Wires to go through 2" diam underground PVC conduit with large diam. bends each end (It already exists and feeding a fish tape was a piece of cake!)

Excellent.

Outbuilding to be a "typical" small workshop, with table saws, band saw, drum sander, of which only one tool would be on at one time. Maybe 8 additional GFCI outlets and assorted lighting to be powered her as well.

Remember one GFCI can supply a number of outlets downstream.

Will install 100 amp sub-panel in outbuilding, controlled by 60 amp breaker at main panel power feed.

Why 60 amp? Go with a 100 amp feeder. Use #2 copper for this distance. #3 would probably be okay, but why take any chances on this most important part.

I believe that pulling 3 #4 copper wires and one #8 copper ground, all in exterior weatherproof casing will be the right mix of wires (THIS is what I am most uncertain about!! - Comments??)

Correct. 4 wire feeder. See above for wire size.

I believe that the neutral and ground bar need to be disconnected at the sub-panel and it should be connected to two 8' grounding rods sunk into the ground outside the building

Right. Separated. Insulated from each other. Rods cannot be more than 6 feet apart. Two!

I want the sub panel needs to have a main disconnect switch right there in the outbuilding, and I believe the panel/disconnect needs to be located within 6' of the outbuilding entrance (Is that right??).

Use a main breaker panel and then you will not need a disconnect inside or outside. If you use a disconnect, you can use a lug panel.

So that's the plan. ANY comments are very welcome, and thanks in advance for sitting through another "dumb sub-panel question"!
Sounds like you have it covered. You have to decide on the size of the feeder. A 60 amp feeder can supply a 100 amp panel. But, you have 2" conduit and you plan to use a 100 amp panel. So why not just pull a 100 amp feeder.

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Old 05-24-2009, 11:51 AM   #3
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Looking for some wiring verification


Thanks for the verification J.V.! I guess cost was the only thing stopping me from going with #2 wire feeders. I will consider biting the bullet a little more upfront and having more flexibility later on. I only reason I went with 100 amp panel is because I could get one pretty cheap from a friend who had one. From what I understand, 60 amps is really all I would need for a small workshop/garage, don't you think? Is 100 amp overkill or is it one of those "if you build it, you will use it" things? ;-) Thanks again!
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Old 05-24-2009, 11:52 AM   #4
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Is a #8 wire still OK for ground if I go with #2 feeders?
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Old 05-24-2009, 11:54 AM   #5
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60 amps is really all I would need for a small workshop/garage, don't you think?
60A = four chopsaws running at the same time at rated load. Is it just you working?

I'd plot the cost vs. the amps. Generally, the more amps the more cost for wire and the less likely that you will be using all those amps. For a constant Circular Mils per amp, the cost of wire should double every 3 gauge numbers.
30A is good minimum starting point. Hopefully the point of diminishing returns will be obvious from the graph.

You can size the lighting based on the sq. ft. of your shop.

Last edited by Yoyizit; 05-24-2009 at 12:08 PM.
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Old 05-24-2009, 12:27 PM   #6
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Yes. #8 is still good with #2. The #8 must be a green wire. You can mark the neutral with white tape on each end.
100 amp is not overkill. IMHO. If you already have the panel and it is a lug panel you MUST install a disconnect. Disconnects are more expensive than some panels. Hopefully your free panel has a main breaker. Your panel might except a main breaker if it does not have one.

Make sure you check around on wire prices. The #2 may be less money at the supply house than #3 is at HD or Lowes. Copper prices change everyday and supply houses follow suit. Box stores have a price and stick to it until they HAVE to either lower it, or raise it. Good luck and keep us posted.
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Old 05-24-2009, 12:38 PM   #7
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I think JV meant to say the two ground rods must be at least 6' apart.
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Old 05-24-2009, 12:46 PM   #8
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Yoyizit...Thanks for the input. It may well come down to cost. I will check Electrical Wholesale. They gave me a price of $300 for 500' of #4 last week (3 runs of 150' plus some slop), when I thought that was what I needed. That was reasonable to me. I will check the #2 as well. I budgetted about $500 for wire, so that may still be OK.

Another bit of info: I will be ripping off the decayed roof of the 15'x40' outbuilding and replacing the rafters and roof. There is a slight chance I may decide to build upward over a portion, and add more loft space. That said, maybe 100 amp service would be the smart choice, as it would become "man cave" space, with refrigerators and beer and a TV and such! There is also another existing 1" conduit already installed for data and telephone ;-)
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Old 05-24-2009, 12:47 PM   #9
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Thanks for the feedback, Speedy. Did everything else in the previous posts, especially my "plan" sound OK to you?
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Old 05-24-2009, 12:51 PM   #10
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FYI - Here is the sub panel I have now:

http://www.lowes.com/lowes/lkn?actio...G1K&lpage=none
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Old 05-24-2009, 03:05 PM   #11
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maybe 100 amp service would be the smart choice
The chance you'd want less amps in the future is 0.0, and the electricians on this site can say how much more amps you'd probably want in how many more years, based on what their customers have done.

Last edited by Yoyizit; 05-24-2009 at 07:03 PM.
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Old 05-24-2009, 05:18 PM   #12
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Looking for some wiring verification


From what I gather, there is only one issue I can see. You say this is going into what sounds like a wood shop.
You're going to want to be carefully about sealing up your penetrations into the panel to keep sawdust out.

Otherwise, sounds like you have a good plan of attack. Good luck!
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Old 05-25-2009, 10:39 AM   #13
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I think JV meant to say the two ground rods must be at least 6' apart.
Speedy. Thats twice this week alone.
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Old 05-25-2009, 12:04 PM   #14
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I know. It's been one of those weeks for all of us.
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Old 05-25-2009, 12:44 PM   #15
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Looking for some wiring verification


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Originally Posted by J. V. View Post
...Right. Separated. Insulated from each other. Rods cannot be more than 6 feet apart. Two!...
Ummm ... that would be the rods cannot be less than 6 feet apart...

Edit to add --- looks like Speedy beat me to this issue. Sorry I missed that ...

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