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Lupus71 11-26-2012 02:58 PM

Installing sub panel
Hey guys, going to give all info I can so here goes, I'm building a 16x24 workshop that will have a few lights,window a/c 110v, various woodworking tools such as bandsaw, table saw, jointer, and the only tool I have have that I will run at the same time as others is a dust collector all which I think will be fine with a 100amp sub. My shop is about 100 feet from my main.My current main breaker is 200amps I'm not sure how to go about getting the current I have coming through it or what not but my main question is from what I gather I need 3 #2 stranded thhn copper wires one for hot,another hot, a neutral and then a #6 stranded ground? I would run that from the main with the meter outside( there's only one 200amp breaker so I wouldn't think) or the 20 circuit panel with I think a 150 amp breaker (at work so can't check)? Also they would have to tie in to the main lugs right? Doesnt seem like there's room. Also read that I need 2 ground rods by the shed and not to bond the ground and neutral together. I'm not sure what that means I thought each wire had its own bar that it went to. I know it's a lot to answer so I really appreciate any help and I know I should hire someone I just can't afford it. Trying to get it right the first time and not burn down my house!

kbc1 11-26-2012 03:39 PM

wires from sub panel would have to go on its on 100 amp breaker in main panel, are you trenching this run , what size pvc are you using

Lupus71 11-26-2012 04:44 PM

Yes. Think I have to use 1.5 conduit. So I need a 100 amp breaker for my existing panel? The main outside by the meter only has one 200 amp breaker and no other slots. I have a sub panel that is full but I can use 2 tandems to free a space if thats where it goes.

kbc1 11-26-2012 05:32 PM

where all your other branch circuits are you will run your feeder wires into that panel and install a 100 amp 240 volt 2 pole breaker , make sure nuetrals and grounds are isolated in sub

teamo 11-26-2012 05:39 PM

Nothing wrong with using #2 copper but you can use #3 copper thhn/thwn for 100 amps. Use a two pole 100 amp breaker in the main panel. The minimum size conduit (pvc) is 1 1/4 but I would go ahead and use the 1 1/2 to make the pull easier. You need the two ground rods at the shed. While you have the trench dug I would suggest that you install a couple of extra conduit runs for low voltage- cable, satellite, alarm wiring, etc.

k_buz 11-26-2012 05:59 PM

You could easily get by with a 60A sub. It would cut the cost of the installation down quite a bit. I would use 1 1/4" PVC, (3) #6's, and a #10 ground (copper conductors).

Lupus71 11-26-2012 09:38 PM

2 Attachment(s)
Ok great! So the main you are referring to would be the existing sub panel that is feeding everything in my house? also as I said it is full so would using 2 tandems to free a space for the 100 amp breaker be ok? Someone said I can have up to 10 I believe, depending on how much is being ran on the main already, I'm not sure how to figure that up.

Attachment 61056

Attachment 61057

This is the panel in my garage which is where I need to make room for the 100amp breaker, correct? Thanks for the help, I've been reading up all I can. Just want to do this correctly.

k_buz 11-26-2012 09:47 PM

You might need to free up a total of 4 spaces. Many panels limit how much can be on each stab of the buss to 100A. Which means, if you use a 100A breaker on one side of the panel, you cannot have any breakers directly opposite.

You will need to verify that this panel is rated for tandems.

Lupus71 11-26-2012 09:55 PM

I read somewhere that the panel numbers being qo2030 means I can have 10 tandems.So I would need 4 tandems to free up what is needed?im just not sure if thats too much for my panel.The old style for mine are costly at $35 used. Wish I could find them cheaper!

Lupus71 11-27-2012 10:02 AM

How can I tell if 4 tandems and adding a 100amp breaker isn't overloading that panel?

Lupus71 11-29-2012 06:20 AM

Bump bump

k_buz 11-29-2012 06:33 AM


Originally Posted by Lupus71 (Post 1061581)
How can I tell if 4 tandems and adding a 100amp breaker isn't overloading that panel?

The circuits that will be protected are already feed by this panel and you know the service is able to handle what is currently there so that point is moot.

The 100A breaker isn't important. The important part is what loads are going to be in the sub panel. Most houses don't draw 100A, so I doubt it will be a problem, but you would need to do a load calc if you wanted to make sure.

Stubbie 11-29-2012 09:55 AM

1 Attachment(s)

Originally Posted by Lupus71 (Post 1061581)
How can I tell if 4 tandems and adding a 100amp breaker isn't overloading that panel?

Put a 100 amp panel with main breaker in your workshop. It needs to have a main breaker to serve as the required service rated disconnect. It can be a 100 amp panel with 'main breaker' or it can have the backfed main option where you can install a double pole breaker with hold down kit. Many times the big box will have a value pack 100 amp panel with a main breaker very reasonable and comes with branch circuit breakers. This type panel will have a 'main breaker' like the one in your garage. The back fed type allows you to install your own main breaker which can be any double pole breaker designed for that panel. So if your running a 60 amp feeder from a 60 amp double pole breaker in your house panel you can install a 60 amp double pole breaker in the workshop panel. The idea is that the breaker in the workshop serves as a required disconnect for the detached workshop and the breaker in your house panel serves as the 'protection' breaker based on your feeder size. You cannot install a breaker that is more than the rating of your workshop panel.
You need 4 wires feeding the workshop panel set it up just like your house panel is being fed from the main breaker on the outside of your home. Notice in that panel there is a ground bar fastened directly to the metal of the enclosure and all the ground wires go to it. Then notice the neutral bar is separate from the ground bar and has all the white wires going to it. Next thing you will see is that the green 'bonding screw' is not installed in the neutral bar. That's the empty hole you see next to where the big gray feeder neutral connects into the lug of the neutral bar. With that bonding screw not installed this isolates the neutral bar from the ground bar and prevents neutral current from getting the the ground bar via the panel metal.Your going to use the same principle in your workshop panel.

When you buy your new panel just repost here and we can tell you how to separate neutral and ground.

I highly recommend using pvc conduit and thhn/thwn wire. A 60 amp feeder like K buz said will be adequate for your needs. Using a conduit size that will accept a 100 amp feeder will allow you to upgrade from the 60 amp feeder if you want in the future. You just use the wires existing to pull in the new wires.
Use the drawing below as your guide and I would strongly suggest you have your work inspected by a qualified person. Understand that the electrical work your doing requires a permit at a small cost. Do not be afraid of inspection it will give you peace of mind.

The drawing is a little different than your situation. The SER cable would be the cable that is coming from your main disconnect to your sub-panel with main breaker in the garage and your panel would be inside not outside other than that the drawing is accurate. The drawing shows a pvc conduit installation. All conduit above ground needs to be sch 80 ... below ground can be sch.40. You can also direct bury but the cost difference is minimal.

Stubbie 11-29-2012 10:39 AM


Originally Posted by Lupus71 (Post 1061328)
I read somewhere that the panel numbers being qo2030 means I can have 10 tandems.So I would need 4 tandems to free up what is needed?im just not sure if thats too much for my panel.The old style for mine are costly at $35 used. Wish I could find them cheaper!

Try Ebay. You only need 2 tandems to free up 2 spaces for a double pole breaker. Bus stab ratings may enter into the picture as K buz stated but on a 200 amp panel you should be fine as long as the breakers across from your feeder breaker are 20 amp or less. Look for a label that states the bus stab rating. Look at your panel starting at the bottom count up 5 breakers in each column. This is the area your tandems can go in.

Lupus71 11-30-2012 05:28 PM

Just looked at my breaker outside (main?) it's actually a 150 amp and the sub panel too. Still ok for the 60 amp breaker? Also I want to put in a window unit a/c that draws 8.5 amps, is 60 amps still ok and could i go to 3 #6 thhn stranded and a #8 or 10 ground? Sorry for so many questions but also does the ground need to be solid?

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