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BOAH 01-04-2011 01:22 PM

Correct way to wire a shed / workshop
I recently built a 10' x 14' shed that I'll be using as a shed / workshop. I have a chop saw, table saw, small compressor, etc. that I'll probably use from time to time. I don't have any tools that require 220 at this time. I ran three different circuits inside the shed. On the back wall of the shed I have three outlets on one circuit. On the front wall where my workbench will be located, I have 6 outlets on a circuit. On the third circuit I have two inside lights and four exterior lights. The reason I put only three outlets on the one circuit is in the possibility that I install a small AC unit in the back wall.

For all of the inside wiring, I used 12/2 armored wire (flexible conduit?). I want to control this with a sub panel so I purchased a GE 6-8 Circuit 125 Amp panel. First thing I noticed is that it didn't come with a ground bar. So I started to do some research and found out there's a few things that I had better check before I go any further and that's why I'm here.

I have a panel (Square D) on the side of my house about 40' away from the shed. This panel currently has 5 breakers in it. 2 - 125A, 2 - 100A and one 50A for a total of 500 amps. There are three open slots in this panel.

I plan on burying the line 18" deep inside of PVC pipe.

So here are my questions:

Q1: What kind of breakers do I need to install in the both panels?
Q2: What kind of wire should I run from the house panel to the shed?
Q3: Apparently, I also need to put in a 8' grounding rod. What is the correct way to connect this to the panel?

Thank you very much for any help!

oleguy74 01-04-2011 02:23 PM

first just beacause the breaker value totals 500 doesn't mean you have 500 amps.the max draw is controled by the main know the load you have to do a load calculation.if you want to have a 100 amp feed you need 3 #2 thwn and 1 #8 thwn wire.put it in conduit al least 24" deep.get a sub with a main breaker.put a ground buss in the sub bonded to sub panel box.neutral must be isolated from will also need 2 ground to ground bar with a #6 bare ground wire.if it is sq D use sqD breakers.

jbfan 01-04-2011 02:24 PM

#1- what ever brand of panel box is the brand of breakers you need to install.
#2-I would run 3/4 pvc and pull4 #12 thwn wires. These wires shall be 1 white wire, 1 green wire, and 2 black, or red, or one of each.
This will require a 2 pole 20 amp breaker for the outside box.
#3-After the ground rod is installed, run a wire from there into the panel and attach to the ground bar.
At the ground bar will also be the ground from the main panel, and the grounds from the receptacles
Make sure that the neutral wire in the panel is isolated from the box.

BOAH 01-04-2011 09:07 PM

Thank you! So I did some calculations and it seems that depending on what tools I might have running, I think I'm going to run #10 thwn. I'm going to put the two different circuits of outlets each on their own 20A breaker and the lights on a 15A breaker. For the outside panel, I'm thinking a two pole 30A breaker. Sound good so far?

Now about the ground rod. A couple of questions. Do I need one or two ground rods?

When I connect the rod with a #6 wire, does the wire just need to be clamped to the rod? Is that what you call bonding it?

If I have to put in 2 of these ground rods, do they need to be connected to each other? How far away from each other?

Thanks again. I'm learning a ton!

oleguy74 01-04-2011 09:34 PM

yes to bonding.rods 6 feet apart.

Saturday Cowboy 01-04-2011 09:55 PM

For a shop you would be better running 60a out there. I would never suggest less, you will use it. The size of the main breaker in the shop sub panel does not matter it is for the disconnect requirement. Protection is provided by the upstream breaker in your main panel, this must be a 2pole breaker and sized to match your feeders. Wire in conduit in a residential back yard must be burried 18" deep. A ground rod(two in over 25ohms) needs driven outside the shop somewhere near the location of the sub panel. And connected with a GEC (Ground Electrode Conductor) of a size determined by the size of the OPCD(breaker)

For sixty amps you will need 1" pvc conduit
4x #6 conductors and a #10 GEC

Mind you are not allow to run more than one branch circuit to an outbuilding.

And you must buy a seperate ground bar. and MUST keep seperate all neutrals and grounds in sub panel.

BOAH 01-05-2011 09:43 AM

Here is where my ignorance really shows itself. I know just enough to be dangerous so I appreciate your help.

I thought if I put a 2 pole 30A breaker in the outside panel, that was 60A?? 60A is what I want to run off of the outside panel feeding the shed. Sorry about that.

Now for the wire. I calculated a 15 amp saw running through 80 ft of wire. According to the table, a #12 would be enough but I thought I would use #10 to err on the high side. You would recommend that I run #6?

Now for the ground rod, I need two if the ohms are over 25, right? That 15 amp saw running on 120v is 8 ohms, right? So I could run up to 3 saws at one time and still be under 25 ohms, right?

I'm just trying to grasp this so I appreciate your patience with me. I never dreamed that running power to my shed was going to be so complicated!

Scuba_Dave 01-05-2011 09:53 AM

A single pole breaker gives the exact amps listed from one HOT feed that goes to your house
30a = 30a 120v

A double pole breaker gives you the same amps listed but on 2 HOT feeds
30a = (2) 30a 120v feeds, or 30a 240v

If either hot feed exceeds 30a the breaker trips

jbfan 01-05-2011 09:54 AM

If you want 60 amps, then you need to run #6 wire to the shed.
You also need 1 inch pvc.
Everything else stays the same as far as instructions.

Saturday Cowboy 01-05-2011 11:59 AM


Originally Posted by BOAH (Post 563255)
Now for the ground rod, I need two if the ohms are over 25, right? That 15 amp saw running on 120v is 8 ohms, right? So I could run up to 3 saws at one time and still be under 25 ohms, right?

no nothing to do with loads. code requires a ground rod, if more than 25 ohms in ground another is required to drop resistance. the test is hard for a DIY to do so most just install two rods. NEC 250.56

BOAH 01-05-2011 10:03 PM

Very good. I'll do what I can and I'll report back. Thanks again.

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