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Wiring 100 amp service to my detached garage

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kkparks_3

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Oct 6, 2012
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Hello guys. Please excuse my ignorance, but I would really appreciate some help with some electrical questions. I am wanting to run power from the 200 amp main feeder breaker that is feeding my house.

I have this breaker box as the feeder to my home:http://www.lowes.com/pd_79498-296-RC816F200C_4294722484__?productId=1196613&Ns=p_product_qty_sales_dollar|1

My plan is to install a 100 amp breaker in this box to feed a subpanel in my shop about 100 feet away. The plan in my shop is to have about a dozen 120V receptacles and 1 or 2 220V receptacles for a mig welder.

Here is where I ask the stupid question. At this link below,
http://www.selfhelpandmore.com/home-wiring-usa/accessory-structures-to-dwellings/wiring-a-detached-garage-2002.php, it shows several different examples of 120v or 240v service feeding the detached building.

My question is do I need to be running 120V or 240V to my shop? Please excuse my electrical ignorance, I'm here to learn. I'm guessing 240V right?

I've read several posts of other guys on this forum doing the same thing that has helped me figure out what size/type wire, etc. that I need, but I need a little help on the specifics of how I properly wire from the 200 amp box to my subpanel in the shop.

Thanks a lot and sorry for the long post,

Kevin
 
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wyliesdiesels

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Is this shop detached or connect to your house? If its detached, then you will need ground rods!


BTW, that's an excellent schematic/pic you keep using pattenp! :thumbup:
 
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Falcon67

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The pattenp diagram covers it completely. I would add that for what you are spec'ing in for the shop, a true 100A is going to be more expensive that it really needs to be. The 4 wire Mobile Home feeder cable breakered at 90 or 70 is going to be plenty, and a lot cheaper. I still contend that if you are one guy in a shop with normal guy tools, if you trip a 70A breaker you are running machinery like the Tasmanian Devil or you have a short. :lol:
 
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absintheisfun

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Bringing an old thread to life...3 questions:
(Found this on a Google search)

Many diagrams online show to use two grounding rods, spaced six feet apart...is it important?
I currently have one ground rod at my sub...should I drive in another?

I'm redoing the electrical in my detached garage and was wondering if a 70amp svc would be enough to cover about 18 110 dual plugs and 2 220v 30amp circuits (compressor and later expantion)

What size wire do you recommend for a 80 foot run between boxes? Is aluminum wire okay? Copper is rediculous right now!
 
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pattenp

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I assume you are in the US. So, typically 2 rods are driven because NEC only calls for one if the resistance is 25ohms or less but it's a pain to show the resistance so driving the second rod is easier.

Aluminum wire is fine and is most common for this type of install. I recommend 2-2-2-4 aluminum mobile home feeder. The #2 Al is okay for up to 90 amps.
 
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Norcal

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pattenp said:
I assume you are in the US. So, typically 2 rods are driven because NEC only calls for one if the resistance is 25ohms or less but it's a pain to show the resistance so driving the second rod is easier.

Aluminum wire is fine and is most common for this type of install. I recommend 2-2-2-4 aluminum mobile home feeder. The #2 Al is okay for up to 90 amps.
Click to expand...

You need expensive testing equipment & be qualified to use it, simpler to drive a 2nd rod & be done with it.
 
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arrowhead

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I'm doing the same thing and I screwed up already, I got 2-2-4 wire. So, looks like I need to add another 2 for the neutral. At least I didn't install it yet and it and will only cost me price of the extra wire.
 
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aandpdan

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arrowhead said:
I'm doing the same thing and I screwed up already, I got 2-2-4 wire. So, looks like I need to add another 2 for the neutral. At least I didn't install it yet and it and will only cost me price of the extra wire.
Click to expand...

You should check with your AHJ on that. Running a separate neutral would never fly here.

NEC 300.3(B) All conductors of the same circuit, including grounding and bonding conductors shall be contained in the same raceway, cable, or trench.
 
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arrowhead

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aandpdan said:
That's why I'm saying check before he does.
Click to expand...

check what? Unrolling a brand new roll for 2-2-4 wire and then unrolling another "2" right next to it and putting all four wires in the trench at the same time so my installation complies with the above diagram needs reaserch?
 
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pattenp

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arrowhead, I hate to ask this because it always ends up being an issue. But are you running this cable inside of the structure and what is the rating that is stamped on the insulation? I assume it looks like the image below. If it is listed as URD with just a USE-2 rating then the cable is not to be run inside of the structure, it needs to be terminated outside.

URD_Alt.jpg
 
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Larwyn

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arrowhead said:
check what? Unrolling a brand new roll for 2-2-4 wire and then unrolling another "2" right next to it and putting all four wires in the trench at the same time so my installation complies with the above diagram needs reaserch?
Click to expand...

Nothing personal against anyone here but once again I cannot help but notice that;

:lol: If only the post being responded to were read with the same care and attention to detail as was applied to the code book there would be fewer cases of quite accurate yet irrelevant knowledge/warnings presented in response to questions never asked about conditions that were never described........:lol: :evil:

NEC 300.3(B) All conductors of the same circuit, including grounding and bonding conductors shall be contained in the same raceway, cable, or trench
 
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aandpdan

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arrowhead said:
check what? Unrolling a brand new roll for 2-2-4 wire and then unrolling another "2" right next to it and putting all four wires in the trench at the same time so my installation complies with the above diagram needs reaserch?
Click to expand...

Check to see if your AHJ will let you just "add" another #2 wire.

It's not CODE. All conductors have to be in the SAME CABLE, since you're running cable, not just the trench.

Get the proper wire, that's the Code approved solution.
 
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A

arrowhead

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pattenp said:
arrowhead, I hate to ask this because it always ends up being an issue. But are you running this cable inside of the structure and what is the rating that is stamped on the insulation? I assume it looks like the image below. If it is listed as URD with just a USE-2 rating then the cable is not to be run inside of the structure, it needs to be terminated outside.
Click to expand...

Ok, even after researching this subject last week and knowing that there is a difference between USE-1 & USE-2, the cable roll at Lowes was marked "Mobil Home Feeder" so I blindly had them cut me 120'. Thanks to your post pattenp, I double checked and sure enough it was USE-2. Luckily I was able to return it this afternoon for full credit(it was still in my car). I'll be getting to proper 2-2-2-4 USE-1 and double checking the marking on the wire this time.



aandpdan said:
Check to see if your AHJ will let you just "add" another #2 wire.

It's not CODE. All conductors have to be in the SAME CABLE, since you're running cable, not just the trench.

Get the proper wire, that's the Code approved solution.
Click to expand...

Now this I'm still having trouble wrapping my head around. Your telling me that a cable assembly make up of three individual wires (as in the picture above ) cannot be added to. This makes no sense at all, there is nothing special about the three conductors, in fact I've read post where they are separated to facilitate snaking though fittings.

Sorry for the thread hijack kkparks_3.
 
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pattenp

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If you get Mobile Home Feeder it should also carry a RHH/RHW-2 rating which allows it to be run inside of the structure, but it does need to be in conduit. Also you can add an additional conductor to that type of cable as long as it's grouped together in the trench or in the same conduit. The cable that you can't run additional conductors with are sheathed cables such as SE and NM.

arrowhead said:
Ok, even after researching this subject last week and knowing that there is a difference between USE-1 & USE-2, the cable roll at Lowes was marked "Mobil Home Feeder" so I blindly had them cut me 120'. Thanks to your post pattenp, I double checked and sure enough it was USE-2. Luckily I was able to return it this afternoon for full credit(it was still in my car). I'll be getting to proper 2-2-2-4 USE-1 and double checking the marking on the wire this time.

Now this I'm still having trouble wrapping my head around. Your telling me that a cable assembly make up of three individual wires (as in the picture above ) cannot be added to. This makes no sense at all, there is nothing special about the three conductors, in fact I've read post where they are separated to facilitate snaking though fittings.

Sorry for the thread hijack kkparks_3.
Click to expand...
 
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Average_Joe

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roblouvasz said:
I don't mean to hi jack the OP's thread, but with a subpanel wired like the diagram, how would a three wire 240v motor be wired? Would the white (neutral) be connected to the ground bar or to the neutral bar??
Click to expand...

Black and red hot, white to neutral bar, bare to ground bar.

Or black and white hot, bare to ground bar (not preferred, but a lot of water heaters are wired this way).
 
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rburke65

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Why would you have....or need....a neutral to a 240v motor.? And, as a side note, a good thing you didn't say a 220volt motor!
 
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pattenp

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Are you talking about a 3 phase motor that has L1, L2, L3 connections? If so, that can't be hooked to single phase power as in the diagram. If it's a single phase 240V motor then there are 2 hots with a ground. Each of the hots goes to each of the hot legs in panel via a 2 pole breaker and the ground goes to the ground bar.

roblouvasz said:
I don't mean to hi jack the OP's thread, but with a subpanel wired like the diagram, how would a three wire 240v motor be wired? Would the white (neutral) be connected to the ground bar or to the neutral bar??
Click to expand...
 
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absintheisfun

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One more question...

In the sub, do I keep the neutral and ground bar linked? I haven't picked up the box yet, but as I have read, there is a green screw that links them. I've only read one thing that says to remove that screw...everything else simply doesn't mention it.

Thanks!
 
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pattenp

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The panel box you get will most likely only have one neutral/ground bar in it. If so, you will need to buy a ground bar kit for the panel box. The new ground bar is directly screwed to the box and the existing bar should have the green bonding screw you mentioned that bonds the existing bar to the box, remove that screw. By removing that green screw isolates the existing bar from the box making it a neutral bar only.
 
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wyliesdiesels

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arrowhead said:
.......

Now this I'm still having trouble wrapping my head around. Your telling me that a cable assembly make up of three individual wires (as in the picture above ) cannot be added to. This makes no sense at all, there is nothing special about the three conductors, in fact I've read post where they are separated to facilitate snaking though fittings.

Sorry for the thread hijack kkparks_3.
Click to expand...

I think he was referring to cable assembly with an outer sheath, such as SER. If the cable has an outer sheath, then u cant have another conductor thats part of the same circuit as the jacketed cable assembly but is outside of the cable assmblies sheath. Direct bury wire such as MHF, does not have a sheath, so the above doesn't apply!

roblouvasz said:
I don't mean to hi jack the OP's thread, but with a subpanel wired like the diagram, how would a three wire 240v motor be wired? Would the white (neutral) be connected to the ground bar or to the neutral bar??
Click to expand...

A 240v motor doesnt need a a neutral!
 
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