Which wire type to use

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Old 09-27-10, 06:13 PM
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Which wire type to use

I am wiring my farm shop with 200 amp service. I have a permit, but the building inspector says he doesn't need to inspect because it's a farm structure. I have existing 400amp service to my house which has split lugs to feed a 200amp panel for the house and a 200amp disconnect that I will be connecting to the shop. The total run will be about 200 feet. I have buried a 3" schedule 40 conduit between the structures and now need to pull the wire. I plan to run 2" conduit in the house cellar to a box where it enters the ground. The 2" conduit will only be for 15' or so. The 3" has 2 90 degree sweeps and then enters into a box in the shop. From there it runs a couple feet up in 2.5" conduit to the service panel.

Questions:
1. What type wire should I use? My local lowes has 4-0 SEU, which is basically big romex with 2 conductors and a braided bare neutral for $3/foot. The other option is 4-0 "mbl" which is 4 separate conductors twisted loosely around each other, the 4th being a green ground, and costs $3.67/ft. All are aluminum. Which type would be best?

2. Should I use the green ground wire to connect the grounds between the house and shop? Doesn't the neutral take care of that? Do I even need the green wire?

3. What size bare copper wire do I need for the ground rods I will install for the shop? #4? I plan to do 2 ground rods 6' apart.

Thanks in advance!
 
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Old 09-27-10, 06:38 PM
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Originally Posted by jrlogan1 View Post
1. What type wire should I use?
SEU is not appropriate for this use. I think "MBL" is the pull tension rating, there's probably another rating on that one that gives information about the insulation.

Basically you should be looking at USE-2 (underground service entrance) or a similar type called XHHW. Call some local electrical supply houses too as the big box stores have a very limited selection.

Size 4/0 aluminum is okay.

2. Should I use the green ground wire to connect the grounds between the house and shop? Doesn't the neutral take care of that? Do I even need the green wire?
The ground is required. The ground and neutral are only bonded in the main panel or disconnect. Your barn panel will need to have an add-on ground bar and the neutral bonder removed.

3. What size bare copper wire do I need for the ground rods I will install for the shop? #4? I plan to do 2 ground rods 6' apart.
You can do #6 (or larger) bare copper. Aluminum is not allowed for this one.
 
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Old 09-27-10, 10:20 PM
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Originally Posted by jrlogan1 View Post
Questions:
1. What type wire should I use? My local lowes has 4-0 SEU, which is basically big romex with 2 conductors and a braided bare neutral for $3/foot. The other option is 4-0 "mbl" which is 4 separate conductors twisted loosely around each other, the 4th being a green ground, and costs $3.67/ft. All are aluminum. Which type would be best?
Myself I rather use the XHHW 120mm˛ { 4/0 AWG } Alum conductor they are cheaper than copper.

due you run all in the conduit I will be extra carefull with pulling it due there will few issue when you hit few diffrent size conduits.
{ this something I generally try to keep them at the same size much as possible }

And make sure you have a bottle or two of wirelube to help to guide it smoother.{ it will get little messy so use a bit of old rag or paper towels to wipe it off when ya get done }


2. Should I use the green ground wire to connect the grounds between the house and shop? Doesn't the neutral take care of that? Do I even need the green wire?

3. What size bare copper wire do I need for the ground rods I will install for the shop? #4? I plan to do 2 ground rods 6' apart.

Thanks in advance!
Keep the netural and ground conductor seperated at the subpanel location and you will end up buy a ground bussbar or two kit depending on how big they are.

Use 16mm˛ or larger { #6 AWG } use either bare or green { I rather have green if possible }

Now for ground rods keep them 6 feet apart and the conductor size use the same one as bare or green { 16mm˛/#6 or larger }

By the way all the 120 volt circuits are required to be on GFCI espcally if you are on 2005 and later code cycle.

Any other question just holler here.

Merci.
Marc
 
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Old 09-28-10, 06:52 AM
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Called the local electrical supplier, and they have direct burial 4 conductor 4-0 for 2.23/ft. I should slap myself for assuming the big box store would be the best price. I will have it in conduit the whole way, so this wire type will work fine, according to them.

So I need to wire the new panel in the shop like a sub panel with separate neutral and ground. I'll run a green wire from the disconnect to the new panel in the shop ground bar, but I also need to do a new ground rod setup because it's a different structure, correct? I've done subpanels before but never in a different structure, and of course they didn't need their own ground.

I am going to put a rope in the conduit and then pull the wire through with wire lube. What is the best way to attach the rope to the wire so it doesn't slip off during the pull??
 
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Old 09-28-10, 09:23 AM
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Originally Posted by jrlogan1 View Post
I also need to do a new ground rod setup because it's a different structure, correct?
Correct.

I am going to put a rope in the conduit and then pull the wire through with wire lube. What is the best way to attach the rope to the wire so it doesn't slip off during the pull??
First use a smooth rope or pulling line if you can. Rough rope will cut into the PVC elbows and make the job much worse. Attaching the wires to the rope is called making the head, and you basically want to make it tapered by staggering the wires. Lay it out so there's a couple inches between the start of each wire and weave the rope a couple times around/through the taper. Tape the heck out of it so it is smooth, especially with your conduit size changes you don't want any sharp edges that will snag on a reducing bushing.

When you actually do the pulling it's really good to have a helper. One person to pull, the other to push the wires in straight (no twists/kinks) and apply wire lube as you go.
 
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