feeding a subpanel

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Old 05-31-13, 08:59 AM
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feeding a subpanel

Hello Everyone,

I am wanting to add a supanel in my shed from my 200amp home panel. I have a couple of questions;
1) What is the safety factor difference if I run 2 (two) 3# copper awg wires from a 100a breaker in my main panel,to my 100 amp subpanel with main breaker, versus running "4(four) wires 2(two) for load wires,1(one) neutral,1(one) ground". I was told by someone that I should keep the neutral and ground of the 2(two) panels isolated.
2)If I run the 4 wire way 3 (three) #3 awg thhn what size ground will be appropiate and the conduit size? will be about 160ft run.

Thanks
Tim
 
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Old 05-31-13, 09:24 AM
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Per newer codes (NEC 2008 I believe), you are required to run a 4-wire feeder to any subpanel (H/H/N/G). You will keep the ground and neutral bars separated in the subpanel and you'll need an 8' ground rod driven into the ground at the shed. See http://www.doityourself.com/forum/el...-diagrams.html for some more details.

100A in a shed is quite a lot, even if you are planning a workshop out there. Nothing wrong with planning on the large side, but for a one-man shop, 60A can usually run just about any tools you need and you'll save $$ on wire. What are you planning to do out there?

I'll leave the wire-sizing to others, I tend to always get it wrong. But at that length, I'd certainly consider aluminum, the cost savings will be significant.
 
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Old 05-31-13, 09:34 AM
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1) What is the safety factor difference if I run 2 (two) 3# copper awg wires from a 100a breaker in my main panel,to my 100 amp subpanel with main breaker, versus running "4(four) wires 2(two) for load wires,1(one) neutral,1(one) ground".
You can't run a subpanel on two wires. At minimum you need three wires for a 120 volt only or a 240 volt only subpanel. For practical purposes most subpanels are 120/240 and require four wires.

I was told by someone that I should keep the neutral and ground of the 2(two) panels isolated.
The correct statement is the ground and neutral can not be connected together except at the first Over Current Protection Device. That usually means the main panel. Therefore at your subpanel the equipment ground is bonded to the metal panel and the neutral is electrically isolated from the panel.

These diagrams might help you: http://www.doityourself.com/forum/el...-diagrams.html
 
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Old 05-31-13, 01:21 PM
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Hi Ray & Zorfdt,

Thak you for the information.

What size Aluminium wire and conduit should I use? # 2-2-2 urd and a seperate ground in 1 1/2 conduit or #1-3 w#2 ground in 1 1/2 conduit.
And will either 1 of those wires fit in a 100amp breaker in my main panel or will they need to be connected to my feed thru lugs? I prefer them to be on a breaker before going out underground to sub panel.

Zorfdt:
right now my biggest draw is from air compressor but I am going to add on some more shop and equipment in future so want it done big enough the first time.

Tim
 
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Old 05-31-13, 01:25 PM
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What is the amp rating of the compressor? Are you planning on a large welder or plasma cutter? AC or electric heat?
 
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Old 06-03-13, 04:19 AM
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Hi Ray,

The air compressor is a 5hp not sure of the amp draw when it was given to me I set it up on 220v as could not read tag info to see specs.

Not planning on a large welder just a small Miller wire welder.And yes AC will be added to building but not fed from the subpanel.

I am just trying to size the wire for 100 +- amps to panel
 
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Old 06-03-13, 07:20 AM
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AC will be added to building but not fed from the subpanel.
How? You can't have two power sources to a detached building so how would it be powered?
 
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Old 06-03-13, 07:39 AM
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Ray,

That is irrelevant to what I was asking but if you must know,when the 30x30 garage is built in the next year or so it will have its own meter and the heatpump for the garage will be about 3 feet from shed,so I will also add a heat pump beside the garage 1 for the shed and it will be fed from 200a panel in garage.

And that will only be 1 power source to the shed.
Tim
 
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Old 06-03-13, 11:01 AM
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Ray's question was entirely relevant to our checking the total load on your planned subpanel. Thank you for clarifying why the future heat pump doesn't need to be included in that calculation.
 
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Old 06-04-13, 04:55 AM
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Nashkat1,

Hello,

Ray's question was irrelevant as I stated in earlier post " ac will be added but not fed from subpanel" so it was not in part of the load on subpanel to be calculated.

Now to my question 1 more time:
What size wire should be run in the 1 1/4 or 1 1/2 conduit to feed the subpanel

What size Aluminium wire and conduit should I use? # 2-2-2 urd and a seperate ground in 1 1/2 conduit or #1-3 w#2 ground in 1 1/2 conduit.
And will either 1 of those wires fit in a 100amp breaker in my main panel or will they need to be connected to my feed thru lugs? I prefer them to be on a breaker before going out underground to sub panel.
 
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Old 06-04-13, 07:43 AM
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One of the biggest problems giving correct information here is people giving incomplete information because they make incorrect assumptions on what they think they know is correct and what we need to know.
 
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Old 06-04-13, 07:59 AM
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Toolman, Rays question did have relevance. It may not impact the sizing of the subpanel, but it does concern the future.

When the other power is added with the new meter, the feeder you are getting information about installing will need to be removed unless the new system is a different voltage.
 
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Old 06-04-13, 09:13 AM
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Well let me restate this 1 last time. I asked for information about adding a subpanel to a shed not 1 time did I mention the garage or any other buildings or feeds.So the information I gave in orginal post was 100% complete and all the replies have gotten totaly away from the original question.

Ray what you needed to know was given in my original post so with your assumptions that I was intending on having the building cooled or heated with heat pump was totaly irrelevant.

pcboss:

Rays question had nothing to do with now or future. I stated wiring a subpanel in shed. No where did I mention building garage at later date and letting that feed my heatpump for shed. The garage is a total seperate building and will have its own meter and nothing to do with shed.The shed and garage are 2 (TWO) seperate buildings.
 

Last edited by the_tow_guy; 06-04-13 at 02:16 PM. Reason: Removed non-beneficial remark.
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Old 06-04-13, 11:47 PM
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Toolmon, if your original statement had been clear, Ray would not have asked for clarification.

You've asked for wire size to feed a subpanel. Two questions:

A) What is the load on the subpanel?

B) How far is it, as the conduit will run, from your main panel to your subpanel?
 
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Old 06-05-13, 06:19 AM
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feeding subpanel

Nashkat1:

Did not know of any other words that would have made my following highlighted statements any clearer or in plain English.


toolman60_99
Hello Everyone,

I am wanting to add a supanel in my shed from my 200amp home panel. I have a couple of questions;
1) What is the safety factor difference if I run 2 (two) 3# copper awg wires from a 100a breaker in my main panel,to my 100 amp subpanel with main breaker, versus running "4(four) wires 2(two) for load wires,1(one) neutral,1(one) ground". I was told by someone that I should keep the neutral and ground of the 2(two) panels isolated.
2)If I run the 4 wire way 3 (three) #3 awg thhn what size ground will be appropiate and the conduit size? will be about 160ft run.

Thanks
Tim

toolman60_99
Hi Ray & Zorfdt,

Thank you for the information.

What size Aluminium wire and conduit should I use? # 2-2-2 urd and a seperate ground in 1 1/2 conduit or #1-3 w#2 ground in 1 1/2 conduit.
And will either 1 of those wires fit in a 100amp breaker in my main panel or will they need to be connected to my feed thru lugs? I prefer them to be on a breaker before going out underground to sub panel.

Zorfdt:
right now my biggest draw is from air compressor but I am going to add on some more shop and equipment in future so want it done big enough the first time.

Tim
 
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Old 06-05-13, 12:44 PM
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Toolmon, the problem here is either that you haven't supplied the two necessary pieces of information I requested in my last post, or that all of us have somehow missed seeing them.

Your repeating and highlighting your questions does not help us answer them. If that was all that was needed we would have already answered them.

This is the information we need:

Originally Posted by Nashkat1
A) What is the load on the subpanel?

B) How far is it, as the conduit will run, from your main panel to your subpanel?
 
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Old 06-05-13, 06:26 PM
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The distance was previously stated as 160'

The 2-2-2 you were mentioning is direct burial and is not put in conduit. Based on copper prices that would be the least costly way to go. You would use 2-2-2-4. I didn't think you could put URD wire in a conduit but the mfg's website states it can be installed in a duct.
 
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Old 06-07-13, 07:24 AM
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Nashkat1 ,

At present time my load will be around 50 amps if I run my radial arm saw,tablesaw ,drillpress, 3 lights,and charger for cordless tools all at the same time.

The total amp draw is usless to you and me as I want it sized for 100 amps as stated in previous post it was a 100a subpanel and I want it sized for 100a +- 5% . And again it is still 160 ft from main panel to sub panel.
 
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Old 06-07-13, 07:59 AM
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PJmax,

Thanks for the information.
I know that it is direct burial but I still want the wire in conduit in case it ever has to be replaced I will not need to redig trench unless the conduit gets damaged also.

So I am debating on the 2-2-2 URD or going with or with copper # 2 thhn
thwn .
 
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Old 06-07-13, 08:25 AM
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With your condescending and argumentative attitude toward the licensed professional electricians participating in this thread, it's a wonder they're still trying to help you.
 
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Old 06-07-13, 01:17 PM
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I do not know if type URD is allowed in conduit or inside buildings. The number 2 aluminum should be okay for 100 amperes at 160 feet. This would be approximately 3.5% voltage drop. Specific conditions not disclosed may change this somewhat.
 
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Old 06-07-13, 01:28 PM
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Cable marked only URD can not enter a building. URD/USE can.
 
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Old 06-07-13, 02:08 PM
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Thanks, Ray.

There you are. If the cable is marked just URD then you will have to have a splice box on the outside of the building to convert to the proper cable for running inside the building.
 
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Old 06-07-13, 05:55 PM
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The total amp draw is usless to you and me as I want it...
You may not care about that information but, if you hadn't provided it, that would have been the end of my answering your questions. As said above,
Originally Posted by PJmax
Thanks for the information.
Now, as far as I can tell you can pull the Type URD through conduit. I would run 2-1/2" conduit, minimum, and install sweeps rather than bends. It won't be an easy pull.
 
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