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Old 08-03-2012, 07:20 AM   #1
mx842
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Default Installing sub panels in pole barn shop.

I'm trying to save a little on wiring in my shop. What I want to do is add a couple small 6 space sub panels in two spots in my shop. I picked up a 70 amp 6 space sub panel yesterday that has no breakers in it. I picked up a ground bar kit also.

When I prepared my floor for concrete I laid conduit to different points in the shop where equipment would be placed. I ran a 1" conduit to my welding room and was also going to run another run to the side wall next to this room where my big lift/welding table will sit but never did get around to it.

When I started running wires is when I remembered I never made the second run to the side wall so I decided what the heck I'll just run three wires over to the welding room and then stub off from that plug to the other location and on to the next one a little further down the wall just like you do with a regular rec. Then came the problem of trying to connect 3 #6 or even 2 #6 and a #8 together was not as simple as It seemed on paper. Then it hit me.......I'll just go pick up a small sub panel and run these leads out of it and I could also have a couple spaces left for lights and rec. in my welding room and parts room. All is good....right?

It was after I went an picked up this 100amp 6 space box that I remembered the part about only 3 wires in the conduit over to that room. I would have pulled those wires out and added a #8 leg but it was all I could do to get the 3 #6 wires crammed into that conduit so adding another wire probably wouldn't fit. I did end up with a #12 wire in there along with the 3 large wires somehow don't ask me how that happened but it did.

What I was wondering was if that #12 wire would be enough to use as the neutral feed wire for the box that will feed two 8' fixtures, one in each room and the rec circuit which would have 3 rec in each room and probably 4 along the wall that connects these two rooms?

Another option would be and I don't know if this is right or not but I remember reading somewhere about wire runs all having to be in the came conduit/tray,trench, etc but I also remember reading about ground connection to a sub could be picked up off the building ground system, ufer, ground rod if it was within 6' from the box. I have looked but I cannot remember where I saw that article.

The reason I'm asking about this is that my ground system has 4 ground rods all connected back to the main feed panel in the barn and one of those ground rods is right there on the outside wall from the new sub panel. Can I pick up my ground there and use the third wire in the conduit for my neutral?

Also can you install an Isolated ground circuit in a building that is powered from a sub panel like in a detached garage where the neutral and ground are separated?
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Old 08-03-2012, 09:48 PM   #2
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Default Re: Installing sub panels in pole barn shop.

I'd rather come to your house and help you rather than to try to figure out all that stuff you have said in this post. Boy is that a boat load.
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Old 08-03-2012, 10:08 PM   #3
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Default Re: Installing sub panels in pole barn shop.

Okay after reading again I'll try to answer the ground part of your questions. The main panel in the barn should be connected directly to the ground rods and any sub-panels off of the main will only have the equipment ground wires going back to the main panel ground bar/buss. The sub-panels do not need to have a direct connection to the ground rods. If the main panel in the barn is supplied from a meterbase then the neutral and ground should be bonded and all sub-panels off of that main will have isolated grounds and neutrals. If the main panel in the barn is fed from a Main in another structure then the barn main panel should also have isolated ground and neutral. Clear as mud?

Last edited by pattenp; 08-03-2012 at 10:14 PM.
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Old 08-04-2012, 09:38 AM   #4
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Default Re: Installing sub panels in pole barn shop.

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Okay after reading again I'll try to answer the ground part of your questions. The main panel in the barn should be connected directly to the ground rods and any sub-panels off of the main will only have the equipment ground wires going back to the main panel ground bar/buss. The sub-panels do not need to have a direct connection to the ground rods. If the main panel in the barn is supplied from a meterbase then the neutral and ground should be bonded and all sub-panels off of that main will have isolated grounds and neutrals. If the main panel in the barn is fed from a Main in another structure then the barn main panel should also have isolated ground and neutral. Clear as mud?
I understand that the main panel (panel at meter base) has the ground and neutral wires bonded together and they are separate in the sub panel that feeds the barn/shop.

I have a 4 ground rod grounding system that I installed ( I know I know a little overkill for sure) but I have a large steel structure that I wanted to ground/ bond to electrical system at both ends because it will have an electric winch running on it and there is also conduit and even a few receptacle boxes mounted to it. I also have a 20' medal container in the back part of the building that is also tied to the bonding system.

The conduit that I ran under the floor has a couple extra bends in it because of the way it had to be run but this was just going to be a welder circuit with only three wire in it and I figured pulling in 3 #6 wires would be no problem but I tried to pull in a #8 wire along with them at first but it would not get past the second 45 degree turn so I pulled it back out and pulled in the 3 #6 wires which was a really tight pull even with wire pulling lube so that is what I ended up with.

I was just trying to figure out a way I could get an extra wire in there some way so I could run my lights and receptacles for that side of the building out of the new sub panel I wanted to add at that location.

Anyway I have scrapped that idea and will just use the three wires already over there to feed my three welder plugs that I have mounted along the wall there and later on run 4 wires overhead to feed that sub panel.

I also realize from what I have been reading that the sub panel does not have to be grounded to a separate ground rod but in your opinion is there any reason it would cause a problem if you did add one?
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Old 08-04-2012, 09:44 AM   #5
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Default Re: Installing sub panels in pole barn shop.

If adding an additional ground rod off of the sub-panel makes you feel better about the earth grounding then by all means do so. I don't know of any problems it will cause.
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Old 08-06-2012, 08:30 AM   #6
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Default Re: Installing sub panels in pole barn shop.

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If adding an additional ground rod off of the sub-panel makes you feel better about the earth grounding then by all means do so. I don't know of any problems it will cause.

Thank you. The extra rods were mainly to bond that medal container and steel structure to begin with but this got out of control like a lot of threads do. I didn't think there would be a problem hooking any other sub panels in the building into this loop but just wanted to get some thoughts.
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Old 08-06-2012, 09:02 AM   #7
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Default Re: Installing sub panels in pole barn shop.

You have to watch a couple things here. First, "bonding" should only be done at one point, the main panel. Second, watch how much wire fill you have within the conduit. Rule of thumb is no more than 50% fill within the conduit. Next is your length of wire and voltage drop over long distance.
If you want to ground your building to a ground grid, then by all means do that, but connecting the N to that ground can cause issues with the path of G and N.
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Old 08-06-2012, 10:30 AM   #8
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Default Re: Installing sub panels in pole barn shop.

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watch how much wire fill you have within the conduit. Rule of thumb is no more than 50% fill within the conduit.
In the US NEC, this varies with the number of wires in the conduit. A single conductor is limited to 53% fill, two conductors are limited to 31% fill and three or more conductors are limited to 40% fill. There are tables and charts in the back of the NEC that list cross sectional area of conductors of various types and also cross sectional area of various conduits.

The code also has notes that define what a multi-wire cable or cord is (its considered a single conductor) and several pages of tables and charts.

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Old 08-06-2012, 06:59 PM   #9
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Default Re: Installing sub panels in pole barn shop.

at least it is well paraphrased...
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Old 08-06-2012, 11:39 PM   #10
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Default Re: Installing sub panels in pole barn shop.

LOL WUT
I read this four times and I am still scratching my head.
Can you post a snapshot of what you are working on or trying to do?

Adam
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Old 08-07-2012, 10:44 AM   #11
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Default Re: Installing sub panels in pole barn shop.

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You have to watch a couple things here. First, "bonding" should only be done at one point, the main panel. Second, watch how much wire fill you have within the conduit. Rule of thumb is no more than 50% fill within the conduit. Next is your length of wire and voltage drop over long distance.
If you want to ground your building to a ground grid, then by all means do that, but connecting the N to that ground can cause issues with the path of G and N.
I understand I can see how there can be so much confusion on this kind of topic. When talking about sub panels that have the ground and N separated it can be especially confusing because sometimes bonding, grounding, return path, terms all get thrown around when talking about different installations and it's hard to figure out just what is what. Then the way some people (like me ) explain their questions everything gets out of hand in a very short time.

I guess I was wondering how would I best go about bonding/grounding or what ever the proper term is this giant hunk of steel that I have running through my building and the medal container that sits right next to it. Both will have electrical wiring mounted to, running along or through them. When I first started thinking about this I figured I needed to connect these two big hunks of steel to some kind of ground system in case lightning hit the building or close to it because we do see a lot of lightning strikes in this area. I guess that is why I was thinking of making a big loop out of the whole system with multiple ground rods....two at the main panel (panel in the building not at the meter base,) one 10' away from the first two that connect to the steel tower that runs through the building to the container, then another rod. I want to put another feeder box back in that area to feed lights, rec, compressor and other equipment. I know that this feeder box/ sub panel needs to have 4 wires run to it from the SE coming into the building but am wondering if I could tie all these panels, steel structure, container, multiple gr rods, #6 wire all together in one big loop without burning down or blowing up my building, electrocuting me and my neighbors or the wildlife that live nearby.
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Old 08-09-2012, 09:36 AM   #12
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Default Re: Installing sub panels in pole barn shop.

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LOL WUT
I read this four times and I am still scratching my head.
Can you post a snapshot of what you are working on or trying to do?

Adam
I don't have a pic of all this stuff the way it is now from the inside but this shot shows the tower and the container before the building was put up around it. The other shot shows the same thing with the shell around it.
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File Type: jpg DSC02160.JPG (113.8 KB, 22 views)
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Old 08-13-2012, 03:08 PM   #13
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Default Re: Installing sub panels in pole barn shop.

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...my ground system has 4 ground rods all connected back to the main feed panel in the barn and one of those ground rods is right there on the outside wall from the new sub panel. Can I pick up my ground there and use the third wire in the conduit for my neutral?
In practice this might work OK and it would give you a low resistance path to ground, but not a low-imedance path to ground. It wouldn't be compliant with current code which requires all conductors (including ground) for a given circuit to run together. From an engineering standpoint it would violate the "net zero current through a metal hole" rule, but only when there was a fault (short circuit from hot to ground.)

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Also can you install an Isolated ground circuit in a building that is powered from a sub panel like in a detached garage where the neutral and ground are separated?
Isolated ground circuits are typically found in a hospital, radio station, recording studio, or sometimes a data center. These are all commercial installations in metal conduit. The isolated ground circuit runs a green insulated wire all the way back to the main building ground point which is held at zero potential with a good earth ground. This minimizes any stray currents on the ground wires and make sure that a short-circuit fault current in one circuit is not energizing the ground conductors of another circuit. This could be done in a detached garage/barn with a 4-wire feeder, but there is really no need unless you are running a ham radio or keeping patients on life support!
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Old 08-16-2012, 08:07 AM   #14
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Default Re: Installing sub panels in pole barn shop.

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In practice this might work OK and it would give you a low resistance path to ground, but not a low-imedance path to ground. It wouldn't be compliant with current code which requires all conductors (including ground) for a given circuit to run together. From an engineering standpoint it would violate the "net zero current through a metal hole" rule, but only when there was a fault (short circuit from hot to ground.)



Isolated ground circuits are typically found in a hospital, radio station, recording studio, or sometimes a data center. These are all commercial installations in metal conduit. The isolated ground circuit runs a green insulated wire all the way back to the main building ground point which is held at zero potential with a good earth ground. This minimizes any stray currents on the ground wires and make sure that a short-circuit fault current in one circuit is not energizing the ground conductors of another circuit. This could be done in a detached garage/barn with a 4-wire feeder, but there is really no need unless you are running a ham radio or keeping patients on life support!
Thank you so much, your answer addressed my original question as asked and for that I thank you.

I gave up on the idea of trying to use the extra ground leg from the rod at the sub panel as my 4th leg for that panel because I couldn't ever get anyone to understand what it was that I was asking. I know it is hard to explain some things on a forum like this and me....I am my own worst enemy when it comes to splaining things, it's a ADD thing I have going.

I only asked the question because I had read something somewhere about grounds for sub panels about in some cases it could be done if the panel and rod was within 6 feet of each other or something to that effect. I'm not sure if what I read even pertained to my application or something else all together. I looked for days trying to fine where I had read it but never got back to the place it was written.

As far as the isolated ground thing I was just wondering how that would work when the N and the ground was already isolated in a sub panel in a detached building. I plan on having a computer line in the building and I need a high speed internet connection also. It's already a long way out there and was thinking that an isolated ground plug might be better, I know it wont give me any more power to a line that is already at the point of being to far away to pick up a signal but was thinking that by cutting down a little AC line noise might help.

Also I do have an old radio that's been in the attic for like 30 years that one day I might want to get out and set up if I ever get my barn up to where I can play with my toys.

Oh! I just decided to take the 3 wires I had already run for the welders out of the sub panel and straight to a series of welder plugs at different places throughout the shop. When I get the money I'll buy enough #10/3 wire to run to the sub panel for the lights and rec on that side of the building.

Thanks for your help. Also, to everybody else that I seemed to thoroughly cornfuse with this thread it's not your fault and I'm sorry for the cornfusion with the way I worded my question. Can't say it wont happen again though sometimes my splainer don't work too good.
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Old 08-16-2012, 08:57 AM   #15
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Default Re: Installing sub panels in pole barn shop.

For your purposes the isolated ground outlet is a waste of money, time and effort. But that's just my opinion.

Here's good info on IG's....

http://www.iaei.org/magazine/2006/03...dirty-grounds/

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Old 08-17-2012, 09:54 AM   #16
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Default Re: Installing sub panels in pole barn shop.

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For your purposes the isolated ground outlet is a waste of money, time and effort. But that's just my opinion.

Here's good info on IG's....

http://www.iaei.org/magazine/2006/03...dirty-grounds/

*
Thanks! That was a good read on the subject and cleared up a few lingering questions I had going on in my head. I came across a box of electrical supplies and in it was several orange colored recs that were isolated ground receptacles and got to thinking about what was the difference between an IG circuit in a building where the N and Gr were bonded together in the service panel. To any receptacle in a sub panel that had the Gr and N separated. Hopefully that makes sense as a question....if not don't worry about it cause it's just something I was wondering about the other day as I was reading on the topic.
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Old 08-17-2012, 11:59 AM   #17
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Default Re: Installing sub panels in pole barn shop.

Keep it simple.
Why all the boxes?
It will just cost you more in conduet and wire to to mention all the extra boxes.
I have 2 bans, 2 large shops and 2 garages. All are on one pannel and box.

I have a wood shop and finishing room. I installed all the electrical in the floor after laying out the shop and machines.
I also have a small machine shop and with an auto bay. Everything including the welders run from one box.

I don't get why you are worried about so many sub boxes. The cost of the boxes is about the same price of wire. I don't see any savings. You just end up with more work.

Just my 3 cents worth. One ground rod is all you need more are ok but if the proper wire size is used for the length of the run and amps there will be no problem with one.
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Old 08-18-2012, 11:31 AM   #18
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Default Re: Installing sub panels in pole barn shop.

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Keep it simple.
Why all the boxes?
It will just cost you more in conduet and wire to to mention all the extra boxes.
I have 2 bans, 2 large shops and 2 garages. All are on one pannel and box.

I have a wood shop and finishing room. I installed all the electrical in the floor after laying out the shop and machines.
I also have a small machine shop and with an auto bay. Everything including the welders run from one box.

I don't get why you are worried about so many sub boxes. The cost of the boxes is about the same price of wire. I don't see any savings. You just end up with more work.

Just my 3 cents worth. One ground rod is all you need more are ok but if the proper wire size is used for the length of the run and amps there will be no problem with one.
I guess I'm just looking ahead. Have you looked at the price of wire lately? I bought a small 6 space sub panel for $14.00 and the breakers for it cost another $30.00. A roll of 12/2 wire is almost a hundred bucks now and running circuits 75 to 100 feet away takes a lot of wire to run. I guess we'll have to agree to disagree this go around, no harm no foul.
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Old 08-18-2012, 07:51 PM   #19
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Default Re: Installing sub panels in pole barn shop.

I was going to post a reply and then remembered I had posted something similar in the past. Here's my copy/paste, lazy version, on why I like subs:

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The beauty of subpanels is they save you money while reducing voltage drop. Say you set a 60 amp sub halfway across the building, with the far half of your building circuits coming to this panel. Instead of sizing ALL the circuits in your building for voltage drop(your method), you're now sizing them like usual(#12 on 20 breaker, etc.) The reason is, your circuits are diversified, they're not all used at once, so now that larger wire that's feeding the sub is helping the voltage drop on several circuits.
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We've wired quite a few shops and the offices usually end up getting their own panels. From a commercial point of view, this makes it easier for the office staff to find breakers and keeps the mechanics/shop folks from messing with the office power.

Subpanels are pretty inexpensive, it's pretty hard to beat a main lug sub fed with 10/8/6-3 versus a whole bunch of 12-2's ran over to the office area individually. Plus you save panel space in your main shop panel.

Personally, I use subs as much as I can. I always price them either way, but if using a sub is break even or even costs just a little more, I'll use them. I like having extra breaker space. Makes adding more circuits easier too in the future.
I tried to trim most of the stuff out that doesn't apply.
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Old 08-19-2012, 10:01 AM   #20
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Default Re: Installing sub panels in pole barn shop.

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I was going to post a reply and then remembered I had posted something similar in the past. Here's my copy/paste, lazy version, on why I like subs:





I tried to trim most of the stuff out that doesn't apply.
Thanks for putting what I was thinking into words even I could understand.
In a shop like mine a 30 or 40 space box can fill up quickly and it's easier/cheaper to run subs before the walls are finished than it is to install them when you run out of space in the main panel and need more space.
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