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Old 12-28-2008, 07:38 PM   #1
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100 amp sub panel/outside ground ?


Hello to all

Im Running a 100 amp sub panel with a question on grounding.

A breif desciption of the job at hand.

Both panels will be within the same household.
They will be connected together with a 50' run of pvc conduit.
I will be running #3 THHN copper as my main 3 conductors.

As for my ground....#4 armor sheathed multistran copper ground .#4 may may be considerd overkill for a ground on a 100 amp sub panel but I have it in stock and would like to put it to use.

My question is, Is it required by code to run the ground within the same conduit with the rest of the conductors or can I make use of this #4 armor ground and run along the outside of the the conuit to join both panels?

Ty in advance for your replies

johne63

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Old 12-28-2008, 10:22 PM   #2
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100 amp sub panel/outside ground ?


Quote:
Originally Posted by JohnE63 View Post
Hello to all

Im Running a 100 amp sub panel with a question on grounding.

A breif desciption of the job at hand.

Both panels will be within the same household.
They will be connected together with a 50' run of pvc conduit.
I will be running #3 THHN copper as my main 3 conductors.

As for my ground....#4 armor sheathed multistran copper ground .#4 may may be considerd overkill for a ground on a 100 amp sub panel but I have it in stock and would like to put it to use.

My question is, Is it required by code to run the ground within the same conduit with the rest of the conductors or can I make use of this #4 armor ground and run along the outside of the the conuit to join both panels?

Ty in advance for your replies

johne63

Your grounding conductor must be run within the same conduit as your feeder.

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Old 12-28-2008, 11:09 PM   #3
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100 amp sub panel/outside ground ?


Not allowed as Chris has stated



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Old 12-29-2008, 01:57 AM   #4
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100 amp sub panel/outside ground ?


chris75,Stubbie

I want to thank both of you for setting me back on the right track.
I was clearly heading in the wrong direction with this one.

Nice pic Stubbie. Looks like something I had in mind for my install,,lol.

I just penciled in a ground wire on my materials list,

With this question answered and some new information I found out about my main panel possibly having a lower tempeture rating,it looks like im going to have to upsize my main wires to 2awg and will more than likely go to 1 1/2pvc to make the pull go a little easier.

I want to thank you guys again for setting me straight.



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Old 12-29-2008, 01:04 PM   #5
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100 amp sub panel/outside ground ?


By all means you can run 1-1/2" conduit if you want, but it is not required. 3-#3's and 1-#8 THHN will go into a 1" conduit with little issue. Make sure you get green #8. That is required.
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Old 12-29-2008, 02:44 PM   #6
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100 amp sub panel/outside ground ?


J.V.

Thank you for your feedback.

Im sure your advice is sound if I were running a straight line with my pipe and using #3 + #8 ground but the situation is bit different here.
Due to the fact that I have to avert few obstacles like gas and water lines and enter the other half of a split-level house through a block wall. I will have 5 sweep 90s and two access elbows/LB to contend with. On top of that, like I mentioned in my last post my breaker box that was built in the early 80s and does not have a temperature rating listed .I will have to assume it 60c. So I canít go with the smaller wire sizes like in a 75c rated box. It looks like #2 + ground will be running in this conduit.

If you have any alternatives of running a smaller wire size and pipe size and keeping it to code I would be glad to hear them.



Thank you

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Old 12-29-2008, 03:13 PM   #7
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100 amp sub panel/outside ground ?


Quote:
If you have any alternatives of running a smaller wire size and pipe size and keeping it to code I would be glad to hear them.
Are you sure you need to have 100A at the subpanel? In many cases 60A is plenty big for a residential subpanel, in which case you could run 6ga wire.
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Old 12-29-2008, 04:03 PM   #8
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100 amp sub panel/outside ground ?


HouseHelper

Excellent suggestion.

But I have already purchased the 100 amp 32 space sub panel and the 100 amp breaker to feed it. I can still purchase the 60 amp breaker and downsize the wire like you suggested, but in my case there are a few more variables involved that I didnít mention.

The new sub panel will be feeding a small workshop as well as some new construction. I will be adding a level on the house and this sub panel well be in the perfect position to feed the new work. If it wasnít for these two factors I would have downsized for sure.

Again, thank you for your input.



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Old 12-30-2008, 11:29 AM   #9
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100 amp sub panel/outside ground ?


I think I would be looking at my main panel first instead of the sub panel. Your panel is almost 29 years old. Why not upgrade it first then install the sub. That makes sense to me. It seems as if you are going in reverse?
You mention all the obstacles for the sub panel run. Remember you cannot have more that 360 degrees of turns in any one run of conduit. Pull boxes ect... will be required if you exceed 360 degrees. Plan the run with the least amount of turns even if you need more wire and conduit to accomplish it.
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Old 12-30-2008, 10:44 PM   #10
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100 amp sub panel/outside ground ?


J.V.

I agree. The main panel I have is up there in age but if you compare the new Square-D panels with the one I have in place now, there is not much difference in design. If anything the bus bars and cabinet on my current box is made with heavier metal. Its almost industrial duty in comparison.
More than likely the modern types of plastics and other insulating materials is what gives the newer panels a higher temperature rating..
.
.
I did have other plans of re Ė running my overhead service lead to underground and the installation of a 16kw back up generator(that will be a topic for another day) so there is no reason why I shouldnít take your advice and re- install the entire service ,new main breaker panel and all. The sub panel will go on hold for now.
.
But since the topic is still on hand, you mentioned that the turns in a single pull cannot exceed 360 degrees with out a pull box in the line somewhere. Nothing would have pleased me more than to be able to run my pipe straight across my basement ceiling and into the adjoining utility room. Due to the other utility pipes being in the way I have no choice but to route around them. Im also dealing with a 7í ceiling height so I donít want to saddle under them either..
Three sweep 90s in the basement, two access elbows/LB s to get through a block wall, and two more sweep 90s in the utility room are in the future for this install.
.
.
My questions here are/...... are the 2 access elbows considered an additional 180 degrees or can they be considered pull boxes?
.
If considered 180 degrees, can I replace one of them with a pull box to set things straight?


J.V. Thank you for your most valuable information and advice.



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Old 12-31-2008, 10:23 AM   #11
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100 amp sub panel/outside ground ?


I am interested in the answer as well. I finished up a 100 AMP Subpanel install and had to use 6 90 degree sweeps and two access elbows to complete the project.

In my case, I used the access elbows as pull boxes, assuming that is acceptable. I used 1 1/4" PVC for a total run of about 70'.
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Old 12-31-2008, 10:31 AM   #12
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100 amp sub panel/outside ground ?


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Originally Posted by AndrewF View Post
I am interested in the answer as well. I finished up a 100 AMP Subpanel install and had to use 6 90 degree sweeps and two access elbows to complete the project.

In my case, I used the access elbows as pull boxes, assuming that is acceptable. I used 1 1/4" PVC for a total run of about 70'.
You can have no more than four 90s before a pull box or other type of access. An LB is not a bend, it is an access. So, you can have 4 bends, then an LB, then 4 more bends and a pull box, then 4 more bends, etc.

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