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Old 08-21-2007, 07:47 AM   #1
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100 amp subpanel install with a couple pix


I'm finishing my basment and needed to add a few circuits and was out of breaker slots. So I had to install a subpanel to pick up those new circuits as well as a few more for the garage. The other large panel in the picture is my dual fuel panel and the small panel is for off peak water heating.


Completed install


Main panel all full now.


Last edited by comp1911; 08-22-2007 at 07:19 PM. Reason: Edit due to discussion below in regard to feeder size
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Old 08-22-2007, 04:39 AM   #2
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100 amp subpanel install with a couple pix


100 amp breaker is too large! Replace it with a 90.

#2 AL is 90 amps (@ 75 deg)

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Old 08-22-2007, 07:46 AM   #3
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100 amp subpanel install with a couple pix


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100 amp breaker is too large! Replace it with a 90.

#2 AL is 90 amps (@ 75 deg)
For discussion below.


Last edited by comp1911; 08-22-2007 at 07:20 PM. Reason: discussion below
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Old 08-22-2007, 09:06 AM   #4
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100 amp subpanel install with a couple pix


In some areas that table is allowed to size your wire for sub-panels. In most it is not. It used to be accepted in my area but is no longer allowed. Clarification I'm told is coming in the 2008 code cycle. The table was intended by the cmp to only apply to MAIN panel feeder(s) and services to dwellings. This confusion has been hashed over many times and only clarification by the cmp for that section of code is ever going to solve the misinterpretations of that article section. I think master electrician Speedy Petey who replies here is from New York and they accept that table in his part of the country to feed subs. The majority of the professionals on Mike Holts forum are of the opinion it should not be used and is being misapplied for feeders to sub-panels. I'm not going to go back and replace all the feeders to sub-panels that were sized by that table and no-one else is either.

Stubbie

Last edited by Stubbie; 08-22-2007 at 10:38 AM.
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Old 08-22-2007, 09:26 AM   #5
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100 amp subpanel install with a couple pix


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In some areas that table is allowed to size your wire for sub-panels. In most it is not. It used to be accepted in my area but is no longer allowed. Clarification I'm told is coming in the 2008 code cycle. The table was intended by the cmp to only apply to MAIN panel feeder(s) and services to dwellings. This confusion has been hashed over many times and only clarification by the cmp for that section of code is ever going to solve the misinterpretations of that article section. I think master electrician Speedy Petey who replies here is from New York and they accept that table in his part of the country to feed subs. The majority of the professionals on Mike Holts forum are of the opinion it should not be used and is being misapplied for feeders to sub-panels. I'm not going to go back and replace all the feeders to sub-panels that were sized by that table and no-one else is either.

Stubbie
Thanks for the comments.

I just took a look at MN Electrical Inspection site and they note table 310.15 for feeders.

See page 6 here: http://www.electricity.state.mn.us/E..._checklist.pdf

Last edited by comp1911; 08-22-2007 at 02:40 PM.
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Old 08-22-2007, 10:51 AM   #6
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100 amp subpanel install with a couple pix


Based on that page I would say that you would not be allowed to feed the sub-panel with #2 aluminum for 100 amps.

Stubbie

Last edited by Stubbie; 08-22-2007 at 10:56 AM. Reason: changed #2 copper to #2 aluminum
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Old 08-22-2007, 11:05 AM   #7
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100 amp subpanel install with a couple pix


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Based on that page I would say that you would not be allowed to feed the sub-panel with #2 aluminum for 100 amps.

Stubbie
Why do you think that?
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Old 08-22-2007, 11:31 AM   #8
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100 amp subpanel install with a couple pix


The table is listed under the heading (above the house image) as "Electrical Services" a feeder to a sub-panel load side of the main panel is not a service feeder or service entrance or service drop overhead or underground. Your sub-panel is a four wire feeder not a 3 wire service or 3 wire service feeder to a dwelling mains as the MN codes people are trying to clarify in the table guidelines they posted. Remember there are feeders and then there are service feeders, they are not the same thing.

One more thing stands out to me... they show the ampacity as a service rating which I think is MN's way of clarifying how they want the table applied....to service conductors. The deal here is that service conductors can be unfused and they have a large diversity. The NEC does not like to see these unfused service conductors past the mains of the dwelling.... usually very near where they enter the house or on the house is the main breaker panel/disconnect. Therefore they allow a smaller conductor carrying more amperage, cause you aint going to be fooling with it as a homeowner after its energized and they consider the diversity of the loads it serves.

Stubbie

Last edited by Stubbie; 08-22-2007 at 12:14 PM. Reason: to add a little more explaination
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Old 08-22-2007, 12:19 PM   #9
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100 amp subpanel install with a couple pix


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The table is listed under the heading (above the house image) as "Electrical Services" a feeder to a sub-panel load side of the main panel is not a service feeder or service entrance or service drop overhead or underground. Your sub-panel is a four wire feeder not a 3 wire service or 3 wire service feeder to a dwelling mains as the MN codes people are trying to clarify in the table guidelines they posted. Remember there are feeders and then there are service feeders, they are not the same thing.

One more thing stands out to me... they show the ampacity as a service rating which I think is MN's way of clarifying how they want the table applied....to service conductors. The deal here is that service conductors can be unfused and they have a large diversity. The NEC does not like to see these unfused service conductors past the mains of the dwelling.... usually very near where they enter the house or on the house is the main breaker panel/disconnect. Therefore they allow a smaller conductor carrying more amperage, cause you aint going to be fooling with it as a homeowner after its energized and they consider the diversity of the loads it serves.

Stubbie
After reading your comments I went and talked to two electricans at work. Like I said above, one is an ex-inspector and the other one is liscensed has his own business as he works shift. He also wired my house.

Both said this install is good to go. I have to run a 10-3 dryer circuit and then I will have the inspector come take a look and let you know how that goes.
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Old 08-22-2007, 12:30 PM   #10
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100 amp subpanel install with a couple pix


Like I said the table is very controversial in its application. I wouldnt sweat it too much. My efforts were to dscuss how I thought the MN codes people want the table applied. If you would like to see how some of the foremost authorties in our insustry and authors of US electrical distribution think about the application of this table go to Mike Holt forums.......

http://forums.mikeholt.com/index.php

and do a search of all forums for Table 310.15(B)(6)....since you are an engineer you will be allowed to join the forum free and ask for comment.

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Old 08-22-2007, 12:47 PM   #11
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100 amp subpanel install with a couple pix


Quote:
Originally Posted by Stubbie View Post
Like I said the table is very controversial in its application. I wouldnt sweat it too much. My efforts were to dscuss how I thought the MN codes people want the table applied. If you would like to see how some of the foremost authorties in our insustry and authors of US electrical distribution think about the application of this table go to Mike Holt forums.......

http://forums.mikeholt.com/index.php

and do a search of all forums for Table 310.15(B)(6)....since you are an engineer you will be allowed to join the forum free and ask for comment.

Stubbie


Lots of good info on that site. I'm interested at what the inspector will say.

As a side note, I have a 100 amp breaker feeding a electric boiler that is #4 copper THHN. That was passed.

Thanks for your help.

Last edited by comp1911; 08-22-2007 at 02:41 PM.
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Old 08-22-2007, 04:00 PM   #12
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100 amp subpanel install with a couple pix


Yeah it is a great resource. Also as a side note the last thing I wanted was for you to tear out that feeder to your sub. That is the inspectors call. I would be interested to know what the cmp feels is the worry for applying that table to other than services. the answer is probably buried in the mike holt forum somewhere, maybe I'll spend some time looking for an explanation later today.

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Old 08-22-2007, 06:52 PM   #13
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100 amp subpanel install with a couple pix


Stubbie,
You are correct. That configuration does NOT rate a 100a breaker. That table shown is for SERVICE FEEDERS only ...

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Last edited by JGarth; 08-22-2007 at 07:27 PM.
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Old 08-22-2007, 07:09 PM   #14
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100 amp subpanel install with a couple pix


Edited per the request of JGarth

Last edited by comp1911; 08-22-2007 at 07:37 PM. Reason: Edited per the request of JGarth
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Old 08-22-2007, 07:16 PM   #15
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Edited per the request of JGarth


Last edited by comp1911; 08-22-2007 at 07:37 PM. Reason: Edited per the request of JGarth
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