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Old 05-10-2016, 09:39 AM   #1
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Flex to Subpanel


As some might remember from my previous posts, my wife wants us to renovate the kitchen. I am looking into how to do it right without spending too much money we do not have.

After taking inventory of the existing circuits and wires to the kitchen it appears that I need three more circuits: the second small appliance circuit, a circuit to separate the microwave from the dishwasher and an individual circuit for the refrigerator. The first small appliance circuit is present as is a separate circuit for the garbage disposal. The lighting circuit is there too even though it might have too many outlets in other spaces of the house which means that eventually I will need to pull another set of wires to split some of its load. At a future point I will need to pull to a nearby location at least 1, but probably 2 more circuits for the GFCI bathroom outlets when we get to renovating the bathrooms. At this point I am looking at at least 5 new 20A circuits running from one corner of the house to the opposite corner (that is in addition to the existing 5 circuits). As it happens the reason for that is that the electrical panel and the kitchen are in the opposite corners of the house and the runs are on the order of 50ft.

I am wondering if it is smarter to place a subpanel in the basement below the kitchen and run the circuits from there as opposed to running them from the main panel and thus saving about 50ft of cable on each run. In either case I will need to hide the wires in the finished ceiling of the basement. My plan for the subpanel is 125A panel connected to the main panel with 1 inch flex in which I plan to run four #3 THHN wires(two hot, one neutral and one ground which I guess could be somewhat thinner, #6?). The breaker will be 100A breaker inside the main panel(the main panel is 200A). The flex will need to make the equivalent of 9 ninety degree turns at various points along its route. The questions are:
1. Am I allowed to use flex conduit for connection from main panel to subpanel fished through wall and ceiling cavities(the conduit will be supported only where I can reach it; there is absolutely no way I can put rigid EMT without opening up the whole ceiling)?
2. Did I get the size of the conduit and the wires correct for the application?(reading the NEC and figuring this out was fun, but it would be nice for someone to confirm that my wires are not too thin)
3. I have access to a location in the middle of the run. Is it a good idea to place a box there to make pulling the wires through the conduit easier?

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Old 05-10-2016, 10:41 AM   #2
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Re: Flex to Subpanel


Am I kidding myself? Should I just use 3-3-3-5 SE cable?

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Old 05-10-2016, 10:59 AM   #3
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Re: Flex to Subpanel


Pulling wire through flex is a huge PITA. You can have no more than 360 degrees of bend between pull points.

You do not need a dedicated circuit fot the fridge.

You could possibly combine the garbage disposal and the DW onto the same circuit, depending on the ampacity of the equipment.
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Old 05-10-2016, 01:23 PM   #4
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Re: Flex to Subpanel


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Originally Posted by mm11 View Post
Pulling wire through flex is a huge PITA. You can have no more than 360 degrees of bend between pull points.
So I need two pull points. I knew about the 360 degrees for EMT and was not sure if it applied to flex. Now I know it does.
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You do not need a dedicated circuit fot the fridge.
The wife wants a big fridge with water dispenser and what not so I thought that individual circuit was warranted.
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Old 05-10-2016, 03:35 PM   #5
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Re: Flex to Subpanel


Pull 2-2-2-4 ser and put it on a 90 amp breaker.
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Old 05-10-2016, 04:28 PM   #6
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Re: Flex to Subpanel


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Pull 2-2-2-4 ser and put it on a 90 amp breaker.
For copper wire am I not allowed to assume the 75 degrees ampacity if the panels say "use 60/75 degree wire"? I won't necessarily be buying southwire products, but here is this table: http://www.southwire.com/ProductCata...rodcatsheet274
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Old 05-11-2016, 09:14 PM   #7
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Re: Flex to Subpanel


With that you are able to derate from 90 degrees but you cannot exceed the lowest temp rating of any of your lugs. So if the cable is rated at 90 degrees but your lugs on the breaker are rated for 60 you cannot exceed the 60 degree column. Let me know if that was confusing I'll try to help more.

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Old 05-12-2016, 02:14 PM   #8
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Re: Flex to Subpanel


That was clear. Thank you. Panel definitely says 60/75 degree wire. I need to check the breaker. I am not running through any insulation, only brick wall, so I believe that I am allowed to use the 75 degree column (even if I was not, the 60 degree column is 95 which with the next standard breaker becomes 100 for 2-2-2-4 copper -- see below why I dropped the 3-3-3-5 copper).

Voltage drop calculation implies I need #2 for 65ft, so I will go with 2-2-2-4 copper. I do not want to deal with aluminum wire and all the issues with it.

The one thing I am not sure is that this cable will run parallel to two 12/3 and three 12/2 MC cables for air-conditioners for about 30 ft. Due to the fact that I am pulling through a finished basement ceiling I cannot maintain spacing between the cables including the SER cable to the subpanel. Am I running afoul of derating of the cables for inability to maintain spacing?

Also my run is parallel and next to (directly next to) black iron pipe for gas and a steel I-beam for another 20 ft. Is that a concern?

Last edited by epsilono; 05-12-2016 at 02:19 PM. Reason: typos
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Old 05-12-2016, 02:31 PM   #9
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Re: Flex to Subpanel


What do you mean by maintain spacing?

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Old 05-12-2016, 03:23 PM   #10
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Re: Flex to Subpanel


What issues with aluminum wire?

Just as safe as copper when installed correctly, and much cheaper also.
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Old 05-12-2016, 04:25 PM   #11
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Re: Flex to Subpanel


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Originally Posted by randyhenke View Post
What do you mean by maintain spacing?

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I am not sure if I am violating 310.15(B)(2)(a). I cannot figure out if it applies to my case or not (cable to be next to smaller MC cables for many feet).
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Old 05-12-2016, 04:27 PM   #12
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Re: Flex to Subpanel


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What issues with aluminum wire?

Just as safe as copper when installed correctly, and much cheaper also.
I agree that it is a lot cheaper, but I just do not feel comfortable with aluminum wires inside my own house. Correctly installed aluminum wiring is fine, I just do not want it in my house.
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Old 05-12-2016, 07:25 PM   #13
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Re: Flex to Subpanel


Quote:
Originally Posted by epsilono View Post
I am not sure if I am violating 310.15(B)(2)(a). I cannot figure out if it applies to my case or not (cable to be next to smaller MC cables for many feet).
I'll get back to you on that I'll pull my code book out later when I get a chance.

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Old 05-12-2016, 09:38 PM   #14
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Re: Flex to Subpanel


OK I think I understand what your thinking. You are not running in a raceway so you don't need to derate for that. If I am missing something or not understanding let me know.

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Old 05-13-2016, 01:50 PM   #15
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Re: Flex to Subpanel


I will take your answer to mean that I am OK to proceed as planned.


Just for the sake of understanding the code, the 2008 version I have reads:
Quote:
Where the number of current-carrying
conductors in a raceway or cable exceeds three, or where
single conductors or multiconductor cables are installed
without maintaining spacing for a continuous length longer
than 600 mm (24 in.) and are not installed in raceways
, the
allowable ampacity of each conductor shall be reduced as
shown in Table 310.15(B)(2)(a).
, why does not the bolded part cover my situation?

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