FHB Logo Facebook LinkedIn Email Pinterest Twitter X Instagram Tiktok YouTube Plus Icon Close Icon Navigation Search Icon Navigation Search Icon Arrow Down Icon Video Guide Icon Article Guide Icon Modal Close Icon Guide Search Icon Skip to content
Subscribe
Log In
  • How-To
  • Design
  • Tools & Materials
  • Restoration
  • Videos
  • Blogs
  • Forum
  • Magazine
  • Members
  • FHB House
  • Podcast
Log In

Discussion Forum

Discussion Forum

Flex conduit sizing for 6 #12 cicuits

wfm246 | Posted in Construction Techniques on January 9, 2005 05:47am

All,

I’m a weekend warrior tackling bigger jobs as I remodel my 1953 duplex.  I’m pulling 6 new circuits to my kitchen.  All will be on 15A breakers and I’ll use 12 gauge.  I’ll have separate circuits for the 1) accessories, 2) disposal, 3) dishwasher, 4) microwave, 5) toaster, and 6) gas range (the refer is already on a separate circuit).  My plan is to run flex conduit from the subpanal, up into the attic, down the inside of the wall that the cabinets are mounted on, exit the wall, and run in flex conduit behind the cabinets to the receptacles.  I intend to use 12/2, strip the cover, and pull the whole bundle into ¾â€ flex.  Does that work?  Do all 18 wires fit?  Does Code allow that many wires in a ¾â€ conduit?  Is that 6 or 12 conductors?

 

Thanks for the help!

 

Warren

 

“If you have not done it three times, you don’t know how to do it right … but if you’re very clever, the first build can be in your head†

                                                — a wise old guy

 

“If you have not done it three times, you don’t know how to do it right … but if you’re very clever, the first build can be in your head†

                                                — a wise old guy

Reply
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Replies

  1. Stuart | Jan 09, 2005 06:24am | #1

    First thing, you can only put 16 #12's in a flex conduit per Code (and that would be a pretty tough pull to get that many through there.)  Also, if you're going to use conduit you may as well buy individual wires instead of going to the hassle of stripping them out of Romex.

    Also, the Code requires derating the wire's current carrying capacity when there are three or more current carrying conductors in a single conduit.  Assuming the conduit was big enough, using #12's on a 15 amp circuit helps you out some but not much.  The amount of derating will depend on the total number of wires.

    It may be possible to share some grounds and neutrals to get the wire count down, depending on how you have the breakers installed in the panel.

    Is there a reason you have to use conduit?  You may be better off running Romex if it's going inside stud walls.

    Sorry I can't give you much of an answer, it's pretty difficult to make any definite statements without actually seeing your particular situation.

    1. wfm246 | Jan 09, 2005 07:04am | #2

      Stripping the cover off of romex: I have a lot of romex and it turns out to be about 30% cheaper then buying spools of wire.

      Derating: I figured on derating the 20A 12G to 75% or 15A to account for putting it in conduit … but I’m not sure that is correct.

      And, yes, I thought it would make sense to share some grounds and neutrals to get the number to 16.  But honestly, I’m not sure about the Code definition of a “conductor”.  I understood the code to be no more then 16 conductors in ¾” … do you count the grounds also?

      I’m using conduit in the wall because it access is tight and this will help make the feed through the top plate and to where it exits much easier.

      Thanks for you feedback ... it sure helps my thinking!

      Warren

  2. pm22 | Jan 09, 2005 07:19am | #3

    Do you live in Chicago?

    If not, why not do the whole thing in Romex? Do you really need that many circuits? You can do a multi-wire and end up with a total of nine wire plus one ground.

    If you need conduit for protection, you could run one or two 2" conduits up to the attic for protection and run Romex through that. Flex is hard to pull through so I would suggest EMT.

    ~Peter

    1. wfm246 | Jan 09, 2005 07:28am | #4

      I'm in southern California (San Clemente).  I think I understand; 3 circuits on one phase, 3 on the other phase, share neutrals for circuits on opposite phases, and use one ground for everything ... that's all legal, right?

      Yes, I'm using the conduit for protection.  Access is very tight and I can't get EMT in there without opening up the whole wall.  So, if I can do it with flex then it's easier and I don't have to add drywall and painting to the work list.  I could use 1" conduit if necessary

      Warren

       

      1. pm22 | Jan 09, 2005 08:25am | #5

        Well then, the wall is your protection. You can legally fish the Romex through a finished wall cavity. Get you some Romex clamps listed for 2 cables, attach them about 3 feet up from the end, take off the lock rings and fish them into the panel. 1 3/8" hole should clear the connector.

        You seem to understand the multi-wire thing which is good.

        Or you could run your flex up to the attic and then transfer to Romex in Junction boxes.

        ~Peter

        1. wfm246 | Jan 09, 2005 10:21am | #6

          Thanks Peter, I appreciate the advice!

          Warren

          1. DaveRicheson | Jan 09, 2005 03:55pm | #7

            Since this is an upgrade, why don't you bring it up to code and add two 20 amp circuits (non lighting) to the kitchen?

            Someone in the future is going to see that #12 wire and think that is what you did, and replace those 15 amp breakers with 20's. Besides, some diposals and microwave can pull close to 15 amp. Nuisance trips of a diposal circuit will drive you or you DW nuts. 

            May as well get it right when you do it, the first time.

             

          2. wfm246 | Jan 09, 2005 06:13pm | #8

            I guess I was getting hung up on protecting half a dozen romex cables snaked down the inside of the wall from an errant picture frame nail at some time in the future.  That’s why I wanted it in conduit for that leg of the run from the sub-panal to the kitchen.  But, it creates this derating problem, I can’t put the #12’s on 20A breakers, etc.  So, should I quit worrying about protecting the romex?  Can romex legally exit the interior of the wall behind the cabinets, running through a hole in the drywall, and run horizontally behind cabinets just stapled to the wall (at the studs, of course)?   If I drop the whole idea of using the conduit and just pull romex everywhere, then it’s easy to add another 20A small appliance circuit.  Now, that’s a buff kitchen!

            I should buy the code book.

          3. User avater
            BillHartmann | Jan 09, 2005 10:24pm | #9

            Well several things. First of all #12 has am ampacity rating of 25 amps nad that is the base current used for derating.If you run multi-wire circuits as you mentioned then you only have the equivalent of 6 current carrying conducting wires.4-6 current carrying conductors require a derating to 80%.So the #12 after derating can carry 20 amps.Now if these where not multiwire circuits then you would have 12 current carrying condutors and that requires a derate to 50%.Also you only need one ground wire.Now for romex. I am not clear on the details, but basically you can run the cable through holes (or parallel on the side of studs) if the edge of the hole (and thus the cable ) is at least 1 1/4" from the surface.Or if it is less than than or installed in groooves or notches or other wise would be within the 1 1/4" of the stud surface then 1/16" steel "nail plate" is needed to protect it.You can also run romex exposed if it "follows the buildigng surfaces" and is not subject to phyiscal damage.Thus you could come of through the wall into a cabinet and running allow the back of the cabinet near the top where no pots and pans which hit it.

          4. DaveRicheson | Jan 10, 2005 02:25pm | #10

            Bill gave you the skinny on your derating issue.

            If you exit the drywall inside of a cabinet, you should enter a  junction box, and from there use flex to each device. Running romex up behind the drawers may be alright, but I would still be concerned about possible damage.

            I would assume that you will re-enter the wall at each receptical location, so there is an additional j-box and hole in the cabinet/wall. This would make a much neater and safer run than loose romex  running through a bunch of holes and stapled to the back of the cabs. (IMHO)

            Figure the house is 52 years old, and you may not be the last owner. Plan your work for future resale, and that inevitable home inspector that is going to point out  anything that might be questionable. Trying to explain code compliance to a buyer that has already seen a negative report is futile. You will either change it then or accept a lower price for not thinking about it now.

             

            Dave

  3. JohnSprung | Jan 11, 2005 03:40am | #11

    If you're running all that many circuits to the same kitchen, another approach would be to run big feeders to a new subpanel in or near the kitchen.  That way you don't have derating to mess with, and if you accidentally get the microwave, toaster, and waffle iron on the same circuit, you don't have as far to walk to the breakers.  A lot depends on distances and obstacles, and whether you have a nice location for a new subpanel.

     

    -- J.S.

     

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Video Shorts

Categories

  • Business
  • Code Questions
  • Construction Techniques
  • Energy, Heating & Insulation
  • General Discussion
  • Help/Work Wanted
  • Photo Gallery
  • Reader Classified
  • Tools for Home Building

Discussion Forum

Recent Posts and Replies

  • |
  • |
  • |
  • |
  • |
  • |
View More Create Post

Up Next

Video Shorts

Featured Story

Picture-Perfect Pergola

Built from locally sawn hemlock, this functional outdoor feature uses structural screws and metal connectors for fast, sturdy construction.

Featured Video

Micro-Adjust Deck-Baluster Spacing for an Eye-Deceiving Layout

No math, no measuring—just a simple jig made from an elastic band is all you need to lay out a good-looking deck railing.

Related Stories

  • Design and Build a Pergola
  • Podcast Episode 689: Basement Garages, Compact ERVs, and Safer Paint Stripper
  • FHB Podcast Segment: Are Single-Room ERVs the Answer?
  • Fire-Resistant Landscaping and Home Design Details

Highlights

Fine Homebuilding All Access
Fine Homebuilding Podcast
Tool Tech
Plus, get an extra 20% off with code GIFT20

"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Fine Homebuilding Magazine

  • Issue 332 - July 2025
    • Custom Built-ins With Job-Site Tools
    • Fight House Fires Through Design
    • Making the Move to Multifamily
  • Issue 331 - June 2025
    • A More Resilient Roof
    • Tool Test: You Need a Drywall Sander
    • Ducted vs. Ductless Heat Pumps
  • Issue 330 - April/May 2025
    • Deck Details for Durability
    • FAQs on HPWHs
    • 10 Tips for a Long-Lasting Paint Job
  • Issue 329 - Feb/Mar 2025
    • Smart Foundation for a Small Addition
    • A Kominka Comes West
    • Making Small Kitchens Work
  • Issue 328 - Dec/Jan 2024
    • How a Pro Replaces Columns
    • Passive House 3.0
    • Tool Test: Compact Line Lasers

Fine Home Building

Newsletter Sign-up

  • Fine Homebuilding

    Home building tips, offers, and expert advice in your inbox.

  • Green Building Advisor

    Building science and energy efficiency advice, plus special offers, in your inbox.

  • Old House Journal

    Repair, renovation, and restoration tips, plus special offers, in your inbox.

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters

Follow

  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X
  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X

Membership & Magazine

  • Online Archive
  • Start Free Trial
  • Magazine Subscription
  • Magazine Renewal
  • Gift a Subscription
  • Customer Support
  • Privacy Preferences
  • About
  • Contact
  • Advertise
  • Careers
  • Terms of Use
  • Site Map
  • Do not sell or share my information
  • Privacy Policy
  • Accessibility
  • California Privacy Rights

© 2025 Active Interest Media. All rights reserved.

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

  • Home Group
  • Antique Trader
  • Arts & Crafts Homes
  • Bank Note Reporter
  • Cabin Life
  • Cuisine at Home
  • Fine Gardening
  • Fine Woodworking
  • Green Building Advisor
  • Garden Gate
  • Horticulture
  • Keep Craft Alive
  • Log Home Living
  • Military Trader/Vehicles
  • Numismatic News
  • Numismaster
  • Old Cars Weekly
  • Old House Journal
  • Period Homes
  • Popular Woodworking
  • Script
  • ShopNotes
  • Sports Collectors Digest
  • Threads
  • Timber Home Living
  • Traditional Building
  • Woodsmith
  • World Coin News
  • Writer's Digest
Active Interest Media logo
X
X
This is a dialog window which overlays the main content of the page. The modal window is a 'site map' of the most critical areas of the site. Pressing the Escape (ESC) button will close the modal and bring you back to where you were on the page.

Main Menu

  • How-To
  • Design
  • Tools & Materials
  • Video
  • Blogs
  • Forum
  • Project Guides
  • Reader Projects
  • Magazine
  • Members
  • FHB House

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Popular Topics

  • Kitchens
  • Business
  • Bedrooms
  • Roofs
  • Architecture and Design
  • Green Building
  • Decks
  • Framing
  • Safety
  • Remodeling
  • Bathrooms
  • Windows
  • Tilework
  • Ceilings
  • HVAC

Magazine

  • Current Issue
  • Past Issues
  • Magazine Index
  • Subscribe
  • Online Archive
  • Author Guidelines

All Access

  • Member Home
  • Start Free Trial
  • Gift Membership

Online Learning

  • Courses
  • Project Guides
  • Reader Projects
  • Podcast

More

  • FHB Ambassadors
  • FHB House
  • Customer Support

Account

  • Log In
  • Join

Newsletter

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Follow

  • X
  • YouTube
  • instagram
  • facebook
  • pinterest
  • Tiktok

Join All Access

Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features.

Start Your Free Trial

Subscribe

FHB Magazine

Start your subscription today and save up to 70%

Subscribe

Enjoy unlimited access to Fine Homebuilding. Join Now

Already a member? Log in

We hope you’ve enjoyed your free articles. To keep reading, become a member today.

Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine.

Start your FREE trial

Already a member? Log in

Privacy Policy Update

We use cookies, pixels, script and other tracking technologies to analyze and improve our service, to improve and personalize content, and for advertising to you. We also share information about your use of our site with third-party social media, advertising and analytics partners. You can view our Privacy Policy here and our Terms of Use here.

Cookies

Analytics

These cookies help us track site metrics to improve our sites and provide a better user experience.

Advertising/Social Media

These cookies are used to serve advertisements aligned with your interests.

Essential

These cookies are required to provide basic functions like page navigation and access to secure areas of the website.

Delete My Data

Delete all cookies and associated data