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

HVAc Disconnect Box

edwardh1 | Posted in Energy, Heating & Insulation on November 11, 2009 05:52am

Situation;
mid 1980s house, 220 volt 3 ton central air. The A/C Disconnect box ( on outside side of house) is wired as follows:

– feed wire coming from the house breaker panel, in the outside disconnect box, has 3 wires. black (a hot), red (a hot) , white.

– line from A/C unit (in the “whip” rubber cable) has 4 wires- black, red, white, and a bare ground wire

-the A/C unit”s black and red wires connect thru the disconnect “pull out” piece to the similar feed black and red wires from the house .

-the two white wires are connected to each other in a metal piece that is screwed on or part of the metal disconnect box housing.

-the bare ground wire is not connected.

question 1 -Should the bare ground be connected to the two white wires which are screwed onto the box housing? Sorta like electric dryers of the same vintage?

question 2 if i buy a new central a/c will I have to run a new 4 wire from the disconnect box back to the inside house breaker panel? or just keep using the same set up?

Thanks

Thanks

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

Replies

  1. gfretwell | Nov 11, 2009 08:23pm | #1

    The white wire should not be used at all. The bare wire is supposed to be your ground. The reality is it really doesn't make that much difference to the electricity and since it appears they cut the bare wire out of the cable feeding the disconnect I would just tape the white feeding the disco with green tape (or strip it all the way back) and get on with my life.
    AC disconnects don't usually have any neutral load (supposed to be the white) so ideally you would not use the white wire at all.

  2. brownbagg | Nov 11, 2009 08:29pm | #2

    just hook the bare to a ground rod driven by the a/c unit

  3. JTC1 | Nov 11, 2009 08:38pm | #3

    My take on your current situation:

    >>- feed wire coming from the house breaker panel, in the outside disconnect box, has 3 wires. black (a hot), red (a hot) , white.<<

    Odd, open disconnect box and look very closely at where the cable enters the disconnect box -- is there a clipped off bare wire visible?

    If yes, open breaker panel, locate #xx-3 entrance to the breaker panel - where do the white and bare wires from that cable go? To the ground/neutral buss? I thought so. Bare clipped off at breaker panel also?

    If yes, the white wire has been utilized as the ground - except for re-coding issues, it is fine and safe. 

    >>- line from A/C unit (in the "whip" rubber cable) has 4 wires- black, red, white, and a bare ground wire<<

    This is unusual - generally done with loose conductors in Carflex or similar flexible conduit here.  "Rubber whip cable" may or may not be legal/safe due to weather/UV resistance (read insulation jacket). 

    >>-the A/C unit"s black and red wires connect thru the disconnect "pull out" piece to the similar feed black and red wires from the house .<<

    Sounds good.

    >>-the two white wires are connected to each other in a metal piece that is screwed on or part of the metal disconnect box housing.<<

    The "metal piece" is a buss bar which connects the two wires AND grounds the disconnect box enclosure.

    >>-the bare ground wire is not connected.<<

    Open connection box at A/C, bare wire not connected there either, right?  Whoever wired this was just barely competent, and used the white as the ground. 

    >>question 1 -Should the bare ground be connected to the two white wires which are screwed onto the box housing?<<

    Only if connected at the A/C unit, otherwise it does nothing. Redundant to connect.

    >>Sorta like electric dryers of the same vintage?<<

    Usually, those dryers were fed by black, white and bare.

    >>question 2 if i buy a new central a/c will I have to run a new 4 wire from the disconnect box back to the inside house breaker panel?

    No. ---- 3 wires is all you will need for 240v. 4-wire required only if there is a 120v component on the circuit - like a clock in a stove, or a timer in a dryer.

     >>or just keep using the same set up?<<

    Assuming black & red are the hots and the white has been used as a ground at all the panel and at the disconnect it will be fine (though not perfectly code compliant).  You will help avoid future confusion by stripping the insulation off of the white wire at the disconnect box and at the panel box.

    When the new A/C is installed, change to an approved method for the disconnect to unit wire run. UV resistant, weather tight conduit - not a "rubber whip" - unless there is something out there which I have not seen, possible...

    WORST CASE SCENARIO:

    Installer used xx-3 Romex from the panel to the disconnect and then clipped the white off at the panel, and then clipped the bare off at the disconnect box. This would leave you with an ungrounded disconnect box and A/C. 

    Mind you the A/C would still run fine..........but it is ungrounded and potentially very dangerous.

    Check for ground path by measuring voltage with a volt meter between red / disconnect box and black / disconnect box. Should read 120v both places.  Red to black should be 240v.

    Jim

    Never underestimate the value of a sharp pencil or good light.
    1. User avater
      BillHartmann | Nov 11, 2009 08:59pm | #4

      "Usually, those dryers were fed by black, white and bare."Not exactly.For stoves and dryers you can use non-metallic cable (romex) and SE (service entrance) amount other wiring methods.Now for ones that are not grounded you run the 2 hots and NEUTRAL.For romex that would be black and red hots and white NEUTRAL. Now for an installation between when grounded wiring was common and 96 NEC where 4 wire circuits where required it is technically not legal to run 10-2 and use the bare wire as the "neutral". I know that it was done, but the wording of the code does not allow it.And safety wise it makes not difference as the neutral is also used as the ground in those installations.Now to confuse things more SE cable is also allowed. 3 conductor SE cable is 2 hots (either black and red or two blacks) and the those inturn are wrapped with a stranded bare NEUTRAL. Now that is common on stoves, but I don't think that it is made in the smaller sizes for use on a dryer..
      William the Geezer, the sequel to Billy the Kid - Shoe

      1. JTC1 | Nov 11, 2009 09:22pm | #5

        I see lots of seemingly wierd stuff here in houses from the late 70's to the late 80's. Inspectors must not have been too fussy about this. 

        For dryers, Cu 10-2 Romex is fairly common, also see lots of AL #8 SE. More AL SE than Cu Romex. Only occasionally see Cu 10-3 Romex with one wire not connected or clipped off.

        4 wire conversions go really easy with a Cu 10-3 with one wire not connected and not clipped off too short.

        It's nice to live and hope......

        Jim

         

        Never underestimate the value of a sharp pencil or good light.

        Edited 11/11/2009 1:25 pm ET by JTC1

    2. edwardh1 | Nov 11, 2009 09:50pm | #6

      will do!
      Thanks
      I will check inside the inside house breaker box and will use my VOM (an OLD big black Simpson meter from the 70s) to do the checks you said to do at the disconnect box.I think I have the right whip- its a semi rubber semi hard / soft plastic tube with three "loose" wires in it red, black, white and a bare ground wire.
      I will look and if the bare wire is grounded in the A/C unit, I will then ground it to the disconnect box white wires/box frame connection, after checking that that is really a ground.Thanks

      1. JTC1 | Nov 11, 2009 09:59pm | #7

        >>....semi rubber semi hard / soft plastic tube....loose wires....<<

        Gray, helical coil like pattern around it? Sounds like Carflex - check printing on exterior anyhow.

        Good luck.

        Jim Never underestimate the value of a sharp pencil or good light.

        1. edwardh1 | Nov 11, 2009 11:58pm | #11

          I did the voltage checks youu suggested. In disconnect bx- feed s from house to white ground (in the disconnect box) were 120 v each, between each feed lead , 220.And the bare wire from the a/c unit when checked on the r x 1 scale shows connectivity with the white wires in the disconnect box, which tells me they are connected together in the a/c unit,
          and that I should/could connect the bare wire to them in the disconnect box too. But connecting the bare wire really doesnt do much as the white wire is the main ground (right??)

          1. JTC1 | Nov 12, 2009 03:35am | #12

            Correct!

            My guess would be the bare wire is just in contact with the junction box wall inside of the A/C unit.

            JimNever underestimate the value of a sharp pencil or good light.

      2. gfretwell | Nov 11, 2009 10:22pm | #8

        It might be easier and more reassuring if you looked in the panel to be sure what is connected there. Testing is still a good idea.

        1. edwardh1 | Nov 11, 2009 10:56pm | #10

          I did (just) look in the inside house panel. looks like 3 wire, 10-3 without ground.

    3. edwardh1 | Nov 11, 2009 10:27pm | #9

      I think from the inside breaker to the outside disconnect box they ran a 10/3 with no ground. (I looked in the breaker box- no bare 4th wire, and the white goes to the grounded buss bar). I can crawl under my house and read the wire printing also.

  4. DanH | Nov 12, 2009 04:59am | #13

    I'm having a little trouble picturing who, in the 80's (and not the 1880s) would have installed anything without a ground. Was this presumably professionally installed, or a DIY hack?

    Check the feed from the house to see if it's in conduit or armored cable. If so, the cable jacket is the ground.

    Tying the ground to the neutral is probably a bad idea.

    Not clear why the AC should need a neutral at all.

    A strong nation, like a strong person, can afford to be gentle, firm, thoughtful, and restrained. It can afford to extend a helping hand to others. It's a weak nation, like a weak person, that must behave with bluster and boasting and rashness and other signs of insecurity. --Jimmy Carter
    1. edwardh1 | Nov 12, 2009 07:18am | #14

      In a 220 v , 3 wire circuit black, red, white is the white the ground,
      and is it only the ground?
      or is it a "grounded neutral also.

      1. DanH | Nov 12, 2009 07:22am | #15

        White is the "groundED conductor", which is to say the neutral. The bare copper is the "groundING conductor", which is to say the ground. They serve different purposes.
        A strong nation, like a strong person, can afford to be gentle, firm, thoughtful, and restrained. It can afford to extend a helping hand to others. It's a weak nation, like a weak person, that must behave with bluster and boasting and rashness and other signs of insecurity. --Jimmy Carter

  5. DaveRicheson | Nov 17, 2009 02:14pm | #16

    "rubber whip" - unless there is something out there which I have not seen, possible...

    Called Sealtight.

    http://www.anacondasealtite.com/products.htm#Sealtite¯%20Metallic%20Flexible%20Conduit 

    or liquidtight.

    Used all the time for motor connections. Provide vibration isolation and moisture/liquid protection.

    1. User avater
      BillHartmann | Nov 17, 2009 07:10pm | #17

      It could also be a non-metallic flex such as Carlon Liquidtight.http://www.carlon.com/Product_CarflexLiquidtightFlexibleNonmetallicConduit.html.
      William the Geezer, the sequel to Billy the Kid - Shoe

    2. JTC1 | Nov 23, 2009 03:49pm | #20

      This product appears to be the competition to Carflex which BillHartmann linked in ####.18.

      Carflex is the our local "standard".

      I just would not describe either one as a "rubber whip". I had visions of a chunk of #10 flexible appliance cord.....

      As it turned out, the unit was connected with a flexible conduit by some manufacturer.

      JimNever underestimate the value of a sharp pencil or good light.

      1. DanH | Nov 23, 2009 04:27pm | #21

        > As it turned out, the unit was connected with a flexible conduit by some manufacturer.

        That's what I assumed when I saw "rubber whip". If nothing else because any regular factory cable would have come with a ground wire.
        A strong nation, like a strong person, can afford to be gentle, firm, thoughtful, and restrained. It can afford to extend a helping hand to others. It's a weak nation, like a weak person, that must behave with bluster and boasting and rashness and other signs of insecurity. --Jimmy Carter

        Edited 11/23/2009 8:28 am by DanH

        1. edwardh1 | Nov 23, 2009 10:43pm | #22

          sorry about the mis info- its (to me ) a legit electrica item, not a "water hose" etc with wires run thru it

  6. Richie921 | Nov 22, 2009 07:05am | #18

    Is the feed plastic sheathed, greenfield, or metal pipe back to panel.  If its greenfield or metal pipe the metal carries the ground.  Just ground the a/c to the disconnect housing.

    Richie



    Edited 11/21/2009 11:06 pm ET by Richie921

  7. RFM 2 | Nov 22, 2009 08:03am | #19
    "  
    "

    126461.3 in reply to 126461.1 
    just hook the bare to a ground rod driven by the a/c unit "
     

     

    That is a good way to kill someone, a overcurrent device (fuse/circuit breaker) will never open to clear a fault & the NEC does not allow that practice.

  8. cussnu2 | Nov 23, 2009 10:51pm | #23

    "Was this presumably professionally installed, or a DIY hack?"

     

    Hackdom is not confined to DIY.  From what I have seen and dealt with, there a lot more hacks hiding in the professional ranks.

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

FHB Summit 2025 — Design, Build, Business

Join some of the most experienced and recognized building professionals for two days of presentations, panel discussions, networking, and more.

Featured Video

How to Install Exterior Window Trim

Learn how to measure, cut, and build window casing made of cellular PVC, solid wood, poly-ash boards, or any common molding material. Plus, get tips for a clean and solid installation.

Related Stories

  • Affordable Scans, Accurate Plans
  • FHB Summit 2025 — Design, Build, Business
  • A Summer Retreat Preserved in the Catskill Mountains
  • Fine Homebuilding Issue #332 Online Highlights

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 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
  • Issue 327 - November 2024
    • Repairing Damaged Walls and Ceilings
    • Plumbing Protection
    • Talking Shop

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