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  • Wire size and amps question for the electricans.

    I have a couple questions for the electricians on here. I am running power out to my garage from the house. The total wire length will be around 150 feet. I recently got a real good deal on some copper 4 gauge THWN. What is the maximum size breaker I can run it from off of the house panel? I could not find a temperature rating on the insulation of the wire. This will be standard 220v single phase.

    Also, around 90' will be in conduit from the garage to the house under ground. Once I get into the house does THWN still need to be in conduit or can it be run like romex? It is running through an un-finished basement to get to the panel. Thanks.

  • #2
    Originally posted by oxford View Post
    I have a couple questions for the electricians on here. I am running power out to my garage from the house. The total wire length will be around 150 feet. I recently got a real good deal on some copper 4 gauge THWN. What is the maximum size breaker I can run it from off of the house panel? I could not find a temperature rating on the insulation of the wire. This will be standard 220v single phase.

    Also, around 90' will be in conduit from the garage to the house under ground. Once I get into the house does THWN still need to be in conduit or can it be run like romex? It is running through an un-finished basement to get to the panel. Thanks.
    I'm no electrician, but I did recently read through the NEC as I was working on my house. The THWN needs to be in conduit; Romex and other non-metallic sheathed cables are permitted by the NEC because the sheathing acts like a conduit to protect the insulation on the individual conductors.

    In order to be compliant with the NEC, you should size your breaker according the following ampacities of the conductor:

    Insulation temperature 60 degrees C: 70 amps
    Insulation temperature 75 degrees C: 85 amps
    Insulation temperature 90 degrees C: 95 amps

    When sizing conduit, you also have to be sure to follow NEC guidelines. I can't remember now the details, but they give you a formula to calculate the size of the conduit needed based on the number of conductors and the percentage of cross-sectional area filled.

    Read this ... think it has everything you need to know...
    http://www.fs.fed.us/database/acad/e...sicdesigns.pdf
    Last edited by Fasttrack; 12-05-2012, 06:49 PM. Reason: Found Good Info!

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    • #3
      Unless everything end-to-end is 90C, you need to default to the lower temperature spec. THWN is 75C, but your domestic panel and breakers may be 60C. Look at the labels inside the source and destination panel. Also, there should be a spec number on the wire that can be referenced.

      Is the 150 feet one way or loop distance? Althought it's not an absolute under the code (but may be in your local jurisdiction), the recommendation is to keep the overall voltage drop less than 3% on branch circuits, and 5% overall.

      Yes, you must protect THWN in L&L conduit and boxes. You are going to need to extend neutral if you want to derive 120v circuits, and install a ground rod at the garage sub-panel (do not extend ground to the garage). If your sub-panel is not acessible and near a door you local codes may require an external full building disconnect switch.
      Last edited by lakeside53; 12-05-2012, 09:05 PM.

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      • #4
        here's a site I've found helpful http://www.make-my-own-house.com/dia...al-wiring.html

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        • #5
          Expanding on what Lakeside wrote......

          The terminals on the ends need to be rated for the wire temp, if you use the wire to full temp rating. Usually the temp rating is marked on the breakers.

          You can use higher temp wire, just not to full temp unless the terminals are equally rated. The exception is if you run through a hot area between cooler areas, like up through an attic and down to the living space again. Then you derate the wire for the higher temp for that part of the run, but since it is rated higher to begin with, the derating does not force you to use larger wire. And the wire is still OK at the lower temp for the terminations.
          1601

          Keep eye on ball.
          Hashim Khan

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          • #6
            Oxford,
            Hope you are in the states, your name implies different?
            The NEC (National Electrical Code) is a minimum guidline that most counties,cities towns and others require you to follow. Now to your questions.
            The above answers are correct you do need to use the 60* rating which does have the wire rated at 70amps, so a 70 amp breaker at the house is what you want, it is to protect the wires to the shop. About the wire in the house yes it will need to be in a raceway and PVC is not allowed inside as it puts off toxic gases when heated or burned. EMT or even rigid galvinized conduit will work. You can pull a ground in with the conductors in PVC pipe underground and I highly recommend it (this is called an equipment grounging conductor, green or bare) to the shop, But YOU MUST Keep the ground bar and neutral connections seperate. Yes most jurisdictions require a seperate ground rod for an unattached building on the same service. A#6 solid from it to the ground bar is what you will need for that part of the install.
            You will want to include a neutral (white wire) so that you can have 120v circuits even though you will use 220v for most equipment and welders.

            I am repeating things already said but it does help to get as much information as possible when taking on a job like this.

            Best of luck and feel free to ask more when you get going.

            Mr fixit for the family
            Chris
            Last edited by Mr Fixit; 12-06-2012, 12:45 AM. Reason: spelling

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            • #7
              Yes OXFORD, please fill in your profile location! If not, none of the above may be correct!

              You local jurisdiction may allow the use of PVC conduit (there is also HDPE, subject to separate rules under Article 353) inside residential single family home, but you need to check with your AHJ - it often depends on whether you are three stories or less. With any conduit runs, pay attention to pull points with no more than 270 degrees of bends between them. And... no mixing plumbing connections with electrical, even if they fit!
              Last edited by lakeside53; 12-06-2012, 11:54 AM.

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              • #8
                Thanks, yes I am in the states. I am pulling a neutral, I have enough wire to pull 3 #4 and have to pick up something for a ground wire. What is considered a pull point? I currently have 6 90 degree bends to get from the house panel to the garage panel. The first 2 will be LB fittings to get from the subpanel to the outside, I then have 1 90 elbow to get heading towards the house. Once inside the house, I could use whatever.

                So at 60 degrees, 150' wire length, I am ok with a 70amp breaker at the house panel?

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                • #9
                  Not sure if this applies but i upgraded my home to 200amp service and it required 2 grounding rods to be installed in the ground no closer than 4 feet i believe. Some new code at the time i blieve.

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                  • #10
                    I have done these things and even with all the lube in the world, there is no way you are going to be able to pull that mass of wire through 6 90 degree bends. For long runs, even one 90 can be problematic. Six 90s is twice the recommended 270 degrees and even 270 degrees can be difficult. You are going to need at least one pull box somewhere along this route and personally, I would use two. I would try to plan a straight run from house to garage with only two 90s to transition from horizontal to vertical. A weather proof, outside box at each end of this run would make pulling much easier and each of these boxes can also function as one of your 90s. Then one or two 90s from these pull boxes to the house and garage panels and you are done. Make these boxes large enough to allow pulling both ways from them and you will not need to splice the wires in them. I would think 12" x 12" or even larger.

                    Oh, and wherever you can, DO use the large radius or "sweeping" 90s. They also make pulling a lot easier. A lot.


                    Originally posted by oxford View Post
                    Thanks, yes I am in the states. I am pulling a neutral, I have enough wire to pull 3 #4 and have to pick up something for a ground wire. What is considered a pull point? I currently have 6 90 degree bends to get from the house panel to the garage panel. The first 2 will be LB fittings to get from the subpanel to the outside, I then have 1 90 elbow to get heading towards the house. Once inside the house, I could use whatever.

                    So at 60 degrees, 150' wire length, I am ok with a 70amp breaker at the house panel?
                    Paul A.

                    Make it fit.
                    You can't win and there is a penalty for trying!

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                    • #11
                      You don't have to count the 'LB's as bends because you open them up to pull the wire to/from them and they become the equivalent of the 'pullbox'. Be sure to use more than enough wire pull lubricant on the wires when you pull them. Lather them up real good as they enter the conduit and keep lathering them up. One person pull and one person lather. Pull all the wires at the same time as one bundle.

                      Pretty sure (haven't kept up with the last few code revisions though) you have to run the ground wire between the two panels too even though you have ground rods at the sub panel.
                      Last edited by dave5605; 12-06-2012, 02:21 PM.

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                      • #12
                        I upgraded my electrical service about two years ago. I had 125 foot run. Not much wire pulling involved. Three strands of 2/0 copper. Two hots and a neutral, with a grounding rod at the garage.

                        They (electricians’) dug a trench. Laid conduit and wire along the trench, then they started at the garage and fed the conduit over the wire one length at a time to the house, laying the conduit in the trench as they went. Then they glued it up.

                        At the garage they installed a junction box on the outside wall where they terminated the THWN wire. There they connected 2/0 Romex and ran it from the junction box, through the wall and up to the panel. They did a similar thing at the house, went through the outside wall underground with the conduit/THWN, then ran it in the crawl space to a junction box, then to the panel with 2/0 Romex.
                        Last edited by Ron of Va; 12-06-2012, 04:28 PM.

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                        • #13
                          Out of curiosity, what makes romex able to be left in the open but thwn needs to be in conduit. Isn't romex just 2/3 pieces of thhn and a bare wire with the jacket around it. Honestly the jacket isn't much of "protection".

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                          • #14
                            Originally posted by oxford View Post
                            Out of curiosity, what makes romex able to be left in the open but thwn needs to be in conduit. Isn't romex just 2/3 pieces of thhn and a bare wire with the jacket around it. Honestly the jacket isn't much of "protection".
                            I don’t know if it was “Romex” exactly, but it looked like it to my untrained eye. They used it because it was more flexible to get into the box. Here it is hanging out of the junction box. They already ran it to the electrical panel. It was never run in the open.

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                            • #15
                              Oxford.
                              I told the contractor that I would fill in the hole. He loved that, 98؛ in June.

                              I covered the electrical conduit with about 10 inches of dirt, then ran about a half a dozen Cat 5 cables, a couple of telephone lines, 4-5 coaxial cables in another piece of electrical conduit right on top and covered it all up. I am thinking about putting in a security system. I didn’t know what I would need, so I though I would cover the bases. I already had most of the cables on hand.

                              Something to think about.

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