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Aluminum Vs Copper Feeder wire

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  • Aluminum Vs Copper Feeder wire

    Hello again everyone,

    About a month or so ago I posted about my Electrical service in a very rural part of Wisconsin. In the township Im in they dont even require inspections unless it's wiring inside your primary house.

    So, over the past few weeks Ive built a new pole building in the same place where the old pole building used to be. Im going to re-run electrical service to the new pole shed. There Is also a manufactured house on the property which is the primary residence on the land. As such, the meter can not be attached directly to the house since the house is considered a "mobile home". About 3 feet to the South of the house sits the meter on a 4x4 post and next to it about 1 foot away on another 4x4 post sits a 100amp distribution disconnect box. This is not considered a Main panel though I guess and as such there are only 3 wires going to the home, hot,hot, grounded neutral and the same for the pole building.

    Because the old 2 guage aluminum wiring going to the pole building was damaged near where it entered the old building I decided to rip out the old one inch pvc conduit that was in the ground and replace it with 1.5 inch PVC conduit going from the distribution disconnect box to the new pole building

    So after all that, my question is, there used to be Aluminum URD Triplex cable run underground in that one inch conduit going into the pole building and there is the same cable going into the mobile home. Now, I read that Aluminum URD Triplex cable is meant to feed the meter from the transformer and is not meant to enter the house. So my plan is to tear out all this cable from the distribution disconnect and replace it with either 2 guage aluminum wire with a rating of RHW-2 and USE-2 or the other option would be to replace the feeders to the home and pole building with 4 guage copper thwn-2.

    The aluminum cable would have a cost of about $175 at the local home depot while the copper cable would cost $365. So, Im wondering which one most of you guys would use. There is a 18' 2 inch ridgid metallic conduit going to the house and a 120' 1.5inch pvc conduit going to the pole shed so I dont think thickness of the wire should be a huge issue here.

    Also, i will post a picture of my distribution disconnect. As you can see, right now there is 1/0 aluminum URD Triplex wire going into the top of the breaker and the feeders going to the house and pole building connect to the bottom of the breaker along with the grounded neutral bar on the right. Apparently 2 two guage wires can be connected to the lugs on the bottom of the breaker and I can confirm that they do both fit.

    If you guys have any opinions or experiences with this Id sure like to hear it. Also if any more info is needed let me know.

    Pics of Distribution disconnect box :

  • #2
    Re: Aluminum Vs Copper Feeder wire

    Copper is IMO a better wire, but for the sake of cost, most of the wire on my place is aluminum being ran on the distribution side of things.

    first of all it will usually take a little larger size of aluminum Vs copper for the same amp carrying capacity,

    I have had aluminum wire need to be retightened after time, (the lugs in the box or connections), (one box one time 20 years later, had a neural loosen up), IN the process when I do an service work on my stuff I will usually recheck the lugs.

    I have never had any corrosion problems but I do use the recommended anti-oxidation inhibitor past.

    But when the time to buy came and the cost difference I usually chose to go for cost, If you can afford the copper go for it.
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    • #3
      Re: Aluminum Vs Copper Feeder wire

      Usually you need number 3 copper for 100amps. This according to the NationalElectricCode(NEC) and depending on the type of insulation. (It is NEC table 310-16 in my outdated NEC book from 1999) Aluminum works fine just use the anti-oxidation as BHD says.

      You can run the wire through a piece of pipe and into the panel in the mobile home.

      Price the wire at an electrical wholesaler. Around here they are usually quite a bit cheaper than HD.
      Last edited by bluecon; 07-09-2007, 06:22 PM.


      • #4
        Re: Aluminum Vs Copper Feeder wire

        Thanks for all the replies,

        My book based on the 2002 NEC table 310.16 says that THWN-2 used as Service entrance at 100amps is #4 copper or #2 aluminum.


        • #5
          Re: Aluminum Vs Copper Feeder wire

          I hope i am not too late to get in here but what you been reading on the NEC part you cant use the #4 thhn as feeder because there is big diffrence between the service entrence conductors and feeder conductors there is two seperated codes to deal with that

          because if you used the #4 for 100 amp feeder that part will not meet the code the feeder is the same as branch circuit and you have to use the 75 C degree colum to get the correct size for 100 amp which that the THHN copper [ if you are going to use it ] it must be #3 not #4 becuse the feeder the #4 is good for 75-80 amp max and #3 is good for 105 amp or you have to use #1 alum for the feeder.

          Please recheck the nec define " Feeder " and " service enterace conductor "

          if you have more question please do post it here

          Merci , Marc


          • #6
            Re: Aluminum Vs Copper Feeder wire

            So is my book that has a table which says it is based on NEC Table 310.16 refering to #4 copper thw,thwn and #2 aluminum thw,thwn for 100amp SERVICE ENTRANCE wrong?




            • #7
              Re: Aluminum Vs Copper Feeder wire

              Also, keep in mind that my setup is a mobile/manufactured house which is covered under I believe section 550 of the NEC.

              I have to have the meter on a 4x4 post not attached to the mobile home itself along with what I believe is called an external/distribution disconnect which in my case is right next to the meter outdoors. From there, there are conduits going to the mobile home about 18' long and also to the garage about 125' long and all the wire from the panels in those two buildings are run to the external disconnect. So, from the external disconnect to the main panel in each building one of my questions would be wheather that section of wire is considered feeder or service entrance. I can tell you that for the last 20 years it was setup as service entrance wiring to the main panels in each building. I believe the cable that was used is called #2 aluminum Triplex URD.

              Is this not the case today?

              Thanks a bunch!
              Last edited by Palomino; 07-10-2007, 08:04 PM.


              • #8
                Re: Aluminum Vs Copper Feeder wire

                For what my 2 cents is worth, I DO believe #4 copper when used as a feeder is allowed for 100 amp usuage and #2 aluminum is allowed for 100A feeders. As far as which to uses AL vs. CU, the Al wire will be less money but the copper wire will be smaller. If you go with aluminum be sure to use the anti oxident on all connections. SInce this is not a "branch circuit" but ratehr a feeder I do believe you can go with #4 copper or #2 aluminum. Now what you have to do regardless of wire type is to run 3 wires to your new electrical panel in the pole building. That would be HOT-HOT-NUETRAL then at the electrical panel you will go out from the nuetral bar with #4 copper to a ground rod and you would treat that electrical panel as a MAIN panel not a sub panel. Lou


                • #9
                  Re: Aluminum Vs Copper Feeder wire

                  NEC 215-2(d) (from the 1999 NEC)
                  Individual dwelling Unit or Mobile Home Conductors.
                  Feeder units for individual dwelling units or mobile homes need not be larger than service entrance conductors. Section 310-15(b)(6) shall be permitted to be used for conductor size.

                  Section 310-15(b)(6) allows #4 cu or #2 al for 100a for a list of conductor types including THHN, THWN and THWN-2 and more.

                  Does the garage fall under this rule? I don't think so.

                  Table 310-16 rates #2 aluminum THWN-2 at 100a or #4 copper THWN-2 at 95a. Aluminum THWN-2 will meet both requirements for 100a and is cheaper.

                  If you want to calculate voltage drop for 125ft run.


                  • #10
                    Re: Aluminum Vs Copper Feeder wire

                    Hey guys thanks for the responses. One place I found has a good price on #2 aluminum with a rating of both RHW-2 and USE-2. How does this cable compare to #2 aluminum THWN-2, which I have not found yet.

                    Also, Ive used that voltage drop calculator but I do have a question. Should I be using the 1 phase 240volt option for the feeder or the 1 phase 120volt option. I cant imagine pulling more then 40 amps at one time with anything Im doing anyway but if I need to go up a gauge or two to make this right I wouldnt mind doing that.
                    Last edited by Palomino; 07-11-2007, 06:33 PM.


                    • #11
                      Re: Aluminum Vs Copper Feeder wire

                      In my 1999 NEC book RHW-2 and USE-2 are rated at 100a. (from table 310-16) USE-2 is underground service entrance cable. Calculate the drop for 240v. Anything like a welder that draws high amps will be on the 240v unless you had some very unusual situation. Actually you are allowed to run a smaller neutral since very little of the current flows there if the circuit is balanced. (Don't bother with that)