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Community and Q&A

Reusing Electrical Cables

Jeff Cooper | Posted in Mechanicals on

I’m building on a site that had a manufactured home some 20 years ago.  The pedestal for the electrical service is still there and powering my tools and the well pump.   Also left in place are the three main cables that used to power the manufactured home, which was farther from the pedestal than the house I’m building.  In the attached photos, you can see the big cables exiting the pedestal through a conduit that’s covered by a rusty steel box on the outside.  My plan is to pull the ends of the cables out of the pedestal so that they extend out of the top of the conduit on the outside and then try to pull the whole cables out of the conduit so that I can use them to power the new house and save a lot of money and materials.   I know I’ll need an antioxidant compound to join the aluminum to my copper service panel inside the house.  The other end of the conduit is buried somewhere that I haven’t found.  Would it be better to try to pull all three cables at once, which is my inclination, or one at a time, and do you have any other suggestions?

If the buried ends of the cables are too bent or attached to something, they may not pull through, in which case I’ll have to find them.  They’re probably around two feet deep.  My understanding is that even the better metal detectors can’t find anything that deep.  Is there another way to find the ends without digging a lot of holes and hoping to hit the right spot?

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Replies

  1. Expert Member
    DCContrarian | | #1

    To your second question, I've had good luck with this underground wire locator:
    https://www.amazon.com/gp/product/B00F5WA6QQ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

    It's $50. It definitely can find a wire down 24".

    The thing you might run into with re-using the wire is that the codes change. The type of wire may no longer be legal where you are. Or the markings may be illegible.

  2. Jeff Cooper | | #2

    Thank you, DCC. It's good to know about that device. The cables are marked as 6/0 AWG aluminum, which should be fine, especially running through new conduit, but I'll double-check.

  3. Expert Member
    DCContrarian | | #3

    It's the insulation that changes. Not really my area of expertise, but the temperature ratings and use classification -- underground, direct burial, etc. -- that have changed over time.

  4. Patrick OSullivan | | #4

    What length cable are we talking about? Aluminum is pretty cheap, and it would have to be pretty darn long for me to think it worth trying to reclaim.

    Also, I've never seen cabled marked "6/0 AWG". After 4/0 AWG, the NEC uses MCM or Kcmil units.

    For the exclusive feeder to a single family dwelling, NEC 310.15(B)(7)(1) and (2) and table 310.15(B)(16) would allow 4/0 AWG aluminum for a 200 amp feeder. However, the presence of this panel leads me to think that that feeder would not constitute all the loads, and therefore you would need bigger than 4/0 AWG for 200 amps.

    Side note: where is the neutral for what's feeding this panel? I would expect it to be terminated on the same bar as the large aluminum neutral on the bottom, but I don't...

    1. Expert Member
      Zephyr7 | | #6

      >"However, the presence of this panel leads me to think that that feeder would not constitute all the loads, and therefore you would need bigger than 4/0 AWG for 200 amps."

      The pedestal is usually the supply end, so that aluminum cable is what would be going to the house. In this case, that cable becomes the feeder to the dwelling, and 4/0 is OK for 200A service. Typical mobile home feeder cable these days is 4 wires, 3 x 4/0 (hot/hot/neutral), and a #4 or sometimes #2 ground. The neutral wire is black with a yellow stripe, the two hots are typically just solid black, and the ground is green. You can actually buy this stuff in most of the box stores, it's sold by the foot.

      Bill

      1. Patrick OSullivan | | #8

        The problem is that there are breakers in that panel serving loads. The NEC allows the downsizing to 4/0 AWG aluminum for the feeder if "the feeder conductors supplying the entire load associated with a one-family dwelling". There's likely room for interpretation here. He mentions a well pump being fed off this panel. One could reasonably argue the well pump is a load for that dwelling, and therefore the feeder to the actual house does not supply the ENTIRE load associated with it.

        Side note: I find this part of the code to be asinine, because peeling off a load ahead of this 'main' feeder results in less actual load on it, but the code is what the code is.

        1. Expert Member
          Zephyr7 | | #10

          I would argue that the run between the pedestal and the house is the feeder to the house, and the pedestal is a seperate service. This would be similar to a farm with different buildings fed off of the same yard pole where the meter would be. I wouldn't count anything fed from that panel as being fed from the house.

          I do agree there are some goofy things in the code book though. I'll cut them some slack though, since they're trying to cover anything and everything that could possibly be done, and there's always going to be some oddities that no one thought of.

          Bill

          1. Patrick OSullivan | | #11

            > I would argue that the run between the pedestal and the house is the feeder to the house, and the pedestal is a seperate service. This would be similar to a farm with different buildings fed off of the same yard pole where the meter would be. I wouldn't count anything fed from that panel as being fed from the house.

            That certainly sounds reasonable. This sort of thing isn't customary near me so I don't have familiarity with those farm setups nor a pedestal situation like this. Hopefully inspectors who deal with this regularly also take a reasonable interpretation of the code!

  5. Expert Member
    Zephyr7 | | #5

    There is no such thing as "6/0" aluminum. Above 4/0, the sizes are given in thousands of circular mills. Next up from 4/0 is 250MCM, then 300MCM, 350MCM, etc. 4/0 is about 232 MCM if I remember correctly. 4/0 aluminum is good for 200A.

    I have actually used the little locator DC mentions. It does work, but is very frustrating if you're used to using the the $1,000+ commercial locators that utility crews work with (which is what I usually have available). My guess is this little locator will probably work for you. You need to be sure to hold the probe very carefully and scan with the probe vertical, and move a lot, listening carefully for changes in signal.

    You have one issue here: you have a main breaker in that pedestal. That means you need a four wire feed from there to your main panel in your new house. The reason for this is that the ground/neutral bond (connection) has to be at the main disconnect per code. The main panel in your house will then have seperate ground and neutral busbars. If you only have three wires right now, you'll need to add a fourth -- and that fourth wire can be sized smaller since it's just a ground. A quick check of the codebook next to me says you're good with a #4 aluminum ground wire for a 200A service.

    Ideally you want to cut off the old ends to get to clean metal, then work the no-ox paste in between the strands prior to terminating. Ideally you'd use a compression lug with pre-loaded no-ox on your new main panel -- those are the safest way to terminate aluminum wire.

    BTW, DC -- you are correct about the insulation. Aluminum wire used for this application is usually XHHW, which is rated for direct burial or use in conduit, and 90*C (although the lugs on the breakers limit you to 75*C).

    Bill

    1. Patrick OSullivan | | #7

      As you can see, I had a similar thought on the 6/0, but evidently this is a notation used at some point. At least one reference here: https://bulkwire.com/help/wire-gauge-awg-reference-table

      6/0 AWG ~= 336 MCM.

    2. Jeff Cooper | | #13

      Thank you for all of these practical tips, Bill.

    3. Trevor Lambert | | #23

      Canadian electrical code allows for an additional ground to be buried at the panel in a case like this. Is that really not allowed by the NEC?

  6. Expert Member
    Zephyr7 | | #9

    British system. Pretty sure it's never been used here though, at least I've never seen it. My guess is the "6/0" is a smeared number that got messed up in pulling and used to be something else.

    Bill

    1. Charlie Sullivan | | #12

      In that first picture, there's what looks like a (smudge)/0 AWG. I bet that wiping some of the mud off would lead to finding a clear marking. A pair of calipers on the twisted bundle would also give a good idea. My guess is that it's actually 3/0, which could look a lot like a 6.

    2. Trevor Lambert | | #24

      If the bulkwire link is to be believed, there is/was an AWG 6/0. American Wire Gauge, definitely not a British unit.

  7. Jeff Cooper | | #14

    Thank you all for your inputs. Attached is a close-up of the markings on the big wire. I flipped it vertically so that it's easier to read.

    1. Expert Member
      DCContrarian | | #15

      The smudged letter doesn't look the same as the "6" in "600V." I'd buy that it's a 3.

      1. Patrick OSullivan | | #16

        In which case, depending on distance and desired breaker size in the house, may be insufficient to reuse.

    2. Expert Member
      Zephyr7 | | #18

      I agree that looks like it's probably 3/0. Code allows 3/0 aluminum up to 175A for a residential feeder. I would probably breaker it at 150A, which would mean a new breaker. The cost of the breaker will probably cancel out the savings over using new wire, so you're probably better off pulling new wire in unless it's a really long run, or the new stuff won't fit in the existing conduit. You can get the 4 wire "mobile home feeder" cable that I described earlier from the box stores for reasonable prices. The version with three 4/0 and a #4 ground is good for 200A in your application.

      BTW, replacing the cable also eliminates any risk of hidden damage somewhere along the line that you can't see. If this place had a demolition crew come through, it's entirely possible that the old cable may have been damaged.

      Bill

  8. Walter Ahlgrim | | #17

    It seems likely you will need a 4 wire to comply with modern codes that will require separate neutral and ground wires when powering a sub panel.

    If the wire was connected to the meter you may not own the wire. Some utility provides the wire until the first disconnect.

    Did you say how long you think the wire may be?

    Walta

  9. Jeff Cooper | | #19

    Thanks again for the inputs. The two 6 numerals do look a little different, so what I thought was a 6/0 might be a 3/0 with a funny looking 3. I'll get back in there and see for sure. The 4/0 4/0 4/0 2/0 cable suitable for direct burial and the 200 amps I need is out of stock at Lowes and unavailable by the foot at HD, but I can get it for around $3.50/ft. plus shipping if needed.

    1. Expert Member
      Zephyr7 | | #20

      You can also run individual conductors if needed, three seperate 4/0 conductors and a smaller ground (at least #4). If they have the individual conductors in stock, that's another option for you.

      Bill

      1. Jeff Cooper | | #21

        Thank you, Bill. HD does have the 4/0 suitable for direct burial in stock for $1.20/ft.

        1. Expert Member
          Zephyr7 | | #22

          Pick up some of the GOOD colored electrical tape ("phase tape" in the trades) while you're there. The "good" stuff is the 3M stuff in the plastic boxes with one roll per box. It's close to $3/roll, but it's worth it. You want white (to tag the neutral), and green (to tag the ground, unless you can get green wire). You can use red to tag the second "hot", but you don't really have to -- you can just leave both hots black since there is no difference between them in terms of phasing.

          Bill

  10. Jeff Cooper | | #25

    I got back into the pedestal and found another marking. It's 3/0 with a funny looking 3. Thank you for making me question my initial reading.

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