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Thread: welding cable -vs- thhn/thwn

  1. #1
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    welding cable -vs- thhn/thwn

    1/0 flex-a-prene -50C to +105C heavy duty welding cable
    -vs-
    1/0 THWN/THHN 90C

    75' feeder to 225A 3ph panel

    1/0 welding cable (according to manufacture) is good for 250A
    1/0 THWN/THHN (according to Table 310.16) is good for 170 A
    1/0 THWN/THHN would require parallel, welding cable would not.
    Welding cable is much easier to manipulate than thwn/thhn, esp
    with the larger gauges.

    I guess my question is, is it a prohibited procedure to utilize welding cable in lieu of THWN/THHN as a feeder?

  2. #2
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    A problem may occur with the ratings of the terminations, or how the cable will be installed; not necessarily an issue with the cable itself.
    "Just because you're paranoid, doesn't mean they're not out to get you"

  3. #3
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    The first issue is you must use a conductor type that is listed in 300.13 if you want to install it in a raceway or a flexible cable type that is listed in 400.4. However flexible cables listed in 400.4 are very limited when it comes to installing them in raceways.

    Next comes ampacity.

    The manufacturer can rate it any ampacity they see fit, we have to ignore that rating and use the NECs ratings which will likely result in the 75 C column of table 310.16 or 150 amps for 1/0.

    While we are at it, yes, table 310.16 shows 1/0 THHN as 170 amp rated in the 90 C column however none of your equipment terminations will be rated higher than 75 C so 1/0 THHN will be effectively good for only 150 amps.

    So....

    1/0 THWN/THHN 90C allowable ampacity is 150 amps and will need over current protection at 150 amps.

    and

    1/0 flex-a-prene -50C to +105C heavy duty welding cable if it is listed in 310.13 also has an allowable ampacity of 150 amps and will need over current protection at 150 amps.

    There is no good reason to use welding cable for this, it will pull hard in the raceway and the termination on your equipment are not designed for the fine stranding which means you will have to use a compression tool and connector.

    I install 225 amp panels quite often and at a minimum we use 4/0 copper with a 75 C rating of 230 amps this allows the use of 225 amp overcurrent protection

    3/0 copper is rated 190 and the largest allowable over current protection will be 200 amps.

    Bottom line is 1/0 of any type does not come close to providing 225 amps.

  4. #4
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    Bob did you mean that 3/0 copper was rated at 225 amps, with a usable ampacity at 75 degrees C of 200 amps.
    Rob

    Chief Moderator

    All responses based on the 2011 NEC unless otherwise noted

  5. #5
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    Quote Originally Posted by infinity
    Bob did you mean that 3/0 copper was rated at 225 amps, with a usable ampacity at 75 degrees C of 200 amps.
    No, that was not really what I meant but I did goof up in saying 3/0 was rated 190.

    What I was trying to get across was that if you want to use a 225 amp OCPD even 3/0 CU is to small.

    Its 4/0 copper or 250 AL minimum for a 225 amp breaker.

  6. #6
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    Quote Originally Posted by iwire
    No, that was not really what I meant but I did goof up in saying 3/0 was rated 190.

    What I was trying to get across was that if you want to use a 225 amp OCPD even 3/0 CU is to small.

    Its 4/0 copper or 250 AL minimum for a 225 amp breaker.
    I figured that. A standard for us is a 225 amp panel with #4/0 Cu feeders also. A 200 amp panel would get #3/0 Cu feeders.
    Rob

    Chief Moderator

    All responses based on the 2011 NEC unless otherwise noted

  7. #7
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    There is welding cable that is dual listed as RHH and can be used for electrical systems, but you have to use the NEC ampacities. The manufacturers use the 90°C rating from Table 310.17. In most cases you are limited to the 75°C rating from Table 310.16. Also as Bob pointed out, you have to use a connector that is listed for use with the fine strands in the welding cable.
    The listing of welding cable does bring up an issue to me. A few years ago, I was doing an emergency feed to an industrial building and we used welding cable as many do for this purpose. I did some reaseach on the welding cable and Type W power cable and found that the only difference was that the insulation on the Type W power cable was thinner than that on the welding cable. Every thing else from the stranding to the type of material used for the insulation was identical except the use of the welding cable with the better insulation was a code violation. Note that both the welding calbe and the Type W cable were made by the same company and I don't not know if this is true in general for all welding cable.
    Don
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  8. #8
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    Quote Originally Posted by iwire
    1/0 flex-a-prene -50C to +105C heavy duty welding cable if it is listed in 310.13 ..will likely (be limited by equip.-termination listings or) the 75 C column of table 310.16. ..There is no good reason to use welding cable for this, it will pull hard in the raceway and the termination on your equipment are not designed for the fine stranding which means you will have to use a compression tool and connector.
    Nice work on clearing up the use of these exotic cables.

    Perhaps switch-gear terminations are rare exceptions, but how much ampacity of such hi-temps in conduit is lost to ambient derating, unless fed from open-air or expensive trays? 310.16 say remove 60% at 80c ambient.

    Should also add, impedance-altering shielding is common to many of these welding cables, which makes more confusion trying to standardize line Z, with different bonding methods employed across these shields.
    Last edited by ramsy; 11-02-06 at 05:24 PM.
    Roger Ramjet NoFixNoPay

  9. #9
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    Good points!

    110.14(C)(1)
    300.14
    400.4
    Just to mention a few.
    However not be cavil, and please correct me if I miss this, but wouldnt
    310.4 (and related articles) get me the ampacity required with 1/0 THWN copper, notwithstanding 310.15(B)(2)(a), ambient corrections, and etc...?

    I questioned the welding cable because I ran into a situation where is was used "as a feeder" as prescribed by an EE and approved by the AHJ. I didnt ask why it was done this way (didnt have time to open the can of worms), I was there to do an unrelated job. I thought maybe I was missing out on something, obviously not. Didnt mean to muddy up the water with the hypothetical numbers. It was just "welding cable"???

  10. #10
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    Quote Originally Posted by vango
    wouldnt
    310.4 (and related articles) get me the ampacity required with 1/0 THWN copper, notwithstanding 310.15(B)(2)(a), ambient corrections, and etc...?
    Sure, more than enough.

    If you keep the runs in separate raceways you would have 300 amps of capacity.

    If you run them all in one raceway you will likely have an ampacity of 272 amps.

    170 * 2 * .8 = 272.

    That is certainly a large enough feeder for a 225 amp panel.

    I don't see many prices but it will surprise me if two sets of 1/0 are not a lot more money than one set of 4/0s.

    Don't forget to order the equipment with lugs for parallel feeds, a 225 amp equipment does not usually come with double barrel lugs unless specified that way.

    Good luck.

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