Anybody ever use 250mcm or 350mcm or 500mcm cable?

softdownsoftdown Posts: 1,814Solar Expert ✭✭✭✭
4/0 welding weighs about .8/lbs per foot.
250 mcm weighs about 1 lb per foot. 
350 mcm weighs about 1.4 lbs per foot. Getting close to double the weight of 4/0.
500 mcm is pretty heavy......about 2 lbs per foot.
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries

Comments

  • softdownsoftdown Posts: 1,814Solar Expert ✭✭✭✭
    I would *think* that one might be able to use two 4/0s rather than...say....350 mcm. 350 mcm is rare. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • VicVic Posts: 2,878Solar Expert ✭✭✭✭

    "Anybody ever use 250mcm or 350mcm or 500mcm cable?"

    YES!!

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • VicVic Posts: 2,878Solar Expert ✭✭✭✭
    softdown said:
    I would *think* that one might be able to use two 4/0s rather than...say....350 mcm. 350 mcm is rare. 


    The rarity of cables larger than 4/0  depends mostly on the application.

    As has been noted here,   in the past:

    Using parallel conductors that are relatively large is permitted in the NEC.
    You will notice,  when looking at Ampacity tables,   that large parallel conductors will have a greater Amapcity per pound of Copper than does the same weight of copper in a single large cable,   probably due to a larger surface area for the parallel conductors (and therefore greater ability to lose heat resulting from voltage drop due to cable resistance*current flow).

    FWIW,   Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • BB.BB. Posts: 27,434Super Moderators admin
    One big "but" about using parallel cables for handling large currents...

    If you have one connection/cable fail, then the rest of the current flows in the remaining conductors.

    And another caveat that I have experienced multiple times in high end test equipment...

    Many times, the test equipment sent (for example) +5 volts on 4-6 parallel wires (and another set for ground/return current). plus other signal cables using one large 24 conductor (for example) mating pairs of connectors.

    What I saw happen was not a somewhat higher resistance current path (say a connector pin+socket connection) that failed.... But the "perfect" pin+socket+crimps+wiring run that had the lowest resistance... The lowest current path would take the most current (I=V/R) and would heat up the most (P=I*2R). Notice that heating goes with the square of the current... And I would pop open a piece of test gear and I would see the connectors "unzipping" from overheating pin+socket connection. First one at the end, then it got hot and caused the next one to fail, which got the next pin+socket hot then in failed... Until the last cables (good connections) had to fail because they were too small to carry the whole current by themselves.

    What should have been done? First, the loads should not have been paralleled, but divided into sections (each less than the rated capacity of the cable+connector). Sometimes that cannot be done--Next, would have suggested longer wire run/smaller diameter cable--You want the resistance of the cable to be the "major" ballasting factor (i.e., if the connector went a little bit low resistance than the cable, it would not matter since the resistance of the cable is >> than connector resistance, or lack of resistance).

    And/or more parallel connections... I used 1/1 = rated current for one cable. For two parallel cables, I used 1/1 + 1/2 = 1.5x single conductor rated current. For three, 1/1+1/2+1/3 and etc. for more parallel connections. I never did have any failures in my designs (that I know of from following that rule--And as you see, 1/N gets very small for lots of parallel paths, and why I suggest more than 3 parallel battery strings is not recommended by me--if at all avoidable).

    Using heavier/higher rated contacts+cables is obviously another answer--But not always possible (costs, space, dealing with >0.5" diameter copper cable, etc.).

    Remember that many times we are paralleling cable to lower voltage drop--And a single cable is "capable" of carrying the current without failure--But would have "excessive" voltage drop--Another issue.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Posts: 1,750Registered Users ✭✭✭✭
    Running parallel conductors is often done for ease of pulling through conduit,  pulling 500 mcm through 90° is tough, one 50' pull I did had 4 × 500 mcm conductors feeding a distribution in a 6 inch conduit, there were 3 × 90's, it took a chain hoist to pull and 4 men to feed with lots of lube, it was like pulling rebar, in retrospect it would have been easier pulling parallel 250 mcm. 

    Where parallel runs are used, it's good practice to check the terminals periodically, in industrial installations thermal imaging is used to check for hot spots as part of regular maintenance. In the solar world it is also good to check all terminals periodically, in leu of a thermal camera, a milli volt meter can be used to check for volt drop. Doing this I've noticed that occasionally a screw terminal needs to be re torqued, especially after the initial installation, this is most important when using aluminum. Some may be under the impression that because it's low voltage there is less potential for things to go wrong, but remember a welder uses ~24V to melt and fuse steel.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • Ethan BrushEthan Brush Posts: 231Solar Expert ✭✭
    softdown said:
    4/0 welding weighs about .8/lbs per foot.
    250 mcm weighs about 1 lb per foot. 
    350 mcm weighs about 1.4 lbs per foot. Getting close to double the weight of 4/0.
    500 mcm is pretty heavy......about 2 lbs per foot.

    As an electrician I use those sizes all the time.  Mostly I use aluminum though as it is lighter and 1/5 the cost.  The largest I have used is 750.   The ampacity really starts to tank when you get above 250-350 size so above that you start thinking parallel. 
  • softdownsoftdown Posts: 1,814Solar Expert ✭✭✭✭
    softdown said:
    4/0 welding weighs about .8/lbs per foot.
    250 mcm weighs about 1 lb per foot. 
    350 mcm weighs about 1.4 lbs per foot. Getting close to double the weight of 4/0.
    500 mcm is pretty heavy......about 2 lbs per foot.

    As an electrician I use those sizes all the time.  Mostly I use aluminum though as it is lighter and 1/5 the cost.  The largest I have used is 750.   The ampacity really starts to tank when you get above 250-350 size so above that you start thinking parallel. 
    Al is poorly regarded in solar applications. I keep wondering what to do with about 500' of 4/0 Al.

    250 Al  should be pretty close to the capacity of 4/0 Cu. The grid is carried on Al for numerous reasons. I would also suspect a Cu grid would sag horribly under heaviest load. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • mike95490mike95490 Posts: 7,647Solar Expert ✭✭✭✭
    softdown said:
    Al is poorly regarded in solar applications. ......
    Which makes no sense at all, because proper terminations are "proper".   It could be conduit fill factor and needing copper for that, but the cable cares not about AC or DC, only if it's prepped/treated and terminated properly.
      I've got a thousand feet of #6 aluminum, for the cost and ease of pulling 3 cables uphill in 1.5" conduit (but it is an AC cable hooked to my inverter)
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Dave AngeliniDave Angelini Posts: 3,693Solar Expert ✭✭✭✭
    Pulling cables uphill Mike?  Downhill is much easier :)
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • mike95490mike95490 Posts: 7,647Solar Expert ✭✭✭✭
    I know that, and knew it then, but the layout and topography wasn't well suited for the easy way.  When is it ever ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Dave AngeliniDave Angelini Posts: 3,693Solar Expert ✭✭✭✭
    I do not do things the hard way anymore. Getting too old/wise for that. Surgeons charge and promise too much also...
    Are you done with your rehab?  My torn meniscus took 7 months but it is a success. 
    Rain is coming!!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • mike95490mike95490 Posts: 7,647Solar Expert ✭✭✭✭
    Shoulder rehab is 12+ months. Really complicated joint, hips and knees are easy.  But I'm pretty much on schedule
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • SaggysSaggys Posts: 43Solar Expert ✭✭
    Yes, as an electrician we use this for large feeders. 750's rarely, usually use parallel cables as much easier to handle and terminate.
Sign In or Register to comment.