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Question for Electricians: Volts, Line Loss and De-rating

Discussion in 'Off Topic' started by AudubonB, Jul 8, 2013.

  1. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    This question has zero to do with Teslas; rather, it is a situation unique to our little community. NB: This is Bush Alaska. Regulatory issues DO NOT apply! Yippee-yi-yay.If one were to offer electricity to a neighbor, and one had a run of about 750 feet, and one were to throw over 120V juice, and one had access ONLY to 6ga Cu....and no transformer....then one could expect unreasonable deterioration, correct? Like something down around the 100-105V range, or even worse. Correct?BUT...if neighbor needs only 120V, not 240V...then, in that case, what if one were to start with 240v (L1 - L2 - Neut)? At the end of the run there still would be the loss, down to the same amount as with 120V (ie, 100+100 = 200, more or less)....So...if this were the case, in this situation, would there be a way then to: (1.) combine Legs 1 & 2 (are they in synch?), and then (2.) drop the voltage from 200v (or wherever it is) to a usable 115-130V??????????? I know it's always easier to drop down in voltage than to jump up, but I fear I'm fighting a losing battle here. At any rate, I know there are those out there with far more knowledge here than I have.
     
  2. qwk

    qwk Model S P2681

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    If I understand your question correctly, and you use 6 gauge copper for a 120V run, there shouldn't be much of a voltage drop over 750 feet. I don't even think you need 6 gauge. 8 gauge would probably be fine. I have plugged the Model S in on a 100 yard run(120V which looks like 10 or 12 gauge wiring) and it charges at 120V 112-115V. The closer outlets run about 117-119V. Not much of a drop. Hope this helps.
     
  3. MichaelS

    MichaelS Member

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    It all depends on how much load the neighbor requires and the type of load.

    A quick calculation reveals that a 15 amp load at 120V with 6 gauge wire will give you about a 9% voltage drop for a constant draw such as lights.

    But if you try to run a motorized load such as a refrigerator that has a high start up current draw, the voltage drop may be so high that the motor cannot start up and may burn out.

    Is the wire 2 or 3 conductor?
     
  4. Cosmacelf

    Cosmacelf Active Member

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    I don't think you can run 240v and end up with something like 120v without a transformer. How many amps is the load? The 6 gauge might be enough depending on what you are doing.
     
  5. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    Warning: my paragraphs run together - am not sure what's happened to my postings. Let's try lots of spaces.....I have on hand three 600' strands of SOOW (I think) 6 ga Cu. One for L1, one for L2, one neutral - if I throw over there 240 volts. OR: I could tap on to a single leg, and use two of the strands for the same 120V and the third one for neutral. Would that pass the smell test?I CAN usually get my hands on 2/0 and even 4/0, if absolutely necessary. That can get a bit spendy. Neighbor definitely will be running refrigerator compressors, etc. - can't run a diner without!!!
     
  6. deonb

    deonb Active Member

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    No. Live and neutral always carry the same amount of current, barring a ground fault. If you double up on live, you need to double up on neutral as well.

    For that matter if you run L1 and L2 and split it on the other side for 110V usage only, you would also need to double up on neutral.

    You can however run one or more 220V to 110V transformers on the other side and then you wouldn't need the neutral return. However, then you create grounding issues for yourself, but those are locally solvable without needing a return.
     
  7. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    Deonb - That latter begins to sound familiar: a degraded (because of length through a less-than-ideal set of wires) 240V (220, etc) single-phase current, passed through a transformer into, ostensibly, "good" quality 120V current. Neutral would need tie back from point of use ONLY to the transformer.

    Query: are transformers good for working with cr*ppy so-called 240 volts (say, in actuality, 200 V) down to 120V exist off the shelf? In any sort of affordable range? Would I STILL have the L1 / L2 problem?
     
  8. deonb

    deonb Active Member

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    True - but keep in mind that you're creating an isolation circuit and you need to probably manually tie a ground (unless you buy a specific grounded transformer instead of an isolation transformer). Otherwise a simple wiring fault somewhere and you can end up having all your metal surfaces sit 110v above ground with nothing that faults on it.

    I'll leave the grounding question to someone more qualified than me.


    I doubt it will be that crappy. With 6 ga wire, even over a 750 foot distance, you can draw 30 amp at 240V and still end up with 220V. So that allows for a 60 amp draw at 110V (you don't need 120 if it's close enough to the equipment). That's probably enough for your needs?

    You're going to need quite a few 220V to 110V off the shelve transformers in order to supply 60 amps anyway. Running 2 neutral wires may end up being cheaper.

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    Maybe this is what you want? I just searched - making no endorsement to the specific product:

    http://www.amazon.com/VCT-AR8000-Stabilizer-Built-Transformer/dp/B0051POYCO

    You can supply 180V to 260V and it will output 110V +- 4%. 8000 W.
     
  9. drees

    drees Active Member

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    Actually, you will have no issue running 240V on a typical split-phase setup using 120V at the other end on both ends. Don't even need two neutrals. If you load up each 120V circuit the same, you'll actually end up canceling out any current on the neutral, not doubling it.

    A few decades ago, shared neutral feeders were common as it saved the cost of the redundant neutral. You'd run 4 wires (L1, L2, N, G) to a junction box, then split off L1, N, G off on one circuit and L2, N, G onto another. They stopped doing this, though as it was too easy to accidentally rewire the service panel and feed L1, L1, N, G to the junction box (or L2, L2) and then you'd end up doubling the current on the neutral under load. Not good considering that your neutral is not protected by an over-current device.

    But you definitely want a ground in there somewhere. I guess instead of running 750ft of ground back to the main service point, it will probably be a lot cheaper to just install a new ground at the the end of the 750ft - definitely violates code!
     
  10. deonb

    deonb Active Member

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    Only if you truly load up both sides exactly the same. However, if one side is an inductive load and one side is a resistive load you can have current draw 90 degrees apart.


    If you're going to violate code, why not just tie neutral to the ground rod over there? :tongue: (DON'T!)
     
  11. drees

    drees Active Member

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    Yes, but you still won't exceed the current rating of the neutral in that scenario and will still have less current on the shared neutral than if you only fully loaded up one phase.
     
  12. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    Am sorting through all this advice....I will say I didn't figure on ground as being any issue at all - an 8' copper rod at point of consumption would be expected and sufficient. Am I wrong somewhere here?Now, it appears that some of the good news is that investing in one more neutral line seems to be the most expensive of outcomes, and even that isn't bad. That is, if the lone loss #s are as satisfactory as posted, then I can indeed throw over "acceptable" 240V in order to use two 120V legs.I guess I'm also fortunate in having around enough high-quality conduit. It helps to have AT&T come through here every so often with Yet Another big project, and leaving lots of Really Nice Stuff.
     
  13. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    They haven't stopped doing this. It's very common to see MWBC (multi-wire branch circuit) to places like kitchens, where multiple appliance circuits are required. They *do* require common-trip breakers, so they simply look like 240V breakers rather than independent 120V circuits.

    As for starting at a higher voltage and absorbing the voltage drop (say starting at 240V and using whatever ends up at the other end), remember that voltage drop is due to ohm's law and that you're dissipating that power as heat throughout the conductors, throwing it away. If your voltage drop is that large, you'll want to back off your current if possible or use larger conductors.

    But you definitely want a ground in there somewhere. I guess instead of running 750ft of ground back to the main service point, it will probably be a lot cheaper to just install a new ground at the the end of the 750ft - definitely violates code![/QUOTE]

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    <sarcasm> And use speaker wire while you're at it... it's cheaper. </sarcasm>

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    Depending upon the current you need, your #6 should work ok over that distance without too much hassle.
     

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