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1000' undergrund

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    #16
    Originally posted by Fulthrotl View Post
    assuming you have 240 single phase at utility demarcation point, you could use a pair of single phase xfmr's
    at 480 volts to bump it up and back down. 100 amps at 480 for 1,000' comes to 2.19% loss on 350 mcm AL,
    so if you were to run direct burial cable in aluminum, you are looking at $1.65 / ft or about $3,500.
    you'll also need a ground. #6 aluminum is what is needed for a 100 amp circuit, but the long length may
    reuqire upsizing that. time to ask an engineer on this one. i've seen engineers specify a ground larger than
    the feeders.

    so you are in prolly about $6k, not counting labor and trenching, and profit. if you are running conduit, i'd
    not go smaller than 3" for that length of run... and i'd blow air thru it pretty often, and make sure to keep
    crud out of the pipe. all you need is a 1k run you can't blow string thru....
    250.122(B) requires the EGC to be proportionally increased in size if the ungrounded conductors are increased from the minimum size that provides sufficient ampacity, so we are looking at needing to increase the EGC by the same proportion that we increased the ungrounded - from a minimum needed 1AWG to a 350kcmil. I come up with needing at least a 2/0 AWG aluminum EGC for that application.

    Originally posted by JDB3 View Post
    A contractor that I know wired a golf course. The largest cable that he used was #10 copper. He used step "up" & step "down" transformers. He had figured it all sort of ways, & this was the most economical.
    total VA of load, number of phases along with how much you step up the voltage are major determining factors in what size conductor is needed. Length of runs factors in as well, but am assuming you are going to have some significant distances on a golf course. Golf courses I have been around in this area simply don't have much for power away from the clubhouse area - or if they do they may have POCO supply a separate service in the area where they do have other structures with power.

    If your friend was using 600 volts as the high voltage - he was limited to 18kVA single phase, or 31.176kVA three phase before even considering voltage drop impact. Those are some pretty significant load values for on a golf course - other then possibly for irrigation pumps/wells, so it still comes down to how much load and how much impact does distance have on voltage.
    I live for today, I'm just a day behind.

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      #17
      Here is an option that makes very efficient use of material.
      Attached Files

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        #18
        Originally posted by texie View Post
        Here is an option that makes very efficient use of material.
        Care to submit the source of that drawing. I am not yet going to totally shoot it down, but I have been back and forth between few code sections trying to verify whether it is a code compliant install or not, but am still leaning towards you needing a separate equipment grounding conductor between the first SDS and the second structure.

        One thing that makes this a little unusual and the reason it is more complicated then usual is the secondary is only two wire secondary. No secondary overcurrent protection is needed, the primary side overcurrent device is allowed to be the feeder or even a branch circuit overcurrent protection device in this situation.

        But your grounded conductor in this case is not just a bonding jumper it is also a circuit conductor and carries same current as the ungrounded conductor therefore it's minimum size is not according to 250.102(C) but rather to general current carrying conductor sizing rules in 310 - it will have same minimum size as the ungrounded conductor because it is carrying the same current.

        I could see 250.32(B) exceptions allowing this - but only where already existing and was once allowed to be done that way.

        I don't see the conductor between buildings/structures as being a supply side bonding jumper if it is also carrying the normal operating current of the circuit either.

        I'm all for more input on this for or against doing it like shown in that drawing. I don't give it a final approval or rejection at this point, but am currently leaning toward rejection.
        I live for today, I'm just a day behind.

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          #19
          Originally posted by MBLES View Post
          i need to get 200amp/240 service from the utility easement 1000' away. the land owner dont want utility poles on land. i fgure i can run parallel with 480 with XFMR. thats one problem,the other is once i get it to XFMR now i gotta terminate these large wires inside...This is a crazy request but if that what the customer wants....... Any Ideas?
          Bringing the HV POCO primary to the house is obviously the way to go if $$ is no object. But of course it is an object and the biggest one, so why not start with getting their price? Underground is implied here since the owner doesn't want poles, but get prices for both OH and UG just to see. Yes it will probably be in the five figure range, but there's an allowance based on the size of the house, so get their proposals first. I know from experience that a fair amount of judgment (and guesswork) goes into the POCO decision models. You might have one guy look at it on Monday and figure $20,000, while another guy comes out on a Wednesday and prices it at $12,000. Just sayin'.

          I think the step-up-and-then-step-down idea is more trouble than it's worth. If we're talking about an 1100' run and we step up to 480, that's the same as a 550' run at 240 from an IR drop perspective. And 550' is too long for a service. Yes it can be made to "work" with big wire, but it's just a poor idea. And that 550' is not including the resistance of the two transformers. Not a huge number, but it's not zero either and there are two of them, adding to the circuit resistance.

          Get the power company out to the site. You need their price to make your best decision and who knows, it may be less than you think.

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            #20
            Originally posted by Iron_Ben View Post
            Yes it can be made to "work" with big wire, but it's just a poor idea.
            Iron, I think that perspective is based on your position, experience, the tools, labor procedures and relaxed requirements opposed to the NEC etc. available to a power company designer.

            On the other hand those of us who do not work with over 600 volts find big wire a fine option many times.

            I still maintain that for 1,000 feet the cost to the customer would be higher to run medium voltage to the home unless the power company is willing to pay for or provide much of the work.

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