Stepping up/down voltage from incoming feed???

Discussion in 'Electrical Forum discussion & Blog' started by cab, Aug 24, 2007.

  1. cab

    cab New Member

    Messages:
    29
    Here is my situation: my home is being built about 2000 feet from my utility transformer which as the end of the utility's line in a very rural, ag area. The utility wanted wayyyy tooo much to extend the line, so I did a little research, some cost comparisons, and found it about 1/3 the price to lay my own cable. I bought a 350kcl cable, and laid it from the transformer to my home. The utility would not supply me with the 480V (I think) from their feed directly, which is what I wanted, so I have the standard 240V service. What I would like to do is to install a step up transformer after my meter to raise the voltage to 480V, then step it down 2000 feet away at the house to 240V. I would like to do this to get more amps at the house. Has anyone had any experience with this sort of thing?
  2. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    988
    Location:
    NY State, USA
    Typically you would run primary (~3000v-6000v) from the utility to near the house (<250') where the transformer is placed. This cable is typically the customer's responsibility.

    Are you saying the POCO will not let you do this?

    There is NO WAY secondary (240v-480v) would be enough to combat voltge drop @ 2000'.
  3. Did you buy the 350 KCM cable ?? for the entrie run ??


    I am going to be very blunt on this one for 2000' of run IMO that is very serious voltage drop for that kind of distance you will really need oversized secondary wire but what SpeedyPete mention there about the POCO will run the wires normally they will put the transformer close to the house useally 250 feet or less

    but you say you want to boost up with the transformer up to 480 volts then use the second transformer to down step back to 120/240 IMO i think not really worth it becuse you have to deal more dangerous poineal with 480 volts and also the POCO will NOT provide 480 for resdentail service it was written in the NEC code for very long time

    you may want to try talk to the POCO to bury the primary line or run the primary with the post along the way to near to your house you will have to deal with this

    if you really want to do this in your way you will have alot of serious issuse will crop up fast


    Merci , Marc
  4. cab

    cab New Member

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    29
    The utility tells me that the voltage at the primary of their transformer is 480V. The 2000 foot cable is in and I have been using it for a year. Voltage drop calculations indicate that I will have about a 8% voltage drop at 100 amp draw, giving 220 at the house. I know that this is quite a bit below the recommended drop but I will not be drawing 100 amp continuous and most appliances are fine at 110V....at more realistic amp draws, I will have a lot less drop. I am interested in using the step up/down transformers to increase the capacity and reduce the drop...

    Yes, the utility would run the line to the house, as I said, but the cost was 4X what it cost me to put in my own line....Again, the utility WILL NOT provide 480V, so what I am asking is, what are the issues with me using a step up and step down transformer to get the voltage up myself? What serious issues will crop up fast? As I said, the cable is in the ground and has been used now for over a year without any issues to date....
    Last edited: Aug 24, 2007
  5. BrianJohn

    BrianJohn DIY Senior Member

    Messages:
    151
    Location:
    VA
    I live about 2000' from the utility street connection, I paid $6,000.00 for primary distribution 15 years ago.

    If I had the time at the time I would have run the priimary myself.

    For $6,000.00 dollars you could buy 2-transformers step it up and down if they will only supply 240, If the give you 480 at the street use it if allowed by the AHJ, then step it down at the house, An other alternative would to be to use a 1 to 1 transformer with primary taps set to allow for the VD. Typical taps are in 2.5% increments. Figure an average so at no load you are not at a excessively high voltage.
  6. cab

    cab New Member

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    29
    My utility is an electric coop and they wanted about 3X your $6000 to extend their primary. That is why I bought the cable and had it trenched in.

    I am hoping someone will elaborate on what, if any, issues there may be in my plan to install a step up after the meter to take the 240 service to 480V, then step it down at the house 2000 feet away from the 480V to 240V....Any takers?

    Thanks to all who have responded....
  7. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    Where is the meter?

    If it will be before the first transformer then the bill will be based on the draw of the primary of the first transformer at 100% 24 hours a day 7 days a week. This would be one hellish bill to pay month after month.

    I think you said;
    Then why mess with something that ain’t broke?
  8. cab

    cab New Member

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    29
    Can you explain a bit why a step-up/step-down set of transformers placed after the meter would run the bill up? As I understand it, transformers don't draw current on their own...

    I am looking at this to increase my capacity should I wish to add additional loads...

    Thanks again.
  9. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    988
    Location:
    NY State, USA
    You will not "gain" much ampacity, if any at all. All you will do with your plan is lower voltage drop.
    You still only have a cable that is just so big. Stepping up and back down will not make the cable any bigger.

    Your thoughts on VD are a bit flawed as well. 120v loads have MUCH higher VD issues than 240v. Thing is your service is what you are worried about. That is 120/240v. In the eyes of VD it is more 240v than anything else. Residential services are typically pretty well balanced.

    Sorry, but I find your particular situation very hard to believe. Not that I think you are lieing, but that your POCO is SO stubborn on this issue.
    They HAVE to allow you primary for a distance like that. Even at 480v (which is NOT primary BTW) that distance is too far for anything practicable.
    Possibly the reason is if there is 480v secondary at the road, the primary is likely 13,200v. Maybe they do not allow that high of a primary voltage to be run to transformers for dwellings.
  10. cab

    cab New Member

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    29
    My understanding is that a conductor has a certain power carrying capacity. Power is volts X amps. Losses are proportional to current carried; raising the voltage drops the current at a given power level which is why the power company transmits their power at high voltages so they can use smaller (= cheaper) cable for a given power level. By doubling the voltage I halve the amps transmitted. This, as you note, allows me to decrease my VD. If I take a 5% VD as acceptable, I can draw more amps with the same VD at higher transmitted voltages, can't I?

    My electric coop gave me one option: pay them $18,000 to extend their service 2000 feet to my house. Their transformer outputs 480V at my property line. They would not give me 480V and allow me to bury my own line and extend the service to my house and step it down to 240V myself. They told me they would give me standard 240V service at my property line and that if I wanted to extend that 240V service 2000 feet to my house, I was welcome to do so. I don't have any other experience with utilities so I do not know if this is hard to believe or not, I only know that they have 480V available at my property line but they would not give me access to that- they would only provide me with 240V unless I paid them to extend their line to my house.

    As I said, I have been using this 2000 foot line for a year with a 3/4 hp well pump, table saws, band saws, lights, etc., and have not had any problems to date. I would like to do this so I can add additional loads in the future with out a larger VD...

    I am assuming that my loads will be well balanced and therefore have not made a distinction for 120V loads.
    Last edited: Aug 24, 2007
  11. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    Sorry my friend but the primary of any transformer is a load in and of itself. There is nothing there but a big coil of wire and it will have a resistance (inductance) in and of itself and with nothing on the secondary side of the transformer you will be paying for the primary load. It will not be cheep.

    You will gain nothing as to the amount of load the you can add by spending all the monies to install a 2 to 1 ratio transformer.

    You have also said something that I am having a problem with.
    I have never heard of a power company that has 480 volts in a residential area. In my area the primary side is 13,000 and a transformer steps this down to 240 to the house.

    If you had installed conductors that could handle the higher voltage then I am sure that your co-op would sit a transformer at your house but with 600 volt conductors they can’t energize these conductors with 13,000 volts.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,814
    Location:
    New England
    A transformer will draw some current regardless of the load on the secondary, after all, it is a coil of wire connecting between both sides of the powerline. When I lived in Germany, trying to use some US appliances, we used some step-down transformers. Even with nothing on the load side, they were warm. No transformer is 100% efficient, and some can be quite inefficient depending on the load or lack thereof. You're paying more for your power than you need to, every day.
  13. cab

    cab New Member

    Messages:
    29
    I understand a transformer would draw a small amount even without a load on the secondary, but I wasn't aware that it would be significant.

    I am in a rural area. All I am relaying is what the electric coop told me- that they had 480V at the secondary...

    Thanks for all the input...
  14. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    It will be quite significant.

    The only way that they can have 480 at the secondary and 240 at the same time is to have two different transformer banks.
  15. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    988
    Location:
    NY State, USA
    This is not something you will see right away. Voltage drop can be a slow killer.
  16. cab

    cab New Member

    Messages:
    29

    According to them, they have 480V. Then you pay them for a transformer that outputs 240V which they place on your property.
  17. cwhyu2

    cwhyu2 Consultant

    Messages:
    1,331
    Location:
    Cincinnati OH
    I know in our area 240 v is max for resdental .I do think 480v would help.
    But if your equipment dims the lights in your house ,v/d &distance is problem.
    If you wanted that much power I would gone 3 phase and then step down
    to single phase.
  18. BrianJohn

    BrianJohn DIY Senior Member

    Messages:
    151
    Location:
    VA
    JW>

    The exciatation current ot the tansformer will be between 1-2 amps. or 240-480 watts INSIGINFICANT, in the overall scheme oif things.

    As noted the amperage gained will also be insignificant. You could save money (as noted above) utilizing one transformer 1 to 1 with adjustable taps set to minimize the efects of the VD.
  19. cab

    cab New Member

    Messages:
    29
    0.240 kw X 8760 hrs/yr X $0.07/KW-H = $147/YR or $12.26/month

    That isn't bad, but with two transformers, this would double. If the loss is more like 480 watts, then this would quadriple. That is getting to be too much. I will look into the single transformer with multiple output taps....

    Thanks again...

    Chris
  20. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Wow! You guys are stealing electricity at $.07 per kwh??? Redo that calculation at $.18 and you are starting to eat into your beer money!

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