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Any home transformer experts? Upgrading service and a bit confused

Discussion in 'Workshop and Home Improvement' started by Lil'John, Mar 17, 2017.

  1. Lil'John

    Lil'John SILVER Star

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    I'm renovating a 1978 house that currently has 100 amp service. I'm not sure what size wire is going from the transformer to my house. But the 3" conduit will support up to 320 amp wiring/service. In order to get bigger service, I will have to dig up/replace the 3" conduit.

    The house is 1900 square feet plus about 400 square foot of basement/temp shop.

    I will be getting a large shop in the future. It will get a lift and hopefully before I die I can find a reasonable price mill or lathe :)

    I'm being told the current transformer is 10kva and it is being recommended I go to 25kva.:eek:

    I will double check but I believe I'm the only one on the transformer... mountain house:hillbilly:

    So the basic question I have is: Is my electric company trying to pull a fast one on me?
     
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  2. mdsims

    mdsims

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    A 100a panel just means that's what the panel itself is rated for, not what you can get out of it.

    Don't dig up the 3". It's more than sufficient for anything you plan to do.

    If your house panel has a main breaker, see what size it is, that governs your service size. You also have at least that much wire from it back to the pole. Typically more.

    A 10kva is the smallest normal pole mount they use for homes. Good for about 40 amps at 240v. If you plan to have a shop, compressor, good sized welder and more activity there, a 25kva xfmr would be a good call, and is good for about 100amps at 240v. That would mean it's possible the wire you have is sufficient and wouldn't need to be changed. Check the size or the utility can tell you. But, you'd be surprised what you can do with 40a at 240v (80a at 120v), maybe you're just fine for a few years? They upgrading the xfmr for free?

    The next size up is 50kva, and most likely you'd need new feeder wire, same conduit. I doubt you'd ever need this size xfmr.

    Many variables, every utility is slightly different, but where I live they typically bring wire sized for 100a to every home as a minimum standard.
     
    Last edited: Mar 17, 2017
  3. Lil'John

    Lil'John SILVER Star

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    I understand most of that.

    Shop is going to start with standard 220V welder and air compressor. I will be stuffing a lift, plasma cutter, and mill as funds allow. So yes, a bit of a draw:censor:

    From what I was told, the current wire in the conduit will not get me to 200 amp. So I need new wire.

    I was told the 3" could be sufficient for 320amp wiring. There is no way to get 400amp or more.

    I was told due to the size of the parcel, there is no way for me to get a separate pull to the shop.

    Free? This is PG&E, they are going to bend me over badly and probably use a cactus... the new estimator has already doubled the old estimator's guestimate.:eek:
     
  4. mdsims

    mdsims

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    There's some disconnect here. You only need enough wire to match the rating of your main breaker, regardless of xfmr size. If they are suggesting a 25kVa xfmr, and you have a 100A MCB, then there is no need for a 200A feeder.

    If you want a true 200A service, in that case yes, they would install a 50kVa xfmr and, to get the full capacity, you'd need to upgrade your house panel and main breaker to 200A.

    Have they told you what wire is in the conduit now? How long is the run from the pole to the panel, and the panel to the future shop?

    Feel free to PM me your number, or I'll give you mine.
     
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  5. firestopper

    firestopper

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    Around here, when a home owner builds a home or upgrades service, the utility company pays/installs the feeders/drops to match upgraded panel.
    200A upgrade is common here with the owner only paying for the new service panel install.

    When I built my home back in 98, I installed a 400A panel that required the utility company to use much larger feeders. They weren't happy about having to return (delay) with larger wire but no charge was incurred on my part. I was responsible trenching and back filling the trench after inspection. They provided the shade (sand).
    3" conduit is pretty big, I used 2" conduit for 200A feeders to the shop's sub panel. Seems they want an easy pull (who wouldn't) but check local code. If you don't need larger conduit per code, a simple call to the cooperation commission can get you results.
     
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  6. LAMBCRUSHER

    LAMBCRUSHER

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    devil is in the details. total load, type of conductor and installation, and length of circuit are needed to finish the math. if the conduit is 3" that means it can house enough conductors of large enough capacity to feed your 320 amps. You should go for the larger pot(transformer), and max the wire in the conduit. 320 amps is alot of juice. the on line calc says you'll be just over 200 amps both legs at 50kva and by the math, 320 amps both legs full on would be
    k(VA){1000 watts} = 320 amps x (actual voltage)240 / 1000
    so 76,800 Volt-Amps(watts) / 1000(k) = 76.8 kVAs
    Now that's alot of welding and air conditioning happening all at the same time.
    Alot of the utilities consideration in saying you can get up to 320 amps might also be based upon your length of run. And that is going to be of a serious concern to you when you run from your service to your shop. Alot of guys don't give the voltage drops enough consideration of the types of loads you're talking about, so make sure your contractor mentions those very important factors and recommends upsizing considerably the wire to the shop. As long as you don't have to battle point of use voltage drop, 320 amps should be enough for a man (and :princess:) to be happy.
    :worms:
     
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  7. Lil'John

    Lil'John SILVER Star

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    mdsims, thank you for the offer for the call. I don't want to waste your time too much with a basic fact checking post :)

    The first guy I talked with back in September gave me a "usually this costs $x" This new guy has doubled it so I'm a bit confused.

    Here is the lot picture:
    shop_2.jpg

    For some specifics:
    Transformer to side of house is under 150 feet. The transformer is at the bottom of the picture below the 06254. The meter is on the north east corner of the house. My under 150 feet guestimate is from the house being 44' long and I used ~80 foot of conduit to pull fiber optic from same pole to the south east of the house ;)
    From NE side of the house to the shop will be about 100 feet... the location is very much in flux... but imagine from the green box or the horse corral below it.

    The house is going to have:
    • Two HVAC systems (upper floor/lower floor, gas heat)
    • Hot tub
    • Fridge and separate freezer
    • Dishwasher/trash compactor
    • Office/network closet (running two 20 amp circuits for network closet)
    • Gas stove
    • Electric clothes washer/drier
    • 50amp 220 run for welder in basement, won't be used once shop is up
    • Unknown well pump and pressure tank
    • Usual mix of indoor/outdoor lighting/electrical for 1900 square foot house
    The shop is going to have:
    • 50 amp 220 run for welder/plasma cutter
    • 50 amp 220 run for air compressor (don't have)
    • Mill, hopefully CNC (eventual)
    • car lift
    • Lots of grinders and power tools :p
    Shop is mostly going to be one man use. Size is lightly in flux: 50x50 will fit corral area, 30x70 is green box ;)
     
    Last edited: Mar 19, 2017 at 8:59 PM
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  8. LAMBCRUSHER

    LAMBCRUSHER

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    For reference, Valley Hybrids service is rated at 100 amps 3 phase 208 volt or a total of 36.25 kVA, if that helps put things in perspective.
     
  9. thatcabledude

    thatcabledude SILVER Star

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    Where I'm at that would get its own meter if you wanted it.
     
  10. 1911

    1911 chupacabra SILVER Star

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    Just FYI, the 10,000 lb. Dannmar D10/ACX lift I just installed requires a 25 amp, 220v circuit.
     
  11. Lil'John

    Lil'John SILVER Star

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    Sadly, they wouldn't do anything for me due to "small" lot size(five acre)

    That is the rating I was expecting on a lift. Fortunately, most of the items would only be used one at a time. The exception would be compressor and plasma cutter ;)
     
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  12. LAMBCRUSHER

    LAMBCRUSHER

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    that's a big motor for a lift. good thing it only runs a few minutes at a time