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The electrician just left. Need validation from smart forum people.

Discussion in 'North America' started by Al Sherman, Jan 16, 2013.

  1. Al Sherman

    Al Sherman It's about THIS car.

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    My trusted electrician just left. We have a 400 amp service with two 200amp boxes in the house with breaker protection on each of them. He is going to add another 400amp service and run it about 125 feet underground around the house and then back into the garage. I'm pretty sure he said he'd use 6 gauge wire for this run. Please correct me if I misunderstood. This would be run to another 200amp panel in the garage for the NEMA 14-50 and the HPWC with 50amp and 100amp circuit protection.
    He said that the transformer is 50Kva (does that sound right?) and is more than enough. BUT the wires from the transformer are ALREADY not enough for the house. As an example he said that the wire he was going to run underground around to the garage will carry more than the wires from the transformer right now. He said the minimum he would accept from the PoCo from the transformer for the new setup would be 750 MCM. Not sure MCM is correct but the 750 is definitely the number he said.
    He is aware that within two years we will most likely have a ModelX in the same garage charging at the same time as the MS.

    Opinions? Advice? Comments? Flasher? Knox? All you smart people please let me know what you think.
     
  2. KKlabunde

    KKlabunde Member

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    Rush-Shelby Energy is getting suspicious having multiple electric car calls back to back. I called Chris this morning and he did a double-take!

    I'm not one of the smart forum people, but another 400 amps is a lot! Isn't each Tesla in-car charger 40A? So two cars with dual chargers running is only 160? (200A protection for 80% load) And one could sit on a 50A NEMA overnight instead if you needed more headroom. Might look into running new larger transformer wires for your existing service instead of adding another 400A. Maybe cheaper...

    My transformer is only 10 KVA -- hoping for an upgrade soon.

    I use Lakers there in Batesville -- the guy named "Moose" is a really good electrician.
     
  3. Al Sherman

    Al Sherman It's about THIS car.

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    It truly IS a small world. Gary Laker is the electrician that just left. He's been doing our plumbing for over 20 years. I too spoke with Cris at Rush Shelby Coop this AM. He mentioned you! We have a pretty large house with two Geothermal units. Gary seemed pretty adamant that we needed the extra 400amp service even if we will only be using half of it at this point.
     
  4. KKlabunde

    KKlabunde Member

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    I've never had reason to question Gary or their pricing. You're in good hands...
     
  5. FlasherZ

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

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    Hi Al,

    Okay, there are a few things that make sense and a few things that don't.

    First, the 50 kVA transformer is roughly 200A sustained, so it should be sufficient unless you have one hell of a mansion or some special requirements that I don't know of. My home and shop are comfortably served by a 37.5 kVA transformer. MCM is also abbreviated kcmil, and means "thousand circular mils". It's how wires are sized beyond 4/0 AWG. 750 kcmil AL wire is rated for 385 or 435 amps on service entrance cable, depending upon type. It's a SERIOUS cable size. Just for comparison, my entire home and shop are served by 350 kcmil AL cable. Your power company is almost certainly going to balk at having to pay for a 750 kcmil cable on a 50 kVA transformer.

    The 6 AWG wire doesn't make sense, that's only used for a 50-60A circuit and you're talking much larger loads. Only the final run to the 14-50R will be 6 AWG.

    Here are the questions I'd be asking:

    1. What does he mean by "adding another 400A service"? Here, that means a second meter, a second facilities charge, and commercial/business rates on the second meter.

    2. If he does mean adding another service / meter, 400A is just way too big for a garage -- even for a combination shop/garage. You would only really need a 400A service for your garage if you insisted upon dual HPWC's and still needed headroom for simultaneous operation of a welder and several other appliances/machines -- at that point you'd probably be looking at 3-phase power and machines anyway. If you were going the separate service route, I'd install a 200A meter and service, which will comfortably handle 2 HPWC's + have headroom for plenty of non-continuous load.

    3. Instead of going the new service route, why can't the existing 400A service handle it? Why wouldn't a garage subpanel off one of the 2 200A panels work? If there's no individual capacity, could some other circuits be shifted between panels to make room?

    Finally, if you are willing to divulge some information (you can do it privately if you wish), what's the square footage of your house? What outbuildings and square footage do they have? Do you have all-electric appliances or gas? How is your home heated? How many A/C units do you have (and the sizes if you know them)? In each of your 200A panels, can you give me a list of any circuits that have a breaker size of 30A or greater?
     
  6. KKlabunde

    KKlabunde Member

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    Al, I think you just found your "Smart Forum People"... This community is incredible!
     
  7. FlasherZ

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

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    Ah, here's some of the information. Geothermal units can be pretty beefy. 2 of them would probably represent somewhere between 80 and 100 A continuous load, plus an HPWC (80A), plus a 14-50 (40A). If you insisted upon both HPWC and the 14-50R charging a model S and X at the same time, you could be bumping up against loading calculation limits for your existing service (especially if you have electric kitchen appliances too).

    Here's something to consider -- where I am, you would have 2 different services already anyway -- the geothermal would be installed on a second meter with its own service conductors, because of the special rates they offer for it. The remainder of the house would likely be on a 200A or 400A service.

    Even if you needed a new service for the garage, I still think 200A is likely sufficient. The 125' run of 3x 750 kcmil AL cables is going to be roughly $1,500 wholesale in wire costs alone...
     
  8. sp4rk

    sp4rk Banned

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    I am not one of the electricians onsite (even though it looks like it by my screen name!) ... but ... if you end up with an S and an X, do you really need to HPWC them both?
    I would have an HPWC in one garage, NEMA 14-50 in the other. Then decide if one needs charging that fast. Do you expect to drive both that far each day?
    This would bring your energy down to, tops, 150A.
    And some think (in our Illinois group) that the HPWC is not even necessary ... I am getting the dual charger, but not the HPWC, not at first at least.
    Still might as well install a 200A sub panel, but 400???
     
  9. Al Sherman

    Al Sherman It's about THIS car.

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    Thanks for the help guys. Flas: I will ask all of your questions.I may have messed up. I think the 750 cable was what he wanted from the transformer to the house and the 6 was for the 125ft run from the new 200amp subpanel (from the new 400amp service) around the yard to the garage. He said the 200 amp subpanel has to be within 10 feet of the 400amp service and the garage is on the other side of the house.
    The house is probably 5000 square feet. Guess. It was a one bedroom cabin when we got married and we went a little crazy with an addition.I digress. There is also another 3 car garage with an 80amp breaker. I'll add the rest up but for now there are two Geothermal heat pumps each on separate panels with a 60amp and a 90 amp breaker.One for the heat pump and one for the auxilliary portion being the 90amp. My wife has a kiln on a 100 amp breaker. There's also a sauna. Not sure of the breaker size. The heat in the attached (Tesla) garage is on a 50amp breaker. The entire operation is electric Including an extra stove, and 2 refrigerator/freezers and a large freezer.
    I apologize for confusing you but good catch on the wire thing. I don't know where I got 6gauge or anything like that. What he said was 250MCM for the run around the house to the Tesla garage. My bad. As far as the extra 400 amp vs 200 amp service he said if I DO want to charge 2 cars on HPWC's the extra 400amp service is the least he would be involved in. He said there would still only be 1 meter and the PoCo should not balk at putting in the 750MCM from the transformer if we are putting in another 400amp service.
    I guess the bottom line is: even if I am doing/spending more than I have to, does it all sound safe as I've described. I am dummer than dirt on electrics and I just want to be able to sleep at night while the S and the X charge on HPWC's and my wife runs the kiln with both Geothermal heat pumps running at full bore with the aux heat on intermittently.:smile:
     
  10. FlasherZ

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

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    #10 FlasherZ, Jan 16, 2013
    Last edited: Jan 16, 2013
    You have a LOT of continuous loads there. 120A continuous load for the geothermal (based on 150A breaker sized), 80A continuous for the kiln (100A). The sauna is also likely to be continuous load (probably 30-40A continuous). Then an HPWC (80A) plus a 14-50R hosting a 40A continuous EVSE... 120A+80A+40A+80A+40A... 360A. You've overrun a 400A service (320A continuous) even without lighting and other non-continuous loads, so yes, you'll need a new service.

    I think I know where he might be going, but I still don't have the full picture. Here's where my assumptions currently stand: 750 MCM (I usually use kcmil but so we don't get confused :) from the transformer to the meter base. If he says a single meter will be sufficient, then it'll likely have to be a 600A or 800A CT meter (which is a different type of metering than what you're normally used to) with a new meter base. But here's where I get confused. I can't figure out why he's calling for a new "400A service" unless he's talking about just a single disconnect outside, then a 200A subpanel inside your home (that "maximum length" requirement), which then feeds a subpanel in your garage over a long run of cable.

    Basically, a "service" is typically the unfused connection to the base of the meter. I can understand him needing another service panel after adding up your loads, but because you already have a 400A service, I suspect that adding another 400A service would require the power company to do some hefty changes in metering. Unless he is using the term differently than me, or it's being translated incorrectly.

    As to your bottom line, it sounds like he knows what he's doing. It sounds like overkill to me (I would pass on 2x HPWC, leaving one for the times you need it, and the 14-50 for standard overnight), but perhaps he's looking at the loads you already have and is thinking your consumption spree will continue. :) Good luck!
     
  11. rolosrevenge

    rolosrevenge Dr. EVS

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    It honestly sounds to me like you're going to blow up the transformer. Pulling 500 A will be 60 kW and that's overloading it even if you are the only customer served by the transformer, which is often not the case. Does the utility know you're doing this?
     
  12. FlasherZ

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

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    Actually, 500A would be 120 kW (240V, 1 ph service).

    These transformers can be oversubscribed and typically are sufficient at even 200% of rated load. My home formerly had a 15 kVA transformer and the PoCo registered the load at 197% several times during peak loading in the heat of summer, without so much as a hint of getting hot. No oil smell or burn-off, no smoke from the vents. That math in hand, a 50 kVA transformer would be sufficient based upon the information presented.

    For the size of home that is mentioned, it's likely it's a dedicated transformer.
     
  13. bluetinc

    bluetinc Member

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    Quick note, 500A is 120kW (240*500A)

    Peter

     
  14. Al Sherman

    Al Sherman It's about THIS car.

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    The utility engineer just left. He feels that the 50Kva is OK. But, now you have me worried again. What would you do to be sure? He DID say that the max both geothermals would draw together is less than 100amps.
     
  15. VolkerP

    VolkerP EU Model S P-37

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    I think that you will waste a lot of $ for a "worst case" electric demand case with two HPC and an additional 400A service. You will have charged your X and S for sure over one night with 40A each.

    Consider a smart home grid: Include a digital meter in your panel that meters the house load and routes the power signal to your EVSEs. They adapt the available current to charge the X and S.

    E.g. 400 A service, safe to pull 320A continuously. Geothermal and kiln demand adds up to 230A. The meter advertises 90A available, the EVSE scale back to 45A each. Whenever one of the loads pauses, the EVSEs can rack up charging current.
    The HPWC is of no use here, you'd have to look into openEVSE instead.
     
  16. rolosrevenge

    rolosrevenge Dr. EVS

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    If the utility says it's fine I wouldn't worry about it. If the transformer blows, it's not your fault since you warned them. I previously was taking the conservative approach (250 A on each phase => 500 A *120 V). While it's true that the transformers can overload up to 200% for short times without blowing, overloading them for hours at a time is never a good thing and will lead to increased loss of life and earlier failure.
     
  17. KKlabunde

    KKlabunde Member

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    I can attest to that! We have a 10 KVA transformer running 48A continuous load geothermal, additional 120A backup heat, two electric hot water heaters, 50A oven, 30A dryer, 2 refrigerators and one large freezer, plus my 100A barn with air compressors, etc., and two other 20A barns. Granted, I've never tried to turn it all on at once. But some of those bigger loads run simultaneously on a regular basis.
     
  18. FlasherZ

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

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    That's not correct, because it's not two-phase power. It's a center-tapped single-phase. As a result, the neutral only carries the imbalance between the two opposing legs. This is why you have to calculate it as the total current across the entire winding of the transformer times the entire winding voltage, and you don't use 120V in the calculation, unless you're talking only in the context of a single 120V circuit.

    For what it's worth, it's not the OP's choice anyway. All he can do is inform his PoCo of his various continuous loads and patterns, hand over a copy of his load calculations, and let them make the decisions about how to provide the service to him. A friend of mine just put in a new 600 amp panel into his new home, from which he runs a small "data center" like environment. The PoCo installed a 50 kVA transformer. Trust me, 50 kVA is plenty.
     

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