Use your 240v Dryer outlet?

Discussion in 'Prime Plug-in Charging' started by PrimeRN2019, Apr 15, 2019.

  1. Peng Xiao

    Peng Xiao Junior Member

    Joined:
    Apr 12, 2019
    50
    6
    0
    Location:
    Cranbury, NJ
    Vehicle:
    2018 Prius Prime
    Model:
    Prime Plus
    Thanks for your advice. I tested mine.
    I used an extension cord plug into a regular wall outlet. I have an outlet tester, it's showing "correct" (proper grounded) when I plug it into the extension cord outlet.
    Plug my homemade 10-30 5-20 adapter cord to dryer outlet. Multimeter shows no voltage between 2 ground on 2 cord outlets, 120V between extension cord ground and both adapter cord hot.
    I think I'm good.

    But are you sure there's no voltage between neutral and ground means neutral is grounded? I'm still not 100% confident.
     
    #21 Peng Xiao, Apr 20, 2019
    Last edited: Apr 20, 2019
  2. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    6,968
    8,574
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    Not sure what you mean by "between 2 ground on 2 cord outlets."

    Anyway. When you have your adapter plugged into the dryer receptacle, you should check at the other end of it where you would plug in your EVSE cable that's built for a regular 120V receptacle. You should get 240V between the two legs that would normally be 120V on a 120V outlet. You should then get 120V between one hot leg and what would normally be ground as well as 120V between the other hot leg and what would normally be ground. Something like this sketch.
    Screen Shot 2019-04-20 at 12.28.37 PM.png
     
  3. Peng Xiao

    Peng Xiao Junior Member

    Joined:
    Apr 12, 2019
    50
    6
    0
    Location:
    Cranbury, NJ
    Vehicle:
    2018 Prius Prime
    Model:
    Prime Plus
    I do get what you are showing.
    My question is, if the voltage between dryer outlet neutral and ground of a regular wall outlet is 0, can I say the dryer outlet neutral is grounded?
     
    #23 Peng Xiao, Apr 20, 2019
    Last edited: Apr 20, 2019
  4. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    6,968
    8,574
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    That would be correct, assuming you got the voltage measurements above.

    (This is WAY easier to demonstrate than to type. :LOL:)
     
  5. Peng Xiao

    Peng Xiao Junior Member

    Joined:
    Apr 12, 2019
    50
    6
    0
    Location:
    Cranbury, NJ
    Vehicle:
    2018 Prius Prime
    Model:
    Prime Plus
    Should neutral be grounded? I'm still not clear.
    What is the voltage between neutral and earth connection in 3 phase power supply? - Quora
    • Zero Reading: A certain amount of Neutral to ground voltage is normal in a loaded circuit. If the reading is stable at close to 0V. There is a suspect an illegal Neutral to ground bond in the receptacle (often due to lose strands of the neutral touching some ground point) or at the subpanel. Any Neutral to ground bonds other than those at the transformer source (and/or main panel) should be removed to prevent return currents flowing through the ground conductors.
     
  6. Old Bear

    Old Bear Senior Member

    Joined:
    Sep 15, 2017
    550
    843
    19
    Location:
    Boston, Massachusetts USA
    Vehicle:
    2017 Prius Prime
    Model:
    Plug-in Advanced
    You may wonder why, if the neutral wire and the ground have no difference in voltage between them, why have them both? The answer to that question is subtle but important.

    When you draw current through a circuit, the inherent resistance of the wires causes a voltage drop. So, when you draw current through the "neutral" wire, the voltage between it and ground is no longer zero. This is something that the engineers who write the electrical safety codes started to worry about several years ago. Their concern was that the neutral wire was not a reliable proxy for ground.

    (Those old style three-wire outlets for clothes dryers which use the neutral as if it were a ground was part of what the engineers were worrying about. Inside the appliance, the "ground" wire is firmly attached to the metal frame of the appliance with the intention of making sure that if something goes wrong, electricity will not flow through anyone or anything touching both the appliance case and a real ground, such as a damp floor, water faucet, or wet earth.)

    I don't know exactly when the code changed. I think it may have been in the 1960s. But that's the logic behind there being a distinction between the white ground wire and the green or bare ground wire.

    Of course, just like standard 120-volt household outlets uses only three conductors (a 'hot', a neutral, and a ground), it's permitted that a outlet providing only 240-volts can also use only three conductors provided that they are two 'hots' and a ground. This arrangement is for devices which only 240-volts and do not need 120-volts.

    If a device needs both 120-volts and 240-volts -- like a clothes dryer with a 240-volt heating element and a 120-volt motor -- then there must be four conductors: two 'hots', one neutral, and one ground.

    Somehow, most people intuitively grasp the fact that you can't safely wire a three-prong 120-volt outlet using cable with just two wires by connecting the ground prong to the same wire as the neutral. When it comes to a wiring a 240-volt, the same logic applies: the neutral wire is not to be used as a ground wire.
     
  7. Peng Xiao

    Peng Xiao Junior Member

    Joined:
    Apr 12, 2019
    50
    6
    0
    Location:
    Cranbury, NJ
    Vehicle:
    2018 Prius Prime
    Model:
    Prime Plus
    So base on what you said, neutral should not be grounded?
     
  8. CharlesH

    CharlesH CA HOV Decal #5 on former PiP

    Joined:
    Nov 27, 2005
    2,546
    997
    0
    Location:
    Roseville, CA
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Advanced
    The Neutral is supposed to be grounded somewhere, like in the breaker box (exactly where the grounding is to be done, I leave to the electricians who know the code). But it is not supposed to be grounded in the outlets or electrical devices. As mentioned, since in the US 120V configuration, power flows through the Neutral, there is going to be voltage drop along the Neutral when under load, in which case it will not be at ground potential. And if there is a problem with the Neutral wiring, it can potentially be at 120V above ground. The Ground is never intended to carry any current; if it is, something is really wrong. That is why it can be (but doesn't have to be) smaller gauge than the other wires.
     
  9. Peng Xiao

    Peng Xiao Junior Member

    Joined:
    Apr 12, 2019
    50
    6
    0
    Location:
    Cranbury, NJ
    Vehicle:
    2018 Prius Prime
    Model:
    Prime Plus
    I check the main panel.
    There're total 3 thick wires coming into my house, 2 of them connect to breakers, 1 connect to a bus (many wires connecting to this bus).
    2 wires (1 red 1 black) of dryer outlet connect to breaker, 1 white wire connect to the bus.
    I cannot tell the bus connect to ground or not, or it is ground. I don't know.
     
  10. Marine Ray

    Marine Ray Senior Member

    Joined:
    Mar 21, 2017
    686
    574
    0
    Location:
    Sparks, NV
    Vehicle:
    2017 Prius Prime
    Model:
    Plug-in Advanced
  11. Marine Ray

    Marine Ray Senior Member

    Joined:
    Mar 21, 2017
    686
    574
    0
    Location:
    Sparks, NV
    Vehicle:
    2017 Prius Prime
    Model:
    Plug-in Advanced
  12. Rob43

    Rob43 Senior Member

    Joined:
    Sep 24, 2014
    1,110
    771
    0
    Location:
    VA, BMW Race Car, BMW R1200R, BMW 330Ci, Ford F350
    Vehicle:
    2013 Prius v wagon
    Model:
    Prime Advanced
  13. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    13,119
    6,659
    90
    Location:
    Western Washington
    Vehicle:
    2012 Prius
    Model:
    Three
    When something goes wrong, Ground must be able to carry a full fault current. This is why is shouldn't be small.
     
  14. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    6,968
    8,574
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    Unless you live in a factory, you have single phase power, not three-phase. Different animal.

    In your breaker panel there is supposed to be a connection between the ground terminal strip and the neutral terminal strip. That's usually where it's done.

    You are having so much trouble with this concept that I think you should bring in an electrician who knows what he's doing. No offense, but I'm getting concerned for your safety.
     
    Mark57 likes this.
  15. CharlesH

    CharlesH CA HOV Decal #5 on former PiP

    Joined:
    Nov 27, 2005
    2,546
    997
    0
    Location:
    Roseville, CA
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Advanced
    I will happily defer to those more knowledgeable in such matters. Maybe I was looking at a non-code installation, but when I have wired wall switches in my homes, it sure looked like the bare ground wire was smaller gauge than the power-carrying wires.
     
  16. jb in NE

    jb in NE Senior Member

    Joined:
    Apr 13, 2018
    2,235
    1,568
    0
    Location:
    Nebraska
    Vehicle:
    2018 Prius Prime
    Model:
    Prime Premium
    Note this is only in the main panel. If it's in a sub-panel, neutral and ground are not bonded. Separate neutral and ground wires run back to the main panel and are bonded there.
     
    jerrymildred likes this.
  17. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    6,968
    8,574
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    Exactly. Thanks for making that clear.
     
  18. Old Bear

    Old Bear Senior Member

    Joined:
    Sep 15, 2017
    550
    843
    19
    Location:
    Boston, Massachusetts USA
    Vehicle:
    2017 Prius Prime
    Model:
    Plug-in Advanced
    Yes, three-phase power is "a different animal" and you probably don't have three-phase power in your home, but the statement about separating ground and neutral is equally true for single phase wiring.

    The only place neutral and ground are bonded together is at the main panel. They are not bonded at distribution sub-panels or at any wiring device (e.g., outlet) or connected device.
     
  19. jb in NE

    jb in NE Senior Member

    Joined:
    Apr 13, 2018
    2,235
    1,568
    0
    Location:
    Nebraska
    Vehicle:
    2018 Prius Prime
    Model:
    Prime Premium
    The auto-switch feature could be handy, but that is the AUTO model and it's $363 before shipping. For $85 at Home Depot you can get a 60 amp manual transfer switch that manually transfers and doesn't let both the dryer and EV loads be active at once. That would likely be cheaper than pulling wires to the main panel and adding a new breaker to allow both loads to be active at once.
     
    #39 jb in NE, Apr 21, 2019
    Last edited: Apr 21, 2019
    jerrymildred likes this.
  20. PrimeRN2019

    PrimeRN2019 New Member

    Joined:
    Apr 13, 2019
    3
    0
    0
    Location:
    San Diego, Ca
    Vehicle:
    2019 Prius Prime
    Model:
    Prime Premium
    I already have a plug that I unused!
     
Loading...