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Question about neutral for HPWC

Discussion in 'Model 3: Battery & Charging' started by Switzch, Jul 30, 2018.

  1. Switzch

    Switzch Member

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    Hooking up a HPWC this week. Permit pulled and electrician booked but I am the type of person who really wants to understand how everything works... Understand the HPWC does not use the neutral wire as the 240v comes from the delta between L1 & L2. My question is what to do with the Neutral wire both in the HPWC and in my panel. Here is my assumption, let me know if this is wrong;

    Inside the HPWC: Ground + L1 + L2 connected. Neutral gets capped (unused).
    Inside the panel: Ground into ground bar, L1 + L2 connect to breaker. Neutral to ground/neutral bar. This is a main breaker panel (not sub panel) and my understanding is that N and G are the same within the panel.

    If the above is correct, the reason why I am confused is because the line in the manual below. Why would the neutral need to be connected to the panel (ground/neutral bar) if its unused in the HPWC?

    Ground connection Always connect the Neutral at the service to Earth ground. Ground fault protection is not possible unless the Neutral (center tap on the service transformer) is connected to an Earth ground. If Ground is not provided by the electrical service, you must install a grounding stake nearby. The grounding stake must be connected to the ground bar in the main breaker panel, and Neutral connected to Ground at that point.​
     
  2. JasJ

    JasJ Supporting Member

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    You don't need to run a neutral to the HPWC - it's just a waste of copper and money.
     
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  3. David Haynes

    David Haynes Member

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    Inside the HPWC: According to all the videos, the neutral is capped.
     
  4. Switzch

    Switzch Member

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    What about inside the panel? That's my question.. is it capped or wired to the neutral bar?
     
  5. arg

    arg Supporting Member

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    Because it's connected (via the supply transformer) to both of the hot wires. If the neutral is connected to true ground, then the hot wires are each 120V away from ground, and any kind of fault to ground will draw current and trip the ground fault protection. If neutral isn't connected to anything, then you can short one of the hot wires to ground and nothing much will happen - just that now one of the hot wires is at ground potential and the other is 240V above ground (rather than 120V as it should be).

    The manual is just reminding you about standard electrical practice, rather than anything specific to EV charging.
     
  6. JasJ

    JasJ Supporting Member

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    if you do run the neutral, then you should/must wire it to the neutral bar in the main panel and cap it in the HPWC.

    It is presumed the main panel already has the Ground and neutral bonded (or you would have major problems in the house with electrical).

    It is further presumed the main panel ground bar is connected to an earth ground.
     
  7. bluetinc

    bluetinc Member

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    Switzch,

    The paragraph that you quoted has to do with requirements on the connections inside the main panel, not inside the HPWC. That's why it's confusing you. They have that there because this needs to be correct for the HPWC to work correctly.

    I'll leave it to others to say what to do with the unused extra wire in the main panel, I wouldn't pull it personally.

    Peter
     
  8. JasJ

    JasJ Supporting Member

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    #8 JasJ, Jul 30, 2018
    Last edited: Jul 30, 2018
    Umm no, a BIG bang and the breaker trips... shorting either Hot (L1 or L2) to ground will result in the full amperage of the circuit dumping to ground until either the breaker trips or the wire melts.

    I agree with @bluetinc - don't pull a neutral.
     
  9. markb1

    markb1 Active Member

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    I think what the manual is saying is the the HPWC's ground needs to be connected to neutral at the panel. I read it wrong at first, too. It's not talking about the neutral wire that you have running to the HPWC. That might as well be capped at both ends (or not present at all).
     
  10. arg

    arg Supporting Member

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    But ONLY if the neutral and ground are connected somewhere in the system - which is absolutely standard practice of course, but if you didn't do it then ground fault protection won't work. That's what the manual is telling you.
     
  11. Kredal

    Kredal New Member

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    The electrician who installed mine snipped the neutral wire at both ends of the conduit, not attaching it to anything. Was that wrong?
     
  12. markb1

    markb1 Active Member

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    No, other than wasting materials.
     
  13. eprosenx

    eprosenx Member

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    Lots of people have touched on things here, but to recap:

    1. Neutral was not needed for a HPWC. If it is already run then it is fine, but you could have saved money by purchasing wire without a neutral conductor.

    2. The manual is talking about making sure that neutral and ground are "bonded" together in *one* place in your electrical system. This is generally the main service entrance panel where power first comes into the house (sometimes it is outside connected with the meter base, sometimes it is just your single internal house panel). This does not have to do with the new specific circuit for the HPWC but just your electrical system in general. This should already be taken care of in your house (and if it is not this is BAD!)

    3. If you do have that extra neutral wire, then cap it in the HPWC and I would tie it into the neutral bus at the panel (if it is the service entrance panel then the neutral and ground busses are tied together and functionally equivalent - if it comes off a sub-panel then you need to keep it separate). I just don't think you want a "floating" conductor that is not tied to anything (not sure what NEC says about this, but my guess is that it would be frowned upon).
     
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  14. Rocky_H

    Rocky_H Active Member

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    I'm pretty sure NEC would have something to say about this situation. My instinct would be that since one end of it is supposed to be disconnected, that the more sensible thing would be to have it not connected on both ends, so it can't get in trouble touching something it's not supposed to. But I know in almost every kind of electrical context, the word "floating" is practically a dirty word, and there's usually something else recommended.
     
  15. Switzch

    Switzch Member

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    I spoke with my electrician and he said the plan is to attach both the ground +neutral in the panel and cap the neutral in the HPWC.
     

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