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NEMA L14-30, Purpose of neutral in circuit (4 vs 3 prong)

Post in 'DIY and General non-hearth advice' started by g1mb, Dec 13, 2011.

  1. g1mb

    g1mb Member

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    What is the purpose of the neutral circuit in a newer 240 volt electrical system?

    I just bought a generator (Generac GP6500) and it has a 4 prong receptacle for the 240 volt connection. I can't find an adapter to convert this to a standard 3 prong plug. Is the neutral actually necessary? Can I make a cord that is 3 prong on one end, 4 prong on the other and eliminate the neutral?

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  2. jharkin

    jharkin Minister of Fire

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    The neutral is there because its a mixed 120/240 v connection. Without that neutral you cannot feed any 120v circuits.

    What are you trying to power with the generator? If you are trying to feed a transfer switch the neutral will be required to break it into 120v circuits. Even many 240v appliances like dryers and ranges are actually mixed 120v and 240v and need that neutral. the "3 prong" outlets you see on such don't lack a neutral - what they lack is a separate ground. Which is why they haven't been code legal for 20 years and are only grandfathered in for existing installs.

    Don't want to make assumptions but I certainly hope you are not planning to backfeed your main through a dryer outlet or something.......
  3. g1mb

    g1mb Member

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    Eventually I will install some type of proper transfer switch. I'm looking at a Generlink setup, a Interlockit device, as well as a standard type transfer switch with a sub panel.

    In the interim, I wanted to backfeed the house through the dryer outlet to make sure the generator works before I store it away. Buying a generator was not high on my priority list until we had 2 prolonged power outages in the last couple of months. I bought the generator last week just to make sure I got one before they ended up on backorder again. I haven't decided on what to do with a transfer switch or panel yet.

    From what I can gather the neutral was added for the purpose of the return current on a 120 volt circuit in a 240 volt appliance. Prior to adding the neutral, the return circuit for a 120 circuit was the ground itself.

    Shouldn't I be able to eliminate the neutral connection at the generator, as I believe it is bonded to the generator ground anyway?
  4. nate379

    nate379 Guest

    That's what I did for mine. Just 8/3 SJOW wire off the 4 prong. 2 hots and the ground, didn't bother with the neutral.

    I made a male male pigtail and I just use my ~100ft welder cord (8/3).

    I don't really care if backfeeding the panel is "wrong". So is drinking crap beer and people still do that everyday too. I'm not going to spend big $$ for a transfer switch and all that for something I might use every few years.
  5. bubba3228

    bubba3228 Member

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    WOW this is not going to end good.

    Nate and g1 you will not be doing any favors to yourself or linemen working on the power distribution system. I would recomend spending some bucks and getting some professional insured and bonded electrical contractor to help you with your installations. :bug:
  6. nate379

    nate379 Guest

    What do lineman have to do with running a gen set to power MY house? The power company owns from the meter and beyond, the rest is MINE!

    Turn off the main breaker, and holy cow, I can power up my house!! WOW!

    IF and I say IF I didn't shut the main, do you think a 4K gen set could actually backfeed an entire grid? No, it can't. It loads the gen set too much and it stalls.

    AND in any case why is a lineman handling wires without the proper PPE and training?
  7. bubba3228

    bubba3228 Member

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    Yea your right. they should not sell them fancy new fangled transfer switches because them generators will just stall out anyway.
  8. nate379

    nate379 Guest

    We have a transfer switch at work and it's nice. Power goes out and 15-20 secs later gen set it running, all without having to move a finger. Of course that gen set is in a nice heated 12x14 room, 6 cylinder Detriot diesel with 150Kw 3 phase gen head.

    Just a "little" bit difference than my 8hp 4Kw Generac!

    The gen set at work could power my whole neighborhood with plenty to spare.
  9. hemlock

    hemlock Feeling the Heat

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    The thing is - transformers work both ways. ie 50,000VAC down to 240VAC = 240VAC up to 50,000VAC the other way.
  10. g1mb

    g1mb Member

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    So the deal is that I could inadvertently forget to turn off my main and create a hazardous condition for someone else on the line, or someone could pull the cord from the backfed receptacle and end up with an exposed hot "male" plug in their hands. I understand that. I intend to install a proper transfer device as soon as it is in the budget. For the time being I just want to test the new generator and see it work before I store it.

    Can I just eliminate the neutral from the 4 wire connector without causing harm to the generator?
  11. hemlock

    hemlock Feeling the Heat

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    What I did was install a "power panel" in my utility room in the basement consisting of a few standard 120VAC receptacles, and one 240VAC receptacle all wired to a cord running to the garage that can plug into the generator outside. For my well, I put a 240VAC plug and receptacle on the wires, and it stays "plugged in" to the normal house wiring. In the event of a power outage, it gets unplugged and plugged into my "power panel". The same with the freezer/fridge, and a few other smaller items.
    It's not as convenient as a hard wired set-up, because you still need a few extension cords, but it eliminates the need for transfer switches, etc.... as the home made "panel" is completely separate from the main panel. The generator is outside, no cords going through windows, and best of all, it is fairly inexpensive.
  12. jharkin

    jharkin Minister of Fire

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    Sorry but stupid ideas like this get people KILLED. Not to mention that its quite illegal.


    I don't care what your excuses are. Stop being cheap and do it the proper safe way. If you don't understand the purpose of a neutral and ground you really have no business working on your house wiring, please hire an electrician.
  13. bubba3228

    bubba3228 Member

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    The main job of the neutral(grounded conductor) is to carry the imbalanced amperes between the hots (phase conductors). The code has changed so that the installation of multi-wire circuits are not sharing neutrals without a means of disconnect. It is not a good practice to allow the bare(grounding conductor) to do the job of the neutral. The grounding conductors job is to bond metallic objects that may come in contact with the phase conductors, so they are not energized without tripping the breaker(over current protection device). Will it harm your new generator? That depends on how you wire your cord end. If you want to test your generator, plug something into it that creates a load and enjoy. If I was out of power and wanted to jerry rig a circuit or two that I wanted to temporarily energize and did not have a transfer switch I would isolate them from the panel and wire nut a cord ends on them plug them into the receptacles on the generator. I would not comfortable back feeding circuits with plugs downstream. That said, electricity will work in many different installations and you may think it is safe, however if you really do not know all the variables what are you energizing you may not want to be?
  14. hemlock

    hemlock Feeling the Heat

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    I'm not sure how my set-up is going to get anyone killed. It's a pretty simple circuit, and isolated from the main feed. I just bascially moved the generator plugs indoors.
  15. bubba3228

    bubba3228 Member

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    I do not recall the code atrticles allowing your method for this application. Will it work? Yes - maybe ? jharkin has the correct advise.
  16. willworkforwood

    willworkforwood Feeling the Heat

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    I wouldn't make any changes that MIGHT affect my generator. All of the non-inverter gensets create "dirty" power, with high enough harmonic distortion to affect some motors and electronic equipment. My generator is a typical non-inverter, and causes my wood boiler controller to be unusable. It also changes the way our microwave runs, which in turn makes the oil burner motor change pitch. So, brand new these gensets aren't producing great power, and chopping off the neutral prong could only potentially make things worse. Unless someone who designs and builds generators for a living can guarantee that this cannot damage a genset, I wouldn't try it. And +1 to not backfeeding, where there is any chance of powering into the grid. I installed a transfer switch/sub-panel and outside receptacle 3 years ago - $300 and a good amount of work to re-route lots of wires. But, there was NO WAY I was going to take even a .00001% chance of killing someone by backfeeding. If you backfeed and kill a lineman who wasn't using PPE, then it's not your fault? :bug:
  17. velvetfoot

    velvetfoot Minister of Fire

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    The thing is, that approach is probably just as expensive than an interlock kit, wire to the outside, and inlet box.
  18. jharkin

    jharkin Minister of Fire

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    That wasn't aimed at you. It was aimed at people backfeeding a dryer outlet with a suicide cable, and using bare grounds as a neutral.
  19. hemlock

    hemlock Feeling the Heat

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    Sorry.
  20. jharkin

    jharkin Minister of Fire

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    Incorrect... ground was never a current carrying conductor in a 120v circuit EVER. Old 2 prong 120v outlets were ungrounded - neutral was always a dedicated, insulated conductor even in the knob and tube days.

    A ground is a safety feature ONLY. It is a path for fault circuit current to go to the ground and not into a human. Its there to insure that a short circuit trips a circuit breaker. When you try to make a ground do double duty as a neutral, any wiring fault in the panel could potentially turn that ground and the metal frame of grounded appliance hot with line voltage. bad bad bad bad bad!!!!


    3 prong dryer outlets were a special exception allowed starting in WW2 to deal with a copper shortage. The third wire was officially a neutral, but allowed to do double duty as ground in this one application only. To be legal it had to be SE or large appliance cable with a braided full size neutral. Junctions and splices were generally not allowed. That exception was discontinued in 1993, and existing installs are only grandfathered in if they are not modified in any way - which is why you cannot buy 3 prong 240/120 outlets or adapters. The only thing you can still buy in 3 prong is the appliance cord to plug a new appliance into an old outlet.

    I'm sure I'm coming off as judgmental but this is seriously risking somebody getting seriously hurt. Please be safe!!
  21. jharkin

    jharkin Minister of Fire

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    not necessary... I didn't make clear what I was addressing so my apologies for confusion.
  22. oldspark

    oldspark Guest

    These posts make for some fun reading, I dont have a transfer swithch but ya gotta know what you are doing, there are ways to isolate from the grid and I get the impression Nate is doing that and said as such, I have a fuse block I remove. Anyone hooking in a gen. and not isolating from the grid (usually easy to do) is asking for a law suit. I agree with comment about if you dont understand neutral and ground facts than you are in over your head.
  23. g1mb

    g1mb Member

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    Maybe I worded my post poorly.

    I was referring to a 240 volt appliance, with the 120 volt portion of the appliance (eg.light bulb in dryer) using the ground (neutral) of the 240 circuit as it's return. I didn't mean that the ground (bare wire) was ever used as a conductor.

    I'm not likely to back feed this outlet anyway at this point, but it uses a 10/3 wire, all of the circuits are insulated, my neutral and ground are bonded in the generator, and my neutral and ground are bonded in my main panel.

    My concern was in causing harm to the generator while checking to make the 240 outlet worked, as I have nothing that is wired for a newer type 120/240 receptacle to test it with.
  24. oldspark

    oldspark Guest

    Oh boy now I am confused, a neutral is a conductor and it is not the same thing as a ground what so ever.
  25. nate379

    nate379 Guest

    No point in continuing on with this thread. I'm still going to do it, no matter what anyone says. I know the "risks" which are all extinguished but simply turning off a breaker.

    AND yes you certainly can still buy 3 prong 240v outlets. Most 240v equipment outside home appliances like dryers and ovens have no use for a neutral.

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