Forgive me for what may be a fairly basic question, but I'm a student and I just happened to run into this while doing a recent project.

I own a hybrid car, and in the cab is a 400w inverter with a standard three prong edison outlet (this came installed from the factory). When I measured the voltage the other day, I read:
63.5v between the "neutral" and the ground,
63.8v between the hot and the ground, and finally
120v between the hot and the "neutral"

I'm fairly new at all this, but I've only ever seen this configuration of two hots and one ground in use for higher voltage services, or in a three phase delta configuration. I'm wondering how this system operates, and why? Does it have something to do with the inverter and converting the high voltage DC the engine uses into a useable 120v AC current?

  • \$\begingroup\$ It is hard to know based on your measurements if the AC output is isolated and just floats at high impedance in respect to the chassis/PE due to some filter caps or is it deliberately bonded with low impedance to output 60V on neutral and live like a center tapped transformer. \$\endgroup\$
    – Justme
    Sep 18, 2023 at 13:49
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    \$\begingroup\$ What are you referring to as an "edison outlet"? The only thing I know of by that name is the edison screw base, which most lightbulbs in north america use. It's definitely not three-pronged. \$\endgroup\$
    – Hearth
    Sep 18, 2023 at 13:54
  • \$\begingroup\$ @Hearth - From Edison plug: An ordinary household electrical plug in the United States. Characterized by having two flat blades and a semi-round ground pin. Presumably, the OP means that. \$\endgroup\$ Sep 18, 2023 at 13:58
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    \$\begingroup\$ @Greenonline Never heard it called that; it's always been NEMA 5-15 to me. \$\endgroup\$
    – Hearth
    Sep 18, 2023 at 14:03

1 Answer 1


This arrangement is fairly common in small inverters and inverter-style generators (such as my Honda EU2000i). It allows the inverter to produce 120 V AC between the Line and Neutral wires without requiring a negative high voltage supply as would be required if the Neutral wire was held at Zero volts.

Any load on an AC circuit should only be concerned with the voltage between the Line and Neutral wires, and not with the voltage between either wire and Ground.


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