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I've lived in a variety of different places where polarities have been different on a per-outlet basis, i.e. the neutral is where the hot should be. I've never noticed any ill effects from this.

Are there any side-effects of having the polarities reversed? My understanding is that almost any AC device out there will just simply flow the other way if the polarity is backwards.

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  • By swapping polarities, do you mean exchanging the LINE and NEUTRAL connections? Or, do you mean flipping the polarity of the LINE, such that when it should be positive, it's negative, and when its negative, it's positive?
    – Pigrew
    Feb 15, 2016 at 14:08
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    @Pigrew Polarity is kind of a misnomer with AC power in the negative/positive sense. DC current flows one-way, from anode to cathode. But AC current constantly changes direction. Forget positive and negative with AC. "Polarity" is really just a reference to the line conductor being connected to one of the poles of the inner coil in the transformer outside. In the U.S., there are two line conductors, one from each pole of the smaller transformer coil, and a grounded "neutral" coming out of the center. AC appliances don't care about polarity, it's a human safety issue. Feb 15, 2016 at 17:19
  • I did once discover that an outlet was reverse wired because I had a light timer that tripped some sort of internal protection when plugged into the outlet.
    – robartsd
    Mar 5, 2021 at 15:44

4 Answers 4

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There's no danger to the attached load. AC current reverses direction 50 or 60 times each second depending on what country you're in.

It literally makes no difference at all for the equipment.

Human safety is another matter. The hot/line conductor is generally dangerous if you touch it, while the grounded ("neutral") conductor is generally (not always) safe. However, if equipment has a single-pole switch, it is only breaking the conductor it assumes is the line conductor. If you have the line and neutral reversed, then the appliance is still energized even if the switch is off.

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    For instance, I had a lamp with this problem. It means that the screw portion of the bulb socket is the hot portion, and if your hand touches the base of the bulb as it is screwed in, you receive a shock. The shock indirectly resulted in the immediate destruction of the lamp. Feb 15, 2016 at 15:57
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You're correct that in an AC system, the electricity flows both directions and therefore will allow items to function.

However, these items can't be regarded as safe.

When two wires come into a device, and it has a switch, the switch is designed to interrupt the hot wire. If the polarity were reversed and the switch on the device were turned off - it would be interrupting the grounded (neutral) wire. This means if you turned off a light and stuck your finger in the bulb receptacle (Safety note: I don't recommend it.) You could be providing a ground-fault current path and complete the circuit!

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  • The question isn't discussing whether I replaced the ground with the hot or the ground with the neutral, but the neutral with the hot. If the hot and neutral were swapped in a switch, the switch would continue to work. Feb 15, 2016 at 5:01
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    @NaftuliTzviKay, not if you consider that the switch is there to make it safe to work on the light!
    – Walker
    Feb 15, 2016 at 11:33
  • Typical single pole switches on equipment in the U.S. are about saving money, not safety. A completely safe switch would be a double pole switch, which is mandated legally in other parts of the world. Nov 27, 2021 at 1:01
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The relative voltage between hot and neutral is constantly reversing but that doesn't mean that the two conductors are the same. Relative to earth the hot is varying (both positive and negative) while the neutral stays at roughly zero voltage relative to earth.

In particular if a single pole switching or protection device ends up in the neutral due to reverse polarity it can leave the appliance in an "off but live" state which is undesirable. A single pole protective device that ends up in the neutral also can't provide any protection against faults to earth.

It is possible to design applicances that meet safety requirements even if live and neutral are reversed and most modern appliances are likely to be built this way since in many parts of the world unpolarised plugs are the norm.

However if you live in a country where correct polarity is expected (such as the US and the UK) you should respect that expectation to ensure that all equipment is safe, even older equipment or equipment that was built in your country and never intended to be exported.

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Technically there should be no difference to the load if the Hot and Neutral are reversed. AC voltage and current switch 60 times per second which means they automatically reverse voltage.

What can happen is if the Appliance manufacturer does a bad job and connects the neutral side to the chassis which should never be done you might notice. The neutral side of the AC circuit is ultimately connected to the Earth Ground at the main service panel with forces it be close to zero volts compared to GND. The neutral wire will not be at zero volts because it carries current and with the voltage drop (IR) across the wiring infrastructure will move around because other loads throughout the house share the neutral bus within the wiring infrastructure. Without the Ground bus connection at the service panel the hot would be 60+ and 60- and the neutral would be 60- and 60+.

The electrons flowing in the wire have no idea which is hot or neutral. Hot and Neutral is a cookbook solution for Electricians. If you run 240 Volts there is no need for a neutral wire. A 240-volt load won't even use it. Other parts of the world with 220 or 240 volts don't even have the concept of a neutral wire. The neutral wire concept originated with Thomas Edison DC electric homes where you could provide a +120 to GND and GND to -120 volts DC.

Eventually, AC replaced DC and the AC voltage was given 120V RMS to be equivalent to a DC circuit. 120 Volts AC has a peak voltage of 169.7 Volts. With a 60 Hz AC circuit there is time at 120 times per second that there is zero voltage applied to the AC line. Every 8.33 ms the entire electrical grid is a zero voltage.

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    Technically electrons don't "flow" through wire. Please consider breaking your wall of text into logical paragraphs. It's a bit tough for tired eyes to read as it is.
    – isherwood
    Mar 28, 2023 at 2:00
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    Also, it is not true that countries with 240VAC don't have neutrals. Here in NZ we have 220V AC and there is neutral and ground. The neutral is tied to the ground at the switchboard. Otherwise, the Neutral and Ground are kept separate throughout the house. In fact, I would argue, that it is with a lower voltage of 110, that you can be a bit loose with your neutral and ground. Mar 28, 2023 at 3:09
  • Electrons don't flow like water but they definitely transverse or migrate inside a metal along a cross section of wire. The work function of electric field times the amount of charge that flows over time is what produces power. The voltage is the electrial field difference and current is the amount of charge (i.e. electrons that transferve a wire) over time that produces power. The electric field is mainly concentrated on the surface of the conductor. The electric field is a force that electons are either attracted too or repulsed by.
    – hypersparc
    Mar 31, 2023 at 10:03
  • A neutral wire is considred a Virtual Ground. It's not a true Ground but should act like a Ground electically. Normally, 240 Volt circuits don't interact or need a nuetral wire. A neutral wire exist in 240 volt plug so one side of the 240 volt A/C line can terminate to the neutral to produce a 120 Volt circuit. For instance an household dryer may have 240 volt cirucit for the heating coil but also one side of the 240 volt circuit may terminate to neuetral for lower voltage circuits like the control or blower motor. With a neutral setup you can get 240V, +120V and -120V at the same time.
    – hypersparc
    Mar 31, 2023 at 10:17

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