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I have already asked this question:

Why AC power plugs have three pins

And from what I understood from the answers a three-wire outlet has a neutral, hot and a ground connection. I am still confused about input voltage. Shouldn't we have two hot wires instead of one for an AC voltage? Two hot lines that supply 120 v rms that are 180 degree out of phase?

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Jack
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  • What country are you in? – Transistor Feb 08 '16 at 19:09
  • @transistor Canada – Jack Feb 08 '16 at 19:09
  • OK. I see you asking questions on power-factor correction on one hand and a basic question like this one on the other. Have you missed something basic at the start of your studies? Let us know what level you're at. – Transistor Feb 08 '16 at 19:11
  • What voltage do you expect at the device? Different countries have different voltages, 2 hots 120VAC phased at 180 degrees would give you 240VAC output. – Marko Buršič Feb 08 '16 at 19:23
  • @Marko Appliances such as stoves use 240 Vrms and for example lamps are powered by a single 120 V rms so I am expecting to use both. – Jack Feb 08 '16 at 19:38
  • The only purpose of the GND wire (in the context of your question) is to carry fault currents. For example, if the hot wire accidentally touches the grounded metal case of an appliance, a fault current will flow through the GND wire and hopefully trip the circuit breaker. So normally the GND wire carries no current. – user57037 Feb 08 '16 at 20:50
  • On the other hand, the neutral wire, practically speaking, is just like the hot wire. All the current that flows through the hot wire, also flows through the neutral wire in the other direction. These are your two hot wires. It is just that in the US and Canada, for various reasons, the neutral wire, if you track it all the way back to where power enters your house, is connected to the GND wire at this one location only (and don't ever connect them together anywhere else, either). So normally, any voltage on the neutral wire will be close to GND. – user57037 Feb 08 '16 at 20:53
  • There are less commonly used plugs that are designed to supply 240V in the US which have two hot wires and a GND wire. You can google NEMA 6-15 and NEMA 6-20 if you want to see what they look like. – user57037 Feb 08 '16 at 20:56

1 Answers1

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In North American house wiring, the single "hot" wire at an outlet varies from 0 to +170 volt peak, through zero, to -170 volt peak, and back to 0 in one cycle, to provide 120 V RMS relative to the grounded neutral wire.

For high power devices (electric stoves, clothes dryer, etc.) there is a second hot wire which is 180 degrees out of phase with the first one (going to -170 V when the first one goes to +120 V) to give 240 V RMS between the two hot wires.

The two hot wires come from opposite ends of a center-tapped transformer secondary. The center tap is grounded, and becomes the Neutral wire in our homes.

Peter Bennett
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  • So these two hot wires that you mentioned enter our home through one of the pins of the socket with three pins? – Jack Feb 08 '16 at 20:02
  • No, they enter our homes through the big fat cable from the utility company, probably close to where you find the electricity meter on the outside of the house. – brhans Feb 08 '16 at 20:20
  • The two hot wires, and the ground/neutral enter the house through the power company's meter, then into the main breaker panel. There, a wire from the neutral/ground goes out to a ground post driven into the earth. The neutral and safety ground leave the breaker panel as separate wires to each outlet. Most outlets will only get one of the two hot wires for 120 V service - they will have single pole breakers in the panel. Electric stoves and other things needing 240 volts will have two-pole breakers, and will get both hot wires, as well as neutral and ground. – Peter Bennett Feb 08 '16 at 20:29
  • @Peter So in simple words the sockets for the lamp and stove are engineered differently? – Jack Feb 08 '16 at 20:36
  • A stove outlet will be rated to carry 40 Amps or more, and will have four contacts: two hot, neutral, and aground - much different than a common duplex outlet. Go to Home Depot or other home improvement store, and look around the electrical department to see the various types of connectors that are commonly used in household wiring. – Peter Bennett Feb 08 '16 at 20:46