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In AC systems the two wires of a circuit alternate polarity many times per second. So positive and negative switch, half of the time a wire is positive the other it is negative.

So why is it important to connect plug sockets to the correct coloured wire? What is the difference between the live and neutral wires?

Chris
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Martin Lowe
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  • If you are speaking of power outlets there are safety reasons. There is info on this online –  Aug 21 '19 at 02:56
  • The neutral wire in the outlet has no voltage (North America) and the alive wire has all the energy. The live wire will tend to be more carefully connected or isolated in the circuit in the appliance. – PhysicsDave Aug 21 '19 at 03:22
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    you are missing that you are being saved from eletcrocution when keeping the rules of the country .. – anna v Aug 21 '19 at 03:32
  • To all future readers of this question: please be aware that the assumptions and statements made by Martin Lowe in the question are substantially wrong, and believing them could lead to considerable safety risks for you or for any others who may interact with your residential electricity. .Commetn copied form @Dale answer – anna v Aug 21 '19 at 05:18
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    I've edited your question to ask essentially the same thing without making incorrect statements that may, if taken as fact by future readers, lead someone to make unwise choices with regard to electrical safety. – Chris Aug 21 '19 at 10:00
  • @PhysicsDave, the idea that the neutral wire "has no Voltage" is a sloppy, and potentially confusing-to-newbies way of saying that the the Voltage between neutral and Earth is kept as close as possible to zero. – Solomon Slow Aug 21 '19 at 13:24
  • @PhysicsDave, I am not qualified to talk about how energy is transferred by electric circuits, but I'm pretty sure that the idea that any single wire can "have all the energy" is just completely wrong. No power can be transferred unless current flows in a circuit. If you disconnect the neutral wire of an appliance, then the transfer of power will stop except in the case where the current finds some other path (e.g., the protective Earth wire, a water pipe, etc.) that eventually connects back to "neutral." – Solomon Slow Aug 21 '19 at 13:30
  • Perhaps it should be noted that the 240VAC delivered to most homes in the US is balanced, i.e., the voltage on the two live wires alternate just as the OP describes. A 120VAC branch is unbalanced because it uses just one of the live wires and the neutral. Note that using an isolation (1:1) transformer safely converts the unbalanced 120VAC to balanced. – Hal Hollis Aug 21 '19 at 14:04
  • @SolomonSlow That is not strictly true. A capacitive path to ground works as well. Since practically speaking everything is capacitively coupled to the earth, it is certainly possible to be shocked by the live wire without any direct (i.e. conductive) connection to the earth, in a way that it is not possible to be shocked by the neutral wire (assuming everything is done properly, at least). – Chris Aug 21 '19 at 14:59
  • @Chris, In AC circuit analysis, a capacitive connection is a connection. But that's beside the point. PhysicsDave strongly suggested that the "hot" wire in a residential power circuit is solely responsible for delivering the power to an appliance. What he thinks the "neutral" wire is for? I don't know. But the truth is, power is not something that flows over one wire or the other. It flows over the pair. They are equally responsible/equally necessary. – Solomon Slow Aug 21 '19 at 16:36
  • @SolomonSlow He's not really wrong. You can get the full amount of power using just the live wire and an independent path to ground, or even just a large enough capacitor. You can't say the same about the neutral wire. – Chris Aug 21 '19 at 16:46
  • @Chris, You can also get power from the neutral wire and an "independent path" to hot. I don't see your point. – Solomon Slow Aug 21 '19 at 17:24
  • @SolomonSlow If you follow the neutral wire from your outlet back to the fuse box you will likely find that the neutral block it is connected to is also connected to your water pipe or similarity grounded object. If you follow the neutral wire on the high voltage tower back to the power plant you will also find it is literally connected to ground. – PhysicsDave Aug 22 '19 at 01:05
  • @PhysicsDave, Overhead wires are connected to Earth at more places than just that. Where I live, there's a ground wire on pretty much every pole, although sometimes they are not obvious. – Solomon Slow Aug 22 '19 at 13:36

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To all future readers of this question: please be aware that the assumptions and statements made by @Martin Lowe in the question are substantially wrong, and believing them could lead to considerable safety risks for you or for any others who may interact with your residential electricity.

So why are people still being told that they need to connect plug sockets to the correct coloured wire? There IS no live and neutral wire as the live and neutral switches many times per second!

This is completely false. In a correctly wired residential circuit the live and neutral wires do not switch many times per second. The neutral wire is a current carrying wire that is maintained at ground potential at all times. The ground wire is also maintained at the same potential, but normally it only carries current in the event of a fault. The live or hot wire has a voltage which alternates above and below the fixed neutral wire, the frequency and voltage varies from country to country. The roles of the neutral and the live wire are not interchangeable.

Your blue and brown wires can be connected however you want in a socket as this is NOT DC, in DC is DOES matter but in AC why the fuss?

The fuss is because we usually want to avoid injuring people or setting property on fire. Incorrect residential wiring is hazardous and connecting the wires contrary to local codes could injure you, people who touch appliances connected to your wiring, or future electricians working on the residence. Connecting the wires wrong could result in the chassis of an appliance becoming live. Do not attempt to wire any circuit inappropriately.

tpg2114
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Dale
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    Indeed. It is usually a surprise to people when they learn that the folks responsible for the (standard) electrical code in the US (usually adopted as-is by state and local authorities) is produced by the National Fire Protection Association (NFPA). – Jon Custer Aug 21 '19 at 13:23