Some basic questions around electricity to clarify some concepts

  1. Why are some plugs have 2 pin while others have 3 pin? I know that 3rd pin is ground but I struggle to understand its purpose.

  2. In a 2-pin, is one pin positive and other negative? I suppose not but just checking as at homes, we have AC power so positive/negative doesn't make sense (because the positive/negative continuously alternate I believe).

  3. What type of devices use a 2-pin plug and what type use 3-pin plug? Could any device be connected with either of these without any issues?

  • \$\begingroup\$ 1. Have you tried the Wikipedia article? 2. No, it's AC. But in some countries wit polarized plugs, you can say that one is hot and the other is neutral. Many countries does not have polarized plugs and you can't tell which is which. 3. Class I devices use 3-pin plugs. Class II devices use 2-pin plugs. \$\endgroup\$
    – winny
    Nov 23, 2021 at 13:31
  • \$\begingroup\$ You appear to be asking about AC outlets and AC appliances, include that information in the question. Why are some plugs have 2 pin while others have 3 pin? My "stupid" answer: because some connectors need 2 connections while others need three is correct but only because you ask an unclear question. Your real question is: Some appliances have a 2 pin AC plug while others have a 3 pin plug. What is the purpose of that extra pin? \$\endgroup\$ Nov 23, 2021 at 13:55
  • \$\begingroup\$ What is a "plug"? Do you refer to where you connect to the mains voltage of your house or what? If so the connectors used depend on which country you are in and if a safety ground is present or not. Also this is only borderline electrical engineering, it might be better to ask questions like this on the DIY site. \$\endgroup\$
    – Lundin
    Nov 23, 2021 at 14:12
  • \$\begingroup\$ Does this answer your question? Why do some electrical devices have a ground and others don't? \$\endgroup\$
    – JYelton
    Nov 23, 2021 at 17:26

1 Answer 1

  1. Ground pin, or earth, is used for safety. E.g. a computer has metal case and it is grounded via mains plug. If inside computer power supply some part malfunctions and mains live voltage gets in contact to computer case, then it will have a safe path to ground and it will blow a fuse. Without ground the metal case would be at live potential and it would be dangerous to touch it.

  2. No, not positive and negative. There is neutral wire, which is at ground potential, and live wire, which has AC voltage.

  3. Some devices are double insulated so they can use 2 pins safely. Some devices are not and they need 3 pins for safety. 2 pin devices can be connected to either socket, but it will be unsafe to connect 3 pin devices to 2 pin socket without ground.

  • \$\begingroup\$ thanks. I liked the explanation of point 1 the most \$\endgroup\$ Nov 23, 2021 at 16:09

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