I'm sorry for asking a question this simple but I can't understand it . Single phase ac has two wires , phase and neutral but I don't know which wire change voltage . Like neutral wire is always 0 v and phase wire changing +V to -V or phase and neutral changes direction ? (Like phase +V , neutral 0V then neutral +V , phase 0V ). Also what's the difference between pulse signal and ac ?


1 Answer 1


The neutral wire is connected to an Earth Ground somewhere, and is therefore defined to be "Zero Volts". The voltage on the phase (or "live" or "line") wire varies/alternates between positive and negative relative to the Neutral wire.

AC normally implies a regular alternating voltage (50 or 60Hz for Mains Power, but any frequency for other uses).

A pulse signal is normally at one voltage (often, but not necessarily, zero), but occasionally changes to another voltage for a short time.

  • \$\begingroup\$ So in ac , live wire changing between +V to -V ... And neutral is always ground (0v)? Also if you make a pulse signal which has +V (high ) and -V (low) , is it counts as ac or pulse ? \$\endgroup\$
    – Mordecai
    Commented Aug 19, 2019 at 23:49
  • \$\begingroup\$ I still can't understand the difference , like if you make live +V and neutral ground then live is ground and neutral is +V . It's seems like same results for me. \$\endgroup\$
    – Mordecai
    Commented Aug 20, 2019 at 0:35
  • \$\begingroup\$ @Mordecai: Many times, technical terms don't have hard-and-fast definitions - the particular definition to use may depend on context. If you are interested in the positive and negative voltages of a pulse signal, you may want to call it "AC", but if the pulse has random timing, or is mostly negative with brief positive periods, I don't think I'd call it AC. \$\endgroup\$ Commented Aug 20, 2019 at 0:35
  • \$\begingroup\$ For AC power, Neutral is always Ground/Zero volts (or very close to it), and the "Hot" wire varies regularly between a peak positive voltage and a peak negative voltage. \$\endgroup\$ Commented Aug 20, 2019 at 0:39
  • \$\begingroup\$ Okay now I think I understand it and I made simple test to check , I connected one probe of my multimeter to ground pin and other probe to live and it shown 220v but when I connect the other probe to neutral it shown 0V . So if these accurate , you can only get electrocuted with live wire ? \$\endgroup\$
    – Mordecai
    Commented Aug 20, 2019 at 0:51

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.