What do the "I" and "O" on the power switch stand for


Joined Apr 2, 2020
They are in Latin
The Latin word for "on" is "in" = I
The Latin word for "off" is (conveniently) "off" = O
No matter how many stories you may be told, the | is simply a line, and the O is simply a circle.
they represent "on" and "off". Many people remember which is which by other lessons they've learned in life but the phrase, "the standard is the standard" applies here - it is just a line, and a circle.
the standards are (yes, a standard for each line and circle)...
Power On (IEC 60417-5007)
Power Off (IEC 60417-5008)
There is also a statement from IEC to dispel any rumors that they are binary one and zero.


Joined Aug 1, 2013
Note that in post #7, images 3 and 4 are switches that must be mounted horizontally; that is, rotated 90 degrees from their orientation in the images. Pedantically (?), the I and O are symbols, not characters. As such, their orientation is part of their definition.

- Like
- - The
- - - Schematic
- - - - Symbol
- - - - - For


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Joined Nov 24, 2022
I = On
O = Off
This is a confusing matter for me also. Whenever I see I and O it makes me confused. It should be easy for everyone.
I just see the colour Green= On and Red = Off. It's better than I and O.


Joined Apr 2, 2020
The other is:

Green = safe (off)

Red = danger (on)

It seems to break down by industry.
A classic inversion if work / life imbalance. Then the employee takes this experience home and their spouse thinks they are complete idiots because they don't know the green light means the power is on.


Joined Oct 2, 2009
Another school of thought:

A red button when pushed turns on the red light.
A green button is pressed to turn on the green light.

Now choose if red light means power is ON or not.