1. Code requires that wiring to a switch be black or painted black (like when a Romex with black and white wires are included) because either one can be hot.
2. 3 way switches have 2 wires running from one switch to the next and then one switch goes to power and the other to load/lamp. As shown in the diagram either both switches are connected to the same wire (then power goes) or they are on alternate wires (and power is off) Changing either switch changes the state. But all the wires can be hot.and must be black.
Firstly, I think what you call 3 way switch in USA, is known as 2 way switching in UK.
Why it's known as 3 way in USA., I don't understand.
Basically it's a single pole change-over switch with 2 positions.
It has a common with either one of 2 outputs, or a common output from either one of 2 inputs.
Normally the live or hot is connected to the common of 1 switch and the common of 2nd switch is the switch wire to the light(s).
The 2, non common terminals are interconnected. Known as "strapping wires" in UK.
If a third switching point is required, then this requires an intermediate switch, which is 2 pole change-over and switches both strapping wires.
This is OK with live and neutral supply, but 2 phases, or 2 hot wires, require double pole change-over switches.
The 2 way circuit may have variations, depending on cable used, ie, 1 core or 2 core.
It is because for the safety regulation reason. Read the electric code book that has a fully explanation why hot line must be installed on switch terminals rather than using neutral line.
Because it had to switch between one of the alternative returns. If one of them was the hot it would not work as a 2 way switch.
look at this image....please
investigate currents paths on four different positions
http://upload.wikimedia.org/wikipedia/co...
you may change hot and neutral wires but we have hot on lamp ( when switches are off ) so this is a non-standard work
In electrical we all know the common wite is the Neutral but why is it that on a 3-way switch the common terminal is Hot?
