basic understanding lol.im in the states and have been a master electrician for over 20 years. voltage is not constant. do you know what voltage drop is? if so then voltage is not constant but we correct it by the size of the conductor.
when your lights flicker because lets say a central air unit comes on. that start up of the compressor draws a hell of alot of current,so your voltage goes down, hence not constant.
yes a step up transformer may be used but now your talking commercial for very long runs. but thats usually 3 phase, a whole different power supply. but for someones house running a circuit to their shed out back you must do the voltage drop calc. and size your wire up accordingly to reduce thevoltage drop.
the power company does certain things to maintain a constant voltage but they cannot completly thats why you see surges and we use surge protectors because the voltage is not constant.
ive seen voltages at peoples houses coming from the power company be 110 volts one minute and 125 the next.
i absolutly see where your coming from. alot of things wont work if the voltage gets too low. and after start up of the equipment the voltage goes back up to normal and the current comes back down to normal, thats why the overcurrent device usually has a time delay.
look up voltage, nominal in you code book. begining of the book in definitions. page 70-31 in the 2008 nec.
