Definition
The maximum instantaneous voltage reached by an alternating current (AC) waveform during one cycle, measured from zero to the highest point of the wave. Peak voltage is higher than the RMS (root-mean-square) voltage commonly listed on equipment ratings; for a sine wave, peak voltage equals RMS voltage multiplied by approximately 1.414.
Plain English
The highest voltage level the electricity actually reaches at the top of each wave, even though the average value used on labels is lower.
Context Anchor
Seen in aircraft electrical system, ignition system, alternator, generator, and test equipment discussions.
Derivation
Peak comes from the idea of the highest point of a mountain or wave. In an AC waveform that rises and falls continuously, the peak is simply the top of each rise.
Why Pilots Care
Confirms that ignition and electrical systems are delivering sufficient power for reliable engine start and stable avionics operation.
Analogy
Think of ocean waves: the peak is the top of the wave, not the water level you would get by averaging the whole wave. Peak voltage is the top of the electrical wave.
Grounding Statement
If you watched the voltage of an AC line on an oscilloscope, the peak is the very top of each hill the trace draws.
Intuition Check
Peak voltage does not mean the normal voltage you usually read on a meter. It means the highest momentary value the voltage reaches.
Example Sentence 1
Although the aircraft AC bus is rated at 115 volts, the technician selected wiring insulation that could safely handle the higher peak voltage of about 163 volts.
Example Sentence 2
A low peak voltage reading from the alternator prompted replacement of the diode assembly before flight.