Are 6 volt fluctuations in a 120 volt home outlet harmful to equipment?
This is typical. Can't exactly say &quot;normal&quot;, because if everything is sized and installed correctly then there should not be significant fluctuations. But it is really quite common, particularly in older homes. In my case, I installed a UPS due to real power outages (used to be common, now very infrequent thanks to Pepco rewiring the neighborhood a few years ago), and it kicks in due to voltage drop every time the laser printer goes on.
Most equipment should be immune to these problems, as long as the range is relatively small - e.g., between 110 V and 125 V. See ANSI C84.1 for more details (thank you @Khrrck).