Transients on the mains in a residential environment

A digital oscilloscope was used to measure transients on the single-phase 120 V RMS mains in a residential environment. Naturally occurring transient voltages between the hot conductor and ground and between the neutral conductor and ground were recorded simultaneously. Each record contains 1024 samples taken at the rate of 10 samples/μs. Waveforms are shown for transient overvoltages on the mains caused by three nearby lightning strikes and one unknown source. Statistical summaries are presented for all naturally occurring transients. It is shown that the common-mode voltage is often larger than the differential-mode voltage. Waveforms from deliberately switching common appliances were recorded at various sample rates between 100 and 1.0 sample/μs. Waveforms are presented for the transient caused by switching on a resistive load, e.g. a tungsten lamp. This transient can have a slope at least as large as 6 kV/μs and may cause problems, although the effect of this type of transient is always to decrease the magnitude of the voltage. Waveforms are also shown for switching the motor in a vacuum cleaner, which has a slope as large as 17 kV/μs