Conducted EMC noise from multiple electronic devices connected to the mains

This paper examines electromagnetic conducted noise in low-voltage power networks, with measurements taken in a private residence and a university building. To capture the true electromagnetic environment faced by end-user devices, a custom Line Noise Interface (LNI) was developed. Unlike standard Line Impedance Stabilization Networks (LISNs), which measure the conducted noise produced by a given equipment by isolating it from the grid to force an artificial 50 Ω impedance, the LNI is specifically designed to measure in situ the conducted noise present at a certain location of the power grid, being connected in parallel with the highly variable real local impedance of the mains. Measurements conducted from 9 kHz to 30 MHz showed substantial spectral variability across locations: in some cases, levels were well below the EN 55032 Class B limits, while in others they exceeded them by nearly 30 dB, particularly near microgrid inverters. These findings emphasize the need for site-specific evaluations to prevent conducted Electromagnetic Interference (EMI) in real-world installations. Finally, the conducted noise produced by two identical non-synchronized electronic equipment was also compared with the noise produced by a single equipment, showing that in these cases the conducted electromagnetic noise is not additive in the mains.