As per Certified Data Centre Professional (CDCP) reference materials, Common Mode Noise (CMN) is a type of electrical noise that appears equally on the line and neutral wires with respect to ground, and it can negatively affect sensitive ICT equipment. Excessive CMN at the rack level can lead to data errors, communication problems, equipment malfunctions, or even hardware damage.

The CDCP training and the official exam preparation guide specify that the preferred level of Common Mode Noise at the rack should be less than 1 Volt, and under no circumstances should it exceed 3 Volts. Keeping CMN at these levels helps ensure the stable and reliable operation of critical data center infrastructure. Higher CMN levels indicate grounding or bonding issues, or possibly interference from electrical or mechanical sources, and must be addressed promptly.

Options A and B (CMN above 5 or 10 Volts) are not acceptable and would present a serious risk to ICT equipment operation and data integrity. Option D is incorrect, as CMN absolutely does affect ICT equipment.

EPI CDCP Exam Preparation Guide: https://www.epi-ap.com/uploads/file/exam%20prep/english_preparation_guide_cdcp_202003.pdf

EPI Certified Data Centre Professional (CDCP) Course Content: https://www.epi-ap.com/services/1/3/4/Certified_Data_Centre_Professional_(CDCP)

EPI Data Centre Framework: https://www.epi-ap.com/content/31/67/EPI_Data_Centre_Framework