CDCS Exam Dumps : EXIN EPI Certified Data Centre Specialist

Electromagnetic field (EMF) strength around cables is primarily influenced by current, not voltage. In a single-phase system, the live and neutral conductors are separated, creating a larger magnetic loop area. This produces stronger stray EMF when current increases.

In a balanced three-phase system, the magnetic fields from the three conductors largely cancel each other out, resulting in much lower net EMF, even at higher currents.

Therefore, the correct statement is that increasing current in single-phase cables produces higher EMF compared to three-phase cables. Options B, C, and D incorrectly link EMF to voltage or incorrect current behavior.

Residual current protection has evolved:

ELCB (Earth Leakage Circuit Breaker): Older type; voltage-operated. It trips when voltage develops between earth and exposed metal.

RCD/RCCB (Residual Current Device/Circuit Breaker): Current-operated. It detects imbalance between live and neutral conductors (indicating leakage current to earth).

Modern data centers use RCDs/RCCBs exclusively, since ELCBs are obsolete and unreliable if multiple earth connections exist. Thermal-magnetic breakers (D) provide overcurrent protection, not earth leakage.

Thus, not all residual current devices are based on the same principle.

Hypoxic systems continuously lower oxygen concentration (~15%) to prevent combustion. While safe for short-term human exposure, standards like ISO 20338 recommend they are not suitable for continuously occupied spaces, because reduced oxygen may cause fatigue, reduced cognition, and health risks for staff.

B is irrelevant—air change rates affect dilution, not feasibility.

C is incorrect—tanks can be remote.

D is false—positive pressure is not required.

Thus, the main disadvantage is restriction to non-continuous occupancy.