Free Exin CDCS Practice Exam with Questions & Answers

The diagram shows three UPS modules, each 100 kW, connected in parallel to support a 100 kW IT load. That means:

One module (100 kW) can support the load (N).

Two additional modules are installed as redundancy.

This equals N+2 redundancy.

2+N+1 and 2(N+1) imply dual active paths not shown.

N+N+N is not an industry term.

Thus, the correct redundancy level is N+2.

NFPA 75 (Standard for IT Equipment Protection) and NFPA 72 (Fire Alarm Code) recommend installing at least one smoke detector per 250 ft² (≈25 m²) in IT rooms. This ensures early detection in high-value environments.

A and B are far too dense, exceeding NFPA minimums.

D is too sparse and would not meet early detection requirements.

Therefore, the correct standard density is 1 per 25 m².

In a data center with noise levels of 91 dB (A), employers are indeed required to take precautions to protect personnel, as this level exceeds commonly accepted safety thresholds for occupational noise exposure. Regulations, such as those from the Occupational Safety and Health Administration (OSHA) or similar agencies, mandate specific controls and protections for environments with high noise levels.

Detailed Explanation:

Noise levels above 85 dB (A) typically trigger requirements for hearing conservation programs. At 91 dB (A), steps like providing ear protection, conducting regular noise assessments, and possibly implementing engineering controls to reduce noise should be taken. Extended exposure to such levels can lead to hearing loss, so regulatory compliance ensures both immediate and long-term protection for personnel.

EPI Data Center Specialist References:

EPI guidelines for data center safety address noise exposure as part of the environmental safety measures. EPI recommends adhering to local occupational health regulations, as excessive noise can harm personnel and affect operational efficiency due to potential health hazards.

Perforated tiles with integrated dampers are common in raised-floor data centers because they allow airflow regulation at the rack level. However, even when the damper is fully open, the mechanism inside the tile restricts airflow. This typically reduces the delivered airflow by around 10% compared to a non-dampered tile of the same type.

Option A is incorrect because dampers do not affect supply temperature; they only throttle volume.

Option B is wrong since dampers cannot increase volume—they only add resistance.

Option D is partially true that dampers help with temperature balancing, but the main effect (in open position) is volume reduction.

Thus, the technical impact of dampers in open position is a slight airflow reduction, usually quantified as ~10%.

The Top-of-Rack (ToR) cabling layout places an access switch directly inside each rack. Each server in that rack only requires a short patch cable to connect to the switch, and only one or two uplinks per rack connect to aggregation switches. This greatly reduces the number of long horizontal cables across the data hall.

In contrast, an End-of-Row (EoR) design centralizes switches at the row end, requiring long horizontal cables from each server to the row cabinet. This can lead to thousands of extra copper or fiber runs in large deployments.

ANSI/TIA-942 and Cisco Design Guides emphasize that ToR is the best solution for minimizing cable bulk, improving airflow, and reducing cost in hyperscale or dense rack environments.

Thus, if the explicit design goal is to minimize cable quantity, ToR design is superior.

In areas with frequent and extended power outages, continuous generators with at least an N+1 configuration are necessary to ensure consistent power availability. Continuous generators are designed for prolonged operation, making them suitable for scenarios where utility power is frequently unavailable, as in this case with outages exceeding 650 hours per year. An N+1 configuration ensures redundancy, which is critical for maintaining uptime in a high-availability data center.

Detailed Explanation:

Continuous generators provide reliable power over long durations, unlike standby generators, which are intended only for short-term use. The N+1 configuration ensures that there is always an additional generator available in case of failure, thus maintaining power supply even if one generator goes offline.

EPI Data Center Specialist References:

EPI best practices recommend continuous generators with redundancy for data centers located in areas with high power instability to maintain reliability and continuous operation.

When calculating Power Usage Effectiveness (PUE) in a data center that uses chilled water from an external source, like from a building owner, a weight factor for district chilled water must be applied. This is because PUE calculations aim to measure the energy efficiency of the data center’s own operations, and external utilities like district chilled water aren’t directly powered by the data center. A weight factor of 0.4 is typically used to account for the energy consumed to produce and deliver the chilled water, reflecting the indirect impact on the data center’s total energy consumption.

Detailed Explanation:

PUE is calculated as the ratio of the total facility energy to the IT equipment energy. If the cooling is provided by an external chilled water source, it’s necessary to adjust the calculations to accurately reflect the energy impact. By incorporating the 0.4 weight factor, data centers can calculate a more accurate PUE, aligning with standard methods and industry best practices.

EPI Data Center Specialist References:

EPI training on PUE highlights the importance of adjusting for external energy sources, such as district cooling, in the calculations. This ensures that PUE values remain accurate and comparable across different data centers, even when external utilities are used.

From an efficiency standpoint, Unit B with a Sensible Heat Ratio (SHR) of 0.9 is preferable. A higher SHR indicates that a greater proportion of the air conditioner's capacity is dedicated to sensible cooling (temperature reduction) rather than latent cooling (moisture removal). In data centers, sensible cooling is more critical since IT equipment primarily generates heat without adding significant moisture.

Detailed Explanation:

An SHR of 0.9 means that 90% of the cooling capacity is used for sensible cooling, which is more efficient for environments like data centers where humidity control is typically less of a concern. Opting for an air conditioner with a higher SHR ensures that most of the cooling energy is focused on temperature reduction, making Unit B more efficient in this scenario.

EPI Data Center Specialist References:

EPI data center best practices recommend choosing cooling units with higher SHR values in data centers, as they better match the cooling needs of IT equipment. High SHR units improve cooling efficiency by concentrating on sensible heat removal, which is vital for maintaining the optimal thermal environment.

SHR = Sensible Load / (Sensible + Latent Load); it describes the portion of the total cooling that is sensible (temperature change) versus latent (moisture removal).

The attenuation factor for shielding material is typically calculated using the formula A = 20 log (R / M). This equation provides the attenuation in decibels (dB), where R represents the measured electromagnetic field strength, and M is the maximum acceptable level. The logarithmic scale helps quantify how much the shielding reduces EMF levels relative to the maximum allowable value.

Detailed Explanation:

This formula calculates attenuation by comparing the measured value with the acceptable threshold, with the result expressed in decibels. A higher attenuation indicates more effective shielding material, essential for environments requiring robust EMF management.

EPI Data Center Specialist References:

EPI standards include the use of logarithmic formulas to evaluate attenuation levels, ensuring that shielding materials provide adequate reduction in EMF to protect sensitive equipment within data centers.