CDCP Certified Data Centre Professional (CDCP) Questions and Answers

The requirement of Concurrently Maintainability becomes relevant starting from Rated-3, according to the Uptime Institute Tier Classification System1. Concurrently Maintainability means that any component or system in the data centre can be maintained or replaced without affecting the availability of the IT equipment. This requires having redundant capacity components and multiple independent distribution paths serving the IT equipment. Rated-3 data centres are designed to achieve Concurrently Maintainability and have a minimum uptime of 99.982%. Rated-4 data centres also have Concurrently Maintainability, but they also have Fault Tolerance, which means that they can withstand any single unplanned event without affecting the availability of the IT equipment. Rated-4 data centres have a minimum uptime of 99.995%. Rated-1 and Rated-2 data centres do not have Concurrently Maintainability, as they have only one distribution path serving the IT equipment and no redundant capacity components. Rated-1 data centres have a minimum uptime of 99.671% and Rated-2 data centres have a minimum uptime of 99.741%.

References:

1: Uptime Institute Tier Classification System2, page 1, section 1 2: Data Center Tiers Classification Explained: (Tier 1, 2, 3, 4)3, page 1, section 1 3: Data Center Tier Standards4, page 1, section 1

According to the IBM document on temperature and humidity design criteria1, the temperature and humidity values indicated on the display of the computer room air conditioner unit are the values measured at the intake of the air conditioner. This is because the intake is where the air conditioner draws the air from the computer room and cools and dehumidifies it before sending it back to the computer room. The display shows the current conditions of the computer room air, which are used to adjust the cooling and dehumidifying operations of the air conditioner. The values measured at the exhaust (outlet) of the air conditioner are not displayed, as they are not relevant for the computer room environment. The values measured at the front of the rack of the aisle the air conditioner is situated are also not displayed, as they may vary depending on the distance and location of the rack. The average value between the intake and exhaust (outlet) of the air conditioner is not displayed, as it does not reflect the actual conditions of the computer room air or the air conditioner performance.

References: 1: Temperature and humidity design criteria - IBM

Busbar trunking systems are a method of power distribution using rigid copper or aluminium conductors to distribute the power around a building. Busbar trunking systems have many advantages over cables, such as lower space requirements, higher short-circuit strength, lower fire load, and easier installation. One of the main advantages of busbar trunking is that it allows for flexibility in terms of power transmission and distribution. Busbar trunking systems can be easily relocated, modified, or expanded to accommodate changes in the building layout or load demand. Busbar trunking systems can also be fitted with various components, such as tap-off units, elbows, tees, and end feed units, to provide power to different locations and consumers. Busbar trunking systems can also be installed both overhead and under the raised floor, depending on the design and preference of the building.

References: Why I prefer busbar trunking systems more than cables | EEP, Why should you choose Busbar over Cable? - E+I Eng, Busbar VS Cables for Riser Applications - An Electrical Engineer.

According to the CDCP Preparation Guide1, magnetic fields of the type ‘H’ or ‘B’ are created when an electric current flows through a conductor, such as a wire or a coil. The magnetic field strength ‘H’ is proportional to the current ‘I’ and the number of turns ‘N’ of the coil, and inversely proportional to the length ‘l’ of the coil. The magnetic flux density ‘B’ is proportional to the magnetic field strength ‘H’ and the permeability ‘μ’ of the medium in which the magnetic field exists. The greater the current, the stronger the magnetic field and the magnetic flux density. The relationship between ‘H’, ‘B’, ‘I’, ‘N’, ‘l’, and ‘μ’ can be expressed by the following equations:

H = N I / l

B =μH

References:

1: CDCP Preparation Guide, page 23, section 2.4.2.1 2: Difference between B and H in magnetic fields?3, page 1, section 1 4: Magnetic field | Definition & Facts5, page 1, section 1

The type of copper wire that is used for grounding the racks to the SRG (signal reference grid) in a data centre is braided copper wire or flat copper strip, according to the CDCP Preparation Guide1 and various web sources234. Braided copper wire or flat copper strip are preferred over thin or thick copper cable for grounding purposes, because they havelower impedance and higher surface area, which allow better dissipation of electrical noise and interference. Moreover, braided copper wire or flat copper strip are more flexible and durable than copper cable, which make them easier to install and maintain. Braided copper wire or flat copper strip should be connected to the SRG using exothermic welding or other code-compliant methods, and should follow the relevant standards and codes, such as ANSI/TIA/EIA-607 and NFPA 70.

References:

1: CDCP Preparation Guide, page 23, section 2.4.2 2: Signal Reference Grid | Enterprise Data Center Design and Methodology5, page 1, section 1 3: Grounding System Ground Rod Stacking Installation - Rain Bird6, page 1, section 1 4: SmartRack Copper Bus Grounding Bar - Eaton Website7, page 1, section 1

According to the CDCP Preparation Guide1, risk can be defined as the product of impact and probability. Impact is the measure of the negative consequences or losses that may result from a risk event, such as downtime, data loss, or damage to the data centre. Probability is the measure of the likelihood or frequency of a risk event occurring, based on historical data, expert judgment, or statistical analysis. By multiplying impact and probability, risk can be quantified and compared, which helps in prioritizing and mitigating the risks. For example, a risk event that has a high impact but a low probability may have the same risk level as a risk event that has a low impact but a high probability.

References:

1: CDCP Preparation Guide, page 25, section 2.5.1 2: Data center risk assessment: A decision-making tool3, page 1, section 1 4: Accounting for Risk in Your Data Center Design/Build Strategy5, page 1, section 1 6: A Novel Framework for Data Center Risk Assessment7, page 1, section 1

According to the EPI Data Centre Training Framework, lithium-ion batteries are becoming more popular in data centres due to their higher energy density, longer lifespan, and lower maintenance costs compared to lead-acid batteries1. However, lithium-ion batteries also have some drawbacks, such as higher initial cost, stricter safety requirements, and potential thermal runaway risks1. Therefore, a battery management system (BMS) is essential to monitor and control the voltage, current, temperature, and state of charge of each battery cell or module, and to prevent overcharging, over-discharging, or overheating23. A BMS can also communicate with the UPS system and provide information on the battery status, performance, and health2.

References: 1: EPI Data Centre Training Framework, Module 5: Power, Section 5.3.2: Battery Technologies, Page 5-19 2: Benefits of Lithium-ion batteries for data centers at the edge,Data Center Knowledge, Page 1 3: Lithium-Ion Batteries in Data Centers, Data Center Systems, Inc, Page 1

Shielded twisted pair cables (STP) are Ethernet cables that feature additional protection against electromagnetic interference from external sources, such as radio waves, microwaves, or other network cables. This is achieved by wrapping each pair of wires with a conductive shield, usually made of foil or braided wire, and then enclosing the entire cable with another shield layer. However, this shielding is not effective against low frequency electromagnetic fields (EMF) from power cables, which can induce currents and voltages in the network cables and cause signal distortion or data loss. Low frequency EMF can only be reduced by increasing the distance between the power and network cables, or by using a tre-foil cable arrangement, which is a special configuration of three power cables twisted together to cancel out the magnetic fields they generate.

References: STP Cable: Your Shield Against Network Disturbances; What is Shielded Twisted Pair Cable? - Advantages, Disadvantages; Shielded vs. Unshielded Cables: What’s the Difference? - Cable Matters.

Direct air handlers are a type of cooling system that use outdoor air to cool the data centre. They draw in fresh air from outside, filter it, and supply it to the data centre at the desired temperature and humidity level. Direct air handlers can reduce the energy consumption and operating costs of data centres by eliminating the need for mechanical cooling or refrigeration. However, they also have some challenges and limitations that need to be considered. One of the main factors to consider when using direct air handlers for data centres is the temperature, humidity and contamination of the outdoor environment. Depending on the location and climate of the data centre, the outdoor air may not always be suitable for cooling the data centre. For example, if the outdoor air is too hot, too humid, or too polluted, it may not provide enough cooling capacity, or it may damage the IT equipment or cause corrosion. Therefore, direct air handlers need to have sensors and controls to monitor the outdoor air quality and adjust the airflow accordingly. They may also need to have backup cooling systems or supplementary cooling devices, such as evaporative coolers or heat exchangers, to cope with extreme weather conditions or peak loads.

References: Data Center Cooling: A Comprehensive Guide - Dgtl Infra, Carrier Data Center Cooling System 39DC, Dublin Data Center: Rooftop Air Handlers.

The UPS (uninterruptible power supply) is a device that provides backup power to the ICT equipment in case of a power outage or a power quality issue. The UPS should be dedicated to the ICT equipment only, and not to other loads, such as lighting, cooling, or security systems. This is because connecting fluorescent lights to the same UPS as the ICT equipment can cause several problems, such as:

•Reducing the battery runtime of the UPS, which may not be enough to support the ICT equipment until the backup generator kicks in or the utility power is restored.

•Increasing the harmonic distortion of the UPS output, which can affect the performance and reliability of the ICT equipment and the UPS itself.

•Creating electromagnetic interference (EMI) or radio frequency interference (RFI), which can disrupt the communication and data transmission of the ICT equipment.

•Triggering false alarms or tripping the circuit breakers of the UPS, which can cause downtime or data loss.

Therefore, fluorescent lights should not be connected to the same UPS that supports the ICT equipment. Instead, they should be connected to a separate power source, such as the utility power, the backup generator, or a different UPS.

References:

1: CDCP Preparation Guide, page 17, section 2.3.1 2: Data Center Lighting Design Considerations3, page 1, section 3 4: Data Center Lighting Solutions5, page 1, section 1 6: Going beyond energy savings in data centers with LEDs7, page 1, section 2

Data centres are essential for supporting the IT operations and applications of various businesses across different industries. Data centre downtime can have a negative impact on the business results, such as loss of revenue, customer satisfaction, productivity, reputation, and competitive advantage. According to a web search, the average cost of data centre downtime in 2020 was $8,851 per minute, and the average duration of a data centre outage was 95 minutes1. This means that a typical data centre outage could cost a business over $840,000 in direct and indirect losses1. Therefore, data centre downtime can have a significant impact on the business results, regardless of the industry or sector.

References: Unplanned Downtime Costs More Than You Think, Downtime, Outages and Failures - Understanding Their True Costs, The Unplanned Downtime Nightmare — And How Operators Can Avoid

A UPS (Uninterruptible Power Supply) is a device that provides backup power to electrical equipment in case of a power outage or fluctuation. A UPS is essential for both CCTV cameras and recording equipment, as it ensures that the surveillance system can continue to operate and record without interruption or data loss. A UPS can also protect the CCTV cameras and recording equipment from damage caused by power surges or spikes. Connecting both CCTV cameras and recording equipment to a UPS is a requirement for data centres, as it enhances the security and reliability of the surveillance system.

References: Technical Specification - GeM, [What is a UPS? | Uninterruptible Power Supply | APC by Schneider Electric], [Why You Need a UPS for Your CCTV System - CCTV Camera World].

The four main components of a refrigeration circuit are the evaporator, the compressor, the condenser, and the expansion valve, according to the CDCP Preparation Guide1 and various web sources234. A refrigeration circuit is a system that transfers heat from a low-temperature region to a high-temperature region, using a working fluid called refrigerant. The refrigeration circuit operates in a closed loop, where the refrigerant changes its state from liquid to vapor and back to liquid, while absorbing and releasing heat. The four main components of the refrigeration circuit perform the following functions:

•The evaporator is a heat exchanger that absorbs heat from the low-temperature region, such as the data centre room, and transfers it to the refrigerant. The refrigerant enters the evaporator as a low-pressure, low-temperature liquid, and leaves the evaporator as a low-pressure, low-temperature vapor.

•The compressor is a mechanical device that increases the pressure and temperature of the refrigerant vapor. The refrigerant enters the compressor as a low-pressure, low-temperature vapor, and leaves the compressor as a high-pressure, high-temperature vapor.

•The condenser is another heat exchanger that releases heat from the refrigerant to the high-temperature region, such as the outside air or water. The refrigerant enters the condenser as a high-pressure, high-temperature vapor, and leaves the condenser as a high-pressure, low-temperature liquid.

•The expansion valve is a device that reduces the pressure and temperature of the refrigerant liquid. The refrigerant enters the expansion valve as a high-pressure, low-temperature liquid, and leaves the expansion valve as a low-pressure, low-temperature liquid. The expansion valve also controls the flow of the refrigerant into the evaporator, depending on the cooling load.

References:

1: CDCP Preparation Guide, page 19, section 2.3.3 2: The Refrigeration Cycle5, page 1, section 1 3: Fundamentals of Cooling in Data Center6, page 1, section 1 4: The Refrigeration System, Its Four Main Components, And Their Functions7, page 1, section 1

According to the IEEE definition, reliability is the ability of a system or component to perform its required functions under stated conditions for a specified period of time. Reliability is a measure of how often a system or component fails, and how long it takes to recover from a failure. Reliability is closely related to availability, which is the degree to which a system or component is operational and accessible when required for use. Reliability and availability are both affected by factors such as design, maintenance, testing, and environmental conditions.

References: EPI Data Centre Training Framework, CDCP Preparation Guide, Reliability engineering - Wikipedia

When having two non-synchronized power sources, the ATS / STS need to be of the type break before make, which means that the switch disconnects from one source before connecting to the other source. This prevents any short circuit, back feed, or phase mismatch that could occur if the two sources were connected simultaneously. Break before make switches are also known as open transition switches, because they create a brief interruption in the power supply during the switching process. This interruption is usually acceptable for most ICT equipment, as they have internal power supplies or batteries that can handle the transient. However, if the interruption is not acceptable, then the two power sources need to be synchronized before switching, which requires a make before break switch, also known as a closed transition switch. Make before break switches connect to the second source before disconnecting from the first source, which ensures a seamless transfer of power without any interruption. However, make before break switches require that the two sources have the same voltage, frequency, and phase, which can be achieved by using a synchronization module or a phase-locked loop.

References:

1: CDCP Preparation Guide, page 17, section 2.3.1 2: STS in data centres - Borri3, page 1, section 1 4: Using Static Transfer Switches to Enhance Data Center … - Donwil5, page 1, section 1 6: What is an Automatic Transfer Switch (Power)? | Ethan Banks7, page 1, section 1

According to the CDCP® Preparation Guide, an audible signaling and notification device is a device that produces a sound to alert or notify the occupants of a data center of an event or condition. Sirens are examples of such devices, as they can emit loud and distinctive tones to warn of fire, emergency, or security incidents. Strobes, on the other hand, are visual signaling and notification devices that produce flashes of light to attract attention or convey information. Alarms and clocks are not specific types of devices, but rather general terms that can refer to various audible or visual devices.

References: CDCP® Preparation Guide, page 30. Audible Visual Notification | System Sensor | Honeywell. Audible-Visual Signaling Devices - AutomationDirect.

Availability and reliability are two important aspects of data centre performance that measure how often the system is operational and how dependable it is. According to the EPI Data Centre Framework, availability is the percentage of time that a system or component is in an operable state, while reliability is the probability that a system or component will perform its required function under given conditions for a specified period of time. Both availability and reliability can be affected by various factors, such as design, maintenance, human error, power supply, security, etc. One of the factors that can have a significant impact on both availability and reliability is cooling. Cooling is essential for maintaining the optimal temperature and humidity levels for the IT equipment and preventing overheating, which can cause failures, downtime, and reduced lifespan. Inadequate cooling can result from insufficient capacity, poor airflow management, faulty components, or environmental conditions. Inadequate cooling can reduce the availability and reliability of the data centre by increasing the risk of thermal stress, hot spots, performance degradation, and equipment damage. Therefore, cooling is a critical factor that can affect availability and reliability in a data centre.

References:

•EPI Data Centre Framework1

•EPI Data Centre Training Framework2

•EPI Data Centre Competence Framework3

•Data Center Availability, Reliability Hinge On Numerous Factors4

•A Look at Data Center Reliability and Availability5

According to the CDCP® Preparation Guide, Class A fires involve ordinary combustible materials such as paper, wood and cloth. These materials leave behind ash or embers when they burn. Class A fires can be extinguished by water or other cooling agents that reduce the temperature of the fuel below its ignition point.

References: CDCP® Preparation Guide, page 30. Basics of Fire Protection in a Data Center. 3 Levels of Data Center Fire Protection Standards. Three Levels of Data Center Fire Protection.