# Power And Cooling CBT

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Switchanddatause
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Quizzes Created: 1 | Total Attempts: 148
Questions: 19 | Attempts: 148

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This Power and Cooling CBT is used to test the knowledge of NAMs on site specs and offerings.

• 1.

### A "One Line Diagram" or a "Single Line Diagram" is:

• A.

A drawing showing the major components of a system and how they are linked together.

• B.

Usually considered “confidential” and rarely shared with Customers.

• C.

Used to show the topology of major facility infrastructure.

• D.

All of the above

D. All of the above
Explanation
A “One Liner,” “SLD,” or “Single Line Diagram” is a drawing that shows the major system components of a facility infrastructure, and how they’re connected so that the topology of systems can be documented. This documentation is usually considered extremely confidential, and is seldom shared externally. Executive level approval is necessary to share a SLD with a Customer. The questions leading to a request to see the SLD can often be answered without showing the actual SLD.

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• 2.

### The two types of power circuits are:

• A.

Amperage Current and Digital Current

• B.

Alternating Current and Digital Current

• C.

Alternating Current and Direct Current

C. Alternating Current and Direct Current
Explanation
Alternating Current (AC) and Direct Current (DC) are the two types of electricity distribution.

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• 3.

### The term, “UPS” stands for:

• A.

Universal Power Supply

• B.

United Parcel Service

• C.

Uninterruptible Power Supply

• D.

Uniform Power Surge

C. Uninterruptible Power Supply
Explanation
The correct answer is “c,” Uninterruptible Power Supply. “UPS” is also an acronym for United Parcel Service, but that has nothing to do with what we’re talking about here.

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• 4.

### Place the following electrical components in order, from highest upstream (utility company) to lowest downstream (IT equipment on the floor).

• A.

PDU, UPS, Generator, Substation

• B.

Substation, Generator, UPS, PDU

• C.

Generator, Substation, UPS, PDU

• D.

UPS, PDU, Generator, Substation

B. Substation, Generator, UPS, PDU
Explanation
The correct order is B. Power from utility lines is stepped down for local service at the utility substation. The facility’s power service is delivered from the substation to the building. A generator is staged at the facility and provides backup power in case the utility service is lost. The UPS accepts power from both the utility line and the generator, conditioning that power and maintaining necessary power levels during the switchover between utility and backup generator power. The power feed from the UPS is delivered to the Power Distribution Unit (PDU), which distributes power to the individual power circuits feeding the racks on the floor.

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• 5.

### Power (Watts) is the product of voltage (Volts) and current (Amps), or  P = V x I.   If we have one, 120 VAC single phase circuit at 20 Amps, the corresponding power is:

• A.

240 W

• B.

2.4 KW

• C.

60 W

B. 2.4 KW
Explanation
The correct answer is “B,” 120 x 60 = 2,400 or 2.4 kilowatts

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• 6.

### Three Phase AC circuits are comprised of three independent electrical potentials, offset by 120 degrees.  Power (Watts) is the product of voltage (Volts) and current (Amps), or  P = V x I.   If we have a single 208 VAC three phase circuit at 30 Amps, the corresponding power is:

• A.

6.2 KW

• B.

749 KW

• C.

10.8 KW

C. 10.8 KW
Explanation
The correct answer is “C,” 10.8 KW. Three phase is a more efficient transmission method than single phase. The 120 degree phase difference between AC waveforms introduces an efficiency gain of the Sin(120°) phase shift for two of the three waves, which introduces a multiplier of 1.73 into the equation. Said another way, if you know you’re talking about 3-phase power rather than single phase power, always remember that the 3-phase power is going to be more than if you were talking about single phase.

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• 7.

### An Uninterruptible Power Supply does what?

• A.

Provides power backup during a power outage

• B.

Conditions power, changing power from “dirty” to “clean”

• C.

All of the above

• D.

None of the above

C. All of the above
Explanation
The role of a UPS is to condition power coming from the generator or utility, and to provide backup power in the case of a utility service interruption. The UPS typically charges a bank of batteries that maintain the power level coming out of the UPS while the power supply is transferred from the main utility power to the backup generator power.

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• 8.

### Utility power is delivered to the data center as DC power.  It is then converted to AC power by the Generator and UPS.

• A.

True

• B.

False

B. False
Explanation
Utility power is AC power. It is not economical to distribute DC power over long power lines. The power that comes into your home or the data center is always AC power.

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• 9.

### Which of the following is a derived unit of heat energy for heating or cooling capacity?

• A.

BTU

• B.

Watt

• C.

Volt

• D.

Amp

A. BTU
Explanation
The British thermal unit (BTU or Btu) is a unit of energy used in the power, steam generation, heating and air conditioning, and data center industries. In North America, the term "BTU" is used to describe the heat value (energy content) of fuels, and also to describe the power of heating and cooling systems, such as furnaces and air conditioners. Heat dissipation through the use of applied power is often also expressed in terms of Watts, but BTU is specifically and only about heat energy. One Watt equals 3.413 BTU’s.

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• 10.

### What is the difference between “Breaker” and “Load” power?

• A.

Breaker power is the rating of the circuit breaker and Load power is the power at which the circuit breaker will trip.

• B.

Breaker power is the amount of power that will trip the circuit breaker and load power is the size of the power feed from the utility company.

• C.

Breaker power is the amount of power delivered to the rack/cabinet and load power is the amount of power drawn that will trip the circuit breaker.

• D.

Breaker power is the amount of power available to be delivered to the rack/cabinet and Load power is the amount of power used by the equipment in the rack/cabinet.

D. Breaker power is the amount of power available to be delivered to the rack/cabinet and Load power is the amount of power used by the equipment in the rack/cabinet.
Explanation
The correct answer is “D.” Breaker power is the power provisioned to the rack or cabinet from the PDU. The amount of power drawn by the IT equipment in the rack or cabinet is referred to as the load or “draw.”

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• 11.

### The capacity of a data center is expressed in terms of:

• A.

Watts per Square Foot

• B.

Watts per Cabinet

• C.

Both “a” and “b”

C. Both “a” and “b”
Explanation
Data center capacity is expressed either in terms of W/sf or W/cabinet… and sometimes both at the same time. Because the consumption of data center capacity is increasingly defined by power and cooling rather than space, the W/cabinet rating is becoming a more relevant way to talk about capacity.

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• 12.

### True or False:  Three Phase DC power is more efficient than Three Phase AC power?

• A.

True

• B.

False

B. False
Explanation
This is a dirty rotten trick question. There is no such thing as three phase DC power. It should be noted though, that DC power is generally more efficient for data centers than is AC power. There just aren’t any phases to talk about in DC power.

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• 13.

### The reason that we have limits on the amount of power we will support in any one rack or cabinet is:

• A.

The size and weight of power cables to any one cabinet has to be controlled because of the limitations of the overhead ladder racks supporting those cables.

• B.

We have allocated a budget for the amount of power we will deliver to any one rack on the floor.

• C.

A “hot” cabinet will negatively impact adjacent Customer cabinets because of the site’s capacity to cool the cabinets.

• D.

The floor space is pre-wired for a certain maximum power, and provisioning power beyond those levels requires additional NRC.

C. A “hot” cabinet will negatively impact adjacent Customer cabinets because of the site’s capacity to cool the cabinets.
Explanation
The best answer is “C.” The balance of power and cooling is very sensitive in building and maintaining the data center. Each site, and each suite within a site, is built with a finite cooling capacity. The cooling technology in most of our sites is an under-floor pressurized cold air plenum. Placement of a cabinet that dissipates more than the maximum per-cabinet heat requires additional air flow at the cold side of that cabinet. Doing so takes away from capacity in other locations on the floor, and complicates the capacity planning for future installations within that suite.

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• 14.

### The Power Rating increments that we use for our basic product set are:

• A.

2KW, 4KW, and 7.2KW

• B.

4KW, 6KW, and 7.2KW

• C.

2.4KW, 4KW, and 6KW

• D.

2.4KW, 4.8KW, and 7.2KW

C. 2.4KW, 4KW, and 6KW
Explanation
The answer is “C.” The three basic Power Rating increments we use for cabinets and racks is 2.4kw, 4kw, and 6kw. A third, higher rated, cabinet offering is being defined as well. These replace our freeform space/power method of developing Customer solutions where we had 4.8kw and 7.2kw standard power limits.

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• 15.

### DC power is a constant voltage and current level that is not time dependent.  AC power, on the other hand, follows a sinusoidal wave form that changes over time at a rate of 60 cycles per second (60Hz) (in North America).  The following is a graph of an AC voltage waveform: If this is the voltage waveform measured at the output of the power circuit, what is the AC power implied by this graph?

• A.

170 VAC

• B.

340 VAC

• C.

120 VAC

• D.

0 VAC

C. 120 VAC
Explanation
The correct answer is “C,” 120 VAC. This is a typical 120 volt AC supply from a wall outlet. AC circuit power is expressed as a root mean square (RMS) of the peak voltage. Said another way, it’s an average voltage potential value. Since it is a sinusoidal wave form, this is derived by multiplying the square root of 2 divided by 2, times the peak voltage (or 0.707*VP). Similarly, one can compute the peak voltage from the RMS value by multiplying the RMS value by the square root of 2. Answer “A” is the peak voltage. Answer “B” is the peak-to-peak voltage.

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• 16.

### IT equipment installed in a colo facility is usually dual corded, meaning it contains two power supplies.  This is so that the equipment can operate even if a power supply fails, which is a fairly common occurrence.  If a server has two, 500 Watt power supplies, what is the maximum power that it will draw?

• A.

500 Watts

• B.

1,000 Watts

• C.

250 Watts

A. 500 Watts
Explanation
The correct answer is “A,” 500 Watts. In normal operation, the dual power supplies load share, and the system is designed so that any one supply can fail but the server will continue to operate. We do not “add up” the redundant power supplies. It should further be noted that the nameplate rating on the power supply, in this case 500W, is a maximum rating of the supply. By design, because power supplies have low MTBF comparatively, the system is designed so that the power supply is not running at maximum load. There are high efficiency power supplies that approach maximum load, but rule of thumb is that the actual maximum draw of a device is less than the nameplate rating of its power supply.

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• 17.

### The term, “Minimum Cabinet Rating” (MCR), is a new term used at Switch and Data that identifies the lowest rating level of cabinet that we will sell to a Customer in a given site.  It is computed by taking the total rated power across all the cabinets owned by that Customer in that site, and dividing by the number of cabinets they own in that site, and rounding up to the next highest cabinet rating.  For example, if Acme Co. has four 2.4kw cabinents, three 4kw cabinets, and five 6kw cabinets, the MCR = [ (4 * 2.4) + (3 * 4) + (5 * 6)] / (4 + 3 + 5) = [9.6 + 12 + 30]/12= 51.6/12= 4.3, rounded to 6… or MCR=6. Use the following example to compute the MCR: The CSE examines the Customer’s equipment inventory, and concludes that there will be five cabinets with actual power draw as follows: Cabinet 1:  4.8kw Cabinet 2:  1.8kw Cabinet 3:  3.5kw Cabinet 4:  5.8kw Cabinet 5:  3.8kw   What is the MCR for this Customer?

• A.

1.8kw

• B.

2.4 kw

• C.

4kw

• D.

6kw

C. 4kw
Explanation
5 cabs with utilization as follows. Assume no growth, etc.
1. 4.8kw =6kw rating
2. 1.8kw =2.4kw rating
3. 3.5kw =4kw rating
4. 5.8kw =6kw rating
5. 3.8kw =4kw rating
Total of 19.7kw, divided by 5 cabs = 3.94kw, and we round up to 4Kw = MCR.
Answer “A” is not a valid choice, as there is no 1.8kw rated cabinet in our product set. Answer “B” is the lowest

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• 18.

### Which of the following is true about “load” versus “breaker” power?

• A.

Load amps is always greater than breaker amps

• B.

Load must be no more than 80% of breaker amps

• C.

Both load and breaker current are important in designing a Customer solution

• D.

Both B and C

D. Both B and C
Explanation
The correct answer is “D.” We create a target of 80% of the breaker capacity as the maximum load allowed on the circuit. It’s important to understand both the running load as well as the breaker capacity when designing solutions, because factors such as start-up spikes and utilization cycles contribute excess draw on the circuit.

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• 19.

### What is the primary purpose of a raised floor in the data center?

• A.

It is a cold air plenum for cooling of Customer equipment

• B.

Enhance survivability of Customer equipment in case of a flood in the data center

• C.

It is where cabling is located so that the raised floor is not cluttered with wiring

• D.

The scaffolding of the raised floor distributes the weight of Customer equipment allowing the data center floor to bear more load