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Electrical Power Terms/Rack PDU Planning for IT Equipment
What You Need to Know
PRESENTED BY
Joe Prisco Senior Technical Staff Member, IBM
Learning Objectives
• Review basic power terms and power consumption values
• Analyze variables that influence power consumption when IT equipment is in operation
• Identify how the IT equipment power train is designed for rack PDU plugging and rack PDU and its limitations
• Review a detailed example of placing IT equipment on rack PDUs
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Basic Electrical Power Terms
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Real Power (Watts)
Apparent Power (VA)
Reactive Power (VAR)
• Watts – Active power or usable
electricity – Heat output (BTU/hr = watts
x 3.413) • VAR (Volt Amps Reactive)
– Imaginary power or wasted electricity
– Stored in capacitors and inductors
• VA (Volt Amps) – Vector sum of the watts and
VAR – Total power available at the
line cord of a piece of equipment
Watts, VA, and VAR are not the same thing VA is the term most useful for electrical planning inside a mission critical facility VA = Volts x Amps
Other Helpful Power Terms
• kWh (Kilowatt Hour) – How the utilities measure
electricity consumption – 100-watt light bulb uses 1 kWh
every 10 hours (0.100 kW x 10 hours)
• PF (Power Factor) – Ratio of the real power (watts)
to the apparent power (VA) – Ranges from 0 to 1
• A higher PF is better • Utilities may impose fees for
low power factor because of the need to increase their generation and transmission capacity
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Low Power Factor High Power Factor
0.1= 100 𝑊𝑎𝑡𝑡𝑠/𝟏𝟎𝟎𝟎 𝑽𝑨
1.0= 100 𝑊𝑎𝑡𝑡𝑠/𝟏𝟎𝟎 𝑽𝑨
Power Consumption Values
• Nameplate – Product safety rating label – Used for electrical code compliance
• Maximum measured power consumption
– Found in physical planning manuals – Worst case power consumption – Used for UPS and switchgear loading
• Benchmark – Power consumption running an
industry standard performance benchmark
– Used in HPC environments to reduce the electrical demand overhead
• Actual power consumption – Typical, every day value – Used for air conditioning heat
rejection calculations
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Nam
epla
te
Actual measured
power
Benc
hmar
k
Max measured
power
Nameplate – PDU (Ships Worldwide)
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• The nameplate includes all the mandatory legal compliance marks and information
• The most important data is about the input electrical service
– Voltage (V) – Amperage (A)
overcurrent protection • 24 amps x 125% = 30 A
service • 48 amps x 125% = 60 A
service – Calculate VA = V x A
• Use low-line volts • 200V x 24A = 4.8 kVA • 200V x 48A = 9.6 kVA
EMC
Compliance ID Product Safety
Environmental
Single Point of Contact
Use nameplate to size your electrical distribution to meet electrical code requirements
Maximum Measured Power Consumption • Worst case power consumption
– Largest configuration – Highest utilization – Abnormal conditions that affect
fan speed • Internal hardware failures (e.g.,
power supply) • High ambient temperature
• Look for published maximum VA (Volt Amps) – If VA is not available, an
alternative is maximum watts • Convert to VA using power factor • VA = Watts / PF • For most IT equipment, power
factor is close to 1
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Maximum Measured Power High Ambient Temperature Impact
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Source: 2011 The
rmal Guide
lines fo
r Data Processin
g En
vironm
ents
• Power consumption is affected by fan power, component power (leakage current), and power conversion
• If the Inlet temperature increases from 15°C to 35°C, the IT equipment power could increase in the range of 7 to 20%
°C
• With the increase in fan speed over the range of ambient temperatures, the IT flowrates also increase
• The cubic feet per minute (CFM) demand of the IT equipment must be satisfied or else recirculation could further increase inlet temperature
Actual Power Consumption
• Expected, steady-state typical value for a specific configuration under normal environmental operating conditions
• The values are very aggressive because they are used in TCO calculations
• The mechanical system can better handle fluctuations and spikes in heat load, even if it crosses a predetermined threshold for a short period of time
• The typical power consumption can be used for all cooling calculations (e.g., kW/rack, heat load balance, watts/square foot)
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Maximum Measured Power Consumption = 1420 W
8286-41A
Next Up - PDUs
• Now you know… – Basic power terms
• Watts • VAR • VA
– Power consumption values • Nameplate • Maximum measured power consumption • Actual power consumption
• Rack Power Distribution Units (PDUs) – What is a PDU? – General planning concepts – Rack PDU design, plugging, and
limitations – Detailed planning example
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PDU & General Planning Concepts
• Rack Power Distribution Unit Definition – Brings electrical power in from the facility and distributes it to server,
storage, and networking hardware inside a rack – Think of it as a power strip with superior features
• Primary circuit breaker protection • Optional: metering, Ethernet communications, relays
• General Planning Concepts – IT Equipment connected to PDU receptacles must be based on either UL
nameplate rating or UL reported maximum measured power consumption • National Electrical Code requirement (continuous load) • Exceptions
– Clearly defined configuration restrictions – Measurements for a period of time in the data center
– Circuit breakers are unforgiving when overloaded, even for very short amounts of time
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Steps to Rack PDU Planning
1. Understand the PDU A. Maximum input amperage B. Output receptacle quantity and limitations
i. Receptacle ratings ii. Circuit breaker ratings
C. Desired level of redundancy
2. Identify the IT equipment to be connected to the PDU A. Find the maximum measured power consumption from the
manufacturer’s technical specification B. Calculate the amperage
3. Place the IT equipment on the PDU and check for rating violations based on item #1
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Step 1 – Understand the PDU
Step 1A – Maximum Input Voltage and Amperage Step 1B – Output receptacle quantity and limitations • Each individual IEC 320-C13 receptacle (1-12) can
support up to 10 amps • Each pair of receptacles (a-f) is protected by a 20
amp circuit breaker derated to 16 amps • Every 4 outlets are on a phase (L1-N, L2-N, L3-N) when
line cord is 3 phase wye (European type electricity distribution)
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Line Cord Plug Voltage Rated Amps
#1 NEMA L6-30 200-208 24
#2 IEC 309-32 220-240 32
#3 IEC 309-60 200-208 48
#4 IEC 309-63 220-240 63
Step 1C – Level of Redundancy
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Each AC power supply (#1 and #2) in a dual corded piece of IT equipment is connected to a separate power panel (typically for maintenance reasons)
The IT equipment is designed to run on a single AC power supply
This data center redundancy layout is designed to carry the IT equipment redundancy to the wall
Typically referred to as A-‐side/B-‐side or leP-‐side/right-‐side redundancy
#1 #2
Steps 2 and 3 – IT Equipment and PDU Calculations and Checks (I) • Dual Corded IT Equipment
– Divide maximum measured VA (Volts Amps) by “lowline” Volts (200 V)
– EQ1 = 1750 VA / 200V = 8.75 amps – EQ2 = 1800 VA / 200 V = 9.00 amps
• PDU Input – Line cord #1 – 24 amps (page 13) – A-side/B-side redundant
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EQ1
EQ2
Equipment Amps Outlet Pair Pair Amps PDU Total Amps
EQ1 8.75 a – 1 8.75 8.75
EQ2 9.00 a – 2 17.75 17.75
P D U 1 & 2
P D U 1
P D U 2
Pair “a” amps less than 16 – Fail PDU total amps less than 24 – OK # of line cords less than 12 per PDU – OK
Steps 2 and 3 – IT Equipment and PDU Calculations and Checks (II) • Dual Corded IT Equipment
– Divide maximum measured VA (Volts Amps) by “lowline” Volts (200 V)
– EQ1 = 1750 VA / 200V = 8.75 amps – EQ2 = 1800 VA / 200 V = 9.00 amps
• PDU Input – Line cord #1 – 24 amps (page 13) – A-side/B-side redundant
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EQ1
EQ2
Equipment Amps Outlet Pair Pair Amps PDU Total Amps
EQ1 8.75 a – 1 8.75 8.75
a – 2
Pair “a” amps less than 16 – OK Pair “b” amps less than 16 – OK PDU total amps less than 24 – OK # of line cords less than 12 per PDU – OK
P D U 1 & 2
P D U 1
P D U 2
Equipment Amps Outlet Pair Pair Amps PDU Total Amps
EQ2 9.00 b – 3 9.00 17.75
b – 4
Steps 2 and 3 – IT Equipment and PDU Calculations and Checks (III)
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EQ1
EQ2
Equipment Amps Outlet Pair Pair Amps PDU Total Amps
EQ1 8.75 a – 1 8.75 8.75
a – 2
Pair “a” amps less than 16 – OK Pair “b” amps less than 16 – OK Pair “c” amps less than 16 – OK PDU total amps less than 24 – Fail # of line cords less than 12 per PDU – OK
P D U 1 & 2
P D U 1
P D U 2
Equipment Amps Outlet Pair Pair Amps PDU Total Amps
EQ2 9.00 b – 3 9.00 17.75
b – 4
Equipment Amps Outlet Pair Pair Amps PDU Total Amps
EQ1 8.75 c – 5 8.75 26.50
c – 6
EQ1
Steps 2 and 3 – IT Equipment and PDU Calculations and Checks (IV)
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EQ1
EQ2
Equipment Amps Outlet Pair Pair Amps PDU Total Amps
EQ1 8.75 a – 1 8.75 8.75
a – 2
Pair “a” amps less than 16 – OK Pair “b” amps less than 16 – OK PDU total amps less than 24 – OK # of line cords less than 12 per PDU – OK
P D U 1 & 2
P D U 1
P D U 2
Equipment Amps Outlet Pair Pair Amps PDU Total Amps
EQ2 9.00 b – 3 9.00 17.75
b – 4
Equipment Amps Outlet Pair Pair Amps PDU Total Amps
EQ1 8.75 a – 1 8.75 8.75
a – 2
EQ1
P D U 3 & 4
P D U 3
P D U 4
Real Life Example
I’m out of power capacity, what can I do to add more equipment?
• Problem – 180 A of ampacity available – 172 A used (sum of values in
green) – Need to add two pieces of
IT equipment @ 11 amps each
• Solution – Use NFPA 70 (National
Electrical Code) – Article 220.87 Determining
Existing Loads
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Circuit breaker rated amperage Derated circuit breaker amperage Calculated maximum measured amperage from planning guide
30 A (24 A) 30 A (24 A)
60 A (48 A) 60 A (48 A)
20 A (16 A) 20 A (16 A)
20 A (16 A) 20 A (16 A)
17 A
200 A (180 A)
41 A
14 A
14 A
23 A
37 A
13 A
13 A
Power Panel
Real Life Example Continued
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30 A (24 A) 30 A (24 A)
60 A (48 A) 60 A (48 A)
20 A (16 A) 20 A (16 A)
20 A (16 A) 20 A (16 A)
12 A
200 A (180 A)
25 A
11 A
10 A
14 A
21 A
9 A
8 A
Power Panel
Circuit breaker rated amperage Derated circuit breaker amperage Measured maximum demand amperage of installed equipment
• NEC 220.87 – Continuously record the demand
(loads averaged in 15-minute intervals) over a minimum 30-day period and find maximum demand
– Factor in conditions that can impact the power consumption of the equipment
• Load Study Analysis – 110 A maximum demand (sum of
values in blue) – Maximum demand at 125% plus the
22A new load does not exceed 180A
• 110 x 1.25 = 138 amps • 138 + 22 = 160 amps
• Tips – Consult your local electrical code
authority – Don’t forget about redundancy – Ensure there is a hardware change
management process
I’ll Leave You With
• Local Fire Marshal was not going to allow a PDU to be fed from a UPS – UPS is considered a power strip because it has multiple outputs – No multiple output strip (power strip, surge protector, PDU) can be plugged into UPS unless
hard wired and/or specifically designed and documented from manufacturer • Solution – Education on product safety certification
– A power strip usually has a single fuse and meets UL 1077 – A PDU has multiple circuit breakers compliant to UL 489 and provides primary branch circuit
protection which is analogous to a room UPS feeding a circuit breaker panel
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