Chapter 6:
Creating Robust Electrical System
What you will learn:
• Key element for building a reliable DC electrical system
• Design strategies for in-room and standby electrical infrastructure
• Best practice for labeling and system monitoring
• End-to-end testing procedures
Recommended Electrical system Features
• The system should be dependable and ensure the continuous running for
DC components (servers, networking devices,…etc)
• Electrical system should be studied and planed carefully
• System features that need to be included in the design:
System features to avert unnecessary
downtime.
•
•
•
•
Isolated Power
Avoiding Single Points of Failure
Maintenance Bypass Options
Remote Infrastructure Management
Recommended Electrical system Features (Cont.)
• Isolated Power
– Different power source for DC equipments than other electrical
devices in the building
• Avoiding single point of failure
1.
2.
3.
4.
5.
provide standby power system
redundancy for critical devices and functions
physical separation for key systems
don’t share circuit breakers
plan for additional electrical power in the future
Recommended Electrical system Features (Cont.)
• Maintenance Bypass Options
•
Design the system so that regular maintenance can be
performed without the taking major components offline
• Remote Infrastructure Management
• Consider computer based building management
system for mid and large size DC
benefits of such systems would include
1.
2.
Early warning of problems
Savings in terms of staff and running costs
Chosen system should provide high interoperability, easy
to program, graphic interface and produce useful data
metrics
In-Room Power
• Electrical infrastructure elements include:
1. Power distribution units
2. Circuit breaker panels
3. Electrical conduits
4. Wiring configurations
• Choose how to terminate, route and label the components
• Pre power cabinet locations with power receptacles
In-Room Power (Cont.)
Determining Power Requirements:
• Electrical infrastructure should support the room with its full capacity
(completely full with servers)
• The more information about incoming DC equipments the more accurate
calculations for electrical needs
• Provide abundant number of circuits
• Basic formula for the maximum power needed:
max kva =(volts * amps)/1000
example: for a DC with 50 cabinet locations each with two power strip (120
volts & 20 amps)
In-Room Power (Cont.)
Power Distribution:
• Run flexible electrical conduits(whips) from large power distribution
units(PDU) directly to each cabinets for small DC
• Use segmented power for large server environment (running electrical
conduits from PDUs to circuit panels at the end of each row and then a
subset of connections to server cabinet locations).
This option would be easier to manage, less expensive more resistant to
physical accidents
Power Redundancy:
• Require for redundant power supply for each server and network
equipment and plug each one into different receptacle
In-Room Power (Cont.)
Figure 6-3. Direct-Connect Power
Figure 6-4. Distributed (segmented)Power
In-Room Power (Cont.)
• Wiring, components &termination options:
• Be familiar with local power requirements (220/240 volts vs.
100/127 volts) and predominant power requirements for incoming
equipments
• Good design practice:
1.
2.
3.
4.
Use flexible whips (easier to install, less expensive, rearranged
quickly)
Use heavy gauge of wire (the lower the gauge the thicker the
wire)
Don’t terminate more than one receptacle on a conduit
Avoid dirty power
In-Room Power (Cont.)
Labeling & Documentation:
•
Use thorough and unambiguous signage, labeling and documentations that is
understandable by everyone
•
Label power receptacles with the circuits they possess and the location in the
circuit breaker panel where they originate.
•
At that breaker panel, list all of the circuits it contains and which cabinet locations
they are located at
•
Use color-code to indicate parallel infrastructure
•
Create a blue print of the room during construction (as-built) and keep it updated
•
Mark electrical equipments that users need to stay away from it with hazard tapes
In-Room Power (Cont.)
Convenience Outlets:
• Install convenience electrical outlets in multiple locations to be used
instead of cabinet power outlets for rechargeable batteries, power drill,
vacuum cleaner, …etc.
• Don’t connect these outlets to the standby power system
Emergency Power Off (EPO)
• Required by fire codes in many countries
• Intended to prevent fire suppression materials from coming into contact
with live electrical current
• EPO types:
1.
2.
3.
Push-up button (easy to use, most common EPO controls)
Pop-up button (second frequently used, require a new piece of glass to
restore power, accidental activation is less likely)
Control Knob (require the knob to be rotated 90 degrees to activate, better
design, simple to use, accidental activation is less likely)
• It is highly recommended to cover EPO controls with a transparent plastic
shell, wired to an audio alarm.
In-Room Power (Cont.)
Figure 6-6. Sample Emergency Power Off Controls
Standby Power
• Aimed to keep servers & network devices running when main
powers fails
• 3 factors for designing standby system
1.
2.
3.
Redundancy (the more level of redundancy the more complex and expensive
the system would be)
Simplicity
Cost
• Load requirements (start with max. kva load the room can produce
and then adjust in 2 ways:
1.
2.
Size the standby infrastructure to handle 110 to 120 percent of the projected
maximum power needs
Build out your standby infrastructure based upon what level of redundancy
you want for your server environment
• Design the standby system to handle both network & server rooms
if they are close to each other, otherwise, have separate standby
infrastructure if the network room is far from the servers room
Standby Power (Cont.)
Batteries:
• UPS is considered the most common source of standby power
• Use one UPS for each cabinet for small server environment or
temporary DC as they are portable and inexpensive
• large floor-standing UPS model installed in the electrical room are
used for all other size of DC as they are more robust, have greater
capacity
• Run time term is used to identify how long standby infrastructure
can support DC electrical load
• Required run time should be built on the assumption that the room
is fully loaded
Standby Power (Cont.)
Generators:
• Size the generator to support at least 10 percent more than DC maximum
power capacity
• Skip installing generators in small server environment with reliable utility
power and invest more in installing UPS that has 2 hrs of run time
• It is recommended to have generators that can run for 8 hrs before
refueling
• Use enclosed protected area to install generators with short distance from
DC
1.
2.
Protect against unauthorized employees
Protect against noise and vibration
• A good ventilation and enough space around the unite is required
Standby Power (Cont.)
Monitoring Lights:
• Install monitoring lights high up on the both side of the wall inside
(DC entrance, end of DC major aisles), outside and other strategic
locations in the DC to indicate standby system activation
• Use different color demes for UPS and generators (avoid amber or
white as they are used for fire alarms)
• Using large rotating beacon-style lights are recommended
• Installing monitoring lights outside the DC with an explanation
signage with emergency phone number would help non DC users to
report such incident
Standby Power (Cont.)
Figure 6-7 Monitoring Lights for the Standby Power System
Labeling and Documenting
• Make the labeling consistent with the servers room as
possible (using the same terms and labeling schemes)
• Maintain a wiring diagram and keep it current
• No common standards for orienting electrical switches, on
common and simple practice is to mark on position for all
circuits and switches
Installation and Grounding
• Installing of grounding system help protecting electrical
infrastructure and people from excess electrical charges (generated
by faulty circuits, static dischargers, or lightening strike)
• Grounding system usually involves copper wires connected to the
building steel and linked to copper rod deep in the ground (moist
soil)
• Install a second grounding system “Single Reference Grid” to
provide more protection to servers and network devices from
interference, it should be connected to each power distribution
unite and air handler
Testing and Verification
• The contractor must perform a series of tests before any servers/devices
are installed in the DC to make sure that the infrastructure work as it
should be
• Area of testing
1.
2.
3.
4.
5.
Load bank test (make sure that both UPS and generator can support the level of
power as designed, the goal is to check the max. capacity and runtime of the UPS)
Injection test (injecting electrical current through circuit breakers to ensure that
they perform correctly during a real life power spike)
Circuit & labeling verification (at least for the main breakers and recommended for
all circuits)
Full power test (cutting DC utility power to verify transferring of electrical load to
standby infrastructure and back again)
EPO system test (activating EPO controls to ensure that all power sources and
outlets shutdown properly)
Testing and Verification (Cont.)
Table 6-1. Typical Load Bank Test
Testing and Verification (Cont.)
Table 6-2. Typical Full Power Test and EPO Check
Common Problems
• Power receptacles or circuit breakers are mislabeled (obtain a
power tester and have two people verify all receptacles in the
room)
• Monitoring lights for standby power are wired incorrectly (having
monitoring lights configured to engage after 30-second which may
result in no one will see UPS monitoring lights activation)
• Circuit breakers are left off (this may confuse people, they may
think serious problem exists)