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The single-line diagram is the blueprint for
electrical system analysis. It is the first
step in preparing a critical response plan,
allowing you to become thoroughly familiar
with the electrical distribution system
layout and design in your facility.
Whether you have a new or existing facility,
the single-line diagram is the vital roadmap
for all future testing, service and
maintenance activities. As such, the
single-line diagram is like a balance sheet
for your facility and provides a snapshot of
your facility at a moment in time. It needs
to change as your facility changes to ensure
that your systems are adequately protected.
An effective single-line diagram will
clearly show how the main components of the
electrical system are connected, including
redundant equipment and available spares. It
shows a correct power distribution path from
the incoming power source to each downstream
load – including the ratings and sizes of
each piece of electrical equipment, their
circuit conductors, and their protective
devices.
In many process facilities, loads are
continually added or removed in small
increments. The net effect is not always
seen until some part of the system becomes
overloaded or exhibits other problems. Many
times circuits are added without appropriate
modifications of the standard settings on
the associated upstream circuit breakers.
Regardless of which protective devices you
use, they must be coordinated with regard to
their time/current curves and with each
other. The single-line diagram provides the
roadmap to enable proper design of
equipment, redundancy, and protection.
NFPA-70E requirements mandate accurate,
up-to-date single-line diagrams
To meet these requirements, Emerson can
conduct a comprehensive site survey to
develop single-line diagrams for your
facility or to update existing diagrams, including:
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Inventory of equipment
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Verify existence of as-built drawings and
that they are adequately available
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Verify process is in place that ensures the
as-built drawings are maintained in a
current
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condition
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Confirm loads connected to emergency /
standby feeders
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Verify potential single points of failure
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Evaluate design redundancy of critical
systems (N, N+1, N+2...) and whether all
critical
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equipment can be maintained without
a shutdown
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Report that outlines the findings by site
along with recommended actions
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Update customer-provided single-line
drawings down to the 480V Distribution
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Switchboards
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Provide a copy of single-line electrical
diagram in AutoCAD format
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Post as-built drawings at each facility
An up-to-date single-line diagram is vital
for a variety of service activities
including:
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Short circuit calculations
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Coordination studies
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Load flow studies
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Safety evaluation studies
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All other engineering studies
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Electrical safety procedures
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Efficient maintenance
Features & Benefits
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Helps identify fault locations and
simplifies troubleshooting
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Identify potential sources of electric
energy during LOTO procedure
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Ensure safety of personnel
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Stay compliant with NFPA 70E requirements
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Ensure safe, reliable operation of facility
Scope
To give you an accurate picture of your
electrical system, single-line diagram
information
normally includes:
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Incoming lines (voltage and size —capacity
and rating)
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Incoming main fuses, potheads, cutouts,
switches and main and tie breakers
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Power transformers (rating, winding
connection and grounding means)
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Feeder breakers and fused switches relays
(function, use and type)
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Current/potential transformers (size, type
and ratio)
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Control transformers
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All main cable and wire runs with their
associated isolating switches and potheads
(size
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and length of run)
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All substations, including integral relays
and main panels and the exact nature of the
load in
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each feeder and on each substation
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Critical equipment voltage and size (UPS,
battery, generator, power distribution,
transfer
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switch, computer room air
conditioning)
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