Pumping Station Desing - Second Edition by Robert L. Sanks, George Tchobahoglous, Garr M. Jones
Подождите немного. Документ загружается.
Figure 8-24.
A
typical
single-line
diagram
for a
small
pumping
station
with
standby
power.
Courtesy
of
Brown
and
Caldwell
Consultants.
Similar
flexibility is
offered
in
Figure 8-25 with
added reliability
from
using
two
utility power ser-
vices. Each feeder
is
provided with
a
full-sized
trans-
former
and
main incoming circuit breakers.
The
motor
control
center
includes
the two
normally
closed main breakers
and a
normally open
tie
breaker interlocked
to
prevent parallel operation
of
the two
incoming
lines.
In the
event
of a
power out-
age on a
utility feeder,
its
associated main breaker
can
be
opened (usually automatically)
and the tie
breaker closed, which allows
the
entire pumping sta-
tion
to be fed
from
the
second source feeder. This
pumping
station includes
two
variable-speed
pumps
(one
dc
drive
and one
wound-rotor, slip-power
recovery)
and two
constant-speed pumps.
As all of
the
motors
are of
equal power
(a
blunder
as
explained
in
Chapter 15),
the
standby pump must
be
one of the
variable-speed
units,
and it
must
be
assumed that
the
other
variable-speed
pump
is out of
service. Hence, under
a
critical condition, there
are
one
variable-
and two
constant-speed pumps opera-
Figure
8-25.
A
typical
single-line
diagram
for a
large,
low-voltage
pumping
station
with
dual
incoming
service.
N.C,
normally
closed;
N.O.,
normally
open;
SCR,
silicon-controlled
rectifier.
Courtesy
of
Brown
and
Caldwell
Consultants.
tional.
A
typical sequence
of
starting pumps
as flow
increases might
be as
follows:
• One
operational
variable-
speed
pump accommo-
dates
low flow.
• A
constant-speed pump
is
added
and the
variable-
speed pump operates
at its
lowest permissible speed
(usually
to
discharge about
35% of its
peak capac-
ity)
in an
on-off
mode until
the flow
increases
to
about
135%
of a
single pump's capacity.
Now
both
pumps
can
operate continuously.
• The
second constant-speed pump
is
added,
and the
variable-speed pump again operates
at
minimum
capacity
in an
on-off
mode until
the flow
requires
it
to
operate continuously.
•
When both
variable-
speed
pumps
are
available,
operational
flexibility is
improved
so
that on-off
operation
can be
avoided.
• If the
capacity
of the
variable-speed pumps were
about
50%
greater than that
of the
constant speed
pumps,
there would
be no
need
for
on-off
operation
(see Section 15-5).
The
pumping station
in
Figure 8-25
is,
however,
an
old-fashioned
design. Wound-rotor
and dc
motors
would
nowadays
be
avoided
in
favor
of
induction
motors
driven
by AF
converters. Note, too, that
the
hydraulic
efficiency
of the
system
is
less than
it
would
be if all
four
drives were variable speed (see
Figure
15-8
for
proof). Furthermore, three variable-
speed
pumping units
is a
viable alternative with sav-
ings
in: (1)
size
of wet
well,
(2)
size
of dry
well,
(3)
number
of
pumps
and
amount
of
piping,
(4)
com-
plexity,
(5)
upsets
at the
treatment plant, and,
of
course,
and (6)
cost
of
power.
Single-line diagrams
are a
very necessary
and
useful
tool
in
short-circuit calculations
and
protective
device coordination studies, because they
are a
skele-
ton
representation
of the
system,
and
thus
it is
simple
to
follow
through
a
number
of
levels
of
protection.
Protective relay settings
are
derived
from
the
dia-
gram
and the
analysis
of the
time-current graphs
of
the
various
fuses
and
circuit breaker trip elements
or
relays.
Control
Diagrams
Control diagrams represent
the
exact connection
of all
the
elements
of a
control system. Interconnections
of
the
elements with other systems that
are
diagrammed
elsewhere
are
also shown. Simple motor control dia-
grams
are
shown
in
Figures
8-26
and
8-27.
All the
ele-
ments
of the
control system
are
usually shown
horizontally
on the
diagram
and the
interconnections
are
drawn horizontally
and
vertically.
The
resulting
diagram resembles
a
ladder
and is
thus termed
a
"lad-
der
diagram"
by
many users.
All
elements
are
identified
and the
function
of
each
is
either noted
on the
diagram
or
included
in a
supple-
mentary
explanation
of the
control element
and its
function.
All
lines
of a
ladder diagram should
be
num-
bered consecutively. Auxiliary relay contacts
are
usu-
ally
shown
to the
right
of the
main diagram
on or
near
the
same line
as the
circuit element.
The
contacts
are
then
individually
identified
with interconnection
information.
Relays
are
identified
as
CRl,
CR2,
and
so
forth,
for
control type units,
and
TR3, TR4,
and so
forth,
for
timing units. Timing relays
are
further
iden-
tified
at the
coil symbol with
the
time setting
and at
the
contact with information, such
as TCE
(time clos-
ing
on
energization),
TOE
(time opening
on
energiza-
tion),
and TCD and TOD for the
respective operations
on
de-energization
of a
relay.
The
ladder diagram
allows
the
engineer
to
follow
the
sequence
of
opera-
tion
of a
complex control system logically. Ladder
diagrams
are
often
used
in
training maintenance per-
sonnel,
but
their most important
use is for
analyzing
systems
that have
failed
to
operate.
Many
PLCs
are
programmed
on a
ladder diagram
basis
for the
convenience
of
technicians
who
have
no
specialized training
in
computer programming.
Coordination
Coordination
of
overcurrent
protective devices
and of
protective relays greatly improves
the
reliability
of a
pumping station,
and it
should always
be
required
by
the
project engineer.
In a
coordinated system,
the
branch circuit protective device (usually
a
circuit
breaker) trips
off a
faulted
circuit. Should
it
fail
to
trip
in a
reasonable time,
the
upstream overcurrent
device will trip,
but the
outage area will then
be
larger. Thus,
all
pertinent overcurrent devices have
proper time delays
and are
said
to be
coordinated
on
a
time basis. Fuses easily coordinate with each other
and
with
a
single downstream circuit breaker. Non-
adjustable
circuit breakers
do not
coordinate with
each other. Short circuit current
to a
faulted branch
circuit
flows
through
the
branch circuit breaker,
the
feeder
circuit
breaker,
and the
service circuit breaker,
and
they
may all
trip instantaneously, thereby shut-
ting down
the
entire station. Fortunately, most
faults
are
ground
faults,
and the
ground-loop impedance
keeps
the
short-circuit current
to a
sufficiently
low
value
to
prevent that
scenario.
Many
commercial
power systems
are
designed with
10,000
A
branch
circuit
breakers
and
fully
rated main circuit breakers
for
low first
cost,
and the
main must trip
to
protect
the
branch circuit breaker
for a
branch circuit
fault
drawing
more than
10,000
A.
This cascade system
is
obviously unacceptable where
a
reliable power
sys-
tem
is
needed.
Coordination studies
are
performed
to
verify
coordination using
manufacturer-
supplied
time-
current curves
on
log-log
graph paper.
The
studies
verify
circuit trip
and
fuse
ratings
and
predict
set-
tings
for
adjustable circuit breakers
and
protective
relays.
8-8. Power
and
Control
System
Practices
Voltage
Terminology
System voltage:
The
root-mean-square phase-to-phase
voltage
on an ac
electric system.
All
subsequent
defined
voltages
are in
terms
of
root-mean-square
phase-to-phase values unless noted otherwise.
Nominal system voltage:
The
voltage
by
which
the
system
is
designated
and to
which certain operating
characteristics
are
related.
Figure
8-26.
A
typical
schematic
diagram
for
booster
pump
number
1.
Booster pumps
2 and 3 are
similar.
L,
line;
OL,
overload;
PSR, power-sensing
relay;
SLS,
suction
valve
limit
switch;
TC,
time
closing;
(
1
F),
motor
temperature
detector (see Figure 8-25
for
other abbreviation). Courtesy
of
Brown
and
Caldwell
Consultants.
To
future
indica-
tion
To
alarm
For
future
pump
Spare
To
chlorine
pump
control
To
level
contact
Maximum system voltage:
The
highest voltage that
occurs
on the
system under normal operating condi-
tions,
and the
highest voltage
for
which equipment
and
other system components
are
designed
for
sat-
isfactory
continuous operation without derating
of
any
kind.
Service voltage:
The
voltage
at the
utility's point
of
service
to the
customer
—
ordinarily
the
metering
point.
Utilization
voltage:
The
voltage delivered
to the
line
terminals
of the
utilization equipment.
Standard
Nominal System
Voltages
Standard
nominal system voltages supplied
by
most
electric utilities
are
given
in
Table 8-6. Utilities usu-
ally
maintain them
to
within ±5%,
but
where energy
conservation
is of
concern,
the
voltages
are
main-
tained
to
within
+0,
-5%.
For
other system voltages
and for
exceptions
to the
values
in
Table 8-6, refer
to
ANSI/IEEE
Std
141-
1986.
In
some localities,
the
voltages
offered
may
dif-
fer
from
the
ANSI standard voltages.
Table
8-6.
Standard
Nominal
System
Voltages
Single-phase
Three-phase
1
20
V,
2-
wire
208/1
20
V,
4-
wire
240/120
V,
3-wire
240/120
V,
4-wire
208/1
20
V,
3-wire
a
240 V,
3-wire
delta
b
480/277
V,
4-wire
480 V,
3-wire
delta
c
240OV
416OV
12,00OV
a
Available
in
some inner-city areas with three-phase networks.
b
Common
in
rural areas with pole-mounted transformers. Insist
on
three transformers
to
ensure balanced voltages.
c
By
special request.
Be
sure
the
utility does
not
ground
the
neutral
at
the
transformer.
Station
Voltage
Selection
The
preferred nominal system voltage
for an
electric
service depends
on the
electrical
load.
For a
pumping
station where
all
electrical devices
may
operate simul-
taneously,
the
connected load
is
used.
It is the sum of
the
ratings
of all
electrical equipment
in the
pumping
Figure 8-27.
Atypical
schematic
diagram
for
pump
selection
and
level
control.
CR,
control
relay;
H,
hot;
N,
neu-
tral;
PSS,
pump
sequential
selector
switch
(see Figures 8-25
and
8-26
for
other
abbreviations).
Courtesy
of
Greeley
and
Hansen Engineers.
To
pump
1
control
To
pump
2
control
To
pump
3
control
station
computed
to the
nearest
hp, kW, or
kVA. Motors
are
counted
at
their horsepower rating regardless
of
their actual loading,
and all
other devices
are
counted
at
their
nameplate rating
in kW or
kVA. Conversions
are
usually
made
on a
one-to-one basis
(1
hp = 1
kVA).
Welding
machines
are
rated
in hp at 1
kVA
per hp.
Recommendations
for
pumping station service
voltages
are
given
in
Table 8-7. Utility limitations
may
be
different
and
must
be
checked.
Voltage
Ratings
for
Utilization
Equipment
Nameplate ratings applicable
to
motors
are
listed
in
ANSI/IEEE
Std
141-1986,
Table
7. A few of
these rat-
ings
are
given
in
Table 8-8.
Motors used
on
208-V
systems should
be
rated
200
V.
Motors rated
220 V or 230 V do not
perform satis-
factorily
and
should
not be
used.
Load Estimating
Load estimating evolves
in
several major stages. Pre-
liminary load estimating
is
done during
the
pre-design
stage
of
development
of
proposals
for the
pumping
station
design
—
usually
with very preliminary esti-
mates
of the
total plant pumping horsepower.
It can be
accomplished largely
on the
basis
of
discussions with
the
project managers
and
reference material
from
company
design
files on
similar previous jobs.
The
complexity
of
load estimating depends
on the
size
of the
station
and the
experience level
of the
project
designers.
For
many years, successful profes-
sional design
firms
have developed estimating infor-
mation
from
preliminary data sheets.
These
sheets
allow
for a
variety
of
useful
information relating
to the
various
plant drives.
The
principal load
is
usually
comprised
of
pumping units. Other important loads
depend
on
whether
the
station
is in an
area
of
extreme
summer
heat
or
extreme winter cold, where extensive
cooling
or
heating equipment
may be
required.
The
number
of
individual pumping units
affects
the
size
of
the
standby generator.
The
number
of
pumps also
affects
the
complexity
of the
control
and
monitoring
system
of the
station.
All of
these factors
affect
the
electrical load estimate
as
well
as the
electrical system
construction cost.
Data
sheets should
be
generated
in a
computer sys-
tem
so
that
the
data
are
accessible
to all
employees
who
are
responsible
for a
portion
of the
total estimate.
Load estimation
for
small
or
"package"
pumping
stations
is
very simple,
as
there
is
frequently
no
spe-
cial auxiliary equipment
to
complicate
the
station
design.
Table
8-7.
Pumping
Station
Service
Voltage
Recommendations
Load
Voltage
5 kVA (7 hp)
240/1
20
V,
single-phase,
3-wire
or
208/120
V,
single-phase, 3-wire
40 kVA (50 hp)
240/1
20
V,
three-phase,
4-wire
or
208/120
V,
three-phase,
4-wire
or
240 V,
three-phase,
4-wire
400 kVA
(500
hp)
480/277
V,
three-phase,
4-wire
a
Above
400
k
VA
(500
hp)
4
1
60
V,
three-phase
b
or
2400V,three-phase
b
a
Should
be
used
for
motors
as
small
as 1/2 hp.
Provide 240/120
V,
single-phase,
3-wire
or
208/120
V,
three-phase, 4-wire
for
pumping
station auxiliaries, derived
from
the
480/227
V
system.
b
Use for
large motors. Provide 480/277
V
three-phase, 4-wire
for
larger
pumping
station auxiliaries, derived
from
the
high-
voltage
system.
Provide also 240/120
V
single-phase, 3-wire
or
208/120
V,
three-phase, 4-wire
for
smaller
pumping
station auxiliaries
derived
from
the
480/277
V
system.
Table
8-8.
Nameplate
Ratings
for
Motors
Nominal
Power
range
system Nameplate
voltage voltage
kW hp
Single-phase
motors:
120 115
<0.37
<V
2
240
230
<1.1
<1.5
Three-phase
motors:
208 200 110 150
240 230 150 250
480
460 300 400
2400
2300
1500
2000
4160
4000
3000
4000
A
few
checklist items that apply
to
load estimation
for
many pumping stations follow:
•
Number
of
pumps
and
required horsepower
of
each
•
Number
of
pumps operating
at any
time
and
sequence
of
starting
•
Special requirements, such
as
adjustable speed drives
•
Auxiliary drives required
•
Preliminary layout
of
structure
and
number
of
oper-
ating
levels
•
Special
use
areas (such
as
shops)
and
their electrical
loads
•
Heating, cooling,
and
ventilating requirements
•
Standby power requirements
(if
any)
•
Applicable
electric
utility rate schedules
•
Available electric utility voltage levels
and
distance
to
their point
of
service
•
Inside lighting requirements/outdoor lighting
requirements
•
Review local electrical
codes
and try to get
infor-
mation
from
the
inspection authority
on
special
interpretations that
may
affect
the
electrical con-
struction
costs.
An
example
is the
treatment
of
pos-
sible hazardous areas such
as
Class
I,
Division
1
versus
Class
I,
Division
2.
8-9.
Reference
1.
O-Z/Gedney, Main Street,
Terry
ville,
CT
06786
8-10.
Supplementary
Reading
1.
Beeman,
D.,
Industrial Power Systems Handbook,
McGraw-Hill,
New
York
(1955).
2. IES
Lighting
Handbook, Illuminating Engineering
Society,
New
York (latest edition).
3.
Lightning Protection, Institute Standard
of
Practice,
3rd
ed., Lightning Protection Institute, P.O.
Box
458,
Harvard,
IL
60033-0458
(1987).
4.
McPartland,
J. K,
National Electric
Code
Handbook,
22nd
ed.,
McGraw-Hill,
New
York
(1996).
5.
Smeaton,
R.
W.,
Switchgear
and
Control Handbook,
3rd
Ed.,
McGraw-Hill,
New
York (1996).
6.
Catalogs
of
various manufacturers, such
as
General
Electric, Square
D,
Westinghouse.
The
primary purpose
of
this chapter,
as
with Chapter
8,
is to
provide project leaders with some understand-
ing
of
electrical design,
to aid
communication with
electrical
specialists,
and to
help
in
coordinating
elec-
trical design with other disciplines.
The
chapter
is
appropriate
for
civil engineers,
and it may
also
be
appropriate
for
electrical
engineers with limited expe-
rience
in
power engineering.
A
working knowledge
of
the
principles
of
electricity, discussed
in
Chapter
8, is
a
prerequisite.
The
topics discussed here include
the
coordination
of
electrical design both
with
other disciplines
and
with
utility
companies (Sections
9-1 to
9-4),
the
suit-
ability
of
materials (Section 9-1), harmonics (Section
9-11),
and
construction services such
as field
testing
(Section
9-12).
Most
of the
essential
electrical
calcu-
lations
for a
pumping station
of
moderate size
are
given
as
worked examples.
The
examples include
electrical load estimation,
overcurrent
protection,
lighting,
engine-generator sizing,
and
conductor,
fuse,
and
breaker sizing
for
main
and
branch circuits.
Terminology
is
given
in
Sections
2-2 and
8-1,
and
abbreviations
are
defined
in
Section
2-1.
The
text
and
computations
in the
examples
are in
U.S. customary
units
for
correlation with present codes
and
standards
in
the
United States Conversions
to SI
units
are
given
in
Appendix
A, and
some
are
also given
in
this chapter.
Chapter
9
Electrical
Design
STANLEYS.
HONG
PHILIPA.
HUFF
PAUL
C.
LEACH
CONTRIBUTORS
Roberts.
Benfell
Mayo
Gottliebson
Stephen
H.
Palac
Patricia
A.
Trager
References
to a
code,
a
standard,
or a
specification
are
given here
in
abbreviated
form,
such
as NEC
(for
National
Electrical Code)
or
NFPA Standard 493-
1978
(for
a
National
Fire
Protection
Association stan-
dard).
The
coded numbers
are
entirely
sufficient
for
identifying
the
reference. Titles
of the
abbreviations
are
given
in
Appendix
E, and
addresses
for
publishers
are
given
in
Appendix
F.
Much
of the
material
in
this chapter
is
referenced
to
the
NEC,
so
read
the
referenced passages
in
sequence
with
this text. Keep
in
mind that
the NEC is
subject
to
local interpretation. Check with local authorities
for
applicable codes
and
regulations.
The
design must fol-
low
safety
and
protection standards established
by
OSHA
and UL.
Standards
and
recommendations
pub-
lished
by
organizations such
as
IES,
IEEE,
NEMA,
ANSI,
and
NFPA should also
be
followed.
9-1
.
Final
Construction
Drawings
Long before
final
construction drawings
are
pre-
pared
—
in
fact,
at the
beginning
of the
project
—
the
project
leader should consult
the
electrical
engineer
to
ensure that
an
adequate space
is
reserved
for
electrical
equipment
and to
forestall interference with mechani-
cal
equipment
and the
building envelope. During
the
appropriate design stages,
the
project leader should
also cooperate
with
the
electrical engineers
to
ensure
that
the
electrical drawings
and
specifications
are
complete
and
compatible
with
all of the
other draw-
ings
and
specifications.
List
of
Electrical
Drawings
The
following
is a
suggested list
of
electrical drawings
required
for a
typical pumping station.
The
list would
be
modified
according
to the
size
and
complexity
of
the
job.
•
Electrical legend
•
Single-line diagram
•
Control diagrams (schematics)
•
Site plan (power
and
lighting)
•
Building power plan (including control wiring)
•
Building lighting plan
•
Fire alarm, communications,
and
security plans
as
required
•
Equipment elevations
and
schedules
•
Conduit
and
wire schedules
•
Details.
Symbols
In
the
electrical
legend, always include
a
list
of
symbols
used.
See
Chapter
2 for
common electrical symbols.
Coordination
with Other
Pumping
Station
Drawings
The
project engineer
is
responsible
for
coordinating
the
electrical design with
the
other disciplines (see
Table
1-1)
—
a
task vital
for the
continuity
and
com-
pleteness
of the
drawings.
The
project engineer
should:
•
Verify
that electrical equipment, including light fix-
tures,
does
not
conflict
with structural elements
or
mechanical
equipment,
and
that necessary space
and
mounting provisions exist.
•
Check
the
plans
and
specifications
of the
other dis-
ciplines (particularly process
and
mechanical disci-
plines)
for
compatibility with electrical systems
such
as
voltage, phase, alarms,
and
controls.
• Be
sure that
the
electrical engineer checks every
piece
of
equipment that requires electrical energy
or
control. Commonly missed items include instru-
ments, limit switches, solenoid valves,
and
alarms.
•
Check
to see
that conductor sizes, dimensions, etc.
are
shown only once.
On
other drawings, these
items should
be
shown
(if at
all)
as
"reference-
only"
data
to
avoid
conflicts.
•
Perform
a final
complete check
of
electrical draw-
ings against
all
other pumping station drawings
and
specifications
just before
the
drawings
are
sent out.
Raceway
System
For
raceway systems,
•
Show conduits only
in
schematic
form
except
where noted specifically
or
detailed otherwise.
•
Electricians
often
double-up home runs
for
lighting
and
receptacle circuits, control wire runs,
and so on.
If
doubling-up
is
undesirable,
so
note
or
detail
the
home runs.
• A
minimum conduit size
of 19 mm
(
3
/4
in.)
is
sug-
gested.
•
Detail and/or
specify
the
mode
of
conduit entry into
structures,
including underground penetrations
for
the
prevention
of
groundwater entry.
•
Detail conduit duct banks carefully: include conduit
layout,
section, acceptable types
of
conduit, rein-
forcing
bar
sizes
and
extent, concrete encasement,
and
slope direction
for
drainage.
•
Remember that
PVC
conduit deteriorates
if
exposed
to
sunlight
or
possible impact damage.
Embedded
PVC
conduit
may
suffer
severe damage
during pouring
of
concrete
in
walls
and
particularly
due
to
vibrators.
• The
installation
of
spare (for example,
not
less than
10%
of the
total) conduits (capped
at
both ends)
from
panelboard
and
motor control center (MCC)
or
motor starter panel
to
exterior
or to
attic
is
sug-
gested.
• In
corrosive areas such
as wet
wells
and
chlorine
storage rooms,
use
only PVC-coated, hot-dipped
galvanized
(inside
and
outside) rigid steel conduits
for
corrosion resistance. Require that
all
bare spots
in the
conduit system
be
recoated with
PVC (or an
equivalent).
• The
trend
is
toward
the use of
aluminum conduit,
but
aluminum reacts quickly with
the
lime
in
damp
concrete,
so it
must
not be
encased
in
concrete.
For
first-class
construction,
use
only PVC-coated steel
conduit
in
pumping stations.
•
Allow contractors
to
size junction boxes
and
wire-
ways
in
accordance with codes unless
the
designer
requires oversize boxes
for
special use.
•
Provide drainage
for
large handholes
and
manholes.
•
Install pulling eyes
on
walls
opposite
every
electri-
cal
conduit entry inside manholes
and
handholes
to
aid in
pulling wires.
• Use
cast, hot-dipped galvanized
ferrous
boxes
for
embedded
systems
—
receptacle,
switch,
and
junc-
tion boxes
in all
pumping station levels where
embedment might
be
allowed
or
specified.
• NEC
370-3
restricts
the use of
nonmetallic boxes
in
metallic raceway systems. Such boxes cannot
be
used
unless
an
internal ground jumper
is
provided
between each metallic conduit. Ground jumpers
are
impractical
with
conduit bodies (condulets)
and
small
boxes
such
as
trade types
FS and FD, so
PVC-coated condulets
and
FS/FD
boxes
are
recom-
mended.
For
larger boxes,
it is
practical
to field
install
an
internal ground jumper,
and
non-metallic
boxes
can be
used. Nonmetallic boxes should have
nonmetallic
or
stainless-steel hinges, mountings,
and
clasps.
Wiring
For
wiring,
•
Show feeders,
the
pump motor branch circuit,
and
the
principal ancillary equipment branch circuit
conductor sizes either
on
plans,
on the
single-line
diagrams,
or on
conductor schedules,
but
show
them only once.
•
Indicate number
and
minimum size
of
control,
lighting,
and
outlet wiring
on
drawings
or
specifica-
tions.
By
note, direct installer
to
adjust
wire size
for
the
type
of
wire, conduit
fill
(defined
in
Section
2-2), voltage drop,
and
need
for
6O
0
C
(14O
0
F)
ampacities
at 15- to
100-
A
circuit breakers
and
fused
switches.
An
installer
can
size conduit
per the
NEC,
but it is
better
for
engineers either
to
size con-
duit
or to
limit
the
percentage
of fill if any
conduit
is
to be
sized
by
others.
•
Coordinate process
and
instrumentation wiring
carefully
with respect
to: (1)
number
of
control
wires serving each instrument
and
device, control
requirements,
and
120-
V
power;
(2)
shielded
cable
for
4- to
20-mA
dc
signals
and
other instrumenta-
tion signals (require
the
shield
to be
grounded
at
one end
only)
(if the
cable
is
double shielded, fol-
low
manufacturer's directions);
(3) for
intrinsically
safe
wiring,
refer
to
NFPA Standard
493-1978
for
complete details;
(4)
combine circuits
carefully
to
avoid
exceeding
the
maximum voltage buildup;
(5)
use
separate steel conduits
for
these circuits;
and (6)
in
panels, separate wiring
a
minimum
of 50 mm (2
in.)
from
all
other panel wiring.
•
Equipment
ground-
wire
considerations:
(I)A
ground
wire
from
the
system ground
to
each 480-V motor
and
panel
is
recommended;
(2)
bond
all
ground wires
to
both ends
of
rigid metal conduit;
(3)
ground
all
metal enclosures, water pipes,
and
machines
as
required
by NEC
250-42,
43,
44(d),
and 80; and (4)
provide
a
ground wire
in
every
PVC
conduit.
• Use
duct seal
in
conduits where they emerge
from
ground
and
enter enclosures
to
prevent passage
of
water into
the
enclosures
and
building. Slope under-
ground
ducts
to
drain water
to
manholes.
•
Number
all
equipment
and
devices. Require num-
bered wire tags
at
each
end of all
conductors.
Equipment
Space
Heaters
All
space heaters should
be
powered
from
a
120-
V
panelboard
so
that equipment that
is
idle
or
down
for
repairs
has
condensation protection.
At
motors, con-
trol panels,
and so on,
provide labeled heater discon-
nects
for
safety
during maintenance. Provide
thermostats
in
equipment
for
operating space heaters
and
connect motor space heaters through
a
normally
closed auxiliary motor starter contact
so
that
the
heater
is on
when
the
motor
is off and
vice versa.
For
large, important motors, consider
a
neon light across
the
contacts
to
indicate heater continuity when
the
heater
is
off. Consider low-voltage motor winding
heating
from
a
separate transformer
in the
motor
starter cubicle (see Chapter 13),
but
note that there
will
be no
heating when motor branch circuit
is
off.
Power
and
Telephone
Utility
Requirements
Instruct
the
contractor
to
contact
the
appropriate
power
and
telephone companies
for all
service
requirements
and to
conform
to
them.
The
engineer,
however, must contact
the
utilities
in the
early stages
of
design
to
obtain their agreements
to
serve
the
facil-
ity
adequately (see Section 9-3).
9-2.
Specifications
Some
specific
hints
for
consideration
in
writing
the
electrical
specifications
are
given
in
this section (see
also
"Specification
Language"
in
Section 28-1).
In
the
"General
Requirements" portion
of the
elec-
trical specifications, provide
an
article titled
"Electri-
cal
Devices Furnished with Mechanical Equipment"
and
have each
specifier
of
equipment include
a
special
callout
of
electrical contacts, alarm
functions,
and any
auxiliary
electrical power requirements. Reference
these callouts
to the
"Electrical
Devices"
specification.
Information
and
sample specifications
may be
obtained
from
The
Construction Specifications Insti-
tute
[I];
their format
is
becoming popular
and is
increasingly being required
by
clients.
Coordination
with Other
Specification
Sections
Coordination
is
very important
to
ensure
the
continu-
ity
and
completeness
of
specifications. Wherever
any
equipment requires electric power, control,
or
instru-
mentation, check
the
following
with
the
designer
and
be
sure that this information
is
included
in the
equip-
ment
specifications:
•
Voltage
and
phase
•
Disconnects
•
Enclosures
•
Control philosophy, such
as a
local-remote
selector
switch
with
an
On-Off
pushbutton
•
Alarm contacts
•
Special features
or
circuits
to
ensure compatibility
with
other electrical equipment
• Any
desired special component
or
wiring specifica-
tions.
In
addition:
•
Require that
all
conductors used
for
interwiring
between panels
and for
input
or
output purposes
be
brought
to
numbered terminal strips
and
that
all
wiring
(internal
and
external)
be
tagged
at
both
ends with preprinted wire markers. Require that
the
wire marking code
be
submitted
for
acceptance
prior
to the
manufacture
of the
equipment.
•
Require that
a
copy
of the final
issue
"As
Deliv-
ered"
control diagram
be
attached
to the
inside
of
the
door
of the
equipment cabinet.
•
Require
the
control diagrams
to be
drawn
in the
lad-
der-diagram
format
with
all
contacts
and
lines iden-
tified
(numbered
or
coded)
and all
relays
and
control devices designated
by
appropriate names
and
numbers.
• If a PLC is to be
provided, require that
a
ladder-dia-
gram
format control diagram
be
submitted
for
acceptance
and
require that
a
tape
or
disk copy
of
the
final
program accompany
the
equipment.
Seismic
Requirements
All
equipment must
be
attached
or
supported
so
that
no
hazard
to
personnel will result
from
any
seismic
force
or
motion. Contact
the
project structural engi-
neer
for
help
in
fulfilling
and
enforcing this require-
ment.
The
seismic zone
for
every part
of the
country
is
designated
in UBC
Section 2332, Figure
No. 1 (in
1996),
and the
contractor
and
suppliers must
be
instructed
to
follow
all of the
requirements. Zones
vary
from
1
through
4. The
worst, Zone
4,
corre-
sponds
to an
earthquake with
a
magnitude
of 8 on the
Richter scale. Although equipment
is
usually
not
required
to
operate
properly during
a
seismic
event,
specify
that large equipment (such
as a
large circuit
breaker) must
not
change position
and
that large
engines
and
motors must
not
start
or
"bump"
from
momentary energization.
Equipment
Labeling
Labeling,
an
indication
of the
testing
and
listing
of the
equipment
by a
recognized testing laboratory,
is
required
by
most local
and
state inspection authorities
and
must
be
required
for all
standard equipment. Cus-
tom
equipment
and
control panels
can be
expensive
if
the
authorities insist
on a
label. Whenever possible,
design around equipment that
is
UL-listed
as a
com-
plete unit (panel
and
all).
Shop
Drawings
With
the
possible
exception
of
standard, widely used
materials,
it is
suggested that shop drawings
be
required
for
each item
for
which detailed specifications
were written. Check
the
shop drawings thoroughly.
Specifications
should include
(1) the
equipment
and in
formation
that must
be
submitted
and (2) a
submittal
schedule.
9-3. Contacting
Utilities
It
is
necessary
to
contact each
utility
early
to
obtain
their requirements
and the
name
of the
person
assigned
as
their representative. Back
up all
telephone
conversations with confirmation
letters,
and
visit
the
site with
the
utility representative.
Electric
Power
Utility
Contact
An
underground (instead
of an
overhead) service
from
the
electric power utility
is
preferred because
of
reliability
and
appearance. Provide
the
service
from
the
nearest pole
or
vault
to the
pumping station.
In
addition,