Electrical Single Line Diagram Guidance

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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.
Why it’s required?
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.
To make all the changes documented in a common file, making the electrical system easily
understandable for any technical person inside/outside of the factory.
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SINGLE LINE DIAGRAM (SLD) Or, ONE LINE DIAGRAM
Short circuit calculations
Coordination studies
Load flow studies
Safety evaluation studies
All other engineering studies
Electrical safety procedures
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An up-to-date single-line diagram is vital for a variety of service activities including:
Efficient maintenance
What Should Be In A Single Line Diagram (SLD)?
SLD must be started with an index, legend, page references.
All proper symbols shall be used.
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A typical package of single line diagram shall include:
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Incoming lines showing voltage and size.
Incoming main fuses, cutouts, switches, and main/tie breakers.
Power transformers (kVA rating, voltage rating, winding connection and grounding
means, % impedance, cooling type).
Feeder breakers and fused switches rating and type.
All incoming circuits shall have a page reference (mention the page number from where
it comes). All outgoing panels shall have a page reference (mention the page number to
where this outgoing circuit is detailed-This link-up is required).
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Electrical Single Line Diagram Guidance_Version 1.0_November 2021
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All service-main cable and wire runs with their associated isolating switches shall be
clearly mentioned.
All substations, including integral relays and main panels with total load of each feeder
and each substation
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Current and / or potential transformers with size, type and ratio
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Relays (function, use and type) is required to be mentioned. The fault current clearing
time setting is required to be achieved from inverse definite minimum time (IDMT) relay
or over current relay (OCR) of the vacuum circuit breaker (VCB) panel. Where only load
breaking switch (LBS) is available and no VCB panel is available fault current clearing
time setting is not required.
Critical equipment voltage and size (uninterruptible power supply or UPS, battery,
generator, power distribution, transfer-switch, computer room air conditioning).
A load schedule for each distribution panels, busbar trunking or BBT, tap-off boxes of
TOB and switch board (load table format is provided later in this guideline) is required to
be prepared.
Rating and dimension of bus bar shall be mentioned. The calculated rating of copper
busbar equals to 1.55 Ampere per mm2 of cross section area. The calculated rating of
Aluminum busbar equals to 1.09 Ampere per mm2 of cross section area.
All outgoing cables shall be mentioned with number of cables, number of cores, cable
size and along with number of poles associated with it. For example, 1x4Cx6mm2, NYY,
TPN represents a 4-core (C) single NYY-type cable of 6mm2 cross section area
connected to 3-phases (TP) and a neutral (N); Again, 3x1Cx4mm2, BYA, TP represents 3
numbers of single-core (C) and BYA-type cable of 4mm2 cross section area connected
to 3-phases (TP). There are many cable types. Here NYY and BYA are only 2 examples of
cable types and used as example
The rating and type of their all-isolating switches and protective devices (e.g. circuit
breaker, fuse, overload relay, magnetic contactor) shall be mentioned.
The set point of all circuit breakers, thermal overload relay, rating of magnetic contactor
shall be mentioned.
Length of Cable laying is required where no protection is provided for an outgoing circuit
or incoming circuit (where rules of tapping circuits is applicable)
PFI, changeover, ATS, generators with associated protection and isolating switch,
synchronizer and interlocking arrangements shall be properly mentioned with rating,
proper symbols and details.
For ATS, all protective ratings of protective device shall be mentioned.
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All earth conductors’ size and type shall be mentioned with quantity
Earth conductors and Earth pit-identification number with page references shall be
mentioned in transformer, generators, panelboards and equipment (if directly connected
with Earth pits)
Total connected load (kilo watt or kW) with their individual load capacity (kW) shall be
mentioned.
All connected equipment (loads) shall be identified with marking and mentioned in the
load description. The marking/identification number of each load shall also be mentioned
in the point reference or load reference column.
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Earthing system (excluding LPS Earth pits) must be included with dimension of earthing
pit, boring, busbar, earth electrode size, earth lead and ECC size and type in a separate
page.
An example of a typical SLD has been given which includes the substation, LT panel,
distribution panel with load table format.
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All spare switches (outgoing circuit breaker) shall be mentioned.
Sketch 1: Example of SLD of typical substation, low tension or LT panel and MDB (main
distribution board)
Table 1: Example of load table of a typical LT panel
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Table 3: Example of load table of a typical FMDB
Table 4: Example of load table of a typical sub distribution board or SDB
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Sketch 2: Example of SLD of typical floor MDB (FMDB)
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Table 2: Example of load table of a typical MDB
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Substation & LT
DRAWING TITLE:
1X1C-300 RM,BYA(MAIN ECC), Earth Pit#9, (Page-29)
1X1C-4 RM,BYA(DOOR)
LIGHTNING
ARRESTER (12kV)
HT CT
ECC-2x1C-50 mm²,
BYA(BODY), Earth Pit#2
500KVA
Step Down
ONAN Type 3-Phase
TRANSFORMER
V :Vs=11/0.415
Dyn 11, 50Hz
Z%=4.5%
ISOLATOR
HT PT
LT PANEL
6x1C-300 RM,NYY(TP)
2x1C-300 RM,NYY (N)
CT RATIO:
1000/5A
RYB-03
LBS 630 A
11KV HT PANEL
(30A FUSE)
Fault current clearing time
for LBS (t>>)=0.2sec
If you do not have VCB but you
have LBS in HT panel
RYB-02
MDB
10A TP
MCB
Cable length 45 ft
Version 1.0
PAGE NO:
ECC- 2x1C-150 RM,BYA (BODY),
Earth Pit#4,5 (Page-29)
ECC- 1x1C-150 RM,NYY (N),
Earth Pit#6 (Page-29)
400 KVA
DIESEL GENERATOR (Standby)
TP+N+E
4x1C-300 mm² ,NYY(TPN)
G
630A TP
MCCB
SET:504A
630A TP
MCCB
SET:504A
RYB-03
APPROVED BY:
1x1C-150 RM,NYY (N)
CU BUSBAR-620A
40mmx10mm(TP)
TOTAL CONNECTED
LOAD:232.04KW
620 A COPPER BUSBAR
TPN:(40mmx10mm)
E:40mmX5mm
MECHANICAL
INTERLOCKING
SYSTEM
775 A COPPER BUSBAR
TPN:(50mmx10mm)
E:50mmX8mm
CT RATIO:
1000/5A
400A TP
MCCB
SET:320A
TOTAL CONNECTED
LOAD:325.04KW
ECC- 2x1C-12.7 mm, HDBC CU(BODY), Earth Pit# 2, 3 (Page-29)
ECC- 1x1C-12.7 mm, HDBC CU(N), Earth Pit# 1 (Page-29)
VCB 630 A
11KV HT PANEL
Fault current clearing time
(t>>)=0.4sec
1X3C-120 mm² (N2XSEYFGbY)
1X3C-120 mm² (N2XSEYFGbY)
DESCO
METER
11KV DROP OUT
FUSE-30A
11KV OVERHEAD LINE
1000A TP
ACB
SET:700A
CU BUSBAR-775A
50mmx10mm(TP)
2x1C-300 RM,NYY (N)
RYB-02
630A TP
MCCB
SET:504A
630A TP
MCCB
SET:504A
RYB-01
CU BUSBAR-620A
40mmx10mm(TP)
1x1C-150 RM,NYY (N)
500A TP
MCCB
SET:0.9
SDB SECURITY POST
=2.745KW
PAGE NO= 19
Date: DESIGNED BY: CHECKED BY:
FMDB-01
GROUND FLOOR
PAGE NO= 02
Rev: 02
Rev: 01
(TP)
1x1C-4 RM,BYA(ECC)
3x1C-6 RM,BYA
4x1C-4 RM,BYA(TP+N)
1x1C-150 RM,NYY(ECC)
Cable length 37 ft
CU BUSBAR 620A
40mmX10mm(TP)
4X1C-300 RM,NYY(TP+N)
TCL:229.295 KW
1x1C-95 RM,BYA(ECC)
RYB-01
1X1C-4 RM,BYA(DOOR)
ADDRESS:
300 KVAR PFI
3X1C-300 RM,NYY(TP)
CU BUSBAR-372A
40mmX6mm(TP)
4X1C-150 RM,NYY(TPN)
CU BUSBAR-496A
40mmX8mm(TP)
1x1C-150 RM,BYA(ECC)
CU BUSBAR 279A
30mmX6mm(TP)
FIRE HYDRANT
PUMP-93KW
4X1C-120 RM,NYY(TP+N)
1x1C-70 RM,NYY(ECC)
250A TP
MCCB
SET:200A
FACTORY NAME:
630A TP
MCCB
SET:320A
FOR FUTURE
EXTENSION
TO A NEW
CONSTRUCTION
CU BUSBAR 620A
40mmX10mm(TP)
SPARE
SPARE
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Table 1: Example of load table of a typical LT panel
From SLD
page-1
LT PANEL, LOCATION: GROUND FLOOR, FEED ROOM: TRANSFORMER
Main Incoming
Ckt.
1000A
MCCB,
set: 700A
CKT REF.
Breaker
MCCB/MCB
Rat/Amp
RYB1
630A MCCB
set:320A
RYB2
250A MCCB
set:200A
4x120.0
1x70.0
RYB3
630A MCCB
set:504A
4x300.0
1x150.0
Phase
Neutral
Size(rm)
Point Reference
Number of
Points/ Pcs
Watt Per Point
Location
Spare
0
0
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Fire Hydrant
Fire Hydrant Pump
Pump
1
93000
Main
Distribution
Panel
1
232140
Earth Size Load Type
(re)
Spare
Future
extension
MDB
Total Watt
Phase Load in kW
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0
0.00
0.00
0.00
Fire Pump
room
93000
31.00
31.00
31.00
Ground Floor
232140
78.12
78.13
75.79
109.12
109.13
106.79
Total Phase Load/kW=
Total Connected Load=
325.04
kW
Remarks
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Table 2: Example of load table of a typical MDB
MDB, LOCATION: SUB STATION, FEED ROOM: LT PANEL, REF: RYB-03.
AND FROM GENERATOR (400KVA)
Main Incoming
Ckt.
Breaker
CKT REF. MCCB/MCB
Rat/Amp
Phase
Earth
Neutral
Size (re)
Size(rm)
Load
Type
Point Reference
Number of
Points/ Pcs
Watt Per
Point
Location
Total Watt
From SLD
page-1
Phase Load in kW
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B
RYB1
500A MCCB
set:450
4x300
1x150
PFI
PFI
1
0
0
0
0.00
0.00
0.00
MCCB 630A
(set:504A) X 2,
RYB2
400A MCCB
set:320
4x150
1x95
FMDB
FMDB-01
1
229295
Ground Floor
229295
77.38
77.32
74.59
(interlocked)
RYB3
10A TP
4x4.0
1x4.0
SDB
SDB-Security Post
1
2745
Security Post
2745
0.74
0.81
1.20
78.12
78.13
75.79
Total Phase Load/kW=
Total Connected Load=
232.04
kW
Remarks
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DRAWING TITLE:
FMDB01/GF
DB-01
GROUND FLOOR
PAGE-03
TCL:28.37KW
TCL:28.37KW
DB-02
1ST FLOOR
PAGE-04
FACTORY NAME:
TCL:38.78KW
DB-03
2ND FLOOR
PAGE-08
ADDRESS:
TCL:36.77KW
DB-04
3RD FLOOR
PAGE-11
TCL:40.85KW
DB-05
4TH FLOOR
PAGE-14
Rev: 01
Rev: 02
TCL:16.54KW
DB-06
5TH FLOOR
PAGE-17
Date:
DB-07
UTILITY SHADE
PAGE-18
TCL:33.00KW
DESIGNED BY:
CHECKED BY:
10A SP
MCB
APPROVED BY:
1X1C-4 RM,BYA(DOOR)
1x1C-6 RM,
NYY(P)
B-11
(SM101--SM106)
2x1C-4 RM,BYA(P+N)
1x1C-4RM,BYA(ECC)
10A SP
MCB
6 nos SEWING M/C, LINE-1
(06X400W)= 2.40KW
Each M/C is protected by a
5A fuse in socket plug
PS101--PS 104.
1x1C-6 RM,
NYY(P)
R-10
1x1C-4RM,BYA(ECC)
6A SP
MCB
2x1C-4 RM,BYA(P+N)
1x1C-6 RM,
NYY(P)
RYB-09
OFFICE-2
4 nos POWER SOCKET(5A, 200W)
(04X200W)=0.8KW
2x1C-4 RM,BYA(P+N)
16A TP
MCB
(L101--L108), F-101.
1x1C-4 RM,
BYA(P)
RYB-08
OFFICE-2
8 nos LIGHT (18W)+1 no FAN (80W)
(8X18W)+(01X80W)=0.224KW
100A TP
MCCB
FIXED
4X1C-6 RM,BYA(TPN)
3x1C-10RM,
BYA(TP)
3x1C-35 RM,
NYY(TP)
RYB-07
1X1C-6 RM,BYA(ECC)
Neutral cable is for control only
63A TP
MCCB
SET:44A
SPARE
25A TP
MCCB
SET:15A
4X1C-25 RM,NYY(TPN)
RYB-06
1X1C-16 RM,BYA(ECC)
100A TP
MCCB
SET:70A
NYY(TP)
3x1C-25 RM,
RYB-05
(EXH101--EXH104)
4X1C-16 RM,NYY(TPN)
NYY(TP)
3x1C-35 RM,
RYB-04
1X1C-16 RM,BYA(ECC)
100A TP
MCCB
SET:70A
4X1C-25 RM,NYY(TPN)
NYY(TP)
3x1C-35 RM,
TPN:(30mmx12mm)
E:30mmX6mm
1X1C-16 RM,BYA(ECC)
100A TP
MCCB
SET:70A
4X1C-25 RM,NYY(TPN)
NYY(TP)
3x1C-35 RM,
RYB-03
1X1C-16 RM,BYA(ECC)
100A TP
MCCB
SET:70A
4X1C-25 RM,NYY(TPN)
NYY(TP)
3x1C-35 RM,
RYB-02
1X1C-16 RM,BYA(ECC)
63A TP
MCCB
SET: 50.4A
4X1C-25 RM,NYY(TPN)
RYB-01
1X1C-16 RM,BYA(ECC)
NYY(TP)
3x1C-16 RM,
558A COPPER BUSBAR
EXHAUST FAN
(4X746W)=2.98KW
Each Exhaust Fan is protected by a 5A
thermal overload relay with
12A Magnetic contactor
SPARE
4X1C-16 RM,NYY(TPN)
1X1C-16 RM,BYA(ECC)
FEED FROM
MDB
(RYB-02, PAGE 01)
GROUND FLOOR
L=Light
F=Fan
SM=Sewing M/C
M/C=Machine
EXH=Exhaust Fan
4X1C-150 RM,NYY(TPN)
1x1C-95 RM,BYA(ECC)
FMDB-01
GROUND FLOOR
TOTAL CONNECTED
LOAD: 229.295 KW
400A TP
MCCB
SET:320A
CU BUSBAR-558A
30mmx12mm(TP)
2x1C-150 RM,NYY (N)
Y-12
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Table: 3 Example of load table of a typical FMDB
From SLD
page-2
FMDB-01, LOCATION: GROUND FLOOR, FEED ROOM: MDB, REF: RYB-02.
Main
Incoming Ckt.
MCCB 400A
(set:320A)
Breaker
MCCB/MCB
Rat/Amp
Phase
Neutral
Size
RYB1
63A MCCB
Set at 50A
4x16.0
1x16.0
DB-1
DB-01
RYB2
100A MCCB
Set at 70A
4x25.0
1x16.0
DB-2
RYB3
100A MCCB
Set at 70A
4x25.0
1x16.0
RYB4
100A MCCB
Set at 70A
4x25.0
RYB5
100A MCCB
Set at 70A
RYB6
Number of
Points/ Pcs
Watt Per
Point
Location
Total Watt
1
28370
Ground Floor
DB-02
1
28373
DB-3
DB-03
1
1x16.0
DB-4
DB-04
4x25.0
1x16.0
DB-5
25A MCCB
Set at 15A
4x16.0
1x16.0
RYB7
63A MCCB
Set at 44A
4x25.0
1x16.0
RYB8
100A MCCB
RYB9
16A TP
4X6.0
R10
6A SP
2X4.0
B11
10A SP
2X4.0
Y12
10A SP
2X4.0
CKT REF.
Earth Size Load Type
Point Reference
Phase Load in kW
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B
28370
9.34
9.21
9.82
Ist Floor
28373
9.76
9.28
9.34
38786
2nd Floor
38786
14.43
12.36
12.00
1
36770
3rd Floor
36770
12.49
12.38
11.90
DB-05
1
40850
4th Floor
40850
13.75
13.85
13.25
DB-6
DB-06
1
16540
5th Floor
16540
5.40
5.80
5.34
DB-7
DB-07
1
33198
Utility Shed
33198
11.00
11.05
11.148
Spare
1
0
-
0
0.00
0.00
0.00
0.99
0.99
Spare
Exhaust Fan
EXH.101---EXH.104
4
746
2984
0.99
Light, Fan
L.101---L.108
F.101
Sample office
room
8 (L)+1(F)
18 (L)+80(F)
Ground Floor
144(L) + 80(F)
0.22
1x4.0
Power Socket
PS.101---PS.104
4
200
Ground Floor
800
1x4.0
Sewing
Machine
SM.101---SM.106
6
400
Ground Floor
2400
1x6.0
Total Phase Load/kW=
Total Connected Load=
Remarks
0.80
2.40
77.38
77.32
229.295
74.59
kW
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Table 4: Example of load table of a typical SDB
From SLD
page-9
SDB-03, LOCATION: WEST, LINE NO-01, 3rd FLOOR,
FEED ROOM: DB-04, REF: RYB-01.
Main
Breaker MCB
Incoming Ckt. CKT REF.
Rat/Amp
MCB
16A TP
Phase
Earth
Neutral
Size
(re)
Size(rm)
Number of
Points/Pcs
Load Type
Point Reference
Light
L.325---L.335
11
Sewing
Machine
Sewing
Machine
SM.347---SM.352
Watt Per
Point
Location
Total Watt
18
West Side ,
Line no-1
198
6
350
"
2100
SM.353---SM.358
6
350
"
2100
Phase Load in kW
R
Y
B1
2A SP
2X2.5
R2
6A SP
2X4.0
1x4.0
B3
6A SP
2X4.0
1x4.0
RYB4
6A TP
3X4.0
1x4.0
Exhaust Fan
Exh.309---Exh.310
2
1125
"
2250
Y5
6A SP
2X4.0
1x4.0
Sewing
Machine
SM.359---SM.363
5
350
"
1750
1.75
Y6
2A SP
2X2.5
Light
L.336---L.346
11
18
"
198
0.198
RYB7
6A TP
2X4.0
Ceiling Fan
70
"
700
F.301-F.310
10
(R-3, Y-5, B-2)
B
Remarks
0.198
2.1
2.1
0.75
Total Phase Load/kW=
Total Connected Load=
0.75
0.75
0.21
0.35
0.14
3.06
3.048
3.188
9.296
kW
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