electrical symbols and 1 standards -...

1.1 NEED OF ELECTRICAL SYMBOLS

Drawing is the language of engineers. For proper communication people must use the same language so that a particular word or symbol means the same thing to every one. In engineering drawing it is common practice to employ graphical symbols to denote the various accessories used. These symbols must convey the same meaning to everyone who reads the drawing. Symbols are, therefore, standardized by the Bureau of Indian Standards (BIS), as far as possible according to internationally agreed conventions as adopted by the International Electrotechnical Commission.

An important consideration in selecting symbols is that they should be, as far as possible, self explanatory and easy to draw.

It must be realized that even though the Bureau of Indian Standards has standardized the symbols for nearly all accessories/components used in the field of electrical engineering, these symbols are not yet universally used. Therefore, it is possible that the reader may come across, in other books, different symbols from the ones used in this text. However, in an attempt to encourage standardization, symbols approved by the Bureau of Indian Standards (BIS) have been used in this text. The reader is advised to make it a habit to refer to the Indian Standard Specifications to ensure the correctness of a symbol. IS: 2032 gives a list of standard symbols.

1.2 LIST OF SYMBOLS

1.2.1 Kind of Current

Direct current — Alternating current Power frequency Apparatus and machines suitable either for d.c. or a.c. (universal)

Chapter1

Electrical Symbols and Standards

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Electrical Design: Estimating and Costing2

1.2.2 System of Distribution

a.c. of m-phase and frequency m fExample

( ) a.c., single phase, 50 Hz 1 50 Hz

(b) a.c., three-phase, 50 Hz 3 50 Hz

(c) a.c., three-phase, 50 Hz, 415 V 3 50 Hz, 415 V

NeutralExample

(a) a.c., three-phase, with neutral, 50 Hz 3N 50 Hz

(b) a.c., three-phase, with neutral, 50 Hz 3N 50 Hz, 415 V

415 V (240 V between phase and neutral)

d.c. two conductors 110 V 2 — 110 V

d.c., three conductors, including neutral,220 V, (110 V between outer conductors

2N — 220V

and neutral)

Positive polarity +

Negative polarity –

1.2.3 Symbols of Lines

Line or cable: existing —

planned

Underground cable

Overhead line (general symbol)

1.2.4 Conductors

Conductors or a group of several conductors —

Flexible conductor

Note: Use one or several half circles reversely drawn; two half circles are never to be used because of a possible confusion with symbol for alternating current.

Electrical Symbols and Standards 3

Two conductors:

(a) Single line representation

(b) Multiline representation

Three conductors: (a) Single line representation

(b) Multiline representation

n conductors: n

ExampleFour conductors:

Single line representation 4

Multiline representation

Indication of conductor particulars (a) Example: d.c. circuit, 110 V, two conductors of 125 mm2 of aluminium

Single line representation – 110 V2 × 125mm A2

Multiline representation – 110 V

2 × 125mm A2

(b) Example: d.c. circuit 220 V (110 V between outer conductors and neutral), two conductors of 50 mm2 with neutral of 25 mm2

Single line representation 2N – 220 V

2 × 50mm + 1 × 25mm2 2

Multiline representation 2N – 220 V

2 × 50mm + 1 × 25mm2 2

(c) Example: Three-phase circuit 50Hz 6 kV, three conductors of 50 mm2

Single line representation 3 50 Hz, 6 kV3 × 50mm2

Multiline representation 3 50 Hz, 6 kV

3 × 50mm2


(d) Example: Three phase circuit, 50 Hz 3 conductors of 125 mm2 with neutral of 50 mm2:

Single line representation 3N 50 Hz3 × 125mm2 + 1 × 50mm2

4

Multiline representation 3N 50 Hz

3 × 125mm2 + 1 × 50mm2

Changing over from a single line 4

4Or representation to a multiline

representation.

Example: Four conductors Group of n conductors which n follow the same way on the diagram.

1.2.5 Terminals and Connections of Conductors

Terminal OR

Junction of conductors

Double junction of conductors Or Or

Crossing without electrical connection

Crossing and connecting conductors

Single line representation

Multiline representation

1.2.6 Circuit Elements

Non-reactive resistance or non-reactive resistor R

Impedance Z


Inductance, inductor L

Winding

Capacitance, capacitor

Note: The distance between the plates should not be greater than one-fifth of the length of the plates.

Earth

Frame or chassis connection

Frame or chassis earth connection

Fault

Example: Position of fault to frame

Screen – – – – – – –

Example: Screened conductor or screened cable

Magnetic core

Laminated core

1.2.7 Variability

Note: (a) Variability is ‘inherent’ when the variable quantity depends on qualities

of the device itself, for example, when the resistance changes with the change of voltage or with change of temperature.

(b) Variability is ‘non-inherent’ when the variable quantity is controlled by an external device, for example, when the resistance is controlled by a regulator.

(c) The sign of variability should be drawn across the main symbol at about 45° to the centre line of the symbol.


Examples of variable resistors

(a) General symbol

(b) Continuously variable

(c) Variable in steps

(d) With moving contact (general symbol)

(e) With moving contact continuosly variable

(f ) With moving contact, variable in steps

(g) Voltage divider with moving contact

1.2.8 Rotating Machines

Mechanically coupled machines:

d.c. two wire series generator (G) Mor motor (M)

d.c. two wire generator (G) or G motor (M), separately excited.

d.c. two wire shunt generator (G) M

or motor (M),

d.c. two wire generator (G) or

Gmotor (M), compound excited,short shunt


Symbol showing terminals, brushes and numerical data:

G 240V

30kWExample: d.c. two wire generator, compound excited, short shunt, 240V, 30 kW

a.c. series motor single phase M1

a.c. series motor three phaseM

3

Synchronous generator (GS) or synchronous motor (MS) single-phase.

GS1

Synchronous generator (GS) or synchronous motor (MS), three-phase, star connected, neutral not brought out.

GSY

Synchronous generator (GS) or synchronous motor (MS), three-phase, star connected, neutral brought out.

GSY

Synchronous generator (GS) or synchronous motor (MS), three-phase, both leads of each phase brought out.

GS

Or

GS

GS

Or


Symbol showing terminals, brushesand numerical data:

Example: Synchronous Generator 6600 V1000 kVA, 50Hz

120 V–GS(GS) or synchronous motor (MS), three-phase, both leads of eachphase brought out, 6600 V, 1000 kVA,50 Hz, 120 V d.c.

Induction motor, Squirrel cage M1single-phase.

Induction motor, squirrel cage, M1single-phase, leads of split phase

brought out.

Induction motor, squirrel cage, Mthree phase delta connected.

Induction motor, three phase, M3

Or

M3

squirrel cage, both leads of eachphase brought out.

Induction motor, three-phase, M3wound rotor.


1.2.9 Transformers

single line representation

multiline representation

Single phase transformers, with two- or three-phase windings:

11000 V250 KVA

50Hz4%

415VExample: 11,000/415 V, 250 kVA, 50Hz short circuit voltage 4%

Three phase transformer with two separate windings:Example: Star delta 6600/1100 V, 4000 kVA, 50 Hz. Connection Y d 11

Y

6600V4000KVA

7.5%YD11

11000V

50 Hz

Short circuit voltage 7.5%

Auto–transformer: single line representation

multiline representation

(a) Auto-transformer, single-phase.

(b) Auto-transformer, three-phase, star connected.

(c) Auto-transformer, single-phase, with continous voltage regulation.


1.2.10 Switchgear

Switch-general symbol

(a) Two way

(b) Intermediate

Three-pole switch, multiline representation

Three-pole switch, single line representation

Circuit breaker

Isolator

Terminal strip 11121314 15 11121314 15

Link

Open link

Distribution board cubical box

1.2.11 Contacts

Socket

Plug

Plug and socket

Relay or contactor contact, normally Oropen (NO)

Relay or contactor contact normally Or

closed (NC)


Push-button with momentary closed

Orcontact (normally open contact)

Push-button with momentary open

Orcontact (normally closed contact)

Thermal overload relay contact

Time-delay relay contact

Limit switch (NC contact)

Limit switch (NO contact)

Or

1.2.12 Relays and Contactors

Coil of electro-magnetic relay or contactor

Thermal overload relay

Electrically operated three-pole contactor

Electrically operated three-pole contactor with thermal overload device in all three-poles

Time delay relay (TDR)


1.2.13 Fuse-boards

Lighting circuit fuse-boards: (a) Main fuse-board without switches

(b) Main fuse-board with switches

(c) Distribution fuse-board without swithces

(d) Distribution fuse-board with switches

Power circuit fuse-boards: (a) Main fuse-board without switches

(b) Main fuse-board with switches

(c) Distribution fuse-board without switches

(d) Distribution fuse-board with switches

1.2.14 Switch and Switch Outlets

One way switch (a) Single pole

(b) Two-pole

(c) Three-pole

Two-way switch

Intermediate switch

Push-button or bell-push

1.2.15 Socket Outlets

Socket outlet, 5 A

Socket outlet, 15 A

Combined switch and socket outlet, 5 A

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