How to Read and Interpret Electrical Shop Drawings

In article “How to Read and Interpret Electrical Shop Drawings –Part One”, we gave a fast overview for the articles/courses that give a preliminary explanation for the different Types of Electrical drawings.

Also we listed the Electrical Drawings Glossary which will be a reference for all the terms and expressions used throughout this course.

Today, we will explain the Resources used to Read and Interpret Electrical Drawings.

3- Resources used to Read and Interpret Electrical Drawings

The electrical installations in any building can be represented on drawings by the use of the various applicable outlet and equipment symbols, together with interconnecting circuit or feeder run lines, supplemented with necessary notations. Many standards were issued to provide guidelines for graphical symbols, abbreviations and device function numbers which will be the basis for reading and interpreting any electrical drawings. These standards are:

1- American National Standards Institute (ANSI):

ANSI Y32.2: The American National Standard Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters).
ANSI Y32.9: American National Standard Graphic Symbols for Electrical Wiring and Layout Diagrams Used in Architecture and Building Construction.

2- Institute of Electrical and Electronics Engineers (IEEE):

IEEE 315: IEEE Standard, Graphic Symbols for Electrical and Electronic Diagrams
IEEE C37.2: IEEE Standard Electrical Power System Device Function Numbers and Contact Designations.

3- Canadian Standards Association (CSA)

CSA Z99: Canadian Standard, Graphic Symbols for Electrical and Electronic Diagrams

4- The International Electrotechnical Commission (IEC)

IEC 60617: IEC Standard, Graphic Symbols for Electrical and Electronic Diagrams

5- The British Standards (BS)

BS 3939-2: Graphical Symbols for Electrical Power, Telecommunications and Electronics Diagrams

A brief description and information about each above standard will be given in below, for more information about each standard you need to download them from the shown download links at the end of this article.

ANSI Y32.2 - IEEE 315 - CSA Z99

American National Standard Y32.2-1975 (IEEE Std 315-1975), with the modifications shown in Section 100, has been approved as CSA Standard Z99. This action was proposed by the Committee on Electrical Symbols, under the jurisdiction of the Sectional Committee on Abbreviations, Definitions and Symbols and was formerly approved by these Committees.

ANSI Standard Y32.2 provides a list of graphic symbols and class designation letters for use on electrical and electronics diagrams. This standard includes the following sections:

Section 1- Qualifying Symbols
Section 2- Graphic Symbols for Fundamental Items {not included in other sections}
Section 3- Graphic Symbols for Transmission Path
Section 4- Graphic Symbols for Contacts, Switches, Contactors, and Relays
Section 5- Graphic Symbols for Terminals and Connectors
Section 6- Graphic Symbols for Transformers, Inductors, and Windings
Section 7- Graphic Symbols for Electron Tubes and Related Devices
Section 8- Graphic Symbols for Semiconductor Devices
Section 9- Graphic Symbols for Circuit Protectors
Section 10- Graphic Symbols for Acoustic Devices
Section 11- Graphic Symbols for Lamps and Visual-Signaling Devices
Section 12- Graphic Symbols for Readout Devices
Section 13- Graphic Symbols for Rotating Machinery
Section 14- Graphic Symbols for Mechanical Functions
Section 15- Graphic Symbols Commonly Used in Connection with VHF, UHF, SHF Circuits
Section 16- Graphic Symbols for Composite Assemblies
Section 17- Graphic Symbols for Analog Functions
Section 18- Graphic Symbols for Digital Logic Functions
Section 19- Graphic Symbols for Special- Purpose Maintenance Diagrams
Section 20- Graphic Symbols Commonly Used on System Diagrams, Maps, and Charts (Communications Equipment)
Section 21- Graphic Symbols Commonly Used on System Diagrams, Maps, and Charts (Generating Stations and Substations)
Section 22- Class Designation Letter
Section 23- Referenced Standards
Section 100- Canadian Standard
Modifications to American National Standard Y32.2-1975
Appendix A Cross Reference List of Changed Item Numbers
Appendix B Reference Data-IEC Publication 117 Recommended Graphical Symbols
Appendix C Revised or Deleted Symbols (ANSI Y32.2-1970)
Appendix D Revised or Deleted Symbols (USAS Y32.2-1967)
Appendix E Revised or Deleted Symbols (USAS Y32.2-1962 & Supplement USAS Y32.2a-1964 or MIL-STD-15-1A)
Appendix F Cross-Reference List of Class Designation Letters- IEC 113-2 vs. ANSI Y32.2

The Quick Reference to Symbols of is ANSI Y32.2 as follows:

ANSI Y32.9

The American National Standard Graphic Symbols for Electrical Wiring and Layout Diagrams Used in Architecture and Building Construction (ANSI Standard Y32.9) provides guidelines for:

Showing symbols in ways that represent the general physical location and arrangement of a wiring system.
Using symbols that specify the physical requirements for materials that are needed in the electrical installation of buildings.

Notes:

Certain electrical symbols that are commonly used in making electrical system layouts on drawings are not included in this standard because they are included in American National Standard Y32.2-1970.
Some examples of items for which symbols are not given in this standard are as follows:

Electric motor
Electric generator
Power transformer
Pothead (cable termination)
Electric watt-hour meter
Circuit element, (for example, circuit breaker)
Fusible element
Single-throw knife switch
Double-throw knife switch
Ground
Battery

The most common ANSI Y32.9 standard graphic symbols used in electrical layout drawings are included in the following images:

IEEE C37.2

IEEE Standard C37.2, Standard Electrical Power System Device Function Numbers

American National Standard Institute, it contains Definitions and applications of the following:

Standard device function number descriptions,
Device contacts,
Annex A (informative) Samples of device function numbers,
Annex B (informative) Bibliography.

Standard device function number descriptions

A device function number, with an appropriate prefix and appended suffix is used to identify the function(s) of each device installed in electrical equipment. This includes manual, partial-automatic, and automatic switchgear. These numbers are to be used in drawings, elementary and connection diagrams, instruction books, publications, and specifications. In addition, for automatic switchgear, the device number may be physically placed on, or adjacent to, each device on the assembled equipment. This will enable a device to be readily identified.

Device function numbers are used in electrical drawings, diagrams, instruction books, and specifications. Device function numbers save space on a drawing or diagram because they eliminate the necessity of printing descriptions of functions next to diagrammatic symbols.

A list of the most commonly used device function numbers from IEEE Standard C37.2 is included in below table.

Prefixes or Suffixes

Letters and numbers may be used as prefixes or suffixes to device function numbers to provide a more specific definition of the function. They permit a manifold multiplication of available function designations for the large number and variety of devices used in the many types of equipment covered by this standard.

They may also serve to denote individual or specific parts or auxiliary contacts of these devices or certain distinguishing features, characteristics, or conditions that describe the use of the device or its contacts in the equipment.

Prefixes and suffixes should, however, be used only when they accomplish a useful purpose. For example, when all of the devices in a piece of equipment are associated with only one kind of apparatus, such as a feeder, motor, or generator, it is common practice, in order to retain maximum simplicity in device function identification, not to add the respective suffix letters F, M, or G to any of the device function numbers.

In order to prevent any possible conflict or confusion, each letter suffix should preferably have only one meaning in individual pieces of equipment. To accomplish this, short, distinctive abbreviations, such as those contained in ASME Y1.1-1989, or any appropriate combination of letters may also be used as letter suffixes where necessary.

However, each suffix should not consist of more than three (and preferably not more than two) letters, in order to keep the complete function designation as short and simple as possible. The meaning of each suffix should be designated on the drawings or in the publications with which they are used, similar to TC-trip coil, V-voltage, X-auxiliary relay.

In cases where the same suffix (consisting of one letter or a combination of letters) has different meanings in the same equipment depending upon the device function number with which it is used, then the complete device function number with its suffix letter or letters and its corresponding function definition should be listed in the legend in each case, i.e., 63V-vacuum relay, 70R-raising relay for device 70, 90V-voltage regulator.

Use of suffix letters

Lowercase (small) letters are used in practically all instances on electrical diagrams for the auxiliary, position, and limit switches, Uppercase (capital) letters are generally used for all suffix letters in 3.4.

The letters in 3.4.1 through 3.4.3, since they should generally form part of the device function designation, are usually written directly after the device function number, for example, 52CS, 71W, or 49D. When it is necessary to use two types of suffix letters in connection with one function number, it is often desirable for clarity to separate them by a slanted line or dash, as, for example, 20D/CS or 20D-CS.

The suffix letters in 3.4.4, which denote parts of the main device, and those in 3.4.5, which cannot or need not form part of the device function designation, are generally written directly below the device function number on the drawings, for example 52/CC or 43/A.

Suffix numbers

If two or more devices with the same function number and suffix letter (if used) are present in the same piece of equipment, they may be distinguished by numbered suffixes, as, for example, 4X-1, 4X-2, and 4X-3, when necessary.

Device Contacts

4.1 Auxiliary, position, and limit switch contacts

The letters a and b shall be used for all auxiliary, position, and limit switch contacts for such devices and equipment as circuit breakers, contactors, valves and rheostats, and contacts of relays as follows:

a Contact that is open when the main device is in the standard reference position, commonly referred to as the non-operated or de-energized position, and that closes when the device assumes the opposite position
b Contact that is closed when the main device is in the standard reference position, commonly referred to as the non-operated or de-energized position, and that opens when the device assumes the opposite position

The simple designation a or b is used in all cases where there is no need to adjust the contacts to change position at any particular point in the travel of the main device or where the part of the travel where the contacts change position is of no significance in the control or operating scheme. Hence, the a and b designations usually are sufficient for circuit breaker auxiliary switches.

Standard reference positions of some typical devices are given in Table 1.

By downloading the IEEE C37.2 standard, you can get more information also about the following parts:

4.1.1 Auxiliary switches with defined operating position
4.1.2 Auxiliary switches for devices without a standard reference position
4.2 Limit switches
4.2.1 Auxiliary switches for circuit breaker operating mechanisms
4.3 Torque limit switches
4.4 Other switches
4.5 Representation of device contacts on electrical diagrams

IEC 60617

IEC 60617 (also known as British Standard BS 3939).

Standard IEC 60617 consists of several parts as follows:

Part 1: General information, general index. Cross-reference tables.
Part 2: Symbol elements, qualifying symbols and other symbols having general application. (For example: outlines and enclosures, qualifying symbols for kind of current and voltage, variability, direction of force, motion and flow etc., mechanical controls, earth and frame connections, ideal circuit elements.)
Part 3: Conductors and connecting devices. (For example: conductors; flexible, screened or twisted, coaxial conductor, terminals, junctions, plugs and sockets, cable sealing ends.)
Part 4: Passive components. (For example: resistors, capacitors, inductors, ferrite cores, magnetic storage matrices, piezoelectric crystals, electret, and delay lines.)
Part 5: Semiconductors and electron tubes.
(For example: diodes, transistors, thyristors, electronic tubes, radiation detectors.)
Part 6: Production and conversion of electrical energy. (For example: windings, generators, motors, transformers, power converters.)
Part 7: Switchgear, control gear and protective devices. (For example: contacts, witches, temperature-, proximity- and touch-sensitive switches, switchgear and control gear, motor starters, all-or-nothing relays, measuring relays, fuses, gaps, arresters.)
Part 8: Measuring instruments, lamps and signaling devices. (For example: indicating, integrating and recording instruments, thermocouples, telemetering devices, clocks, position and pressure transducers, lamps, horn, bell.)
Part 9: Telecommunications: Switching and peripheral equipment. (For example: switching systems, selectors, telephone sets, telegraph and data apparatus, transducers, recorders and reproducers.)
Part 10: Telecommunications: Transmission.
(For example: telecommunication circuits, antennas, radio stations, waveguides, one-two or multi-part devices, masers, lasers, signal generators, changers, threshold devices, modulators, demodulators, discriminators, concentrators, multiplexers, frequency spectrum diagrams, fiber optics transmission lines and devices.)
Part 11: Architectural and topographical installation plans and diagrams. (For example: generating stations and substations, networks, cabled distribution systems for sound and television, installation symbols for switches, socket outlets, lighting outlets, etc.)
Part 12: Binary logic elements. (For example: qualifying symbols, dependency notation, combinative and sequential elements such as buffers, drivers, coders, arithmetic elements, delay elements, bi-stable, mono-stable and a-stable elements, shift registers and counters, memories.)
Part 13: Analogue elements. (For example: amplifiers with qualifying symbols, function generators, coordinate converters, electronic switches.)