Your head electrician just delivered the bad news. Three major feeders are wrong, and you have to redo them. Unfortunately, they are the service entrance feeders, and you've already poured cement over them. Not only that, 10 of your lighting runs don't meet Code, and you have to replace 37 receptacle circuits because the receptacles are in the wrong places. Bad working drawings have struck again!
If you've spent much time in the field, you probably agree there is an epidemic of bad working drawings. This epidemic affects not only those of us in the electrical industry, but also the civil, architectural, manufacturing, and mechanical engineering disciplines. You may look at a typical drawing today and ask: "Are you kidding?" Unfortunately, there's no simple cure to this complex problem. However, EC&M Magazine continues the grass-roots movement Editor-in-Chief John DeDad started just a few years ago. Together, we can make good working drawings a reality.
A major impetus behind the deterioration in drawing quality has been cost-cutting in the name of delivering a set of drawings under a reduced fee. Anyone who's had to deal with poor documentation or poor as-built drawings knows the falseeconomics of this approach. Still, the pressure for cost reduction remains. Some "non-answers" include "drawingless installations" and "minimum documentation installations." Both of these are examples of saving pennies while wasting dollars. Other answers are much more useful and far less costly.
One useful solution to the cost reduction problem is Computer Aided Drafting (CAD). Unfortunately, many firms implemented CAD without considering traditional drafting principles or the needs of the people using the drawings. To make matters worse, they ignored the fact that CAD systems and electronic formats must follow certain principles of electronic drawing production. These principles include proper grid orientation and layer management, among others. This resulted in many CAD users wiping out the cost savings the software would otherwise provide them. So, not only must we contend with poor working drawings, but we also must deal with poor electronic sources of those drawings.
The working drawing is where the rubber meets the road. Even if we do all other steps correctly in the drawing process, the fruit of our labor isn't sweet-unless our working drawings follow certain principles and meet certain requirements. You can sum up these principles with one sentence: The drawing must be a well-thought-out plan to get you from start to finish. Think of the drawing as a road map. Do you correctly identify all the detours and details? Will the user, or a crew of users, have to stop and ask for directions?
If the layout looks good, the plan is usually successful. This is true partly because the appearance of a drawing indicates what to expect in terms of accuracy. It's also true because the layout of the drawing will determine if people can understand and work with the content. A clear, thoughtfully laid-out drawing is conducive to a thorough and proper review before it hits the field. The drawing is a perfect place to save time and money. Changing your plans electronically or on paper is cheaper and faster than doing reconstruction; plus the end result looks like a designed project instead of a patch job. A good rule of thumb is: "Measure twice, cut once." Here are the requirements your drawings should meet, if you want them to work for you in the field. Make sure your drawing:
Contains all relevant title block information. Title blocks are for reference purposes. A person in the field will examine the title block to make sure the drawing is the correct one with all current revisions. The worker will also rely on the title block for contact information, in case of a design error or another issue you must resolve or clarify.
Let's take a look at what Power Engineering, Inc. (PEI) , Shawnee Mission, Kan., uses for a title block in Fig. 1, on page 32 (original article). The title block should contain this information: Company name, Engineer/Designer, Reviewer/Checker (checked by), Date drawn, Date revised, Project name, and Drawing number (Sheet X of Y). Drawings with architectural elements should have a scale. If your drawing does not have a scale, the words "not to scale" should appear in the title block or other prominent spot. Your drawing must indicate the purpose or description of any revision. One way to do this is to indicate the revised item with a number inside a triangle, and then describe the changes in a list on the drawing. Some firms use a general description in the title block instead, and some do both. Some also "cloud" the revised area on the drawing and mark the cloud with the revision number. This makes it very easy for the field crew to spot the noted changes.
Uses standard symbology and nomenclature. Fig. 2, on page 32, and Fig. 3, on page 34 (original article), show some standard symbols used in the electrical industry. Close is not good enough. Most skilled trades are familiar with the standard symbols.
A good source of symbols is the Electrical and Electronics Graphic and Letter Symbols and Reference Designations Standards Collection, 1996 Edition (IEEE Item No. SH94458-NZU). It consolidates 12 IEEE standards related to electrical diagrams in one handy volume. Included are graphic symbols for circuit diagrams, architectural plans, logic circuit diagrams, device function numbers for electric power systems, letter symbols for units and measures, and more. This 688-page book sells for $165 for nonmembers of IEEE and $140 for members. To order, call (800) 678-IEEE.
Besides symbols, the designer must use standard industry terms, Xrefs for continuation from one drawing to another, and proper combinations of terms. For example, in your Bill of Materials (BOM) or Equipment Schedule (ES), you don't list "Green No. 2 wire." You list "Wire, No. 2, green" to facilitate alphabetical sorting.
Identifies components and their capacities clearly. Your BOM will list every item-an Equipment Schedule will not. The electrician usually doesn't care how many of each generic fitting an engineer estimated for the job. The electrician cares very much about the specifics of major or unusual components. If your job does not require a comprehensive BOM, then prepare an Equipment Schedule. Other names for Equipment Schedule include Master Equipment Listing and Major Component Schedule. The name itself varies by region, but the content is similar. The BOM or Equipment Schedule will give you more detail than the drawing.
The drawing must identify the components and their capacities so the electrician can compare the items in the drawing with those in the field. Large items, such as transformers and panels, require significant information. The drawing must show enough information to identify these items beyond a doubt. For a panel, show the wiring system and number of circuits (4-wire grounded wye, 480/277V 3-phase, 42 circuits, for example). You also may need to show the manufacturer and model number on the drawing to avoid confusion among similar equipment.
Shows wireway sizes and lengths. If you were going to "pipe" an electrical distribution system, would you be able to do so from the information given on the drawing? You should see, without much effort, what sizes of conduit you need and how many feet of each size. This helps you plan for laying out hangers, developing your critical path (see EC&M, May 1998), and scheduling the work.
Shows conduit content. Anyone who reviews the drawing must be able to see the wireway contents (and sizes) at a glance, for comparison to the National Electrical Code. Having the information "20 No. 12 AWG, THHN" is also a big timesaver during wire pulls. If putting all this information on a drawing makes it too crowded, you have some options. One is to reference a separate wire schedule. Another is to break the drawing into smaller drawings. Which one you choose is a judgment call. If you reference a wiring schedule, it becomes part of the drawing package, subject to inspection and the official stamp.
Uses good aesthetics. If your drawing requires a magnifying glass, highlighter, or scratch pad for someone to work with it, you have a bad drawing. Use good spacing, standard fonts (e.g., Arial, Times Roman), and only a few line styles (thickness or line type). If you use more than one thickness, represent main circuits with heavy lines and control circuits with light ones. Or, use heavy lines for new circuits and/or equipment and light lines for existing circuits and/or equipment.
Don't depend on shades of color or marginally different line styles to differentiate meanings. Make drawings as large as practical, so people don't have to squint. Leave some white space for notes and field changes. As-builts suffer when an electrician can say: "I had no room to make notes on the drawing." Don't put too much in one drawing.
As a contractor, this writer once received a CAD drawing as the basis for doing the electrical portion of a project. We had a four-pen plotter, but the original drawing had more than a dozen colors. This meant reloading the pens and drawing several times into the plotter. The extra colors added nothing, so we converted them to a set of three colors.
Ed Rafter, president of PEI, contributed drawings for background to this article. He had a similar experience with fonts. The architect who'd provided the basic drawing used a font pack that prevented Ed from opening the drawing. So, he had to purchase and load the memory-hogging fonts onto his machine. Unusual fonts also cause problems with reproducing the drawing. In short, don't use them.
Makes proper use of notes. If a wire size exceeds Code, a note should explain why. Otherwise, electricians may see the excess as an error and not incorporate it. Notes show other information like allowable substitutes to specified equipment, work method cautions or requirements, reference document names, "typical of" notations, "approval pending" notations, and lockout/tagout information.
Drawing packages. In a set of drawings, reserve Sheet One for symbology tables, legends, and other clarifying information common to all drawings. This sheet serves as a Table of Contents for the drawing package. When do you need such a sheet? The need depends on the type of information, project scope, project duration, and number of pages. If Sheet One will help the person in the field, include it. If not, leave it out. Make it comprehensive, but also make it lean-usefulness is your overriding concern. With huge amounts of information, you may have to reserve a block of drawing numbers, say Sheets 1 through 9, for clarifying information.
Use main plan diagrams to show the switches, contactors, relays, etc., as close to their actual arrangement as possible. Show panel-mounted devices enclosed in a rectangle made up of broken (or dashed) lines that represent the panel, to clarify what is in each panel. Indicate coupling between process loads and items like motors, generators, and exciters. This type of drawing gives you a quick overview.
Use external wiring diagrams to show how to make up the external connections-nothing else. If the connections are on the rear of a panel, the drawing must show this view. Use arrows to point to the cabinets to which wireway runs connect. You can draw lines across wireway runs to show the number of included conductors, but it's better simply to write the information, as described earlier. This type of drawing is useful for equipment layout and installation.
Use simplified wiring diagrams (also known as ladder diagrams) to show the operation of a control system. This diagram uses two vertical lines, with the control elements represented between them. You arrange the elements in the order in which they energize. This type of drawing is useful for troubleshooting control problems.
Use wireway charts to give details beyond what the wiring diagrams can contain and to give a concise visual representation of all pertinent information. Typically, you'll list the wireway ID number down the left side and have headings across the top. Headings should include wireway size, wire size, wire type, wire quantity, function, and "from and to" information. Note: You might have several entries under each heading for a given wireway ID.
Use single-line diagrams (one-lines) to show the layout of power generating and distribution systems. In this drawing, you show the wires to an instrument or the conductors in a power line or feeder with a single line. You can find these symbols in Fig. 4, on page 36 (in original article).
Taking the time to produce a good working drawing just makes sense. Don't get stuck with a bad working drawing. Remember: A thoughtfully laid-out drawing will almost always lead to success.