Electrical Shop drawings are prepared as separate sheets to give the installer more complete details of a specific, nonstandard installation requirement. below Figure is a detail drawing of a section through the wall of an office warehouse. It provides details of how and where hanger fittings and boxes are to be placed between a column and insulation to support a run of bus duct.
Any set of electrical drawings might require additional “blowup” drawings of certain technical details that are not clearly indicated on small-scale drawings, particularly plan views. In this example, it is an elevation view of a section wall shown on a plan view. It includes both mechanical and architectural details. Other drawings might show section views of special foundations or footings, or suspension systems for electrical equipment.
These detail drawings might be drawn by the consulting architectural or engineering firm on complex projects, but they might also be supplied by the manufacturer of the equipment or hardware to be installed. The consulting firm will collate these drawings into the related set with appropriate sheet numbers.
Many items of electrical equipment such as motors and motor control cabinets are standardized by the manufacturer, and the outline and footprint dimensions are included in their catalogs. However, large, costly electrical equipment such as high-voltage switchgear, transformers, motor control centers, HVAC (heating, ventilating, and air conditioning) systems, and elevators are usually custom made for each project. Project shop drawings for this equipment are usually drawn by the manufacturer and furnished prior to the delivery of the equipment. They might also include installation and maintenance manuals custom-prepared for the specific project Electrical Shop drawings.
The architect/engineer requires dimensional outline information to lay out the location of the equipment on the elevation drawings and check for any possible interference conflicts that could develop. For example, the equipment must be positioned to provide, safe easy access to the equipment for routine maintenance. Allowance must be made for the swing radii of all doors, and adequate space must be allowed for maintenance personnel to gain access to the equipment through removable cover panels as well as enough room to work Electrical Shop drawings.
In some cases, special concrete footings must be prepared with specified lag bolts for anchoring the equipment before it is delivered. This work must be completed and the concrete must be sufficiently cured to accept the load when the equipment arrives on the site Electrical Shop drawings.
Shop drawings also are helpful for the contractor responsible for installing heavy equipment, so any required cranes or other heavy moving equipment will be on the site prior to the delivery of the equipment. In addition, the contractor must make sure that any existing openings in the walls or doorways are wide and high enough to provide adequate clearance for the entry of the equipment. Advance information will give the contractor enough time to install any conduit, cable trays, or plumbing that would be difficult or excessively costly to install after the equipment is in place.
As-built drawings that include detailed “factory-wired” connection diagrams will assist the installer in performing any “field wiring.” Later they will be important if any commissioning procedures or final acceptance testing is required. These drawings will then become part of a maintenance file to assist the maintenance personnel in the performance of any troubleshooting that might be required at a later date, after the equipment is operational. These drawings and any operation and maintenance manuals are essential documents of record that will be useful for making any later additions to the facility.
Power riser diagrams are single-line diagrams showing electrical equipment and installations in elevation. It shows all of the electrical equipment and the connecting lines for service entrance conductors and feeders. Notes identify equipment, the size of conduit necessary for each feeder, and the number, size, and type of conductors in each conduit.
Electrical schematic drawings are usually prepared by equipment manufacturers to show the electrical connections that must be made by the electrician or installer. They are also used for testing, troubleshooting, and maintenance of the equipment. As an example of an electrical schematic diagram, below Fig. shows an across-the-line starter for a three-phase motor powered from a three-phase, three-wire supply.
It can be seen from the diagram that the motor starting equipment is housed in two separate enclosures. This starter would normally be shipped by the manufacturer with the motor it will control. The contactors, overcurrent protective devices, transformer, and operating coil are in one enclosure, and the start/stop pushbuttons are in a separate enclosure so that they can be mounted some distance from the motor.
In this schematic each component is represented by a graphic symbol, and each wire is shown making individual connections between the devices. However, multiple wires could appear as one line on the drawing. As on this drawing, each wire is usually numbered to indicate where it enters the enclosure, and those numbers are repeated for the same wires connected inside the enclosure.
The three supply wires are identified as L1, L2, and L3; the motor terminals are designated T1, T2, and T3; and the normally open line contactors controlled by the magnetic starter coil C are designated as C1, C2, and C3. Each contactor has a pair of contacts that open or close for control of the motor
The remote control station consists of the stop and start pushbuttons connected across lines L1 and L2 by the primary of an isolation control transformer. The transformer secondary in the control circuit is in series with the normally closed overload contactors (OC) and the magnetic starter coil (C). The stop button is also connected in series with the starter coil, and the start button is connected in parallel with the starter coil.
In this circuit, the control transformer isolates the control circuit and prevents it from responding to any ground faults that could cause the motor to start accidentally. The isolating transformer can have its primary winding identical to its secondary winding so that input voltage equals output voltage, or it can step the motor circuit voltage down to a lower level as an added safety measure for the control circuit.