EC&M’s Electrical Calculations Handbook - Chapter 15 potx

Electrical Cost Estimating Determining the cost of an electrical installation is done professionally using a set mechanical technique that termi- nates in a complete listing of electrical equipment, race- ways, luminaires, and devices to “build into” the installation and a detailed listing of installation personnel hours that the construction work will require. This chapter provides insights and templates for use in calculating elec- trical estimates. Electrical Takeoff and Personnel-Hour Cost Estimating Calculating the value of a typical electrical construction pro- ject consists of counting the luminaires and devices, mea- suring the cables and raceways, listing the electrical equipment, and determining the necessary fittings and hardware required to complete the installation. The first step in this work is the takeoff sequence, which includes the following: ■ List switchgear, including switchboards, panels, trans- formers, bus duct, motor starters and motor control cen- ters, and similar equipment items Chapter 15 371 v Copyright 2001 by The McGraw-Hill Companies, Inc. Click here for Terms of Use. ■ Count lighting fixtures, lamps, and hanging material ■ Count switch and receptacle devices ■ Count devices in special systems, such as fire alarm sys- tems, sound systems, security systems, telephone sys- tems, and other special systems ■ Determine the amount of feeder conduit and wire, listing fittings and elbows as well ■ Count junction and specialty boxes ■ Count fuses ■ Count connections to large pieces of equipment, such as air-handling units, chillers, pumps, kitchen equipment, and similar items ■ Determine the amount of branch-circuit conduit and wiring ■ Sketch and take off control wiring for HVAC and other systems ■ Count and list all items on drawings or in specifica- tions that are not colored in at this stage of the takeoff procedure. After listing the items to be installed, they must be entered into an estimate sheet such as the one shown in Fig. 15-17, onto which materials prices and labor unit pricing can be entered. The labor unit insertion is to determine how many personnel hours of installation time will be required to complete the work. This estimate is most easily and exactly done from personnel-hour tables made from recent- ly completed similar work. When such tables are not avail- able, the following can be used to determine approximate installation personnel-hour budgets: Lighting fixtures (Fig. 15-1) Switches and receptacle devices (Fig. 15-2) Outlet boxes (Fig. 15-3) Conduit elbows and fittings—EMT (Fig. 15-4) Conduit and elbows—heavy-wall rigid steel (Fig. 15-5) 372 Chapter Fifteen Conduit and elbows—IMC steel (Fig. 15-6) Conduit and elbows—aluminum (Fig. 15-7) Conduit and elbows—plastic underground (Fig. 15-8) Cables (Fig. 15-9) Wires and connectors (Fig. 15-10) Transformers (Fig. 15-11) Switches (Fig. 15-12) Panelboards (Fig. 15-13) Cable tray (Fig. 15-14) Motor connections, by horsepower (Fig. 15-15) Motor controller, individual (Fig. 15-16) The blank pricing sheet shown in Fig. 15-17 is useful in preparing electrical estimates. An example of its use is shown in Fig. 15-18 for the following project: A single-floor commer- cial building will contain ten 2/96 fluorescent luminaires, five 20-ampere (A) duplex receptacles, and one light switch. It will be energized through a 100-A, 480-volt (V), two-fuse switch, a 15-kilovoltampere (kVA) 480-120/240-V transformer, a 6-cir- cuit 480/277-V lighting panel, and a 12-circuit 120/240-V pan- el. The service feeder is four no. 6 copper THHN conductors in 1-inch (in) EMT that is 100 feet (ft) in length. Determine the installation cost of this electrical system. The electrical estimate must be done in stages, none of which should be omitted: 1. Perform an electrical equipment listing. This is done most easily from the electrical one-line drawing. 2. Perform a feeder takeoff using the feeder takeoff sheet found in Fig. 15-19. The completed feeder takeoff for the present project is shown in Fig. 15-20. 3. On a blank sheet, make a branch-circuit takeoff sheet by listing all the symbols shown on the electrical draw- ing. One symbol is for the fluorescent luminaire, another is for the light switch, and another is for the duplex Electrical Cost Estimating 373 374 Figure 15-1 Lighting fixture installation personnel hours. 375 376 Figure 15-2 Switch and receptacle device installation personnel hours. 377 Figure 15-3 Outlet box installation personnel hours. 378 receptacle. Then count the symbols from the drawing, marking them out fully on the drawing with a colored pen- cil as their quantities are placed onto the takeoff sheet. 4. Under the quantity of each symbol on the branch-circuit takeoff sheet, write down every piece of material required to install that symbol, along with how many pieces of that material will be required for each symbol installa- tion. For example, mounting a chain-hung 8-ft fluores- cent luminaire would require two pieces of allthread rod, two quick bolts, two allthread rod couplings, four hex nuts, four fender washers, two red/yellow wire nuts, 6 ft of 1 ր 2 -in flexible conduit, 18 ft of no. 14 THHN wire, two 1 ր 2 -in flexible conduit connectors, and two lamps. 5. List each piece of electrical equipment on the pricing sheet found on the branch-circuit takeoff sheet and on the feeder takeoff sheet, marking it off in colored pencil from the takeoff sheet as it is transferred to the pricing sheet. When all items are listed on the pricing sheet, then all items on the drawing will be colored and all items on the takeoff sheets will be colored as well. 6. Price and assign personnel hours to the pricing sheet, referring to the personnel-hour tables found earlier in this chapter. Current material pricing is normally pro- cured from an electrical supply house due to the fact that it changes frequently, and therefore, material pricing is not shown here. 7. Multiply the quantity of each item by its price and then by its personnel-hour installation requirement, and then sum the columns. The totals are the project totals for “raw cost,” to which labor rate ($/hour), expendable tools, miscellaneous expenses, and the “labor burden” of fringe benefits, taxes, and insurance must be added to obtain actual cost. A project expense sheet, as described below, should be completed for every project to determine the cost of all project-related items that are not actual mate- rials and installation labor items. A complete pricing sheet for the subject project is shown in Fig. 15-18. Electrical Cost Estimating 379 (Text continues on p. 397.) 380 . (Fig. 1 5-1 2) Panelboards (Fig. 1 5-1 3) Cable tray (Fig. 1 5-1 4) Motor connections, by horsepower (Fig. 1 5-1 5) Motor controller, individual (Fig. 1 5-1 6) The blank pricing sheet shown in Fig. 1 5-1 7. energized through a 100-A, 480-volt (V), two-fuse switch, a 1 5- kilovoltampere (kVA) 48 0-1 20/240-V transformer, a 6-cir- cuit 480/277-V lighting panel, and a 12-circuit 120/240-V pan- el. The service. fixtures (Fig. 1 5-1 ) Switches and receptacle devices (Fig. 1 5-2 ) Outlet boxes (Fig. 1 5-3 ) Conduit elbows and fittings—EMT (Fig. 1 5-4 ) Conduit and elbows—heavy-wall rigid steel (Fig. 1 5-5 ) 372 Chapter