Electrical estimating, CSI Division 26, is the business of turning an E sheet set into a priced material and labor bill. You are working from the power plan, lighting plan, riser diagram, panel schedules, and the lighting fixture schedule. Every receptacle, switch, fixture, conduit run, wire pull, junction box, and panelboard has to be counted or measured, then priced, then labored, then summed into a bid that holds margin. On a 6 story office building the electrical package can clear 3 million dollars, and the work is won or lost in how carefully you read the plans.
What You Are Estimating
Division 26 covers everything that carries power through a building. You are estimating the service equipment, the distribution gear, the branch circuit wiring, the devices, the lighting, and the low voltage systems that ride on the electrical drawings. The major cost buckets are switchgear and panelboards, conduit and wire, wiring devices, lighting fixtures and lamps, and specialty systems like fire alarm, nurse call, and lightning protection.
On a typical commercial floor you will count receptacles by type (standard, GFCI, isolated ground, weatherproof), light fixtures by fixture type from the schedule, switches and dimmers, fire alarm devices including smokes, pull stations, horn strobes, and addressable modules, and data outlets. You will measure conduit routes in linear feet, calculate wire pull lengths from the home run to the last device, and list every panelboard with its ampere rating and circuit count. The riser diagram gives you the feeder sizes from the service through the transformers down to the branch panels.
Units and Workflow
Electrical quantities come in three flavors: counts, linear measure, and loaded assemblies. Devices are counted. Conduit, wire, cable tray, and branch circuitry are measured in linear feet. Panels, breakers, transformers, and gear are counted and then built out as assemblies, meaning the can, the breakers, the lugs, and the trim are all line items that roll up to one equipment price.
The workflow follows the drawings. You start with the one line diagram and the panel schedule to build the distribution backbone. You move to the power plan for receptacles and branch circuits. You take the lighting plan for fixtures and lighting controls. You pull the fixture schedule for lamp and ballast or driver data. You finish on the low voltage sheets for fire alarm, security, and communications. Each sheet feeds a section of the estimate, and the sections sum to the bid.
Step by Step Estimate
First, set up the estimate with the labor units and the labor rate. Most electrical contractors work from NECA manual labor units, which give you the hours per device, per foot of conduit, and per foot of wire by wire size. The labor rate comes from your shop average or your foreman rate plus burden.
Second, do the takeoff. Count every device on every floor and tag it by type. Measure every conduit run, noting the conduit type, the size, and the fill. Calculate the wire from the circuit loading, the conduit fill percentage, and the NEC ampacity tables. List the panels and build each one as an assembly with the main breaker, the branch breakers, and the trim.
Third, price the material. Apply your vendor quotes for gear and fixtures, your commodity pricing for conduit and wire, and your package pricing on devices. Watch the copper pricing because it moves. Fourth, apply labor. Multiply each quantity by the NECA unit and the labor rate to get installed labor dollars. Fifth, add the spreads: labor burden, subcontracted fire alarm, bonding, permits, and your overhead and profit. Sixth, review the bid against the last job you did that looked like this one.
Where the Money Goes
On most commercial electrical packages the gear and the lighting together run 40 to 55 percent of the job. Gear, meaning the service, the transformers, the distribution panels, and the breakers, is bought in a small number of expensive line items. Lighting is bought in bulk and the fixture price drives the section. Conduit and wire together run 25 to 35 percent, and this is where small takeoff errors compound because the quantities are large and the unit price swings with copper. Devices, including receptacles, switches, and plates, run 8 to 12 percent. Labor runs 20 to 30 percent of the total installed cost depending on whether the job is new construction, renovation, or tenant buildout, with renovation and tenant work carrying more labor hours per unit.
Fire alarm and low voltage are often subbed out. If you carry them in your bid you price them as a subcontract line with a contingency, because the fire alarm shop drawings almost always change after the alarm subcontractor does their device layout.
Common Mistakes
The first mistake is missing branch panels. A missed junction box costs you twenty dollars. A missed branch panel costs you the panel, the breakers, the feeders, and the labor to set it, easily two thousand dollars or more on a 208 volt panel and multiples more on a 480 volt distribution panel.
The second mistake is undercounting conduit and wire. If you measure the home run but miss the branch drops you cut your conduit and wire by a third. If you ignore vertical risers between floors you underprice the feeders. The third mistake is using stale copper pricing on a job you will not buy material for six months. Copper moves, and a 10 percent swing on a 400,000 dollar wire package is 40,000 dollars.
The fourth mistake is forgetting the trim and the support. Conduit hangers, straps, boxes, cover plates, wire nuts, and labels are small line items that add up to real money. The fifth mistake is not building the panel as a full assembly. If you price the can but forget the branch breakers, or price the breakers but forget the main, the panel is short.
Putting It Together
A clean electrical estimate is built from the sheets up. You take the one line for distribution, the power plan for devices and branch circuitry, the lighting plan for fixtures, the fixture schedule for the lamp data, and the low voltage sheets for the specialty systems. You count the devices, measure the conduit, build the panels, price the material, apply the labor, and load the spreads. When the bid number lands, it has to make sense against the last similar job you bid. If it does not, you go back to the sheets before you submit. The work is detail heavy and the margin for error is small, which is why the electrical bid is the one most subs lose in the takeoff, not in the pricing.