Electrical estimating

Electrical work powers, lights, connects and protects a building. It typically accounts for 10 to 20 % of the construction cost of a commercial building and more in data centers, hospitals and laboratories. Like mechanical work, it is almost always subcontracted by the general contractor, and like mechanical work it is full of interfaces where scope can fall between trades. This lesson explains how electrical contractors build their estimates, how to check them and what the general contractor must look for on bid day. Labor units and prices in the examples are illustrative.

What electrical work includes

In MasterFormat, electrical work falls under Division 26 (electrical), Division 27 (communications) and Division 28 (electronic safety and security), with utility work in Division 33. In the United States, installations must meet the National Electrical Code (NFPA 70) as adopted, sometimes with amendments, by the state or local jurisdiction, and are inspected by the local authority. Electricians and electrical contractors are licensed by states or localities.

How an electrical contractor builds an estimate

An electrical estimate starts with a count of every device and fixture on the drawings and a measurement of every conduit and cable run. Lighting fixtures come from the fixture schedule; receptacles, switches, data outlets, fire alarm devices and equipment connections are counted from the plans; switchgear and panels come from the single-line diagram and panel schedules. Conduit and wire are measured for feeders (from the service to distribution panels) and for branch circuits (from panels to devices).

Material is priced from distributor quotes, often with large items such as switchgear, lighting packages and generators quoted separately and late in the bid. Labor is priced with labor units per item, such as hours per hundred meters or feet of conduit by size, per device, per fixture, per termination, adjusted for conditions such as working height, concealed versus exposed work, existing buildings and congestion. Many electrical contractors use estimating software with labor-unit libraries based on industry manuals and their own history.

Conduit and wire

Branch circuit conduit is measured along the actual route, including vertical drops to devices and rises to panels, not as straight lines across the plan. Wire is then calculated from the conduit length times the number of conductors in the run, plus an allowance for terminations and slack at panels and boxes. Many jurisdictions and specifications permit armored or metal-clad cable instead of conduit and wire in some locations, which changes both material and labor. The specification's wiring method section is therefore one of the first things an electrical estimator reads.

# Branch circuit conduit, wire and labor for one floor (illustrative labor units)
runs = [  # description, conduit length ft, conductors per run, count of runs
    ("Office receptacle circuits", 125, 3, 24),
    ("Lighting circuits",          145, 3, 18),
    ("Dedicated equipment",         98, 4, 8),
]
allow = 0.10                    # terminations, makeup and slack
cond_ft = wire_ft = 0.0
for name, L, n, k in runs:
    cond_ft += L * k
    wire_ft += L * n * k * (1 + allow)
lab_conduit = 0.037             # hours per foot of 3/4 in EMT installed
lab_wire = 0.0037               # hours per foot of conductor pulled
hours = cond_ft * lab_conduit + wire_ft * lab_wire
print(f"Conduit {cond_ft:,.0f} ft, wire {wire_ft:,.0f} ft")
print(f"Labor {hours:,.0f} h; at $96/h = ${hours * 96:,.0f}")

Conduit 6,394 ft, wire 21,963 ft
Labor 318 h; at $96/h = $30,513

Conduit labor is much larger than wire-pulling labor, which is why wiring methods that avoid conduit can save significant cost where they are allowed. The estimate would then add boxes, devices, cover plates, supports, fittings and terminations, each with its own material and labor.

Devices, fixtures and connections

Devices (receptacles, switches, occupancy sensors), fixtures and equipment connections are priced per unit. Each unit carries material, labor to mount and terminate, and its share of boxes and supports. Lighting is often a large part of the electrical price; the fixture package may be quoted by a lighting distributor as a single lot, with substitutions allowed or forbidden by the specification. Lighting controls (networked control systems, daylight sensors, occupancy sensors) have grown in cost and complexity with energy codes and must be read carefully in the specifications.

Service, distribution and utility work

Service and distribution equipment, such as switchgear, transformers and panelboards, is priced from manufacturer or distributor quotes, which may be among the last prices received on bid day and can change sharply with market conditions. Lead times for switchgear and transformers have been long in recent years, which affects schedule risk as well as price (CON-330). Installation labor covers setting, anchoring, terminating feeders and testing.

Utility work needs special attention. The serving electric utility decides how the building is served and charges for the connection, which may include transformers, primary cables and metering. The electrical contractor's price often excludes these utility charges, which can be large; the bid documents should say who pays. Similar questions arise for temporary power during construction.

Fire alarm, communications and security

Fire alarm systems are designed and certified to their own standards and are commonly supplied by a fire alarm manufacturer or its distributor, with the electrical contractor installing conduit and wire and the supplier verifying and programming the system. Prices are checked per device: smoke and heat detectors, pull stations, horns and strobes, duct detectors, monitoring and control modules, and the panel and annunciators.

In the United States, fire alarm systems are designed and installed to NFPA 72, and the estimate must allow for acceptance testing and any inspection required before occupancy. Communications cabling is priced per drop (outlet) and by cable length to the telecom rooms, with racks, patch panels and testing; the owner's IT department often supplies network equipment.

Where the gaps are

Electrical scope gaps tend to appear at the same interfaces as mechanical ones, viewed from the other side.

Checking electrical prices on bid day

The checks are similar to those for mechanical work: cost per unit of floor area against comparable projects, electrical as a share of total cost, unit prices per device, fixture and drop, implied labor hours and crew size against the schedule, and confirmation that major equipment and the lighting package are included at current prices. Because switchgear and lighting quotes often arrive late, electrical contractors sometimes carry allowances for them; the general contractor should know which parts of the price are firm and which are allowances or budgets.