Electrical Estimating Guide: Branch Wiring, Switchgear, and Lighting

Electrical estimates are built from thousands of small quantities: feet of conduit, feet of wire, boxes, devices, fittings and terminations. They also carry a few very large items, like switchgear and generators, that come in as vendor quotes. A good estimate handles both. Count the small items carefully, and make sure the big quotes actually cover the scope on the drawings.

This guide walks through how commercial electrical estimates are commonly organized. It covers what to take off and how to check conduit fill against the 2023 NEC (NFPA 70), and it includes a worked conduit and wire example.

Division 26 Scope and Related Divisions

In CSI MasterFormat, electrical power and lighting fall under Division 26 – Electrical. The main level-2 sections include:

• 26 05 00 – Common Work Results for Electrical (conductors, grounding, raceways and boxes, hangers, identification)
• 26 10 00 – Medium-Voltage Electrical Distribution
• 26 20 00 – Low-Voltage Electrical Transmission (switchboards, panelboards, transformers, low-voltage distribution equipment)
• 26 30 00 – Facility Electrical Power Generating and Storing Equipment (generators, UPS)
• 26 40 00 – Electrical and Cathodic Protection
• 26 50 00 – Lighting

Two related divisions often get missed or double-counted. Division 27 – Communications covers data, voice and pathways. Division 28 – Electronic Safety and Security covers fire alarm, access control and video surveillance. Read the bid documents to see which of these belong to the electrical contractor and which go to a low-voltage sub. Then state that split clearly in your proposal.

Organizing the Takeoff

Most electrical estimators split the work into systems so each one can be checked on its own:

1. Service and distribution: utility service, switchgear or switchboards, transformers, panelboards, feeders
2. Branch power: receptacles, equipment connections, home runs
3. Lighting and controls: fixtures by type, emergency lighting, occupancy and daylight controls
4. Mechanical and equipment connections: RTUs, pumps, VAV boxes, kitchen equipment, disconnects
5. Special systems: fire alarm, data pathways, security (when in scope)
6. Temporary power and general items: temp service, permits, testing, as-builts

Conduit and Wire

• Measure conduit by type and trade size: EMT, rigid metal (RMC), IMC, PVC Schedule 40/80, and flexible (FMC, LFMC).
• Include vertical footage: stub-ups, drops to switches and receptacles, and risers between floors. Plan-view measurements leave these out.
• Count fittings, couplings, connectors, straps and supports separately, or use a per-100-LF allowance that you track against past jobs.
• Wire length is roughly the conduit length plus makeup at each termination. Separate it by conductor size, insulation type (THHN/THWN-2, XHHW-2) and system voltage (120/208V vs 277/480V).
• Feeders and branch circuits should be separate line items. Feeders are fewer and larger, and their cost is driven by conductor size.

Distribution Equipment

Price switchgear, switchboards, panelboards, transformers and motor control centers from vendor quotes whenever you can. Compare each quote to the one-line diagram and panel schedules. Check ampacity, AIC rating, voltage, number of circuits, spare spaces, metering and enclosure type (NEMA 1, 3R, 4X). Also confirm that the quote includes freight, rigging and startup. If it doesn’t, add them.

Lighting

Count fixtures by type tag straight from the lighting plans, then reconcile the counts with the fixture schedule. Emergency lighting (battery units, inverters, generator-backed circuits) and the controls package (sensors, relay panels, networked control systems) are often shown only in notes or specifications, so check there.

Conduit Fill Basics (2023 NEC)

The NEC limits how much of a raceway’s cross-sectional area conductors can occupy. Chapter 9, Table 1 allows:

Number of conductors	Maximum fill
1	53%
2	31%
Over 2	40%

To check a run, add up the conductor areas from Chapter 9, Table 5 and compare the total with the 40% column for the raceway in Chapter 9, Table 4. For example, 3/4” EMT has a 40% fill area of about 0.213 sq in. A #12 THHN conductor is about 0.0133 sq in, so 0.213 / 0.0133 = 16.0, which means 16 conductors maximum. That matches the Informative Annex C table for #12 THHN in 3/4” EMT.

Fill is a physical limit, not an ampacity check. Once a raceway holds more than three current-carrying conductors, the adjustment factors in NEC 310.15(C)(1) apply (80% for 4-6 conductors, for example). Heavily loaded conduits can force you to upsize wire or split runs. If the drawings show circuit numbers without home-run groupings, note your assumption in the estimate.

Worked Example: Conduit and Wire for a Lighting Home Run

Example (not a real project): A home run carries three 20A, 277V lighting circuits from a panel to a corridor. Each circuit has its own neutral, and there is one equipment grounding conductor.

Conductors: 3 hots + 3 neutrals + 1 ground = 7 #12 THHN

Fill check: 7 x 0.0133 sq in = 0.0931 sq in. That is under the 0.213 sq in limit for 3/4” EMT, so 3/4” EMT works.

Ampacity check: There are 6 current-carrying conductors (the neutrals count because they are separate circuits), so the 80% adjustment applies. #12 THHN at the 90°C column is 30A, and 30 x 0.80 = 24A, which is still at least 20A. The branch circuit is still limited to 20A overcurrent protection, and termination temperature ratings still apply.

Conduit footage:

• Horizontal run measured on plan: 145 LF
• Vertical at panel: 8 LF
• Three switch drops at 6 LF each: 18 LF
• Subtotal: 145 + 8 + 18 = 171 LF
• Routing allowance for offsets and coordination (assumed 10%): 171 x 1.10 = 188.1, so use 188 LF
• EMT comes in 10-ft lengths: 188 / 10 = 18.8, so buy 19 sticks

Wire footage:

• Per conductor: 188 LF + 6 LF makeup (panel and boxes) = 194 LF
• Total: 7 x 194 = 1,358 LF of #12 THHN (1,164 LF of phase and neutral colors, 194 LF green)
• Purchase with 5% waste: 1,358 x 1.05 = 1,425.9, so order 1,426 LF

Labor (illustrative units, check them against your own source): At 5.0 hours per 100 LF for 3/4” EMT, conduit takes 188 / 100 x 5.0 = 9.4 hours. At 0.7 hours per 100 LF for #12 wire, wire takes 1,358 / 100 x 0.7 = 9.5 hours. The total is about 18.9 labor hours before adjustment factors.

Labor Units and Adjustments

Many contractors start from published labor units, such as the NECA Manual of Labor Units or the unit libraries built into electrical estimating software, and then adjust them with their own historical data. Base units assume normal conditions. Common adjustments include:

• Working height above about 10-12 ft (lifts, ladders)
• Congested ceilings or heavy coordination with other trades
• Renovation in occupied buildings, and working around existing systems
• Small quantities, where setup and layout don’t spread across many units
• Schedule compression and overtime

Apply these as separate, visible factors. Don’t quietly inflate the base units. That way a reviewer can see exactly what you assumed. For labor rates, use a burdened rate built for the local market. Our labor burden guide shows how to build one.

Electrical Estimating Checklist

• Confirm which edition of the NEC is adopted locally and any local amendments
• Reconcile the one-line diagram, panel schedules and floor plans
• Take off feeders separately from branch circuits
• Include vertical conduit and wire makeup, not just plan-view runs
• Check conduit fill and ampacity adjustments on crowded home runs
• Reconcile fixture counts with the lighting fixture schedule
• Build a mechanical equipment connection list from the HVAC and plumbing schedules
• Confirm the split between Division 27/28 scope and the electrical sub
• Include temporary power, permits, testing and as-built drawings
• Get current quotes for gear, lighting packages and generators, and record the quote dates

Common Mistakes

• Measuring only plan-view conduit. Drops, stub-ups and risers can add a lot of footage.
• Taking gear quotes at face value. Missing spare spaces, the wrong AIC rating, or excluded freight and startup all come back as change orders.
• Leaving out equipment connections. Every RTU, exhaust fan, water heater and pump needs a circuit, a disconnect and a connection.
• Guessing home-run groupings. Unclear circuiting can change conduit sizes and wire counts.
• Double-counting or dropping low-voltage scope. Fire alarm and data pathways fall between divisions.
• Using unadjusted labor units in renovation or high-ceiling work.

For a deeper look at raceway takeoff, see how to estimate electrical conduit. For how electrical fits into the full MEP package, read our MEP estimating guide.

How F&K Estimatings Can Help

F&K Estimatings prepares Division 26 takeoffs organized by system and CSI section, using Bluebeam Revu and PlanSwift. Scope gaps and unclear circuiting are flagged as RFIs rather than guessed at. See our electrical estimating services, review pricing, or send your drawings for a quote.