Project Context
This walkthrough uses a representative high-rise: a 42-story, roughly 680,000 SF Class A office tower in a major US metro, bid design-bid-build with a short bid window. The estimate covers Division 26 (Electrical), Division 27 (Communications) and Division 28 (Electronic Safety and Security, including fire alarm).
What the Estimate Needs to Answer
- Do the feeder sizes on the schedule match the loads they serve and the NEC ampacity rules?
- Is a prefabricated busway riser worth pricing as an alternate to conduit and wire?
- Where does cable tray conflict with structure or ductwork?
- What temporary power does a multi-year high-rise schedule need?
Typical Challenges
1. Feeder Schedule Checks
The feeder schedule drives a large share of the copper cost. Before pricing it, the estimator cross-checks each feeder against the panel and equipment it serves:
- Conductor size versus the overcurrent device rating and the ampacity tables in NEC Article 310
- Adjustments the design may have missed: ambient temperature correction and adjustment for more than three current-carrying conductors in a raceway (NEC 310.15)
- Voltage drop on long vertical runs, which may justify upsizing even where ampacity is adequate
- Equipment grounding conductor sizes per NEC Table 250.122
When a feeder looks undersized for its load, the estimator does not quietly re-engineer it. The discrepancy goes to the engineer of record as a pre-bid RFI, and the bid states which size was priced.
2. Busway Versus Conduit and Wire Risers
When the design calls for conduit-and-wire risers, a common alternate is prefabricated busway. The comparison is labor-driven:
| Method | Material | Field labor | What to watch |
|---|---|---|---|
| Conduit and wire (as designed) | Lower per foot | Higher: conduit install, pulling, terminations on every floor | Pull points, conduit fill, splice boxes |
| Prefabricated busway (alternate) | Higher per foot | Lower: bolted sections and plug-in or tap boxes | Lead time, fire-stopping at floor penetrations, engineer acceptance |
Which is cheaper depends on local labor rates, riser height and the number of taps. The estimate prices both and shows the difference so the owner and engineer can decide.
3. Cable Tray Coordination
Cable tray elevations are overlaid on the structural and mechanical drawings. Wherever the tray crosses beams or main duct runs at the same elevation, the estimator notes the conflict and raises it as an RFI, because rerouting in the field adds fittings, supports and labor.
4. Temporary Power
Temporary power on a multi-year high-rise is a real cost center, not an allowance. A typical scope includes:
- Temporary service and main distribution at grade
- Temporary distribution panels on working floors, relocated as the building rises
- Dedicated circuits for hoists and tower cranes, with lockable disconnects
- Temporary lighting and GFCI-protected receptacles for the trades (NEC Article 590; OSHA 29 CFR 1926 Subpart K)
- Monthly utility and maintenance costs over the schedule, if they are the electrical contractor’s responsibility
Applicable Codes and Standards
- NEC (NFPA 70) Article 310 – conductor ampacity and adjustment factors
- NEC Article 250 – grounding and bonding
- NEC Article 590 – temporary installations
- NEC Article 725 – Class 2 and Class 3 power-limited circuits
- OSHA 29 CFR 1926 Subpart K – electrical safety on construction sites
Software Workflow
| Software | Purpose |
|---|---|
| Accubid | Electrical takeoff, labor units and pricing |
| Bluebeam Revu | Markups, counts and quantity verification |
| AutoCAD | Tray routing overlays and conflict checks |
Common Estimating Risks
| Risk area | Why it matters | Mitigation |
|---|---|---|
| Feeder sizes that do not match loads | Copper cost and change orders on the largest line item | Cross-check feeders against loads; RFI before bid |
| Tray and duct conflicts | Rework, fittings and schedule | Overlay trade drawings before bid |
| Temporary power left as an allowance | Unpriced multi-year cost | Price as line items with monthly durations |
| Labor rates from national averages | Labor is the largest cost driver in this scope | Use current local rates for the jurisdiction |
Takeaways
- Feeders are where copper money is. Check them against the loads before pricing.
- Price riser alternates. Busway versus conduit and wire is often a meaningful decision on tall buildings.
- Temporary power is scope. On a multi-year job it deserves its own line items.
How We Apply This on Real Bids
For electrical bids, we take off Divisions 26, 27 and 28 separately, check the feeder schedule before pricing it, and list every discrepancy as an RFI. See our electrical estimating services, the conduit estimating guide, or pricing.