If you track your estimates, you will find that the branch wiring is approximately 60% to 80% of the estimate. When I say branch wiring, I mean all of the conduit and wire one inch and less in all systems. Estimates are won and lost in efficiency of the branch wiring take-off and projects make money or lose money in how efficient the branch wiring is installed. Most estimators do not like estimating branch wiring because it is the most tedious part of the estimate.
It is a common practice among estimators to use an average foot per device. Let’s suppose you use an average of 15 feet when in reality the average was 18 feet per device. Three feet over on 15 feet is 20%. Therefore, you are off 20% on 60% to 80% of the estimate.
Using averages per branch device is acceptable, once you have established an average for the current project. Using averages from a previous project could provide you with an estimate light or heavy in labor and material dollars.
Therefore, focus on the branch wiring in your estimates. Accuracy in all systems will provide you will a solid estimate.