Overhead as a total may be, Les, but if you made a pie chart of individual expenses with the total as your breakeven, wouldn't labor (or payroll including taxes, Workman's Comp. and benefits) be your largest expense?
Overhead as a whole is our biggest expense. If you want to look at line by line, labor would be second to materials. We watch material waste and costs very closely. We try to keep to trucks stocked and jobs planned well to prevent wasted labor due to wrong or missing materials.
The ratio of labor to materials depends on what you're installing, I'd think. I do a lot of remodeling type wiring---fishing in walls for extra outlets, or running pipe. The materials are usually much less than the labor. If you're installing expensive fixtures, the materials will be more.
Material, is not even in the picture, material is listed as cost of goods when purchased, and then recovered when sold or installed, not even on the chart, with the exception of mark-up that would reflect additional profit.
As Eagle noted:" try to keep the trucks stocked and jobs planned well to prevent wasted labor due to wrong or missing materials.