Covered parties include the general contractor, subcontractors, and in some cases suppliers and manufacturers of equipment. Examples of the types of projects for which erection all risks coverage is typically purchased include power plants, manufacturing and fabrication facilities, water and wastewater treatment facilities, and telecommunications centers (particularly where the erection of signal towers is involved). Some insurers combine erection all risks and contractors all risks coverages into one form. Although these terms are sometimes used interchangeably, there are some substantive differences. Coverage for delay in start-up costs is typically an optional coverage.