NESC Grades of Construction

The National Electric Safety Codes (NESC) offers a set of minimum guidelines for designing and constructing electric infrastructure.

Under the NESC, utility poles can fall under three grades of construction. The grade generally determines the margin of safety. Generally, higher grades of construction mean a higher degree of system resiliency.

The three construction grades are:

GRADE B: High margin of safety

Required when the pole supports spans that cross limited access highways, railroads, and navigable waterways.

GRADE C: Most common and provides a basic margin of safety

• Utilized for the typical power and joint-use distribution pole
• Two separate grades for line crossings and elsewhere

GRADE N: The lowest grade of construction

• Mostly used for emergency and temporary construction
• Not used for poles permanently supporting electric facilities

For each NESC construction grade, safety factors – both load factors and material strength factors – are applied during the structural analysis process.

• Load factors are safety factors that increase the loads applied to the structure. Wind, wire tension, and the weight of equipment and ice all have different factors.
• Strength factors are safety factors that decrease the allowed strength of poles and equipment. Wood, metal, concrete, and fiberglass all have specific strength factors that are applied.

Each grade of construction requires different load and strength safety factors, with Grade B requiring the strongest construction.

Why are these requirements so important? Most importantly, they are intended to keep the public and utility workers safe. They set the bar for mitigation against environmental factors and help measure a system’s resilience.

Know the Code. Stay safe.

Learn more about NESC and OSHA training classes with IKE

Grant Glaus is a registered professional electrical engineer with 25 years of experience in electric utility engineering, including line design, planning studies, joint use, and teaching NESC®, OSHA, and distribution line design classes. He has served on NESC® Subcommittee 5, Overhead Lines – Strengths and Loadings since 2006.