The purpose of the National Electrical Code (NEC) is to:

A.
Standardize electrical product manufacturing.

B.
Regulate power usage throughout the United States.

C.
Standee electrical voltage throughout the United States.

D.
Set safety standards for electricaldesign construction and maintenance.

Explanation:
The most widely adopted element of a building code in the United
States and the world, NFPA 70, National Electrical Code (NEC) is the benchmark
for safe and efficient electrical installations.
Source: http://www.nfpa.org/nec/thenec/index.asp