This thesis is based on the investigative studies performed on fiberglass crossarm, which will be used in the distribution line structures as an additional insulation component. Lightning impulse voltage tests were conducted on the fiberglass crossarm alone to determine its critical flashover (CFO) voltage, and also the critical flashover voltage of 15 kV polymer suspension insulator plus the fiberglass crossarm. The Added CFO voltage of the fiberglass crossarm to the insulator was determined with polymer suspension insulator as the primary insulation component and the fiberglass crossarm as the secondary insulation component. Added CFO voltage was evaluated for 1 ft through 5 ft length of the fiberglass crossarm for positive and negative polarities, under dry and wet condition. The thesis also presents a comparison of the obtained results made with the previous results of the wood crossarm and polymer crossarm with the polymer suspension insulator.