Complex electronic control networks manage critical infrastructure systems such as the electric power grid across the United States. These networks are subject to failure due to the effects of naturally occurring or man-made electromagnetic pulses. Mitigation of these effects is necessary for the safety and security of our nation. Carbon nanotube based plasma limiters can provide a first line of defense against high energy pulses which are able to damage sensitive electronic circuits. Plasma limiters placed on the power and data lines into the control equipment can prevent the damaging pulses from reaching the semiconductor devices. During Phase I existing plasma limiter technology developed for RF systems in the Department of Defense will be modified to protect AC and DC power sources, data lines and sensor inputs which support the control networks of the electric grid. Modifications include new packaging to interface with each type of power supply, data interface and sensor input. Carbon nanotube geometry and the penning gas mixture which support the plasma formation will be altered to allow the limiter to activate at the proper overvoltage condition for the circuit being protected.