The EFW (Electric Field and Waves) instrument consists of four orthogonal spherical sensors deployed from 50 m cable booms in the spin plane of the spacecraft, plus four deployment units and a main electronics unit. Each deployment unit deploys a multiconductor cable and tip-mounted spherical sensor. Each opposing pair of cables will be symmetrically deployed to a tip-to-tip distance of approximately 100 m, except for about a week at the beginning of the mission when 70 m will be used for one boom pair (the Z-booms) and 100 m for the other pair. The potentials of the spherical sensor and nearby conductors are controlled by the microprocessor to minimize errors associated with photoelectron fluxes to and from the spheres.