Much of the structure of the ISS is a dielectric material. It will have the voltage of the surrounding space, essentially 0-volts. But the solar arrays conduct 160-volts. The result is a 140-volt potential difference across the vehicle that could be a hazard to crew members and also produce the risk of dangerous arcing. Here's a picture of a solar array that experienced such arcing.

The ISS has a piece of hardware called the PCU (Plasma Contactor Unit). The PCU uses a hollow cathode assembly to create a low impedance plasma bridge in order to control the spacecraft potential with respect to the local space plasma potential. Here's a picture of the PCU. It's located on the Z1-Truss.