Unsafe electric energies can exist in aircraft fuel tanks as a result of static build-up or induced currents from lightning strikes. The invention provides an aircraft having a ground circuit 19 and including a fuel tank having a fuel probe circuit having its own ground circuit. Multiple discharge paths allow the safe discharge of electricity from the tank before it reaches levels where an arc, spark or other electric discharge, able to ignite fuel in the tank, could occur. The discharge paths all pass via a conductive foam having a relatively high impedance that allow static bleed, but does not significantly increase the risk of currents induced by lightning reaching levels at which an ignition-causing electrical discharge might occur. The foam is securely bonded to both the aircraft ground circuit and the fuel probe ground, the bonds having a large area of surface-to-surface contact.