  Magnetic Johnson-Nyquist noise (JNN) originating from metal electrodes, used
to create a static electric field in neutron electric-dipole-moment (nEDM)
experiments, may limit the sensitivity of measurements. In this study, we
derive surface and volume-averaged root-mean-square normal noise amplitudes at
a certain frequency bandwidth for a cylindrical geometry. In addition, we model
the source of noise as a finite number of current dipoles and demonstrate a
method to simulate temporal and three-dimensional spatial dependencies of JNN.
The calculations are applied to estimate the impact of JNN on measurements with
the new apparatus, n2EDM, at the Paul Scherrer Institute. We demonstrate that
the performances of the optically pumped $^{133}$Cs magnetometers and
$^{199}$Hg co-magnetometers, which will be used in the apparatus, are not
limited by JNN. Further, we find that in measurements deploying a
co-magnetometer system, the impact of JNN is negligible for nEDM searches down
to a sensitivity of $4\,\times\,10^{-28}\,e\cdot{\rm cm}$ in a single
measurement; therefore, the use of economically and mechanically favored solid
aluminum electrodes is possible.
