  Recently, we have shown that the continuity equation for the nuclear vector
and axial current operators acquires additional terms if the latter depend on
the energy transfer. We analyze in detail the electromagnetic single-nucleon
four-current operators and verify the validity of the modified continuity
equation for all one- and two-nucleon contributions up to fourth order in the
chiral expansion. We also derive, for the first time, the leading contribution
to the three-nucleon charge operator which appears at this order. Our study
completes the derivation of the electroweak nuclear currents to fourth order in
the chiral expansion.
