  As the only lattice vector current that does not require renormalisation is
the point-split conserved current it is convenient to have a robust, precise
and computationally cheap methodology for the calculation of vector current
renormalisation factors, $Z_V$. Momentum subtraction schemes, such as RI-SMOM,
implemented nonperturbatively on the lattice provide such a method if it can be
shown that the systematic errors, e.g. from condensates, are well controlled.
  We present $Z_V$ calculations for the conserved current in both the RI-SMOM
and RI$'$-MOM momentum subtraction schemes as well as local current
renormalisation in the RI-SMOM scheme. By performing these calculations at
various values of the momentum scale $\mu$ and different lattice spacings we
can investigate the presence of power suppressed nonperturbative contributions
and compare the results to expectations arising from the Ward-Takahashi
identity. Our results show that the RI-SMOM scheme provides a well controlled
determination of $Z_V$ but the standard RI$'$-MOM scheme does not.
  We then present some preliminary uses of these $Z_V$ calculations in charm
physics.
