  There are a number of constraints which limit the current and voltages which
can be applied on a multiple drive electrical imaging system. One obvious
constraint is to limit the maximum Ohmic power dissipated in the body. Current
patterns optimising distinguishability with respect to this constraint are
singular functions of the difference of transconductance matrices with respect
to the power norm. (the optimal currents of Isaacson). If one constrains the
total current ($L^1$ norm) the optimal patterns are pair drives. On the other
hand if one constrains the maximum current on each drive electrode (an
$L^\infty$ norm), the optimal patterns have each drive channel set to the
maximum source or sink current value. In this paper we consider appropriate
safety constraints and discuss how to find the optimal current patterns with
those constraints.
