We recommend you NEVER rely on any internal protection that a c.t. might have, but always ensure that it is removed from the cable (split-core types) or that the circuit is not energised, before disconnecting.
Note that it is always safe to short-circuit a c.t. In some cases (e.g when there is an internal burden), it _might _ be safe to open-circuit it, but in general terms it is not.
Therefore, if the c.t. must be left in place and the circuit needs to be put back into service when the instrument connected is removed, you should short-circuit the c.t.
(The mechanism that creates the danger is this: Without a burden, all the primary current is magnetising current and the core will be completely saturated except for a very short period at the zero crossings. There, the rate of change of flux is so great that voltages of several kV can be generated, and (usually) the insulation flashes over, destroying the c.t. There is obvious danger if this happens and anyone is too close.)