The cascade control strategy is used in thermal and chemical processes to avoid the propagation of intermediate disturbances in the control loop. This technique measures an intermediate variable whose response to process disturbances can be observed earlier than in the controlled variable response. An internal or slave controller is implemented to establish an internal control loop in the intermediate variable. There are different methods to tune the internal PID controller, such as: quarter decay ratio, Dahlin tuning method and Lambda tuning, all of them based on off-line process identification as a FOPDT (First Order Plus Dead Time) model. To tune the Master or external controllera few tuning equations have been developed. The main sets of tuning equations were developed by V. Austin (1986) and Lee and Park (1998), but they operate in a narrow range of dynamic process parameters. M. Sanjuan (1999) found a set of equations to tune the master controller in PI - P and PID - P configurations. In this paper, we present a set of equations to tune the master controller as a Proportional Integral (PI) controller when the slave controller is either a PI controller or a P controller, based on FOPDT identification for the internal and external processes. These equations were obtained by running computer simulations of FOPDT processes in Matlab and Simulink and designing a three level factorial experiment. Performance evaluation is also carried out, comparing with Austin, Lee and Sanjuan tuning equations.These equations are valid for a wider range of process identified FOPDT parameters.