This paper presents an effective method for placement of DG units in multiphase distribution networks based on system voltage profile. The approach consists of utilizing the positive sequence voltage ratio V collapse /V no-load to identify the weakest three-phase bus for the installation of DG units. DG ratings are determined by evaluating their impacts on voltage profile, grid losses and maximum loading factor while considering the voltage limits at all buses. Detailed simulations are performed for the placement and sizing of a doubly fed induction generator (DIFG) in the IEEE multiphase 34 node test feeder using DIgSILENT PowerFactory software. The impacts of DIFG on voltage profile, active power loss and voltage stability margin are highlighted. Finally, simulation results indicate that voltage limits should be considered as a constraint for the methods of DG placement. Index Terms--Multiphase network, weakest bus, DG, DIFG, voltage profile, grid loss, and maximum loading factor.