Integration of renewable energy resources with the electric grid is necessary for a sustainable energy future. However, increased penetration of inverter based resources (IBRs) reduce grid inertia, which might then compromise power system reliability. Therefore, power utilities are often interested in identifying the maximum IBR penetration limit for their system. The proposed research presents a methodology to identify the IBR penetration threshold beyond which voltage, frequency, and tie-line limits will be exceeded. The sensitivity of the IBR penetration threshold to momentary cessation due to low voltages, transmission versus distribution connected solar generation, and stalling of induction motors are also analyzed. Dynamic simulation studies conducted on a 24,000-bus model of the Western Interconnection (WI) demonstrate the practicality of the proposed approach.