The 17.5kV 50kA switchgear is primarily used in steel plants, where all switches in a 50kA system must meet short-circuit breaking requirements. This includes an outgoing circuit breaker rated at 1250A 50kA and an incoming breaker rated at 4000A 50kA. Additionally, the F-C contactor-fuse combination requires fuses capable of breaking at the expected 50kA current. The switchgear itself must withstand a short-time current of 50kA and a peak withstand current of 125kA. Customers also require the 50kA switchgear to pass a 50kA 1s internal arc fault test across the busbar compartment, truck compartment, and cable compartment. The metal-clad switchgear must achieve AFLR 50kA 1s internal arc fault rating, and the busbar compartment in the F-C cabinet also needs to pass the 50kA 1s internal arc test. Given the current-limiting fuse protection in the compartment, the cable compartment does not require testing. However, there is significant debate over truck types. If a short circuit occurs at the lower contact arm, it falls within the fuse-protected compartment, but if it occurs at the front arm, it must pass the 50kA 1s internal arc test.

Arc calculations based on IEEE1584 show that the 50kA arc energy is nearly triple that of a 31.5kA arc, with a safety boundary distance almost doubled. This implies that the switchgear design must be strong enough to withstand the overpressure impact and thermal effects caused by a 50kA internal arc fault.

Due to low demand for 50kA circuit breakers, the availability of 17.5kV 50kA vacuum interrupters is limited. Generally, only a 4000A 50kA option is available. Thus, for 1250A or 2000A 50kA circuit breakers, a 4000A-rated interrupter is used, though with a smaller diameter of components like contact arms and star contacts.

The conductive path requires a cross-sectional area greater than 524.6mm², meaning conductor size cannot be based solely on rated current. For example, the contact arm diameter for a 1250A breaker must increase from 50mm to 60mm, and the stationary contact diameter for the star contact should be 79mm. For 1250/2000A 50kA breakers, a phase distance of 210mm and switchgear width of 800mm is feasible. The primary limitation on switchgear width comes from the star contact rather than the encapsulated pole size, i.e., the contact box size. For 2500A circuit breakers, the stationary contact requires a diameter of 109mm with 64 contact fingers, and the 50kA star contact must use a retaining ring, increasing the outer diameter to 158mm. This makes it challenging for the contact box flange to be less than 210mm. Thus, for ratings of 2500A or more, 1000mm switchgear is needed. Temperature rise is also a factor, though high-quality contact systems and efficient cooling can enable 2500A at 800mm width, as seen in Siemens switchgear.

The contact pressure of a 50kA vacuum interrupter is typically 6200N, double the 3100N needed for a 31.5kA interrupter, necessitating an increase in energy. The closing spring count rises from two to four, and the main shaft diameter is 40mm. The operating mechanism must deliver sufficient energy to counteract contact pressure and maintain the closed position under electrodynamic force. The energy requirement doubles, with each phase needing 27.175 joules and all three phases totaling 81.5 joules. In comparison, a 31.5kA breaker requires only 44.25 joules for all three phases, meaning the operating mechanism for 31.5kA is inadequate for 50kA use.

The contact pressure requirement for 50kA is 766N, which is 2.44 times the 314N needed for a 31.5kA contact.