Generally all spot welding electrodes are made from a copper alloy. During the resistance welding operations if their tensile strength is exceeded they will bend or collapse and fail from the mechanical force being exerted on them. RWMA Fig 18.3 in the RWMA Manual 4th Edition, shows the relationship of electrode weld face size, applied force and maximum capability. Similar information is shown in the following table.
This data is related to force applied to the electrode. Always be sure that your electrode size and taper are adequate for the force being used in the welding operation. The force is determined by your developed weld schedule.
Reference: RWMA - "Resistance Welding Manual 4th Edition"