1. Electrode stress status from downward force on the order of decreasing; the joint of electrodes and nipples under clamping device take maximum force.

2. When electrodes receive external force; Stress concentration of the external force is greater than the electrode can withstand then the strength will lead the electrode breakage.

3. The causes of external force are: melting of bulk charge collapse; scrap non-conductive objects below the electrode: impact of massive steel bulk flow and etc. Clamping device lifting response speed uncoordinated: partial core hole lid electrode; electrodes gap linked with bad connection and nipple strength is not up to compliance.

4. Electrodes and nipples with poor machining accuracy.