This is a Transient Voltage Suppressor (TVS, transzorb). It will dissipate (short) pulses of over 6.8 V. It is rated at 1500W for 1 milliseconds. This TVS is bi-directional.
Related products:TVS-B400V-1500 | 1.5KE400CA bi-directional TVS 400V 1500W/1ms |