342V standoff — this is a 342V nominal line protector
The P6KE400CA is a bidirectional TRANSIL™ TVS diode from STMicroelectronics, part of the P6KE series. Its 342V reverse standoff voltage means it sits across a 342V DC or AC-rms nominal rail and stays out of the way until a transient hits. The 600W peak pulse power rating tells you how much transient energy it can absorb in a 10/1000 µs waveform — enough for industrial power supplies, motor drives, and AC line protection where the working voltage is in the 300-400V range.
706V clamp — what the downstream gear must survive
When the transient fires, the diode clamps at 706V maximum at the peak pulse current of 5.7A. That clamp voltage is the ceiling your downstream rectifiers, capacitors, and switching transistors need to handle without failing. The bidirectional channel means one part handles both positive and negative surges — useful on AC lines or floating DC rails where polarity isn't fixed.
DO-15 axial — field-swappable with a soldering iron
The part comes in a DO-204AC, DO-15 axial package with through-hole mounting. That axial lead form is a field-service win — you can pull the old part and solder in a replacement with a standard iron, no hot-air station needed. Mark the orientation band: the cathode band is present even on a bidirectional part, but since it's bidirectional the polarity doesn't matter for circuit function. It ships in cut tape or tape and box, so small-quantity replacements are easy to source.
Active production — no obsolescence worry
No last-time-buy, no replacement hunt. It's a current-production part from STMicroelectronics, quoted to order against your BOM quantity. The base product number is P6KE400, and the full suffix 'CA' denotes the bidirectional version — the unidirectional sibling would be 'A' or 'C' depending on the variant.