Motor Start Capacitor - 'P2 Protected'

A P2 capacitor has a built in safety device to stop it from catching fire in the event of say an overvoltage.


Rob

you may  find that pages 6 and 7 of   here   satisfy your curiosity more fully - the over pressure protection is basically to prevent the thing going off like a bomb if gas is produced internally from overheating - there is a deliberate expansion 'wrinkle' and the internal wires are short enough to tear off and disconnect from the terminals from the inside, if the case starts to lengthen significantly.

The other safety aspect is the self healing  whee the metallisation vapouries and burns back if it breaks down from over-voltage.  The 'lunar craters'  are typically 1-10 um across. I have had capacitors lose 20% of their value through repeated damage - upon forensic examination, held to the light,  the foils looked like some sort of modern art meets paper doily.

I'll get a better look at the document linked by Mike later, but from the descriptions above it sounds similar to a BS EN 60384 Class Y capacitor in that its intended failure mode is to open circuit?


I'm now debating whether to keep it in my miscellaneous spare parts box or whether to cut it open for educational / curiosity purposes!


Many thanks!

Ross Currie said:

Whilst dismantling an old household appliance, I noticed that the motor start capacitor is prominently marked as being 'P2 PROTECTED'.


I've had a quick look on the internet - but whilst I can find many manufacturers offering capacitors with P2 protection, none really explain what the protection is or where it is required.


Is this something similar to Class X / Class Y capacitors as defined in BS EN 60384 or is it something else entirely?

Sorry I missed this at the time ... BS EN 60252 is the relevant standard. Quick description of the ratings available here: https://en.wikipedia.org/wiki/Motor_capacitor

The 'P' ratings in older Editions of the standard are now 'S' ratings - P0 is now S0, P1 is now S1, P2 is now S2, and, with the move to 'S' ratings, a new rating of S3 (for which there is no Px equivalent) was introduced.