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Motor Start Capacitor - 'P2 Protected'

Ross Currie
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?
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    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.

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    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.

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