Running caps near voltage limit

[Pharos]

Surely, won't allow the current to increase.

 

[VivaVee]

Don't keep the cap above the rated level for longer than 10 minutes - any part from a reputable manufacturer is compliant to that level of stress.

From the Panasonic Technical Guide, see https://www.ttieurope.com/content/dam/tti-europe/manufacturers/panasonic/resources/Technical_Guide.pdf
Excessive voltage over the rated should not be applied.
Note 1) In short time (with in 1sec), surge voltage can be applied

 

[trobbins]

Oops typo - 1 minute (not 10 minutes as in post #39).

Many e-caps will comply with IEC 60384-4. That standard specifies a surge voltage rating:
The surge voltage is the maximum voltage which may be applied to the capacitor for short periods of time, ie. up to 5 times for 1 minute per hour. And the surge voltage is rated as 1.15 x VR for VR < 315 V, or 1.1 x VR for VR > 315 V and <500V.

Testing conditions are:
From source of 1.15 x VR for VR < 315 V or 1.1 x VR for VR > 315 V.
RC = 0.1 s ± 0.05 s; 1000 cycles of 30 s on, 330 s off, at upper category temperature.
Result must be no effective change in specs.

Specific manufacturers may not comply with that standard, or likely in Panasonics case, provide technical guidance to users about their applications.

My comment in post #39 was related to a testing situation (as compared to an application).

 

[egellings]

Failure mode due to over-voltage in a cap is dielectric breakdown, which means arc-over. Some dielectrics, like air and polypropylene (so-called self-healing), can survive after a limited breakdown event but are weakened nonetheless. Just go with a higher voltage rated cap and be done with it.