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We have 470pF 500VDC caps (Kemet part number C1206C471KCGAC Ceramic, SMD, MLCC, Ultra-Stable, Low Loss, Class I, 470 pF, +/-10% Tol, 500V, C0G, -55/+125C, 1206, 0.1% DF, Dielectric Strength=750V) on 110VAC 400Hz signal and chassis ground (I think for EMI purposes after main design was completed) in our Controller circuit. This should be okay. Is it or can it cause problem since these caps are DC rated? What would happened if they mistakenly placed 100VDC rated caps with the same spec in place of 500VDC caps?

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The dc rating should be the same as the peak ac rating. A 110Vac supply may be expected to be as high as 125Vac and the peak voltage seen could therefore be approaching 180V so no, I would change the caps rated at 100V to higher voltage ones such as at least 250Vdc.

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  • \$\begingroup\$ Thank you. SO you don't see any problem of using the 500VDC caps on 110VAC 400Hz lines. I have Quality engineers here that do not think using ceramic DC rated caps on AC lines is wise. They say this cap would break down soon under this conditions. \$\endgroup\$ – Kamran Sep 13 '13 at 20:48
  • \$\begingroup\$ @Kamran I guess the designers would be best placed to comment on this because there may be power line resonance issues caused by sudden transients when other devices are switched on or off on the 400Hz supply and they may have considered this. If there are NO issues that can cause sudden +/-500V transients (and I have to say this would be a rarer situation than what most folk would think) then they should be fine. \$\endgroup\$ – Andy aka Sep 13 '13 at 22:31

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