09-05-2016, 01:57 PM
Generally class Y caps aren't available in the values you would often use for class X applications. Also they are physically bigger for a given value.
As you say class Y caps mustn't fail short circuit because they are used between live and earth and could cause shock hazard if they short. Their maximum value is quite low to limit the normal reactive current that will flow between live and earth. Class X caps are for use between live and neutral (or phase to phase) must merely fail safe. Failing short and blowing a fuse is allowed AFAIK.
There are subclassifications of X and Y (X1, X2 etc) but X1, Y1, X2, Y2 are all suitable for the ordinary single phase 230V stuff that we usually deal with. You rarely see X3, Y3, Y4 which may not be adequate for our use.
You may also find dual rated (eg X1 and Y2) caps. These meet both specifications.
As you say class Y caps mustn't fail short circuit because they are used between live and earth and could cause shock hazard if they short. Their maximum value is quite low to limit the normal reactive current that will flow between live and earth. Class X caps are for use between live and neutral (or phase to phase) must merely fail safe. Failing short and blowing a fuse is allowed AFAIK.
There are subclassifications of X and Y (X1, X2 etc) but X1, Y1, X2, Y2 are all suitable for the ordinary single phase 230V stuff that we usually deal with. You rarely see X3, Y3, Y4 which may not be adequate for our use.
You may also find dual rated (eg X1 and Y2) caps. These meet both specifications.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
