Hi Richard. Sorry, I'm a bit late with this.
You wrote: < Must the cap be X-rated in this particular application? In general, when does a cap connected to the mains no longer need to be X rated?> Basically, an X rated cap is one that can safely be placed before the inlet overcurrent protection because in the event of a short circuit, it heals itself, and is therefore not going to need protection. So, any caps connected before your first fuse or MCB should be X types, or Y types, depending on where connected. (Y's go to earth). Hope that helps. Chris Dupres Surrey, UK.
