Sorry - don't agree with you there. There's two main relays/contactors. One is pulsed appx 900 times per firing - that's the one that, if it fails 'on', will cook the kiln (the situation I'm trying to avoid)
The safety relay is in series with this, and, under my planned scheme, will be pulsed once on/off (to test it) at the start of each 7-hour long firing sequence, and will then be 'on' for the 7 hours of the sequence, simply to enable the main relay.
Sure, in theory, that halves the life of the safety relay - but in practical terms, it'll still last some tens of years. It's the other (pulsed) relay that's got a short lifetime - which I plan to address by replacing it every 2 years..
Well - maybe - but the commercial controller I'm using has one switched output - so I'm stuck with switching all 7.5kW at the same time. Not a problem. Thanks Adrian