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Two Faults.

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I went to explore the reason for a failed immersion heater. The element tested out o.k. The rod 'stat had its main operating contacts welded together and the safety trip had operated and switched the element off. I renewed the rod 'stat. Then upon turning on the 20 Amp D.P. switch with neon it flickered the neon momentarily then it died. There was a supply in from a good old 60s M.K. 20 Amp switch down stairs, still operating perfectly, but its neon is a little dim. But the newish 20 Amp D.P. switch by the immersion heater had failed after about 2 years use from new. So I found one fault, and by operating the switch by the heater that switch then failed. You couldn't make it up, and then trying to explain that to the customer isn't easy.

Has anybody else had similar experiences?

Z.

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    The problem of running warm, 30 degrees outside and 30-40 degrees hotter inside at the terminals is dependant on materials - if switches were still made of ceramic and contacts of brass, then not a lot. Maybe the brass tarnishes, but until it gets so hot that contacts lose their 'spring' it is not an issue.

    But some plastics soften when warmer than 100 or so,  and slowly distort reducing the pressure on the mating contacts, maybe then raising the resistance and the self heating. With extreme over heat, some materials may char and become sooty, and conducting,

    The current rating of a switch is decided n by looking at the the end of life (so worn) contact resistance, and seeing if that leads to unacceptable heating. If it doesn't then the value engineering team  say the rating can be increased, or the contacts made smaller...

    Mike.

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  • 0

    The problem of running warm, 30 degrees outside and 30-40 degrees hotter inside at the terminals is dependant on materials - if switches were still made of ceramic and contacts of brass, then not a lot. Maybe the brass tarnishes, but until it gets so hot that contacts lose their 'spring' it is not an issue.

    But some plastics soften when warmer than 100 or so,  and slowly distort reducing the pressure on the mating contacts, maybe then raising the resistance and the self heating. With extreme over heat, some materials may char and become sooty, and conducting,

    The current rating of a switch is decided n by looking at the the end of life (so worn) contact resistance, and seeing if that leads to unacceptable heating. If it doesn't then the value engineering team  say the rating can be increased, or the contacts made smaller...

    Mike.

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