Thanks you for your response Dave. The fifth switch from the right in the main fusebox trips and switches everything off. I have also posted a pic of the shed showing the two switches for the Lights & fountain. There is no RCD as far as I can see.
I have a garden fountain powered by an mains electric Eden model 128 pump. The electric feed comes from my garden shed where there is a junction box - this also powers the garden lights. There are two switches - lights & fountain.
Occasionally when I turn off the fountain the mains breaker...
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