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Old 20th Jun 2021, 8:10 pm   #74
ms660
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Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Vintage Sears Silvertone radio safety question

Draw a simple schematic showing the current path, all should become clear, draw showing for both normal and possible fault conditions, do a drawing with Neutral routed through to chassis via any switch or fuse that's fitted in that line then do the same and the same analysis with the Live being routed through to chassis, in the receiver in question, under certain conditions being powered by your auto transformer a voltage that equals the mains supply voltage will be available between the chassis and Earth and the available current will be approx. 15mA, the amount of current that will flow will depend on the impedance between the chassis and Earth.

For a chassis that's connected in DC terms to one side of the mains then under certain conditions again there will be a voltage that equals the mains voltage between the chassis and Earth but in that case the available current will be much higher and if for some reason the RCD fails to trip then that available current at that voltage can kill.

Last time I tested an RCD with a fault current to Earth I think it tripped at somewhere around 22-25mA but don't quote me on that.

Remember that a fault condition is a normal condition gone wrong....

Lawrence.

Last edited by ms660; 20th Jun 2021 at 8:25 pm. Reason: typo
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