Re: RF quiet 12 V 2 A power supply


David Cutter
 

Thanks David and Martin

The supply in question is in a plastic box, so there are no exposed metal parts (that I can see). Wouldn't that make it a Class 2 equipment? My other power supplies (apart from wall warts) are in metal boxes, ie Class 1 with earth to the chassis.

I can understand why an earth is supplied to the mains side for filtering purposes, but I haven't fathomed out the mains earth connection to the dc output.

David G3UNA

On 15 October 2021 at 15:50 David Wilkins <davidrwilkins88@gmail.com> wrote:


“but I'm missing why some power supplies have negative output and mains earth connected inside the supply”


Hi - afaik - if the appliance has an external conductive part (ie a battery charger in a metal box) then that conductive part must be connected to the circuit protective conductor (which in turn will connected to the supply earth). This is for “automatic disconnection of supply” to function as intended during a fault and protect us.

Whether the power supply output is floating, +ve earthed or -ve earthed is a design choice.

Cheers,
David.

On 15 Oct 2021, at 15:39, Martin - G8JNJ via groups.io <martin_ehrenfried=yahoo.com@groups.io> wrote:

but I'm missing why some power supplies have negative output and mains earth connected inside the supply



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