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I have to offer a "FG" connection for the product I am designing.

The product is isolated in many parts, so, which part of the circuit should i connect the "FG" to?

Below is rough scatch of the block diagram of each isolated parts of the product

enter image description here

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  • \$\begingroup\$ I don't think we give the word isolated the same meaning, especially for the DC PS. You mean that's isolated from the mains, is that right? What is your ground connection expected use? If I read frame ground on a panel I expect the terminal to be connected to the metallic frame, that is possibly not exposed, and the whole thing to be connected to ground through the protection conductor in the power chord. \$\endgroup\$ Jan 23, 2015 at 10:45
  • \$\begingroup\$ @VladimirCravero Yes, the product takes DC power supply and galvanically isolates it within the product \$\endgroup\$
    – Steve
    Jan 23, 2015 at 10:58
  • \$\begingroup\$ @VladimirCravero I only know that "frame ground" is supposed be connected to the metal chassis. Now, which part of my circuit should be connected to the metal chassis? \$\endgroup\$
    – Steve
    Jan 23, 2015 at 10:59
  • \$\begingroup\$ I guess it depends on where are these part connected afterwards. I mean, you're isolating everything for a reason don't you? Maybe the RS485 is sitting above your DC supply of some 100V, while the analog output is at a lower voltage, or whatever. I'm guessing your DC PS has a ground connection, connect that ground to the chassis and FG to the chassis. IF that applies to your requirements. \$\endgroup\$ Jan 23, 2015 at 11:02
  • \$\begingroup\$ @VladimirCravero I guess the user can choose either RS485 ground or power ground, or signal ground to be connected to chassis? Then, I can practically remove one port from the product \$\endgroup\$
    – Steve
    Jan 23, 2015 at 11:09

2 Answers 2

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"Frame Ground" should connect to the frame/chassis of the equipment, and to any exposed metal parts. It will also connect to the green safety ground wire in the power cord.

Whether any part of your circuitry connects to the frame ground is up to you.

Many OEM power supplies have a frame ground terminal that is connected to the metal case, but the power output terminals are not connected to that ground.

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Frame ground it is not a signal path. Usually it is the RS232 DE9 (or ACC DAE15) shell connector screw. So connect this screws to chassis via proper lug.

enter image description here

If you have more than one apparatus on a rack, connect each chassis to the main ground bus bar. The electrical safetry ground it is also connected to this reference point.

In any case it is used for the signals entering (or leaving) an apparatus which may have an electrical shock potential.

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