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In an AC-DC power supply, how is earth ground typically used?

Take a common PC power supply as an example, does the earth ground connect to the metal chassis? Does it connect to the DC ground on the outputs? What about ground loops?

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2 Answers 2

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Not sure if this is what you were looking for, but here goes.

Earth ground is attached to the metal chassis, which should be common to all metal chassis parts. It is typically for safety and shielding. The AC ground (green) connection would be tied to earth ground, or chassis ground as its often called. The Ov or negative of the DC can be tied to chassis ground, but not always, depending on the system.

I work with life safety equipment, and all of our power systems are electrically isolated from earth ground.

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    \$\begingroup\$ Just a small note: in some places the ground cable is green with yellow. It really depends on the region you live in. \$\endgroup\$
    – Count Zero
    Jan 27, 2012 at 19:26
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Great question

Generally AC earth is generally first considered to provide a safety grounding system for faults and stray currents in the a AC system

AC earth is tied to metallic cases, components, some PCB back planes, etc to provide a path to ground other than you!

Importantly AC earth also dissipates static electricity

AC earth can also used in some radio transmission and reception to couple to the true ground plane

I dont know of any PSU that ties AC earth to DC ground

For saftey Never connect AC earth and DC ground

Simply stated: there is a very real chance of some other equipment failing and feeding AC onto your unprepared and exposed DC bus

I have NEVER measured a zero volt difference between AC earth and AC neutral in a powered residential system and RARELY seen a low resistance power earthing system

There are sensitive fault monitors available

AC wiring is generally installed in a spider or branching configuration using a single path to avoid large ground loops

However even when AC and DC systems are not physically connected my metal there can be several coupling mechanisms that allow them to interact and create transient ground loops

So large transient AC earth coupled ground loops can exist between devices plugged into different outlets through data interfaces

Gotchas: MANY of the common two plug three prong PC PSU cords are not actually grounded, this can be a problem, a solution, or a test of AC earth related data corruption issues

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