Computer smps ground shorted with earth ground

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raman00084

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in my usb cable if i keep a multimeter in pin 1 and pin 4 i am getting 5v. if i keep one probe in +5v and and another in body of the computer are smps i am getting the same 5v in the meter. generally the body is connected to earth ground of the 3 pin socked the center pin.

this means the smps supply ground(-v) and earth ground are shorted internally?
 

In the USB cable,pin no. 1 is bus voltage and pin no. 4 is ground.So,you are getting the voltage right.
I did not understand the second part..where in the SMPS(Inside the CPU) are you connecting the multimeter probes,so that you are seeing +5V as the output?
Most likely,there are connections within the motherboard that connect the "ground" in USB ports to "ground" in the SMPS,which finally ends up as the big ground pin in the 3 pin plug,which connects in the wall socket.
 
Yes All grounds are connected internally with SMPS output and usually CPU pannel earth. if you have leakage earth in cpu cover you will get it on USB too. for that you need a proper Body earthing.
 
what is the advantage and disadvantage by connecting smps 0v to earth ground that is the center pin of 3 pin socket

- - - Updated - - -

in my ac servo drive i am giving 24v external dc supply. the servo drive body is earth grounded, can i connect the 0v of my smps to servo drive body?

it is safe?
 

advantage is noise free and robust operation. safe against shock.

disadvantage, we have to think about connecting to other equipments, like you do.

Why do you needed to connect that 0 V to servo motor body, can you say little more elaborate.
 

my doubt is simple can i short 0v of 24v smps to earth ground. it is safe?

regards
kalyan
 

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