Connecting rectified output to frame ground

[kittydog42]

Is there any problem with the following:

I am connecting 120VAC main power to a transformer to generate 12VAC. I am then running the 12VAC through a bridge rectifier. I am filtering the rectified DC output across a 220uF 25V cap, then going into a Linear LT1076 switching regulator to generate 5VDC. Can I connect the DC ground out of the regulator to the frame ground of the 120VAC main so that my DC ground and AC neutral have the same potential? Do I do this by grounding the secondary of my transformer?

 

[ericgibbs]

hi,
Do NOT connect it the way you have described.
>>>frame ground of the 120VAC main so that my DC ground and AC neutral have the same potential
They are not at the same potential.

See the attached rough sketch.

If you are not clear, ask again.

Regards

 

[kittydog42]

That is what I was looking for. I want the 0V and earth to connect. I just did not know where to make the connection. Thank you.

 

[chemelec]

hi,
Do NOT connect it the way you have described.
>>>frame ground of the 120VAC main so that my DC ground and AC neutral have the same potential
They are not at the same potential.

See the attached rough sketch.

If you are not clear, ask again.

Regards

Be Aware that the Neutral is "NOT Necessarly GROUND".
At least not in Canada and the USA.

There may be a Slight voltage difference between these two wires.

 

[ericgibbs]

hi chemelec,

Also in the UK,[ in my area] the ground and neutral are not at the same potential, it varies +/- 20 to 30Vdc, with superimposed Vac.

My concern with connecting the neutral as a 'common' to equipment, is the situation where the equipment is plugged into a incorrectly wired 'reversed' mains socket. As you know, this will put the Line supply to the equipment common.

 

[Nigel Goodwin]

hi chemelec,

Also in the UK,[ in my area] the ground and neutral are not at the same potential, it varies +/- 20 to 30Vdc, with superimposed Vac.

That sounds FAR too high, more like 2V to 3V between them, just due to the voltage drop across the neutral cable from the sub-station really. Many houses also now have PME earths, where the earth is simply connected to the incoming neutral wire, so there's then no difference at all.

My concern with connecting the neutral as a 'common' to equipment, is the situation where the equipment is plugged into a incorrectly wired 'reversed' mains socket. As you know, this will put the Line supply to the equipment common.

I have the same concern - it's seriously dangerous to connect either live or neutral as 'ground' in the equipment. Old TV's used to do this, but the chassis's were insulated (unless you took the back off) so it didn't matter too much.