Please comment on this grounding scheme.

[VictoriaGuy]

I came across this advice 'on the internet', and it was something I had not seen previously.
Quote:
Since you're using a three-wire plug, how are the other two wires connected? The white wire in the AC cord is supposed to be neutral, and black is the hot. The white wire should connect to circuit's ground. The green ground wire should go to the chassis. A 47k resistor and a MOV would connect circuit ground to chassis. Might be easiest to simply disconnect the green wire as suggested and make sure the circuit's "ground" side goes to the white wire.
End quote

I'd appreciate comments from knowledgeable builders.
Thanks.

[DigitalJunkie]

NO!

The only thing that should be (firmly) connected to the chassis is the GREEN earth ground wire.
It can then connect to your circuit ground,in whichever method you like (directly,or through a resistor/ground loop breaker,etc.)

Neutral should NEVER connect to anything other than the 'primary' side of your power transformer,and any associated switch,etc. that may be located there.
It should NOT be connected to your circuit ground or anything other part of your circuit.

This way the chassis is 'firmly' earth grounded,in case anything should malfunction. And,the power transformer provides galvanic/magnetic isolation from the mains for your circuit to use.

Again,no part of the mains wiring should be connected to the chassis/circuit -EXCEPT- the Green Earth Ground.


EDIT: A second thought, Is this pertaining to Line-Operated circuits? !ALWAYS! use an isolation transformer with those type of circuits!

[HollowState]

I second what Digital Junkie says. No part of the AC line should connect to the chassis. In a perfect world the white wire could be relied on as being neutral if everyone did their job correctly. But this is not always the case. And this is the reason that neither side of the line should be grounded.

The purpose of an MOV is to protect instruments from over voltage. If used, they should be connected across the AC line after the unit's local fuse. Should the AC line go too high, the MOV will conduct heavily (short out) and blow the fuse. It should not be used to connect the mains or circuit to ground in any way.

If you have a third "green" wire connected to chassis ground, do not remove it! It's there for safety reasons.

[VictoriaGuy]

Thanks for the comments, guys. That's what I think as well, but just needed a 'reality check'. I really don't like to see stuff like that hangin' out on the 'net where some beginner might take it seriously.

Originally Posted by DigitalJunkie

Neutral should NEVER connect to anything other than the 'primary' side of your power transformer,and any associated switch,etc. that may be located there.

And then, only if you are switching the neutral and line with a DPST switch. The switch and fuse should both be in the line ('hot') side- not like those hundreds of thousands of old Fenders with the switch in one side, fuse in the other. Of course, with them it didn't matter, since the 2-prong plug wasn't polarized- so the wiring was always 'half-right'. You see that style copied in a lot of amateur-built guitar amps with 3-wire plugs, still.

[stratus46]

It's not supposed to happen but sometimes the hot and neutral get swapped in the house wiring. NEVER assume the neutral is in fact neutral. If you build gear that requires the neutral in fact be neutral, it is a foolish design.

G²

[DigitalJunkie]

And then, only if you are switching the neutral and line with a DPST switch. The switch and fuse should both be in the line ('hot') side- not like those hundreds of thousands of old Fenders.......

Exactly correct!