to where do I connect the grounding terminal of an IEC connector?

hey all-

I'm just wondering where to connect the grounding pin of the main power connector? Do I connect it to the center tap on the primary side of my transformers? (I'm using five)

Good Grief. NO to the center tap of the primary. AC power is not a balanced line (though I worked at a place where is was). The chassis is the most common place to connect the ground but in many consumer devices there is no 3rd wire at all and it can cause problems with units in other rooms. In those cases it makes more sense to isolate the audio / video / antenna cable with items designed for that purpose. It's not a good idea to 'float' the 3rd wire if supplied.

 

diymixer

Member
2010-06-05 5:28 pm
Good Grief. NO to the center tap of the primary. AC power is not a balanced line (though I worked at a place where is was). The chassis is the most common place to connect the ground but in many consumer devices there is no 3rd wire at all and it can cause problems with units in other rooms. In those cases it makes more sense to isolate the audio / video / antenna cable with items designed for that purpose. It's not a good idea to 'float' the 3rd wire if supplied.


well, the PSU I'm building has a true ground plug. But the chassis is not metal (it's made of plastic). How would I ground it then?
 

Pano

Administrator
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2004-10-07 6:05 am
Panama
I don't think you really can, then.
Sometimes it gets connected to the negative DC rail, or common ground of the circuits. But that can often cause more problems than it solves.

The ground in North America serves to protect you from over voltage spikes, lighting and such. If tied to a metal chassis, it can serve to trip the circuit breaker if there is a 120V short to the chassis.
 
Hi,
the exposed conductive parts must be connected to the Safety Earth.
Without a chassis this may be a little difficult.
There is the additional condition that the PE to chassis and exposed conductive parts to chassis may have to pass Fault current approaching kA. Will a connection to metal foil satisfy this?
Will that potentially leave your exposed conductive parts Live and no effective connection to a PE protected chassis?
 
Don't use metal foil to pass a fault current. Connect all exposed metalwork to the IEC ground using reasonably thick wire - this is your safety ground, as AndrewT says. An internal metal screen can also connect to this, but using a separate piece of wire.

You need to think about connections to signal ground too, as somewhere this needs to be referenced to safety ground. This is a complicated topic, if you want both safety and good sound. Do a search on here - it has been covered in lots of threads.
 
You need to think about connections to signal ground too, as somewhere this needs to be referenced to safety ground. This is a complicated topic, if you want both safety and good sound. Do a search on here - it has been covered in lots of threads.

No, the signal part (anything on the secondary side of the power transformer) does not need to be referenced to earth/safety ground. It is in fact safer left floating. Plus, you will mitigate ground loop problems.
 

Pano

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2004-10-07 6:05 am
Panama
Andrew - Please explain.

In the USA this is done for 2 reasons.
1) Over voltage (spike) protection
2) Fault protection. If the hot wire comes in contact with the chassis, the ground will trip the breaker quickly because neutral is tied to earth.

But if he has no exposed metal parts? What then?
 
Maybe he has no exposed conductive parts, but so far al he has given us is that he is using a plastics case/chassis.

If I come along and plug in an RCA interconnect, what do we have at the other end of that interconnect?

Two conductive parts: the Signal Flow and Signal Return.

Connect a pair of speaker cables. What is at the other end?
 
The ground in North America serves to protect you from over voltage spikes, lighting and such. If tied to a metal chassis, it can serve to trip the circuit breaker if there is a 120V short to the chassis.

In theory this is what's meant to happen only with you in the middle of the live and the earth! So when they trip when you make the circuit you don't die!

But tbh I don't know where to earth it in you case. You might not have to bother I have seen endless amount of audio equipment not earthed from big name manufacturers.
 

Pano

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2004-10-07 6:05 am
Panama
Good point Andrew.
But his low voltage audio section should be completely isolated by the power supply transformers. Thus the voltage on his RCA shield has no direct relation to earth, or to mains hot. That's how the mainstream ungrounded stuff works.

The problems come when it does get tied to earth. There may be one or more grounded devices in the system, or even the cable TV ground.
 
After a discussion with some of you in another thread and reading http://www.diyaudio.com/forums/diya...udio-component-grounding-interconnection.html I decided to connect any mains powered DIY project I built or will build to PE (Protective Earth or Safety Earth). I even connected an appliance class II CD-player to PE after getting a jolt (see http://www.diyaudio.com/forums/everything-else/177206-high-potential-chassis-cd-player.html). This means I have several pieces of equipment not only interconnected but to PE too. In theory this would mean groundloops. But I have not found any discernable ill effects of this (and I know very well what a groundloop can do as I had to solve a horrible one once). To quote David Davenport, author of the abovementioned article, "Loops aren’t bad – it depends on what is on the loop.". This turned out to be very true.

I have several commercial devices that are connected to PE. Some of them have circuit ground connected to PE and some do not. I think it depends on whether a fault in a transformer can cause mains voltage to be shorted to the secondary windings or not. If it cannot PE is not connected to circuit ground.
 
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If it possible for someone to touch a conductor in or around your circuit, either directly or indirectly, then that conductor must be referenced to ground so that it cannot become live. The exception is double-insulated equipment, but I understand that the regulations for that are difficult for a DIYer to achieve. So for almost all DIY the signal ground must connect somewhere directly to safety ground, and everywhere else it should connect indirectly to safety ground so that fuses still blow. Floating circuits are potentially dangerous, except where is it impossible to touch them.
 

Pano

Administrator
Paid Member
2004-10-07 6:05 am
Panama
DF96. Do you really see a hazard on the secondary side of a low voltage transformer?
Now I might see that in a big power amp with high voltage rails and high current. But in signal level devices? What do you think?

Signal ground can and often is connected to earth with no problems, so you can at least try it and see.