Ground termination in an appliance?

[ScorpFire]

Ground termination?

Hi guys i am designing an appliance and have some problem. My appliance will be plugged into the mains, like this

Now inside this box i have some circuits. Some of my circuits need a ground like this
**broken link removed**

Where can i connect this to? Can i connect it to the Earth wire on the 3pin plug? The green/yellow wire...

**broken link removed**

 

[betwixt]

Re: Ground termination?

That is correct for a UK appliance.

Brian.

 

[hameeds01]

Re: Ground termination?

Yes u have connected in a right way green/yellow to Earth

 

[ScorpFire]

Re: Ground termination?

So i can connect all ground terminations to the green/yellow wire?

 

[hameeds01]

Re: Ground termination?

yes u can do that there is no harm in doing so

 

[angryjohnny]

Re: Ground termination?

Just ensure that you have no neutral to ground bonds occuring in the appliance as this would violate NFPA 70.

 

[praveensss]

Re: Ground termination?

The Earth Pin is for protecting the person operating the device. If your device (box) is made of metal, it has to be grounded to the earth pin.

Now your circuits would have a ground and have to be connected to the neutral, I guess that is what you have shown. So connect your metal casing to the Earth Pin and the circuit grounds to the Neutral.

 

[eem2am]

Ground termination?

sorry but i beg to differ, ...your circuits dont want connecting to neutral.........welll only at the input.........becasue the rectifier bridge occurs, and you cannot connect around it.

metal casing should be connected to earth for safety reasons.

 

[praveensss]

Re: Ground termination?

Hi eem2am !
So where do we differ???
Connect rectifier gnd to neutral and ain't all ckt grounds automatically shorted to neutral?
Now we do not want to connect neutral to Earth do we? The utilities would then have given us only 2 termianals!

Glad, I don't differ!

 

[betwixt]

Re: Ground termination?

The difference is that on many (possibly most) power supplies, the output is 'floating' having been isolated by a transformer, either a normal power transformer or one in an SMPS. The line and neutral (brown & blue) wires go ONLY to the primary side and the earth (green&yellow) wire goes ONLY to the secondary side.

Special conditions apply when double-isolated transformers are used and the earth wire is then not needed at all.

ANY connection between earth and neutral wires will almost certainly operate a safety trip. Almost all safety trip units use the imbalance of line and neutral currents to detect a fault condition and the neutral wire will normally be at higher potential than the earth due to resistive and inductive effects in the power cables. A short to earth will divert neutral current and it will no longer match the line wire current causing the trip to operate.

Brian.

 

[praveensss]

Re: Ground termination?

There! Brian has really made it clear. If an isolated power supply is used, the only thing connected to neutral is the transformer primary. Use it, it is simple and safe!

The ground of the circuit is just a reference and not really ground, ground, mother earth.