How Exactly Does Earthing Work?

[Electroenthusiast]

It's difficult to make a computer monitor with no exposed metal parts because of the video cable.

Can i know why?

This is another ques:
Please tell me the differences in power consumption(when appliances is earthed/ and not earthed)

Will Power consumption increase, due to the complementary earth-chasis path.

 

[mneary]

1) With CRT monitors, the outer shield of the video connector was usually connected to the monitor chassis. The video connector is exposed to the user.
1a) With LCD monitors, it is common to use an external supply which is already isolated, and the chassis has no mains supply at all. Thus 'double insulation' is easier.

2) The earth-chassis path is not intended to carry current unless the equipment has failed. In that case the equipment should not be used. But no mattter where the current flows, the unit will use no more power than it uses.

 

[Electroenthusiast]

1) With CRT monitors, the outer shield of the video connector was usually connected to the monitor chassis. The video connector is exposed to the user.
1a) With LCD monitors, it is common to use an external supply which is already isolated, and the chassis has no mains supply at all. Thus 'double insulation' is easier.

Thnks...Feels like i require more knowledge about them CRT Monitors & TV...
Your answer brought me an idea... If i continue to ask, there will be no end to this thread!

The earth-chassis path is not intended to carry current unless the equipment has failed. In that case the equipment should not be used. But no mattter where the current flows, the unit will use no more power than it uses.

Usually metal casing of the appliances are earthed; When the insulation fails, there will be contact between the internal circuitry and the metal casing. Since the metal casing will be earth, there should be some amount of current-flow. Hence Power Consumption should increase...
Correct me if i'm wrong, Tell me why its Wrong...

 

[Nigel Goodwin]

Usually metal casing of the appliances are earthed; When the insulation fails, there will be contact between the internal circuitry and the metal casing. Since the metal casing will be earth, there should be some amount of current-flow. Hence Power Consumption should increase...
Correct me if i'm wrong, Tell me why its Wrong...

You're wrong, there will be a big BANG, the mains fuse will blow, and no current will flow.

 

[Electroenthusiast]

You're wrong, there will be a big BANG, the mains fuse will blow, and no current will flow.

oh! OK,. but still: >my computer requires earthing...
whenever when i connect it using 2 pin plug, i get electric shock
so when ever i use 3 pin plug, i wont get shock; even then fuse wont break, computer remains ON.
THIS SHOULDN'T HAPPEN THEN

 

[Nigel Goodwin]

oh! OK,. but still: >my computer requires earthing...
whenever when i connect it using 2 pin plug, i get electric shock
so when ever i use 3 pin plug, i wont get shock; even then fuse wont break, computer remains ON.
THIS SHOULDN'T HAPPEN THEN

You get a minor tingle, it's through the suppression components from live/neutral to earth. You get the exact same thing on diouble insultaed items as well, although in that case it's to prevent a high static charge building up on the appliance.

If an item has a three pin mains connection, then it's there for a reason - NEVER use it on a two pin circuit.

 

[Electroenthusiast]

You get a minor tingle, it's through the suppression components from live/neutral to earth. You get the exact same thing on double insulated items as well, although in that case it's to prevent a high static charge building.....

Thanks;Not a Minor tingle :O High static charge? I get the shock, even when monitor is switched off,(with mains ON).


This is another ques:
Please tell me the differences in power consumption(when appliances is earthed/ and not earthed)
Will Power consumption increase, due to the complementary earth-chasis path.

**broken link removed**

 

[Nigel Goodwin]

Thanks;Not a Minor tingle :O High static charge? I get the shock, even when monitor is switched off,(with mains ON).

Minor tingle - don't be a girl! (apologies to our female friends).

This is another ques:
Please tell me the differences in power consumption(when appliances is earthed/ and not earthed)
Will Power consumption increase, due to the complementary earth-chasis path.

**broken link removed**

As you've already been told it makes no difference, or at least far too small to be of any consequence.

 

[mneary]

The device will consume precisely the power that it wants, no more and no less (exclusive of failures). The appliance is ignorant of the path upon which it arrives.

 

[Electroenthusiast]

Minor tingle - don't be a girl! (apologies to our female friends).

Hi again,
I measured the Voltage b/w the chassis (appliances that needs grounding) and the Earth ground.
It measured 256V AC, and the input is 240V AC.
So it's not a Minor Tingle.

 

[solis365]

The Hot or Phase wire carries the +/- 150V sinusoidal AC signal
The Neutral wire sits at 0V at the electric company. it carries the RETURN current of whatever load is attached.
the Ground wire carries NO current and has NO voltage. it is not connected to any electrical circuit that you plug into the wall. It is only connected to the metallic CASE of an electrical circuit - that way, if there is a mechanical failure and something inside the case that carries a high voltage touches the metal case, a person who touches the case will not get shocked since all of the current will take the easier path to 0V through the Ground wire.

 

[Dx3]

The earthing wire is supposed to be a safety wire to carry away accidental leakage or blow the fuse if a serious leak happens. Some appliances like microwave ovens have high frequency filters that are attached to the earthing wire and some small intentional current is caused by this.

Because the leakage is supposed to be zero on most machines, the absence of current in the earthing wire does not cause increased power consumption.

If your machine has voltage on its case when you are improperly using a 2 wire cord, use a 3 wire power cord. You could also investigate where the leak is, and repair the machine.

 

[Nigel Goodwin]

Hi again,
I measured the Voltage b/w the chassis (appliances that needs grounding) and the Earth ground.
It measured 256V AC, and the input is 240V AC.
So it's not a Minor Tingle.

Your voltage reading is incorrect, and it is only a minor tingle, VERY low current capability (which is what matters).

The actual voltage will normally be half the mains voltage, but even if it's only connected to the live side, it can't exceed the incoming mains.

 

[colin55]

Your body does not feel 256V it feels 360v. That's why you get a shock.

 

[Electroenthusiast]

Your voltage reading is incorrect

The actual voltage will normally be half the mains voltage, but even if it's only connected to the live side, it can't exceed the incoming mains.

Yes, but it reads correct when i connect it to mains (240V), wont it mean that it's reading properly?;
I'm not sure why 256V came there...even i know it cant exceed 240V...

Your body does not feel 256V it feels 360v. That's why you get a shock.

 

[colin55]

In fact the voltage is firstly 360v above ground and then 360v below ground and your body sees this 720v differential. If I gave you a simple 360v pulse in the positive direction and nothing in the negative direction, your body would hardly react at all. It's the fact that it goes positive then negative that throws you off the wire.

 

[Electroenthusiast]

In fact the voltage is firstly 360v..............ative that throws you off the wire.

I'm sure, its 256 V...
dont know such an high voltage hasnt caused anything wrong to my computer...
whenever i touch the USB Socket, i get tingle... so as when i touch screen (CRT).
But still it hasnt caused any harm to my pendrive/ other peripheral to which its connected

 

[colin55]

There is not such thing as 256v. It doesn't occur anywhere.

 

[Electroenthusiast]

There is not such thing as 256v. It doesn't occur anywhere.

i'm totally confused...
I've heard that CRT has very large voltages inside...( more than Mains)
Would it be causing that?

It'll cause me a severe tingle every time i touch USB/Screen... So what would you say?
I'm also sure that my multimeter is TRUE...

 

[colin55]

The voltage to draw the electrons to the screen is somewhere between 10kV and 26kV, depending on the size of the screen. This can be leaking somewhere inside the monitor and produce electrostatic shock, if the chassis of the monitor is not earthed.
Alternatively, if the reading is 250v, the leak is coming from the mains transformer.