Power Line Comunication simple question

[zahiy]

Hello,

We all know that there is somethiing called "Power Line Comunication", they use the Zero and the Hot for comunication, I have a question:

every houses there are three wires, Power - Zero - Ground ,

why not to use the Zero as common and sending data through the ground?!? we dont even need the Hot wire!

 

[SPDCHK]

Most houses have an Earth Leakage (EL) unit that monitors for a short between the live and earth, like when you get shocked. This EL will trip out the house power if a stray current of about 20mA is detected.

If you now use this line for communication, it will seriously confuse the EL and may trip when not really needed.

In South Africa there is no way that we can use the earth wire for communication because of this very reason. My house's power keep on tripping

 

[zahiy]

You are right but I am talking about home automation system that sends a fews bytes one in a while, maybe using RS-485 which I don't think it going to exceed a few mA's..

do you know easier way to comunicate devices thought the power line without complications, just a few byts transfer! I dont want to buy the emedded power line modem..

 

[blueroomelectronics]

You need two wires for data, signal & return (GND)
So you can't use Ground for the data. You also must modulate it like X10 does (120kHz carrier)
Microchip has an app note on X10 including schematic.

 

[preeste]

Hi there...i was looking at the Micrcochip application note for x10. I think it is called An236. Can someone help me with this....i dont have a basis in electrical circuits but am looking at carrying out this project for something. I need to know what modifications to make if this is being done with AC of 230/220V at 50HZ. please help!!! urgent

 

[Arkham00]

Ground and neutral

Indeed, ground wire and neutral wire should have the same voltage because neutral is usually connected to "real ground" at the power company transformer while home ground is connected to "real ground" just outside home. The two "real ground" should have the same potential because "real ground" is usually a good conductor (few ohms between the two "real ground" points).

You cannot send a signal on two wires connected "almost together".

 

[Nigel Goodwin]

Indeed, ground wire and neutral wire should have the same voltage because neutral is usually connected to "real ground" at the power company transformer while home ground is connected to "real ground" just outside home. The two "real ground" should have the same potential because "real ground" is usually a good conductor (few ohms between the two "real ground" points).

You cannot send a signal on two wires connected "almost together".

You would be wrong, using neutral and ground is just as common (and effective) as using live and ground.

In a separate earth spike like you mention, there's even a voltage drop you can measure between earth and neutral. But in any case, it's a completely different thing at RF frequencies, which are used for data communication.

 

[Arkham00]

Nigel,
I think that the following is the typical scheme of the power connection of a house. If the connections are well done, the "earth points" E1 and E2 should be at the same potential because earth itself is a very good conductor so neutral and "protection earth wire" are almost the same wire (from very few tenth to very few units of ohms depending if ground is wet or dry) so I think it will be impossible to use them as wires for a communication. Am I wrong?

 

[Nigel Goodwin]

Nigel,
I think that the following is the typical scheme of the power connection of a house. If the connections are well done, the "earth points" E1 and E2 should be at the same potential because earth itself is a very good conductor so neutral and "protection earth wire" are almost the same wire (from very few tenth to very few units of ohms depending if ground is wet or dry) so I think it will be impossible to use them as wires for a communication. Am I wrong?

Like I said before, you are wrong - you are considering DC or very low frequency AC - the circuit bears no relation to this at RF frequencies.

But even at low frequencies you are still wrong, there's commonly a couple of volts difference between neutral and earth.