Using AC GND as digital GND?
Clock Loop
Posts: 2,069
Im building this circuit, and want to eliminate the GND wire so I can use standard phone cable instead of ethernet cable.
Could I tie my digital GND to my AC GND wire (the 3rd prong)? Is there a safe way to do this?
Does this depend on how my power supply is built?
Post Edited (BPM) : 11/24/2005 6:01:50 AM GMT
Could I tie my digital GND to my AC GND wire (the 3rd prong)? Is there a safe way to do this?
Does this depend on how my power supply is built?
Post Edited (BPM) : 11/24/2005 6:01:50 AM GMT
Comments
I am not sure if this was orginally an intentional safety feature [noparse][[/noparse]the isolation from ground] but it certainly has not hurt people.
Fooling around with a house current AC ground as a transmission line for data seems to be an invitation for trouble.
Other people use the outlets and may remove the mysterious wire or unknowingly reconnect it to hot side of the AC.
In many older buildings, the third prong grounds are not properly connected, but just there to provide convience of use to people that have grounded plugs on devices. And, in other older building, someone may have non-standard hot and grounded sides to outlets without a third ground plug. Everything must be carefully verified. You actually begin t have to do all the things an electrican must do [noparse][[/noparse]and do them safely] to make the whole thing work.
It really is best to have a completely separate cable for low voltage communications. Of course, there are exceptions, such as X10. But these are rigoursly tested, certified safe, properly housed, and clearly marked.
The question here is what kind of ground are you trying to have? Generally - Don't mix purposes.
1. A safety from shock and fire [noparse][[/noparse]forces the circuit breaker or GFI to shut down]
2. A protector from spikes in the data line caused by lightning or heavy equipment switching [noparse][[/noparse]needs all three wires to dampen the problem]
3. One side of a communications circuit.
What it sounds like is that you wish to save one strand of ethernet wire and run one wire into the house's ground plug. It may work, but then again it may be a very poorly connected ground network which will provide nothing but headaches. You may actually introduce unwanted spikes and noise into the system. Possibly, you might cause damage to the low voltage circuits.
Phone wire comes in 2 wire, 4 wire, 6 wire, 8 wire and more. If you are just trying to skimp by on 2 wire, it seems a bit silly. Four wire phone line is everywhere. Shop around. Look around. You can buy 1000 feet of 8 wire twisted pair for $40USD and put your own connectors on it. Try looking in second hand stores and recycle depots for ethernet wire from old computer networks. Try looking in the trashbins behind computer stores and thrift shops.
Bingo.
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Basically I have an extension cable between my DEVICE and my CONTROLLER. Neither my DEVICE or my CONTROLLER have ANY kind of ground protection circuitry. Alot of devices we buy acutally don't. Lights, christmas lights, soldering irons, etc...
But thanks, you made me realize the answer I was seeking.
I just wonder if the GROUND wire in the extension cable will pick up EMI from the 120v 60hz AC mains.
You might be right about the ethernet.
I have plenty of extra ethernet cable, and connection ends.. Just didn't want to use it for this.
The function of the ground in an AC power circuit is to provide a safety path for the AC should a problem arrise in the Neutral conductor. The Ground and Neutral are connected together at the Mains entrance, and also grounded to earth at ths point.
Should you have a fault, the power will travel through the ground back to the mains neutral.
In general use, it is a good ground, but during a fault it is a current carrying conductor. If your project makes a better ground connection than the ground wire, that current will flow through your project with potentially leathal/dangerous results.
The cost of ethernet cable will be less than the cost of a funeral or accident lawyer.
Thanks,
Alan Bradford
Plasma Technologies
www.plasmatechnologies.com
That reason alone is why one should not use the ground wire for anything. The OTHER devices hooked up to your AC, that have a ground wire might short out and make use of the ground wire, frying your device.
I understood that before, thats is why I added the """ IS THERE A SAFE WAY TO DO THIS? """ Question in my first post.
I was asking if anyone knew of a way to SAFELY use it as a D-gnd. I.E. via some kinda circuit.
If I didn't know and respect the hazards of AC I would prolly not be sitting here asking the question. eH?
But anyway, my question was solved. So nevermind.
Post Edited (BPM) : 11/24/2005 2:28:00 PM GMT
BPM had found a solution. I had to reread his solution several times to get what he was saying. (I'm just not that fast with werds that I read, ya know?) Anyways, what he's saying is that the device that he needed help with figuring something out, doesn't use the AC ground. So, he's going to use a 12/2 with ground, and use the ground wire in the cable as a ground for his digital ground. He just has to make sure he removes that ground from the cable before it gets to the AC plug. It makes sense, and this will never touch the AC's ground. His power supply on his device doesn't use a ground, so it's already got the issue mentioned about if there is no safe way to get rid of the energy. As he points out, alot of "simple" devices don't have a ground on them, such as soldering irons (cheap ones), lights, christmas lights, etc.
Hopefully that makes sense. BPM's explanation does make sense, it just takes a little rereading. [noparse]:)[/noparse]
However, BPM, I would suggest that you do not use the ground in the cable and simply wire tie a cable to the AC cable. I picked up for realativly cheap, a 4 wire shieled cable (technically 5 conductors) from Home Depot, 500' for something like $35. They also have 7 wires (8 conductors) and I think 2 wire shielded. The shield would prevent any interference from AC mains.... At least, it's the best solution that is easy, you are still running it RIGHT next to the mains.... I have also seen shielded AC lines....
Knight.
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This message transmitted with 100% recycled electrons.
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Gravity doesn't exist. The Earth sucks.
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Make a man a fire, and he will be warm for the night.
Light the man on fire, and he will be warm for the rest of his life.
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Imagine your washing machine with a metal case has the hot wire loose inside and rests against the case, and somebody cut off the third leg of the plug.
The washing machine case is now HOT, and you touch the case, you become the path to earth.....OUCH.
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Ken
There are a lot of things that you can do that your probably shouldn't.
This is one of them.
Have you ever siphoned gasoline out of a gas tank? It works, but a mouthful of leaded gasoline is not particularly healthy either.
I hope you can understand the analogy.
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Ouch 5 minutes later when you realize you're on the other side of the laundry room clutching your chest and wrist. If you're lucky enough to be around 5 minutes later. When your working on the coolers at a restaraunt, be sure the power is cut, even if you're just looking.
but yeah, I think this entire thread is to illustrate that the ground of an AC house circuit is not the same as the ground of a DC electronics circuit. the Vcc on your basicstamp is the negative place for the +5VDC to terminate. The ground in your house is so a fault doesn't terminate you.
The horse has already been electrocuted by 120v AC at 60hz. Because his feeding trough had its digital GROUND tied to the AC GROUND.
And the case for the trough touched a hot AC live wire...
blah blah blah...