Strange grounding problem in old house

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  #1  
Old 08-15-05, 07:45 PM
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Strange grounding problem in old house

I have a 1920's house with newer 200A service. Some outlets are fed by romex and are properly grounded, but many are fed by a fuse panel and do not appear to be properly grounded.. they seem to be "sort of" grounded though.

When using a multimeter, I get anywhere from 65 to 75 V between hot and ground. I also get somewhere between 1 to 16 V between neutral and ground. Wiring is the old 2 conductor, fabric-covered wiring. The boxes are all metal. The outlets are a mix of two prong and 3 prong.

In the crawl-space, I do have a little ceramic box with terminals on it with the words "lightning protector" or something. It has several single wires coming from it. Not sure if this is related to my ground or not.

Basically, I would like some insight as to why I have the strange voltage readings, and what I could to to get a proper ground.
 
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  #2  
Old 08-15-05, 07:56 PM
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The only way to get a proper ground is to run a new line with ground.

It maybe a phantom voltage. look at this link.
http://www.nema.org/prod/wire/build/...088%202003.doc
 
  #3  
Old 08-16-05, 04:22 AM
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The strange voltage readings are referred to as phantom voltage, and occur because you are using a digital voltmeter. The grounds are open (not connected to anything). If you use an analog multimeter you will not get a voltage reading on those ground lines. Google the term "phantom voltage" and look at some of the sites that come up for more information.

If there are three prong receptacles installed where there is no ground, and if those three prong receptacles are not GFCI protected, then you have an unsafe situation and a code violation. You should correct what is wrong.
 
  #4  
Old 08-16-05, 09:29 PM
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When ever you excite an input on an electronic device while floating the ground no reference can be made and the results will be unpredictable. Digital multimeters have high impedance active buffers which produce this result with out a proper ground. In a nut shell they need a reference.

When it comes to electricity i don't believe in phantoms, only gremlims.
 
  #5  
Old 08-17-05, 05:07 AM
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Thanks for the replies, guys. At least the meter will tell you that there's voltage there when there isn't as opposed to reading no voltage when there actually is some.

Time to start fixing my lack-of-ground problem. Some of the wiring is in metal flex, so I may be able to get some of the outlets grounded. Ultimately, a rewire is needed, it seems.

One last question though .. everyone always says how three prong outlets on an ungrounded circuit is dangerous. Is this any more dangerous than using a three to two prong adapter on an ungrounded circuit? My understanding is the 'danger' comes from using an appliance that expects to be grounded, on an ungrounded circuit. And that using an appliance (or light, etc.) with a two prong plug is just as safe in an ungrounded two prong or three prong outlet. There's nothing inherently different about the hot and neutral sides of the outlet, right?
 
  #6  
Old 08-17-05, 05:25 AM
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Let me see if I can clear up your misconceptions. There is a big difference between the neutral and the ground in a properly grounded circuit. The neutral side of the circuit carries current, whereas the ground does not carry current under normal operation. You can and will receive a shock from the neutral wire in a circuit, but you wonít receive a shock from the ground wire (assuming everything is wired properly).

The ground wire exists as a safety mechanism. It provides a path for current to flow back to the source in the event of a problem with the circuit. For example, if the something goes wrong in your washer and the metal frame of the washer becomes grounded, the ground wire will provide a path back to the circuit breaker panel for this current. The current will very quickly exceed the breaker rating and the breaker will trip.

Homes were originally wired with ungrounded circuits because most electrical devices donít need the ground. Copper was needed, especially during war time, and it was cheaper to manufacture cable without that extra ground. They only provided grounded circuits where a ground would likely be needed, such as kitchens, laundry rooms, etc.

You are correct, electrically speaking a three to two prong adapter is no safer than an ungrounded three prong receptacle. However, using the adapter you (hopefully) realize that the circuit is ungrounded, and perhaps will think twice about really using the receptacle. If the receptacle is ungrounded three prong you may well not even know (or forget) that the receptacle is not grounded and assume that it is.

As for you having anything to fix, that is up to you. Certainly if you have three prong receptacles that are not grounded then you do indeed have something to fix. However, if all your ungrounded receptacles are two prong, then you have nothing wrong and nothing to fix, unless you want to. I do recommend a ground where you need it, such as for a computer or other electronic device that needs a ground, and of course for kitchens
 
  #7  
Old 08-18-05, 01:30 AM
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racraft,

If I may butt in here for one question...I appreciate it.
I understand everything you said above, except for one thing that is bothering me. If the ground wire is there only for safety reasons, then why do electronics need it? Since the neutral is connected to the same ground at the panel why doesn't it perform the same function?

Thanks...Randy
 
  #8  
Old 08-18-05, 04:30 AM
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Electronics use the ground for reference, as well as for safety.

For example, computers have a power supply that converts the incoming AC power into the various voltages needed for the computer components. The case of the power supply is metal, and there is also metal used in the computer case. The metal is grounded for safety reasons. The voltages generated by the power supply are in reference to something called 0 volts. This 0 volts is tied to the ground, meaning that two computers next to each other will have the same voltage reference, even though they are not necessarily connected.

Some surge suppressors also need the ground wire. In the event of a power surge, the excess power needs to be placed somewhere. The power is shunted (not all at once) to the ground wire.

The neutral cannot be used in place of the ground because the neutral carries current.
 
  #9  
Old 08-18-05, 08:13 AM
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Originally Posted by rcash54
Since the neutral is connected to the same ground at the panel why doesn't it perform the same function?
They do not perform the same function, because the neutral and ground are only connected at the panel, not at the receptacles and appliances. If you were to connect the neutral and ground together outside of the panel box, you would create a serious hazard. Instead of 100% of the current returning to the transformer on the neutral wire, roughly 50% would return by way of the neutral wire and 50% by way of the ground wire. The ground wire is bonded to your plumbing and metal appliances; if it has power flowing through, touching anything metal in your house could be fatal. That is why the neutral and ground wire must remain seperate outside the main panel.
 
  #10  
Old 08-19-05, 01:30 AM
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OK, I understand about the electronics. That makes sense, but what I don't understand is since the neutral is connected to the ground at the panel, which is connected to a ground rod buried 8 feet into the ground, how does the current ever get back to the transformer?

I've always been taught that current will take the path of least resistance to ground, so wouldn't it all just go into the earth?

I have been schooled in DC electrics and have been working with DC for the past 35 years, but it's pretty much negative and positive, where negative is referred to as the ground. I've found AC to be similar but sometimes more complex than the DC circuits. But one thing I believe is constant. The current must always return to its source to complete the circuit, which is what is confusing me here. How does it get back to the transformer, and subsequently the generator, when it is actually going into the ground?

Thanks guys.
 
  #11  
Old 08-19-05, 04:55 AM
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Originally Posted by rcash54
I've always been taught that current will take the path of least resistance to ground, so wouldn't it all just go into the earth?
You have been taught wrong, at least to some extent.

The electrical current must get back to the transformer, that is true. However, it takes EVERY path back to the transformer, not just the path of least resistance. The amount of current on each path is related to the resistance of the path, with more current flowing where there is less resistance.

The ground rod is there for two reasons. It is there for safety, and it is there for reference. It is not there to provide a path back to the transformer. That is the responsibility of the neutral wire.
 
  #12  
Old 08-19-05, 05:20 AM
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I've always been taught that current will take the path of least resistance to ground, so wouldn't it all just go into the earth?

I have been schooled in DC electrics and have been working with DC for the past 35 years, but it's pretty much negative and positive, where negative is referred to as the ground.
The problem in your understanding is that 'ground' has nothing to do with it. The electric current wants to return to its _source_. It needs to travel in a closed circuit.

In general, and in a properly operating system, the current flows in a closed loop between the transformer and the loads, with no current going into ground, and no current returning anywhere else, including the generator! The current is created right at the transformer. (The power to create this current comes from the magnetic fields inside the transformer, and this is provided by a _separate_ current flowing on the primary side, and the primary side current was caused by a transformer at the substation....all the way back to the generator, individual _separate_ circuits all coupled in terms of power by magnetic fields inside transformers.)

If your power supply is connected to ground at _one_ point only (say by a ground rod), then no current will flow in that ground connection, because there is no closed circuit. If the circuit is then connected at _two_ points (say by a ground rod and a ground fault), then current will flow through the ground connection, because there is now a closed circuit which includes the ground.

Having current flowing in your grounding system is _not_ in itself particularly dangerous, and in earlier versions of the electric code, there were specific circumstances where current was permitted to flow in the grounding system. What gets dangerous is when something breaks and you have current flowing in your grounding system.

Currents are often permitted to flow in the grounding systems of cars, but the circumstances (and rules) are different for cars than for homes. Low voltage DC systems often use equipment chassis as both ground reference, 'safety ground', and current path. Again, the circumstances and rules are different.

In the case of home wiring, the return current is carried on insulated conductors ( the 'neutral' or 'grounded' conductors), and the safety ground is left as a non current carrying backup. I guess if houses were essentially solid metal shells with lots and lots of metal, it would probably be safe to use the house itself as the return conductor, and simply run a single 'hot' wire to each receptacle, trusting the house as both safety ground and circuit return conductor. But in houses we are talking about skinny little wires and pipes (large chance of the return circuit failing and opening) and higher voltages...so we have a safety ground and a separate current return conductor.

Finally, there is nothing special about the negative terminal of the battery being used as 'ground'. You can just as easily select the positive terminal as your ground reference, and some cars were built this way. Using the negative terminal of the battery as the ground reference is simply convention.

-Jon
 
  #13  
Old 08-19-05, 07:01 AM
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The power into your house consists of the 2 secondary terminals of the transformer. 24o VAC exists between these two wires. If all your equipment ran on 240, that would be end of story. But, many years ago it was decided that lights and things should run on 120. So, a center tap was connected to the transformer secondary. Now, we have 120 between each "hot" and this center tap, which we now call neutral. From an electrical standpoint, it doesn't need to be earth grounded. Current flows in the windings, through the load which is connected to the wires we call hot and neutral.

Now, we had an undefined situation , safety wise. If you were standing on earth and touched EITHER the black, red, or white wire , how much voltage was your body exposed to? Could be a lot. Sooooooo, it was decided that the neutral side should be connected to earth ground AT THE HOUSE. Now, touching that wire was "safe" relatively speaking, and touching either of the others gave you a max of 120. In more recent years, it was realized that because of the current flowing in the white wire, whose resistance cannot be zero, then at various points in the house the voltage measured to earth from a white wire will not be zero and could be dangerous. So the saftey GROUND wire was added. Because under normal circumstances there is zero current flowing in the grounding wire, the voltage will be zero. This is a safer situation.
 
  #14  
Old 08-20-05, 11:18 AM
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I think my confusion lies in where I was focusing on the generator as the source, where as it is actually the transformer that is the source. That makes sense to me now that I consider that part of the equation. The generator is only providing the excitation current for the transformer, and the transformer is what is actually generating the current for the house, as you stated in your response, Winnie, so it makes sense that the current will need to return back to the transformer to complete the loop. Otherwise, you have no current flow. ding, ding, ding.

Wow, ok, I think I got it. So that now helps me to understand the importance of the neutral wire and also how it could be so dangerous if not used correctly, and even though it is connected to ground at the panel the current will take the path back to the transformer.

One thing I'm curious about, though, was the reason to go to 120V due to safety, whereas, 120V would be safer than 240V?

I know 120V can kill, but I believe in actuality it is fairly tame. I've been zapped many times by it. In fact, when I was very young I was helping my Dad install a TV antenna on a pole that was buried in the ground. I was drilling a hole through it with an aluminum case drill that had been repaired once and a wire has been pinched in between the case halves. As I was drilling the pole all of a sudden my hand clamped down on the drill and I felt the electricity going through my body. I couldn't let go no matter how hard I tried. I guess my body shook hard enough to where the cord finally pulled loose from the extension cord and I was able to finally let go of the drill. I don't khow exactly long it was but I know it was at least 10 to 15 seconds. I was not permanently injuried (although some may disagree, lol), but it did scare the begeeses out of me.

I have never been hit with 240V and I hope I never am. That, I believe would have killed me for sure.

Thanks guys for the mini lesson in AC Theory and for taking the time to help me understand it.

Randy
 
  #15  
Old 08-23-05, 07:36 PM
ELECTRI-KAL
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Getting Back To Your Original Problem Of Part Of The House Grounded And Part Not, Since You Have A Crawl-space, One Of The Easiest Ways To Ground All Outlets Is To Drill Down Through Each
Outlet Box Into The Crawl Space And Install A #12 Green Ground
Wire And Connect Each To Your Building Ground (usually A Copper
Rod Tied To A Cold Water Pipe).

Then, Replace All 2 Prong Outlets With 3 Prong Ones With This New
Ground Wire Landed On The Green Lug Of The Receptacle And Bonded To The Metal Box.

Be Certain That The Old Cloth Wiring Is Properly Installed To,
Silver To Nuetral And Gold To Hot With No Frayed Ends Etc..

Use A "sweephand Meter" To Check Voltages. You May Have Actually Read Some Incidental Grounding Before If Your Metal Boxes Were Touching Lath Wire Or Plumbing Within The Walls Which Can Give A Mock Earth Ground But It Is Not Solid.

The New Ground Wires Will Be Solid. One Other Thing, All
Sub-panels Sould Have Floating Nuetral Bars Or In Other Words
Only The Main Panel Should Have Nuetrals And Grounds Tied
Together, All Other Panels Should Be Seperate Nuetrals To
A Non-grounded Nuetral Bus And Grounds To Ground.

E Me Back For More Ideas! Electri-kal
 
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