low voltage

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  #1  
Old 01-31-02, 03:54 PM
EdgarF
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low voltage

Is it normal to read low voltage (12-50V) off neutral to any ground at an outlet or should you always read zero?

Is this low voltage due to other items plugged into the circuit such as nightlights, alarm clocks, etc?

If this is not normal, what could cause the reading of the low voltage? Any help would greatly be appreciated! Ed
 
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Old 01-31-02, 08:34 PM
Wgoodrich
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The white wire is a current carrying conductor that carries the unbalanced load of a neutral of a 240 volt branch circuit or the current back as a return path to the panel on a 120 volt branch circuit.

The equipment grounding conductor is isolated from that smaller current found on the white wire. Therefore it would not be uncommon to read the voltage you picked up between a white wire and a bare wire.

hope this helps

Wg
 
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Old 01-31-02, 08:38 PM
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A low voltage on the neutral due to other loads is normal. However, even 12 volts does not qualify as "low" in this case. In a perfectly functioning system, you wouldn't expect to see more than 2 or 3 volts on the neutral wire.

The most likely explanation is phantom voltage. Shut off the circuit breaker and use your ohmmeter between the neutral and ground. There should be very little resistance. But you may find a lot of resistance (i.e., an open). In this case, your neutral is disconnected and the voltages are phantom (i.e., unreliable values for any purpose).

If you find only moderate resistance (say, less than 10 ohms) between neutral and ground, then the next most likely explanation is a poor connection somewhere in your neutral line. You should double-check all wiring on the circuit.

What do you think?
 
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Old 02-01-02, 07:27 AM
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Edgar, I believe your ground is open. The grounds and neutrals are supposed to be bonded at your panel, and since the impedance of #12 copper is about 2 ohms per thousand feet, it is unlikely you could have enough current flow to produce even a 12 volt drop in a typical run in your house. For example, a 100 foot run of no. 12 would be 0.2 ohms. It would take 60 amps to give a difference of 12 volts between neutral and ground. A load of 20 amps would give only a 4 volt difference between neutral and ground at the end of the 100 foot circuit.

With the ground isolated it is coupled by the cable's inductance and capacitance to the hot conductor in the cable. It can produce fairly high voltages.
 
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Old 02-01-02, 12:15 PM
Wgoodrich
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While I agree with a perfectly balanced neutral having 10 amps on line one and 10 amp on line 2 you would find 0 amps on the shared neutral. However houses are by far perfectly balanced. If you have line one pulling 10 amp and line 2 pulling 5 amps you would find 5 amps on the shared neutral carrying the unbalanced load. Same would happen on a grounded leg. If you have 5 amps on the neutral which is easily found in a home then how can you have amps with current without voltage? If you are reading between an equipment grounding conductor and a shared neutral or grounded leg you will find a difference of potential showing the voltage readings he is finding. A 120/240 volt single phase system is not and can not be perfectly balanced due to the intermittent loads that are applied and any one given time especially when you are using 120 volts where there is no unbalanced load equalized by two hot phases. A grounded leg is a return path and definitly a current carrying conductor. Disconnect one white grounded leg under load and strike it to a good grounding path and you will find a pretty good spark showing a pretty good voltage is present on that white wire.

Curious

Wg
 
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Old 02-01-02, 12:38 PM
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The explanations already posted are very good but another explaination to your problem is the meter itself some of the less expensive models are not that good and can register a low voltage which is higher then what is present. It might make one volt appear as 10. Although you should be conserned about any reading that is not 100% correct most instalations are not 100% of what they should be, check the reading against another meter.
 
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Old 02-01-02, 04:05 PM
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Good point gard. So Edgar, what kind of meter are you using? Also, where are you reading this voltage? I'll try to explain my theory a little better. If you take a voltage reading between neutral and the grounded conductor at a point 100 feet away from the panel, you are essentially reading the voltage drop on the neutral conductor between the panel and the remote location where your meter is located. That is because there should be no current on the grounded conductor, therefore no appreciable voltage drop or rise. So that grounded conductor is just a long meter lead. As I stated above, the impedance of #12 copper is about 2 ohms per thousand feet, so according to Ohm's law, to get 12 volts drop on 100 feet of wire would require 60 amps. Either the meter is wrong or the ground is open and floating. Of course the neutral could be open and floating, too. Edgar, is this circuit working?
 
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Old 02-01-02, 06:29 PM
EdgarF
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To everyone - thanks so much for your replies. Here is more information: I currently added a couple of outlets and a switch plug to an existing circuit. When I went to test the switch and put the switch in off position, is when I discovered "phantom voltage" in the outlet of 50V. I found it on two testers. The first tester was just a light meter that went on. The second tester was a digital voltage meter that read 50V. I disconnected every outlet in the circuit to try to trace back the voltage which I was finding on the neutral. The voltage was everywhere within this circuit. From there I tested other outlets on other circuits and found 12V on the neutral in another switch plug when the switch was in the off position. Can't find any loose neutrals anywhere, and since then I discovered that my ground from the main panel is only grounded to the plumbing in the house (see my other post) because the pipe going out to my well is plastic. All circuits in the house work including the one that I added the new switch plug and outlets to. My electrician is coming next week - we are going to test the neutral to ground at the panel like John Nelson suggests. My electrician agrees with John that the probable cause is a loose neutral somewhere, and we are not ruling out a problem outside the house, i.e. at the pole. We are also going to drive a couple of grounding rods and properly ground the panel. I will post back and let you all know the results of this problem. Thanks to everyone for your insights. Edgar
 
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