View Full Version : Ground Leak?
08-30-2007, 06:36 PM
I have a strange problem in 4 outlets in one room of my house. It seems that the potential between hot and neutral is correct (about 118 volts). But when I test hot to ground I measure about 73 volts and neutral to ground is about 45 volts -- adding up to about the same total of 118.
Seems like some kind of short to the ground.
However the problem only exists on these 4 outlets and one wall switch (which doesn't appear to be connected to anything). The other outlets on the circuit are normal -- 118 volts hot to ground, zero volts neutral to ground.
The wires feeding the outlets and switch box are visible in the basement, but I haven't yet attempted to trace them -- but it does appear the problem outlets are in sequence. I don't know yet if the good outlets are closer to or further from the circuit breakers.
Anybody have hints as to what the problem might be or how to fix it without rewiring the whole circuit?
08-30-2007, 07:05 PM
It could be an open neutral.
Try plugging an incandescent light into one of the receptacles of the duplex outlets while you measure the voltage on the other receptacle.
08-30-2007, 07:34 PM
I tried plugging in an incandescent light as you suggested, but saw no difference in measurements, no dimming of the light or anything. Although I don't know what I should have been looking for. Can you explain what you mean by open neutral?
I could add that I've already tried unplugging everything plugged into this circuit and saw no change in behavior.
08-31-2007, 01:15 PM
What kind of meter?
1. Possibility an open or ungrounded system. With an imbalance load reading like yours are possible. Go to the Main Service panel and measure from L1 to Neutral and Ground and and to L2, do the same with L2.
2. Open ground.
08-31-2007, 01:32 PM
I vote open or "partially" open ground.
08-31-2007, 01:34 PM
If you suspect a short, you can always turn off the house power and measure resistance between terminals with an ohmmeter. Often though something is floating. Check to see if neutral and ground are bonded by checking the continuity between them.
08-31-2007, 05:46 PM
Thanks for all the responses. But could someone explain what is meant my an "open grouond". Or an "open neutral."
Regarding the suggestion to measure from the service panel (implying a system wide problem) -- I've checked the other circuits in the house from the other outlets and there is no problem -- and in fact, some of the outlets on the same circuit have no problem.
In answer to the question "what meter" from BrianJohn, it's a basic multi-function meter -- measuring volts, ohms or amps, direct or alternating.
08-31-2007, 06:30 PM
-- and in fact, some of the outlets on the same circuit have no problem.
Go to the last working, and the first non-working receptacle and test. The problem is in either one. It could be in between (but that is not likely unless there is a splice or box you are not seeing).
08-31-2007, 06:43 PM
Electrical connections should be tight with no resistance between like leads. If a lead is loose or corroded, it will not pass all of the voltage or current it was designed for. If the connections are not 'good', it is sometimes referred to floating or open. A great open analogy is the light switch, it is either on (closed) or open (off). It gets a little more complicated if it is controlled by a dimmer, then, not all of the voltage can get to the light. By design in the USA, at the power panel, the ground and neutral are supposed to be 'bonded' or electrically shorted together...there should not be any resistance between them. There obviously is a problem with yours since there is a difference in voltage between the two...it should be nearly zero, if not zero depending on conditions.
08-31-2007, 07:59 PM
Jadnashua -- thanks for the good definition of open or floating. Now another question. How could a floating or open neutral result in the condition I'm seeing? I would expect a floating or open neutral to result in lower or zero potential between hot and neutral -- but I'm seeing full voltage there.
08-31-2007, 08:29 PM
You can get "phantom" voltages with standard Volt-Ohm meter when there is no load on the circuit because the meter has very high resistance. That is why I suggested plugging an incandescent light into an outlet where you are measuring strange voltages.
If the light is normal then you should have a good circuit and you will not get phantom voltages due to induction from one wire to an adjacent wire.
09-01-2007, 06:03 AM
1. Check the voltage at the panel, does the problem exist at the panel?
2. Check various outlets does the problem exist at only 1 or 2 outlets? Does this problem exist only one circuit? or is it house wide?
3. I ask again what type of meter are you using? It makes a difference?
If the neutral is not bonded (solidly connected to ground at the Main Service Panel), you can have what is referred to as an ungrounded system*. When you measure voltage from either conductor (hot and neutral) if there was a perfectly balanced load in your house on "hot" L1 and "hot L2" you would read
60 VAC to the ground wire from each conductor, if the load in not balanced between L1 and L2 you would read some voltage difference between L1 and neural and L2 and neutral.
So this is where I would start.
An ungrounded system while safe is not the best way or legal way to operate a residence.
If this is a hot conductor or neutral issue this can be a major problem resulting in the loss of your residence.
In either case if you cannot isolate the issue in quick order I would call a GOOD electrician, expierenced in trouble shooting residential branch circuit issues.
*Usually an ungrounded residential service is difficult to achieve as the utility also grounds the system)
If I am reading your post correctly, where is the voltage from neutral to ground coming from? In an ideal situation, both would be at the same potential.
09-01-2007, 08:28 AM
In an ungrounded system you have a capacitive ground, depending on the load on each leg will determine the voltage from L1, L2 and neutral to ground.
09-01-2007, 09:40 AM
Thanks for everyone's help on this.
In answer to BrianJohn's questions:
1. At the panel I have 120 Volts from L1 to ground/neutral and 120 from L2 to ground/neutral. Also I have 120 from the circuit breaker for the problem circuit to the ground/neutral. I can't actually see if the same problem is in the box because the probelm I see upstairs is different potentials from hot to neutral and from hot to ground. In the box all the grounds and neturals are connected to the same bus so it's unlikely that I would see the same problem there, isn't it?
2. As I said in my previous posts, the problem is only in 4 outlets. All other outlets I have tested (most of them) do not have this problem. This includes several outlets on the problem circuit which also test normal.
3. The meter I'm using is a Sperry DSA-500 "Digisnap".
How can I tell if I have an ungrounded system? I have three service lines coming into the house (two insulated, one uninsulated) and three lines going all the way through the meter box into the panel. In the panel box, two of these lines are connected to L1 and L2. The other is connected directly to the ground/neutral bus in the panel box. In addition there is a ground wire connected from the outside meter box to an in-the-ground ground post.
09-01-2007, 01:54 PM
It is highly unlikely that the system is ungrounded based upon what you said, but one of the branch circuit conductors is open.
What I would do next.
1. Utilizing a 3-wire extension cord plug the cord into a good outlet and then from each of the four outlets in question take readings. I WOULD LIKE TO YHINK THE READINGS ARE ACCEPTABLE.
2. With the power off remove each of the outlets try and determine the circuit circuit wiring determining what is the last and what is the first with an issue.
3. Either at the first outlet with this issue and the next outlet in the circuit the problem exist.
One way to determine wiring direction is with your ohm meter, or a practice electricians utilize sometimes is back feeding the circuit, this can be a dangerous practice if your are NOT CAREFUL.
If you did the back feed utilizing a 3-wire extension cord you could verify at all outlets that readings were normal.