Reply With QuoteOriginally Posted by jadnashua
I agree. It could just be a bad or dirty breaker or a splice.
As always , Be careful playing with electricity.
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For the voltage to drop that low with essentially no load ( a modern DMM has a HUGE input impedance, and thus little load when measuring volts), there has to be a bad connection acting like a resistor. This is likely either corrosion or a near total break in the wire. If it was connected to a load (it doesn't appear to be from the description), it could be extreme voltage loss because of excessively long or undersized wire. But, that does not appear to be the case, either. If there is a switch or splice somewhere in there, one or the other may be bad.
Jim DeBruycker
Important note - I'm not a pro
Retired Defense Industry Engineer
I agree. It could just be a bad or dirty breaker or a splice.
As always , Be careful playing with electricity.
Don't pay someone to do a job fast, when you can do a half-fast job yourself.
There is nothing wrong with having a forum for the Do-it-yourselfer as long as any and all advice given is compliant and safe.
When doing a voltage check using an approved meter no load on the circuit is required to get a valid reading. When a load is connected in series with the source then the entire amount of voltage applied will be dropped across that load.
Take a single pole light switch and with the light turned off there will be a reading at the two screws on the switch of ~ 120 volts. Now turn that switch on so the bulb is burning and the voltage reading at the switch will be zero. The voltage is being dropped across the bulb instead of the switch. The difference of potential has moved from the switch to the light bulb. Understanding how meters work and the theory of current flow is just as important as what the meter tells us.
quote; But if their was a short then the breaker feeding it should trip
Not necessarily. EVERY appliance and fixture is a connection between the hot and neutral. Whether it is a "short" or not depends on how it makes the connection between the two. IF there is some resistance between the broken wire and the 'earth" for example it would NOT trip the breaker but would raise your electric bill. I have worked on a lot of situations where the wire was defective, but did not trip any "fuse", but it was still uncomfortable to put your hand in a pool of water next to it. And you did not do it for very long.
Licensed residential and commercial plumber
I think that silverfox has some training and has and can use a Volt meter.
Using a light bulb in the place of the pump for testing should not be a problem. Why would it be ? Just plugging a nightlight into the GFCI is easy to do, and safe.
If you have a high Resistance (bad) connection that has a resistance lower than your voltmeter (1-10Meg) then without some load, Many times the meter will read full voltage unless there is some load on the line.
Obviously the line or circuit is open. But you have to start somewhere when troubleshooting, and not just guessing.
What is your suggestion for troubleshooting a problem like the Original Poster has ?
Can You offer some help here ?
Don't pay someone to do a job fast, when you can do a half-fast job yourself.
The simple fix would be to replace the underground circuit based on the information given.
The original poster made three statements
1- Low voltage reading from the hot to neutral
2- 2- low voltage reading from hot to EGC
Placing any type of load in series with this already voltage drop will not make the voltage be higher but instead it would make the voltage lower. The load of the light will drop the remaining voltage.
3- I then tested the voltage at the breaker and had 120 volts
Now we know that the problem is with the conductors somewhere between the breaker and the receptacle so what would you suggest to look at for the problem?
True, but the voltage readings are suspect. The OP should repeat the test at the breaker with a load on the circuit to verify there is no voltage drop at the breaker. A light bulb as in a work light plugged into the GFI outlet would provide a load that is safe to use. Unlike a motor, that can burn out from under-voltage, I've yet to see a light bulb do so. I fail to see what hazard there is in loading the circuit with a light bulb.
I would not trust a reading with a high impedance voltmeter on a circuit with no load.
If the voltage is normal at the supply and low at the end of the wire, the wire is the likely problem. Course, he could reattach the GFCI and plug a lamp into it to see what's there, but if the breaker was bad, the vast majority of the time, you'd read the same voltage there and at the end of the wire, which is not the case.
Jim DeBruycker
Important note - I'm not a pro
Retired Defense Industry Engineer
In the first post of this thread the statement was made; “I removed the gfi receptical and put my tester on the wires comming out of the ground and got a reading of 62 volts”
If he is getting a reading of 62 volts without the receptacle being installed why would he need to reinstall it to plug something into the receptacle to see if the voltage is the same?
It doesn’t matter if it is an analog or DVM type of meter reinstalling the receptacle and plugging in a load will not make the voltage somehow peak out to an average of 120.
This same meter got a reading of; “tested from the breker to neutral and got 120 volts” and this was out any load on the breaker.
Unless it is your contention that this meter and circuit is somehow loaded at the breaker in order to get these readings then the simple answer is replace the underground circuit.
All of this hogwash of “high impedance voltmeter” and needing a load to check voltage leaves me asking questions.
Why did they ever come out with such an item and why would anyone ever buy one if it entail all this extra work?
Could someone explain to me just how one could be used to trouble shoot a motor control center if every one of those control circuits will require a load to check for voltage?
Recon this feller needs to get a light bulb?
So now you want to divert attention from your knee-jerk over-reaction to using a lightbulb in a test by ridiculing? Then you go off topic about how to troubleshoot a motor control centre? How you!
I never said it wasn't the underground wire. It most likely is. All I said was the test procedure is flawed. Before I dug up the yard to replace the wire, I would verify the test procedure.
I'm out of here.
If you would be so kind before you leave please explain just what you mean by; “All I said was the test procedure is flawed.”
Just how is the test procedure flawed? As a licensed electrician with over 44 years of experience I would have done nothing different except I wouldn’t have removed the receptacle, I would have done my voltage readings with the receptacle in tack using this meter,
He tested the voltage at the receptacle and got 62 volts. Then he checked the voltage at the breaker and got 120 volts. What is flawed in his procedure?
By the way there is no difference in checking voltage in a residential setting than checking voltage in a motor control center or in your car for that matter.
In my entire electrical experience the only place I have ever heard of plugging in a light to test voltages is on DIY type web sites where the knowledge of the posters are very limited and most will swear by something they read that another limited knowledge person has posted.
OK JW, since you asked nicely...
My background is in electronics where the impedance of a voltmeter can more commonly influence the result. Voltage across a series of resistors gets divided based on the resistance values. The voltmeter is one of those resistors.
In one of your examples, you were measuring the voltage across an open switch wired to a light bulb. With the switch open, you would see essentially the full voltage despite the bulb itself being a resistor in series with the neutral. When the switch was closed you said, the voltage would read zero which is very true. You could simulate similar results by closing the switch and lifting the return conductor and measuring the voltage between the threaded base of the bulb and ground. That way, the resistance of the bulb would be in series with the hot instead but still, the voltage would show very near to that of the panel. This is because the voltage divided by the very high impedance of the meter has little influence.
The OP's measurement obviously included an in-line resistance or else there would not have been a voltage drop. The inline resistance however of the test I outlined above would not have indicated that much of a drop despite there being an in-line resistance. The difference is in current flow. Adding a bulb at the GFI introduces another series resistor (the first being the fault) and induces some current for accuracy.
I could much easier explain this in person on a workbench with a series of bulbs and a voltmeter.
A motor control center wiring is tested using a continuity tester before power is applied.
And they do use Lightbulbs, a bunch of them for testing the SCR Motor drivers, Before it is connected to a motor or when a motor is not available. They also use giant Resistor banks for load testing.
Light bulbs give a visual indication if all is working properly without smoking the scrs, Just in case there is a wiring or component fault.
I used to work on Oil Drilling SCR motor controls, But we are working on a pump motor here.
But the same theory applies.
Maybe a meter with 100+ foot test leads would make for a better test.
Sure would not want to mention shorting the conductors together for testing continuity if a light bulb is not allowed.
Don't pay someone to do a job fast, when you can do a half-fast job yourself.
Maybe another example would be easier to visualize. Take an old fashion string of Christmas tree lights... the kind where the bulbs are in series... one burned out bulb and none of them light. Pull out the last bulb in the series. Check the voltage sequentially at each good bulb and they should all read close to full voltage because there is no current to divide the voltage. Of course YMMV depending on the impedance of your voltmeter.
If the pump didn't run, he measured 120vac with no load, then it went down to 62vac with a load, that would indicate one thing, but if it reads 62vac without a load and it reads full voltage on the other end of the wire, no load is required to further test this...there's a problem in the circuit somewhere. For all practical purposes, a modern DMM is effectively an open circuit. As part of a voltage divider circuit, it can become critical in an electronic circuit, but seldom is a factor in a power circuit. Now, if he also got 62vac at the breaker, that would be telling - indicating the breaker was bad.
Jim DeBruycker
Important note - I'm not a pro
Retired Defense Industry Engineer
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