# Voltage drop in underground cable

Discussion in 'Electrical Forum discussion & Blog' started by silverfox52009, May 16, 2012.

1. ### silverfox52009New Member

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I have a problem with the underground wire feeding my cabana I run a 110 volt pump to water my lawn as I am on a river ,I have done this for the past twenty years . This year I plugged in the pump and nothing so I removed the gfi receptical and put my tester on the wires comming out of the ground and got a reading of 62 volts. I then went to the panel and tested from the breker to neutral and got 120 volts.I am wondering if maybe something has bitten through the neutral wire ? Is this possible I would appreciate any advice you can give thanx in advance Fred

2. ### jadnashuaRetired Defense Industry Engineer xxx

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A loose or corroded connection anywhere on the run might show up as a low voltage at the end. Does the cable have a ground wire? What's the voltage between hot and ground?

4. ### ActionDaveElectrician

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My bet would be a break in the wire underground somewhere.

5. ### silverfox52009New Member

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yes it does have a ground wire and the voltage between hot and ground is the same 62 volts

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A high resistance on the feed would result in a voltage drop that is commensurate with the current draw. A high impedance voltmeter testing a circuit that is not under load usually does not give a true picture since it in and of itself, provides no current draw.

My guess is that along with the high resistance, there is also a short to ground.

7. ### hjModerator & Master PlumberStaff Member

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quote; yes it does have a ground wire and the voltage between hot and ground is the same 62 volts

That would imply a problem with the "hot' wire, not the neutral.

8. ### DonLJack of all trades Master of one

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I don't think that is correct.

hj is correct.

A short reading from Ground to Neutral is normal, at the source.

The open is on the Hot leg, if there is a open.

Or if the pump is trying to run, it may be locked up and not running. that could explain the voltage drop.

You can use a light bulb for better testing under a small load.

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If he removed the receptacle I very much doubt there is any load on the circuit beyond that of the tester alone.

10. ### DonLJack of all trades Master of one

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Very True.

But if their was a short then the breaker feeding it should trip.

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Depends on your definition of a short. There is a good chance you could tie the hot to a ground rod and it won't draw enough current to trip the breaker. I've seen where a bad heat shrink splice on a pump would leak current to the earth through the water. I've also seen bad elements in a water heater leak current through the water.

12. ### ballvalveGeneral Engineering Contractor

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If its not in conduit, its time for a new run.

13. ### jwelectricElectrical Contractor/Instructor

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This is a very bad idea and very dangerous.
Don Be warned that another post suggesting the use of a bulb for testing will be deleted

14. ### DonLJack of all trades Master of one

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Why is that ?

It is safer than using the Pump that is in water.

15. ### jwelectricElectrical Contractor/Instructor

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Ground fault is a connection between the neutral point of a power supply and one of the phase conductors.
Short is a connection between two phases or a phase and the neutral point without load other than the conducting path.
Open circuit is a break in the path from the source back to the source be it in the phase conductor or the neutral conductor.

In order for current to flow there must be a source and a path from one potential of the source to the other potential of the source.
Current CAN NOT leak out of this path and must always return to its source.

The power companies connect the neutral point of their systems to earth and we also connect the neutral point of our systems to earth. The idea that current is trying to get to ground or earth as ground is defined by the NEC, or that current is â€œleakingâ€ to earth is only founded in the amount of resistance there is of the earth in that area.

Letâ€™s be fair and say that the resistance to earth is as low as 100 ohms there could only be 1.2 amps of current flowing through earth. The true resistance of earth would be better than 500 ohms just about anywhere you would want to test. Now the current is less than Â¼ amp. The resistance in my neck of the woods between my service and the transformer that supplies me would be more like 1000 ohms and now only a little more than a tenth of an amp will flow through earth back to its source.

We would hope that there is an equipment grounding conductor connected to the exposed metal of the pump motor and now we have only the resistance of the equipment grounding conducting path back to the neutral point of the power supply and at least 125 amps will flow back to the source causing the overcurrent device to open.

Knowing this, should a well pump or water heater for that matter is leaking current and it is installed properly then this leaking current will be carried back to its source through the equipment grounding conductor. It will not be leaking through the water to earth or to be correct very little will ever see the earth path back to its source.

A little test is to connect one side of your car battery to a driven ground rod and see how dead the battery is after a couple of hours, days, weeks, or however long you want to test it. See how much current leaks out of it to earth.

Last edited: May 18, 2012
16. ### jwelectricElectrical Contractor/Instructor

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Don, Telling untrained people to use a light bulb for testing purposes around electricity is dangerous. If you don’t see the danger there then you need a safety class yourself.

I have explained the dangers to you before and will not let this thread to be high jacked into a safety course.
If you don’t truly understand the dangers then start a new thread with any question you feel needs addressing.

17. ### jadnashuaRetired Defense Industry Engineer xxx

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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.

18. ### DonLJack of all trades Master of one

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I agree. It could just be a bad or dirty breaker or a splice.

As always , Be careful playing with electricity.

19. ### jwelectricElectrical Contractor/Instructor

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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.

20. ### hjModerator & Master PlumberStaff Member

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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.

21. ### DonLJack of all trades Master of one

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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 ?