240 One Leg Voltage Bleed

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Clearwater

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Scottsdale, AZ
Have a 240v circuit (Red, Black, White, Ground) running between main panel 30amp breakers and subpanel (103 ft away using a buried cable (#4 wire) running through attic and conduit outside to sub-panel). Vltage was OK until a lot of rain which could have cause some swelling of infrastructure or ground sepage. Did a visual check for leaks or wet spots and found none. Also dug up duried run and found no damage or wetness.

Issue is that one hot leg is 123v while the other is 45v instead of 123v. Disconnected Red, Black, and White legs and performed an Ohms test. Got zero between Red & Black and zero also between white and red and white and black.

Disconnect Red at both ends and checked voltage. Black was 123v and Red 45v. Also did Black test with same results. I had also checked all connections for corrorsion and found none and tighten all conections... no voltage change. With the circuit off, I got around .28v and .19v on the legs.

I verified my testing equipment on another circuit too.

Anyone got a good idea what could be causing the voltage drop/bleed and the best way to correct it?

Thank you.
 
Having a hard time following. Post these measurements, for both ends of the cable:
Feed end:
black to red
black to white
black to ground
red to white
red to ground

Far end:
black to red
black to white
black to ground
red to white
red to ground
 
mdshunk said:
Having a hard time following. Post these measurements, for both ends of the cable:
Feed end:
black to red
black to white
black to ground
red to white
red to ground

Far end:
black to red
black to white
black to ground
red to white
red to ground
Click to expand...

My preliminary guess is that your red is rotted off underground and the 45v measured is phantom voltage.
 
Readings

Readings

At the main panel, the circuit breaker reading was 123v on both red and black. At he juntion box (100' from mail panel) before burial (cable looped only), removed some sheathing and did a pin test and got the voltage drop same as the sub panel measurements. They was no difference in the Red Black to White or Ground measurements. Checked both the ground wire and White for proper connections to the main panel and sub panel.

Note: I'm not currently at the job site so I don't have exact measurements. Noted nothing significant except for valtage drop.
 
mdshunk said:
the 45v measured is phantom voltage.
Click to expand...

45v struck me as phantom voltage as well.

ENGINEERING DEPARTMENT



BULLETIN



No. 88

October 1998

Revised February 2003

Phantom Voltages


This Bulletin is intended to address the occurrence of so-called ?phantom? voltages, a phenomenon detected during the testing electrical conductors in the field.



Due to the high impedance of measuring instruments, a voltage reading may be detected on open conductors where there is no hard electrical connection to a voltage source. Conductors that are installed in close proximity to one another, and are capacitively coupled to each other, can cause this a.c. voltage reading. Such a reading could be 2 or 3 volts, or it may be as high as the voltage on the adjacent conductors. This is what is referred to as a ?phantom? voltage.



According to Underwriters Laboratories Inc., this can be a harmless reading and can be caused by the high input impedance of the measuring instrument, which places very little loading on the circuit under test. The capacitance is increased as the length of the run is increased. A 50-foot run may produce a pronounced capacitance effect whereas a one-foot sample may not produce any. This effect has such high impedance that, although a voltage can be detected, there is little or no available current.



Since the ?phantom? voltage is a physical phenomenon involving very small values of capacitance, it cannot energize a load or cause physiological damage to a person.



Care must be taken to be sure that the voltage reading is a phantom voltage, which is caused by improper use of high impedance multimeters, and not as a result of a cable defect or improper installation, which may result in a shock hazard.



In order to help minimize the likelihood of reaching a wrong conclusion from this phenomenon, NEMA recommends the use of a UL Listed or OSHA-approved low impedance multimeter in place of a high impedance multimeter or other high impedance measuring device for testing on open conductors where there is no hard electrical connection. Without a low impedance measuring device, a high voltage reading is an inconclusive indication of possible faults in the cable.



Distribution List:

Standards and Conformity Assessment Policy Committee

Codes and Standards Committee

NEMA Executive Staff
Click to expand...
 
Phantom Voltage

Phantom Voltage

I would agree, except the two 240v motors connected to the sub panel would not start. Only 120v light and circuit worked. The motor circuit breaker(s) measured 120v and 45v to ground.
 
Clearwater said:
I would agree, except the two 240v motors connected to the sub panel would not start. Only 120v light and circuit worked. The motor circuit breaker(s) measured 120v and 45v to ground.
Click to expand...

Seems like you lost a leg and the lighting is on the good one.
 
Clearwater said:
I would agree, except the two 240v motors connected to the sub panel would not start. Only 120v light and circuit worked. The motor circuit breaker(s) measured 120v and 45v to ground.
Click to expand...

Which to me sounds like verification of the loss of one leg or phase.

The leg or phase with 45 v reading is not continuous all the way back to the source.
 
Lost Leg

Lost Leg

Although the potental lost leg can be duplicated by both switching the Red and Black legs at the main panel. If either leg is left disconnected, that leg indicates the drop.

I did the test switching the circuit breaker legs at the main panel too and left the sub panel legs disconnected to isolated any circuit breaker issues. When all is connected as normal, the loss is on the Red Leg.
 
Help, still looking for an answer

Help, still looking for an answer

Although some have responded with some ideas. The lost leg doesn't seem logical given the know facts. The voltage drop moves to the line disconnected. Has a zero ohms reading across all lines indicating no corrosion.

Please review the problem and my feedback. This one has me stumped as I cannot locate what has caused the voltage drop... enough that the motor won't start. I've had this happen in 12vdc systems due to corrosion but never in 240vac.

Appreciate any guidance you can give me or a reference to a document that would describe the problem and its correction.
 
Clearwater said:
Although some have responded with some ideas. The lost leg doesn't seem logical given the know facts.
Click to expand...

Lets see, you are a Data Center Design Engineer and mdshunk, frizbeedog and I are electrical troubleshooters each with at least 20 years in.

Yeah your right, the obvious is not logical. :grin:

Or your just not describing the situation accurately
 
Clearwater said:
Appreciate any guidance you can give me or a reference to a document that would describe the problem and its correction.
Click to expand...
The document is in my head, and it's entitled "The Voice of Experience". The corrective action is to pull a new red or replace the cable if it's a cable assembly. This isn't some exotic problem you're having. It's a pretty textbook situation.
 
Clearwater said:
Although some have responded with some ideas. The lost leg doesn't seem logical given the know facts. The voltage drop moves to the line disconnected. Has a zero ohms reading across all lines indicating no corrosion.
Click to expand...

How did you measure that? What kind of meter?

Meters suitable for use in a data center are not suitable for use on AC voltages.

Please review the problem and my feedback. This one has me stumped as I cannot locate what has caused the voltage drop... enough that the motor won't start. I've had this happen in 12vdc systems due to corrosion but never in 240vac.
Click to expand...

Most likely all the guys here are right -- L2 (that red wire) is gone and the voltage you're reading on the other end of the cable is actually inductive or capacitive coupling between the leftover part of L2 and L1 (black). If the wire was direct burial (which it sounds like), odds are the wire broke somewhere along the line.

If you really are a data center design engineer, this is the same problem as running data cables (especially the old RS-232 stuff) over top of power, and especially 277V cables that feed most data center lighting. You should have experience troubleshooting data cables that have noise. Well, this is the same problem, except it's not a data cable.

Appreciate any guidance you can give me or a reference to a document that would describe the problem and its correction.
Click to expand...

Take ptonsparky up on his offer to send an apprentice out your way.
 
lost leg

lost leg

I work with burried cable a lot and can tell you one or more legs is damaged .It will give all kinds of crazy readings when the conductors are exposed to wet dirt. I dont understand part where you said you dug up the buried section. How could you dig up 105 ft of wire without damaging it?
 
Would You Believe!

Would You Believe!

I didn't dig it up. I just uncovered the conduit (20') the cable was in from the structure to the sub-panel to ensure no damage was apparent... found none nor dampness enought to have entered the buried conduit (nonconductive).

Yes I very familiar with noise and shielded cable issues especial when using them to support 10-BaseT networks.

The surprise is that I decide to cut the legs at the junction box just before it is buried in the conduit and run a test. The measurements to the main panel were all right on at 123v. I then used splices to reconnect the three legs and ran a test from the sub-panel. Again just as they should be 123v... motors ran.

Now the only thing I feel I did was to take a tight loop out of the cable by cutting the cable at the top of the loop and making it a nonstressed run in the juntion box.

Now the concern I have is could that loop have been the cause? Or could their be another area where the circuit is rubbing up against another circuit and that swelling from mositure or mosture itself was the cause of the drain? What baffles me even more is that the low volatge leg could be transferrred between Red and Black and the condition was present just before I cut the cable.

Hopefully it is corrected and wet weather doesn't make it happen again. Should it, the only economial way to make a new run of the circuit is to go burial all the way... overhead is a sealed area and would require a lot of sheetrock openings to make the pull... owner says no to that. lol

Feedback is greatly appreciated as I don't feel comfortable about the fix.

The offer to send an apprentice out to diagnose this problem is greatly appreciated! Although it most likely needs to wait for a reamergance of the drop voltage... please give me an easy way to contact you should it happen via clearwater@mail.com

Thank you
 
Bob warned me earlier, so I wont partake in this. #2, the name FLUKE should of been left out of it. #3, I need another cold one, Kool-Ade that is:grin:
 
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