Abnormal voltages to ground

[iwire]

170104-1594 EDT

Continuing with my comments on voltage measurement.

To track the path of a circuit greater sensitivity is obtained by measuring the voltage drop along the neutral relative to the potential of the EGC bus at the main panel.

You can get the main panel EGC reference in two ways.

One is to run a wire or extension cord from the EGC bus at the main panel to wherever you want to make a voltage measurement relative to said main panel point.

The second way is to use the EGC wire at the measurement point. This second way requires that the EGC is intact back to the main panel, and that no current is flowing in the EGC. For this thread this is not a good assumption.

This approach of measuring the neutral voltage relative to the main panel EGC bus is only going to be seeing small voltages normally. Thus, I can possibly use a 100 W incandescent rather than a 1500 W heater as the load.

My following sample voltages are read with a Fluke 27 with no filtering. Ideally I should have a narrow band 60 Hz band pass filter at the meter input.

At my main panel the Fluke reads 0 or 1 mV between the Sq-D EGC bus and the neutral bus. At my work bench area, about 50 ft away, the reading is about 3 mV. Also about 3 mV between an extension cord EGC and the bench neutral.

With a 100 W lamp load at the bench area at the lamp outlet neutral to EGC is about
120 mV. Going to a point on the benches closer to the wall the reading is about 50 mV. There are three benches with cascading of power from one to another, not short cords. The lamp was located at the middle bench. I use #8 for 50 ft from the main panel to the bench area. Without making an actual measurement I estimate the #8 drop at about 25 mV.

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Wow, thanks for missing my message and proving my point. :roll::huh:hmy:

 

[jaggedben]

Sounds a lot like an open or high resistance connection in the neutral feeding those receptacles.
The ground (EGC) path sounds solid, and there is no good reason for the ground to be offset one way or the other from neutral if only the ground is open.
With an open neutral, putting a line to neutral load on one phase will offset the neutral to the point where it will blow line to neutral surge protectors on the other phase.
To my mind that is the first thing an experienced electrician would check for on a service call given those symptoms.
If that has been ruled out, the next likely problem would be two simultaneous faults: an open ground and a short or high leakage from one of the lines to ground, possibly in connected equipment.
Given that line to neutral has been checked (under load???) to be 120 at each receptacle the double fault becomes more likely.
A power strip probably has voltage limiters from phase to ground as well as or instead of phase to neutral.

From the OP's description, the red part is anything but obviously true.

 

[gar]

170105-1353 EST

iwire:

I did not miss your post, but so far the KISS approach has not seemed to work.

Is it simpler to open boxes and outlets all over the place to look for the problem, or to make some well chosen measurements to point you in the direction of the problem?

Consider a 5 tube radio, a rather common device in the past. And moderately simple if you understand how one works. You are told it does not work. How do find the problem? Just guess and start replacing parts, or use some more systematic approach?

.

 

[kwired]

170105-1353 EST

iwire:

I did not miss your post, but so far the KISS approach has not seemed to work.

Is it simpler to open boxes and outlets all over the place to look for the problem, or to make some well chosen measurements to point you in the direction of the problem?

Consider a 5 tube radio, a rather common device in the past. And moderately simple if you understand how one works. You are told it does not work. How do find the problem? Just guess and start replacing parts, or use some more systematic approach?

.

Today's service people - a little of both. Systematic approach may narrow things down to certain items, they still don't know how those items work and then just start throwing parts at it hoping one of them will make it work.

 

[GoldDigger]

Today's service people - a little of both. Systematic approach may narrow things down to certain items, they still don't know how those items work and then just start throwing parts at it hoping one of them will make it work.

An old joke from the days of minis and mainframes: (Highlight to read the answers)
Q: How many DEC (Digital Equipment Corporation) Field Service Engineers does it take to change a flat tire?

A: Five. That's four to lift up the car and one to change tires until he finds the one that is flat.

Q: How long does it take?

A: That depends on how many flat tires they brought with them.

 

[Barbqranch]

170105-1353 EST



Consider a 5 tube radio, a rather common device in the past. And moderately simple if you understand how one works. You are told it does not work. How do find the problem? Just guess and start replacing parts, or use some more systematic approach?

.

Reach around to the back of it, and gently touch each of the tubes. The cold one is dead.

 

[gar]

170105-2005 EST

Barbqranch:

A very good approach for a set with a transformer and paralleled tube heaters. Good for couple reasons, one requires no additional equipment, and second tubes were probably the most likely component to fail.

If the average tube life was 1000 hours, then on average you can expect the 5 tube radio to fail because of a tube every 200 hours.

If the set was AC/DC then, a slightly different approach would be required, but still directed at tubes.

In the 1940s I heard stories about how a final inspector at Zenith, on a car radio line, would troubleshoot non-working units. His ears, fingers, and a screwdriver were his test instruments. A vibrator could be heard, noise or or an actual signal could be heard in the speaker, the screwdriver could test for voltage, and the screwdriver or fingers could be signal generators.

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[n1ist]

Consider a 5 tube radio, a rather common device in the past. And moderately simple if you understand how one works. You are told it does not work. How do find the problem? Just guess and start replacing parts, or use some more systematic approach?

You take the tubes down to the drugstore and use their tube tester...

 

[gar]

170105-2351 EST

n1ist:

There are persons that troubleshoot a system by pondering all the possible things in the system that could cause the problem. This is very inefficient compared to making measurements within that system to point in the direction of the problem. I really don't want to get into radio troubleshooting, but it still serves as an illustration.

Usually you can quickly determine if a tube filament (heater) has failed by observation. If a tube filament is visible, then it is unlikely that a tube is totally bad. Thus, probably does not cause complete failure of the radio. In this case why take tubes out and go to the drugstore? Search for the problem somewhere else.

I had quality control come to me one day on a differential assembly line and said that pinion position was jumping around and they were going to do a statistical analysis to try to spot the problem. That was the wrong approach.

The first thing to do was to see if the pinion position machine was working correctly. In a matter of minutes after I went to the machine I determined that it had excressive variance on a repeat cycle on the same part.

This variation was in the range 0.000,8 of an inch and I would expect no more than about 0.000,3 variance on this machine. Looking at various components that were visible and can contribute to gaging variation nothing was obvious. Thus, my best guess was a failing thrust bearing in the machine. This is not a visible component, and about a 3 hour repair.

So production continued until the shift end when the repair was done and this proved the thrust bearing to be the problem.

When I could go to the machine and quickly determine that there was a machine problem it made no sense to go looking for some sort of part problem. No statistical analysis was needed.

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[iwire]

170105-1353 EST

iwire:

I did not miss your post, but so far the KISS approach has not seemed to work.
.

How do you know it has not worked? The OP has one post in this thread to your six posts

Please, let the OP respond before continuing to take over this thread.