High current on neutral with a balanced load

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Do you have any surge protectors on your circuits? You might try unplugging them to see if that has any effect on the current waveform.
Also, if you have a whole house surge protector that's wired in (not the kind that looks like a circuit breaker) then try putting your current probe on each wire of the protector to see if any significant waveform is present.
I had a thought that maybe a defective surge protector could be drawing current near the peaks of the voltage waveform and thereby cause the sharp peaks in the current waveform on phase B. Although if that was happening I'd expect the surge protector to get hot and eventually burn out.
 

McLintock

Senior Member
Location
USA
Occupation
Electrician
The clamp I got does measure DC as well. It is a TA019 from the same company as my scope. Yesterday I did in fact see some DC components on my scope, but it must be intermittent because it was not present while I measured today. I was specifically looking for it since you mentioned it the other day. I'll keep monitoring it to see if it shows up again and I will ask the engineer about it as well. What could cause that? Seems really strange. Also, should the current frequency be 60hz just like the voltage frequency? I was seeing some fluctuation. It spiked a few times, the highest being 72hz for a split moment then returned to bouncing up and down between 59hz-61hz. It may not matter but figure I should ask anyways.
Do you have anything with a DC motor, like a garage door opener?


“ shoot low boys their riding shetland ponies”
 

kwired

Electron manager
Location
NE Nebraska
Do you have anything with a DC motor, like a garage door opener?


“ shoot low boys their riding shetland ponies”
GDO's only operate for maybe 10-15 seconds at a time.

Not that they can't introduce any problems, but you would need to operate them while monitoring the o-scope to see what their impact may be.
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
Do you have any surge protectors on your circuits? You might try unplugging them to see if that has any effect on the current waveform.
Also, if you have a whole house surge protector that's wired in (not the kind that looks like a circuit breaker) then try putting your current probe on each wire of the protector to see if any significant waveform is present.
I had a thought that maybe a defective surge protector could be drawing current near the peaks of the voltage waveform and thereby cause the sharp peaks in the current waveform on phase B. Although if that was happening I'd expect the surge protector to get hot and eventually burn out.
No surge protective equipment here. I am posting some new findings
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
Here is an update. These wave forms were captured at my neighbor's home who shares our transformer. It appears that he has the same current harmonic distortion as me.
 

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jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
This leads me to believe that the root of this issue is not within my home. Is there any possibilty of that being the case? I understand that current harmonics are generated by the load, but is there any possible way of something upstream of the load to create issues like these without clear voltage distortion?
 

Julius Right

Senior Member
The absolute values of the two currents are close but the power factors are different. For instance, I1 20.1 A cosfi=0.8 but I2=20.3 A cosfi=0.957.

The real part of I1=16.08 A and the reactive -12.06 [absolute=20.1]

The real part of I2=-19.426 A and the reactive +5.89 [absolute=20.3]

The real part of Io=-3.346 A and the reactive -6.17 [absolute=7.018]
 

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jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
The absolute values of the two currents are close but the power factors are different. For instance, I1 20.1 A cosfi=0.8 but I2=20.3 A cosfi=0.957.

The real part of I1=16.08 A and the reactive -12.06 [absolute=20.1]

The real part of I2=-19.426 A and the reactive +5.89 [absolute=20.3]

The real part of Io=-3.346 A and the reactive -6.17 [absolute=7.018]
Thanks for doing the math. Does this give you any ideas on what could cause this? Also, the engineer I am working with thinks we might having a failing buried cable. We are discussing megging from the transformer to the meter.
 

gar

Senior Member
200917-2128 EDT

This thread is far too long without getting anywhere. There are many posts that make no sense relative to the problem.

The problem and experiments are not described clearly.

I have only intermittently read some of the posts.

Apparently we have a single phase system with a center tapped secondary from the power company. Really a two phase source when viewed relative to the center tap. We can expect the power transformer center tap is grounded (earthed) via a ground rod at the transformer. Then three wires come from the transformer to the main panel. At the main panel the neutral wire is again grounded (earthed).

We need to know if the Pico common (shell of the BNC connector) has a DC path to the EGC of the AC power cord to the computer. If it does, then this has to be opened.

I suggest that the AC neutral at the main panel be used as the scope common reference.

We need to know what is being used for current transducers. Coordinates on plots need proper labeling.

The wiring to the water pump needs to be completely opened.

With the main panel disconnect open we need to see the voltage waveforms of each hot to neutral, the EGC to neutral, and a screw driver somewhere in the yard to neutral. Also separately the currents in each hot, and neutral coming into the meter, and the grounding wire to the meter ground rod.

This is the starting point.

.
 

gar

Senior Member
200920-2041 EDT

Since my post, numbered #196, of several days ago there have been no additional posts.

So I will continue.

If the voltage waveform at the main panel is clean and smooth with the lower portion a good replication of a sine wave, and the top a somewhat rounded off sine wave peak, then I don't believe that the high frequency ripple seen in some of the current plots results directly from the power company. In power company voltage plots I made at my home back around 1960 the sine wave was very good. Starting around 1980 with the advent of personal compiters with capacitor input filters in the DC power supply there began a gradual rounding of power line peak voltage.

With voltage and current measurements made at the main panel being clean, and as expected in shape and value with the main breaker open, then open all branch breakers, and close the main breaker. There should be no change in current values (zero), and voltage waveforms and magnitudes.

Pick a 120 V circuit with no load turned on. Connect a 1500 W space heater to this circuit. This will place a linear resistive load of about 10 A RMS on the circuit. The current waveform should replicate the applied voltage waveform. This will provide some verification of your instrumentation.

Turn this breaker off. Then one at a time turn on and off a breaker until you fine a circuit with an abnormal load current. Somehere you have one or more very non-linear loads.

Report what you find.

.



, en
 

jhardy13

Member
Location
Joplin Missouri
Occupation
Industrial Engineering student
200917-2128 EDT

This thread is far too long without getting anywhere. There are many posts that make no sense relative to the problem.

The problem and experiments are not described clearly.

I have only intermittently read some of the posts.

Apparently we have a single phase system with a center tapped secondary from the power company. Really a two phase source when viewed relative to the center tap. We can expect the power transformer center tap is grounded (earthed) via a ground rod at the transformer. Then three wires come from the transformer to the main panel. At the main panel the neutral wire is again grounded (earthed).

We need to know if the Pico common (shell of the BNC connector) has a DC path to the EGC of the AC power cord to the computer. If it does, then this has to be opened.

I suggest that the AC neutral at the main panel be used as the scope common reference.

We need to know what is being used for current transducers. Coordinates on plots need proper labeling.

The wiring to the water pump needs to be completely opened.

With the main panel disconnect open we need to see the voltage waveforms of each hot to neutral, the EGC to neutral, and a screw driver somewhere in the yard to neutral. Also separately the currents in each hot, and neutral coming into the meter, and the grounding wire to the meter ground rod.

This is the starting point.

.
Okay I tested most of what you asked for in post #196. I will try to keep everything as organized as possible so it will be easy to follow.

To address the DC components discussed in previous posts, this was a result of not zeroing the PA-9 and ammeter probe before recording data (I am still learning). There are no DC components now.

I measured each hot to neutral, EGC to Neutral, and an unbonded reference to neutral 15ft from the bonded ground rod. I am attaching each photo below. The isolated reference is an 8ft ground rod out in our yard not bonded to anything. I drove it in myself.

What I found is that there is voltage on our EGC and neutral that can only be seen when measuring from the isolated reference. This voltage fluctuates between 1v to 5v but on average it stays around 1.6v and it has a lot of distortion and high frequency noise as well as notching. I also measured both hots to the isolated reference and this shows that there is a voltage difference between the hots that is directly impacted by the amount of voltage on our EGC. This EGC/Neutral voltage is present with every breaker in our main panel turned off including the 200amp breaker and the breaker that powers our shop, so that should eliminate any possibility of it coming from one of our hots.

This leads me to believe this voltage is entering my home on the mains neutral and is affecting my circuits. It can be seen on everything bonded to the mains neutral which includes all of our circuit neutral wires, ground wires, and even our garage door and the rails it rolls on. Just a reminder, we share our transformer with one neighbor and a well pump that has its own meter out on the transformer pole.
 

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mivey

Senior Member
1.6 volts sounds like normal neutral to earth (NEV) voltage to me. Pretty common on utility systems and nothing to worry about. The 1 to 5 volt swing doesn't sound unusual either.
 

oldsparky52

Senior Member
Hi, I have run into a strange issue and can't seem to find any good information on this so I am hoping someone here can help me understand how this can happen. We have been having some mild electrical issues in our home ranging from flickering lights to computer hardware damage. We have had 2 electricians out to check the electrical wiring in our panel and everything seems to check out. We then had our electrical provider out to check the wiring in our meter base and the guy they sent said all the wiring looks good, but he also measured the current on both of our hot legs and on our neutral and discovered that our neutral current is not equal to the difference of the two hot legs. I spoke to our electrician again and he told us to get both hot legs to 20 amps and check the neutral current again. I got phase A to 20.1 amps and phase B to 20.3 amps and our neutral current was still showing 7 amps. Clearly something isn't how it should be. So my question is how is this possible?
You guys are way more educated than I am, so ... if I make you laugh, don't insult me too hard.

It seems to me that the OP has gotten way off track. While it's intriguing to see all the different wave forms, the original problem seems to have either disappeared or has been put on the back burner.

If the power company has a deteriorating neutral in their distribution system, there can be current flowing through their neutral to a very well grounded house panel because the earth is a parallel path for the distribution system neutral.

Jhardy13, did you ever check for a deteriorating neutral coming into your service by checking voltages between L1/N, L2/N, and L1/L2 while unloaded and then again loading just one L?

Let me share this story with you. The PoCo service man showed up at my neighbor's house one day. Being the inquisitive guy I am, I asked my neighbor what was going on. They said they were having some light dimming and flickering problems. The tech checked the voltages and said everything is fine. Well me being me, ... I asked if he could hold on for a minute (he was packing up to leave). I had my neighbor turn on a hair dryer while I was watching voltages and one L went up while the other went down when measured to N and L/L was stable. I told the tech that they had a neutral going bad and everything is not okay. He argued a little but went to his truck and called his supervisor.

He came back with what he called "the beast". Plugged it into the meter socket, did some testing, then told my neighbor they had a neutral problem and a digging crew would be out to find the problem. It turned out there was a splice (that was deteriorating) near the street and they were able to repair it that day.

I had a marina one time that had a voltage between the waterway and the ground of the electrical system. The only way to get rid of that voltage was to disconnect the PoCo neutral. This told me the PoCo neutral had enough VD that a couple of volts developed between the waterway and the PoCo neutral.

Electricity takes all paths.

So, being the dummy I am, I would check voltages while loading one L, and I would check for current on the PoCo neutral with all breakers off. If there is current on the PoCo neutral, then I would try to determine if it's going to ground through the GEC or if it's going to ground through the well connection.

Flickering lights and computer damage are typical signs of a deteriorating neutral. I think this has been covered already, but since this thread keeps going I thought I might repeat some of these things. Smart people sometimes overthink things. Sometimes.
 
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