Understanding current on L1, L2 and N

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Old 08-29-20, 05:03 PM
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Understanding current on L1, L2 and N

Setting up a generator interlock and reading some of the threads here made me aware of load balancing. Out of curiosity, I checked main panel (on utility power) and I'm getting the following readings (using clamp-on ammeter):
L1: 5.4A
L2: 2.8A
N: 3.0A

Why is neutral showing 3.0A and not the difference between L1 and L2?

Checked again a few minutes later:
L1: 5.1A
L2: 2.8A
N: 3.8A

The difference between L1 and L2 amps decreased, but neutral amps increased. Why is that?
 
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Old 08-29-20, 06:06 PM
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What is ground current? Rod plus water pipe
 
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Old 08-29-20, 06:17 PM
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current changing on the lines as you move your meter between them?
meter accuracy?
Possible ground current?
If you can clamp both hots together and see if that equal neutral.
 
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Old 08-29-20, 06:20 PM
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Many electrical loads have reactance as well as resistance. In capacitors, current leads voltage by 90 degrees. In inductors, voltage leads the current by 90 degrees. In resistors there is no phase shift between the current and voltage. The clamp-on ammeter reads the current in the wire, independent of the phase shift that exists between the current in the wire being measured and the other 2 wires. If the currents were added vectorially, they will balance. You need a simultaneous plot of the 3 currents or a 3 channel oscilloscope to see the phase shift between currents in the 3 wires.
 
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Old 08-29-20, 08:36 PM
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No ground rods yet. Am planning to install in next couple of days.

Amperage does jump around a bit, so the readings are different than if I could read all wires simultaneously. Can't clamp L1 and L2 together.

Took some more amperage measurements, and included ground to water pipe. Happened to be with AC and dishwasher running.
L1: 27.9
L2: 38.0
N: 3.5
G: 7.1

With AC off and dishwasher running:
L1: 2.5
L2: 10.9
N: 4.1
G: 5.4

So that makes a lot more sense when I add N+G and compare that to abs(L1-L2).

L1 voltage to panel ground: 122.1
L2 voltage to panel ground: 120.0

Why is there current on the GEC? Maybe a reversed outlet somewhere?

How to track down the source? Shut off all breakers and start turning on one at a time, and running a load on that circuit before turning on the next breaker? Could it be the service neutral has a weak connection between panel and transformer? How could I rule that out before trying to find a circuit with an issue?
 

Last edited by cartman; 08-29-20 at 08:53 PM.
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Old 08-29-20, 08:50 PM
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And with AC on, dishwasher off:
L1: 29.6
L2: 28.4
N: 1.8
G: 1.7

Seems like much less current flowing to ground with dishwasher off. Maybe an issue with the wiring at this appliance? Or since this is a 120V appliance, maybe this suggests an poor neutral connection?
 

Last edited by cartman; 08-29-20 at 10:42 PM.
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Old 08-29-20, 09:20 PM
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You are doing or reading something incorrectly. There is never any current on the ground wire.
The only time there would be current on the ground wire was during a direct short from hot to ground.

If you are seeing current on the ground wire..... you need to inform the power company of a problem with the neutral. Your service is not supposed to be supplying the neutral buss with ground.
 
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Old 08-29-20, 10:00 PM
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You are doing or reading something incorrectly. There is never any current on the ground wire.
The only time there would be current on the ground wire was during a direct short from hot to ground.
That makes sense to me. But a direct short should trip a breaker.

Those ground amperage readings were made with the ammeter around the wire that connects the neutral bus (main panel, first disconnect) to the water pipe. Just checked now and it's 1.4A.

If you are seeing current on the ground wire..... you need to inform the power company of a problem with the neutral.
Trying to understand this - so if there's a problem (loose connection) somewhere in the path of the neutral between my panel and the transformer, then it would make sense that some current would flow through ground to the transformer, correct?

What if a neighbor had a problem with his neutral? Could current flow from his ground to my ground to my neutral to the transformer? But I guess that wouldn't account for the readings I'm getting on L1, L2 and N wires, where abs(L1-L2) amperage is not very close to N amperage.

Your service is not supposed to be supplying the neutral buss with ground.
I don't follow this. Could you rephrase please?

Is there a way for me to determine definitively that the problem is a weak/loose neutral connection between my panel and the transformer?

Do the voltage readings I posted earlier comport with a problem with the neutral connection? I thought I read somewhere that neutral problems can cause problems with voltage on the two 120V lines, like too much one line and too little on the other.
L1 voltage to panel ground: 122.1
L2 voltage to panel ground: 120.0
 
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Old 08-29-20, 10:42 PM
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The power company supplies you with 120/240v power. You should be able to connect that directly to your panel with no ground connection needed. The power company neutral is supposed to be at 0v potential. Your neutral is not at 0v potential. Your ground is attempting to bring the neutral to 0v. .

This is a vicious problem. I know an electrician that got hurt changing his own service. His cold water ground was supplying his house and his two neighbors with neutral. When he pulled the ground he got walloped. Young guy.... knows better now.

There is supposed to be a ground rod at every telephone pole where there is a transformer. There are many that are missing the ground rods or the wires have broken off.

Don't mess around..... call the power company.
 
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Old 08-29-20, 11:13 PM
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What should I tell them?

If their neutral is OK, will they disconnect my service until I have an electrician check neutral between panel and weatherhead and then get any work he does inspected?
 
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Old 08-30-20, 06:32 AM
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I have seen an el water Heater defect cause ground current issues across the street. U could start with all power off at your home and insure ground current is zero. How many homes on your pole transformer?
 
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Old 08-30-20, 08:48 AM
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If their neutral is ok they will notify you of that. It's up to you to to troubleshoot further.

If you have an aerial service. Find the pole with the transformer. See if it has a wire coming down the pole to a ground rod. Just look.... don't mess with it.
 
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Old 08-30-20, 08:55 AM
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If your neighbour has a neutral issue his neutral current could be flowing out the waterline ground to the water main, your water line and out your neutral wire.
 
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Old 08-30-20, 09:25 AM
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I have seen an el water Heater defect cause ground current issues across the street. U could start with all power off at your home and insure ground current is zero. How many homes on your pole transformer?
If your neighbour has a neutral issue his neutral current could be flowing out the waterline ground to the water main, your water line and out your neutral wire.
As soon as a family member's Zoom conference call ends, I'm going to turn off main breaker and see if there is still current on GEC. At least then I'll know if that current originates from my service or a neighbor's service.

Looks like ~8 houses have service coming off pole with transformer, or poles downstream of that pole (I am downstream). I know one of my neighbors has an electric water heater.

If their neutral is ok they will notify you of that. It's up to you to to troubleshoot further.

If you have an aerial service. Find the pole with the transformer. See if it has a wire coming down the pole to a ground rod. Just look.... don't mess with it.
OK, great, thanks. I was worried that if their neutral is fine, they might pull my meter and then force me to scramble to find an electrician, get inspection, etc. What should I tell them? Something like "There is current on my grounding electrode conductor, so I think there may be a problem with utility's neutral"?

Yes, aerial service. Runs through backyards, so I can see the pole with transformer, but can't see the base of it without walking into neighbor's backyard. Doesn't the fact that I have current on my GEC suggest that the transformer is probably grounded? Or I suppose even if it was ungrounded, and the neutral is open/weak, that current would still flow on GEC, but instead of returning to source, it would energize the water pipe and local earth?
 
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Old 08-30-20, 10:07 AM
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Ok, got a chance to power down house.

With main breaker off (main panel, first disconnect):
L1: ~0.002
L2: ~0.010
N: ~0.8
G: ~0.8

With main on and all circuit breakers off:
L1: ~0.007
L2: ~0.010
N: ~1.3
G: ~1.3

1. Why is there current on L1 and L2 with main breaker off? Aren't L1 and L2 wires essentially dead ends at the lugs? And even with main on, but all CB's off, isn't the power all dead-ending at the CB's? Where is this current flowing? If it's getting to neutral, how is it getting there? Or is this due to measurement accuracy of my cheap Chinese ammeter?

2. I guess this confirms that one or more neighbors' service is using my grounding electrode (water pipe), GEC and neutral to return to source?

3. And I guess my earlier measurements showing ~5A on GEC with dishwasher (120V) on suggests that my service is also using the GEC to return to source.

4. So if multiple houses are all using ground to return to source, it seems likely that there is a loose (not fully open because then we'd all be having more obvious issues) neutral connection at the transformer?

Does my reasoning here make sense?
 
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Old 08-30-20, 06:52 PM
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For anyone. When the poco says their neutral to your home is okay. does it also mean the transformer neutral is attached to a poco ground rod?
 
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Old 08-30-20, 07:00 PM
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POCO ground rod connection has no effect on your power supply. It is just for lightning protection.
 
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Old 08-30-20, 07:05 PM
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POCO ground rod connection has no effect on your power supply. It is just for lightning protection.
Doesn't it also allow at least some current to return to the transformer in situations where the neutral connection either at a house served by the transformer, or at the transformer itself, is poor?
 
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Old 08-31-20, 05:23 AM
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Joed, please explain the current path which opens a breaker when a grounded appliance ( in off condition) has a hot to frame short?
 
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Old 08-31-20, 05:59 AM
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The current path for a short to ground inside the house is because the ground wire inside your house is connected to the neutral. It has nothing to do with ground rods installed in the ground outside your house. If you remove the ground rod from outside your house the inside protection is still there.
 
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Old 08-31-20, 06:44 AM
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Pretty clearly, the earth/dirt grounding arrangement and the wired/overhead neutral conductors are parallel paths to the the pole transformer center tap secondary. While the overhead wires are intended to carry the vast majority of neutral current, some will always flow in the ground system. When several homes are in the circuit, the earth system becomes a bit more complicated. Especially with copper water piping involved. If the homes share the very conductive piping without PVC breaking the path, then there is a low impedance path from house to house via the piping, which is likewise connected into the power neutral system. So, don't expect zero Amps of ground current in these cases with unbalanced loads. So, the real question is how much is too much. I have not seen a spec, but I would raise a flag if more than 10 or 20% of neutral current is returned via the piping system.
 
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Old 08-31-20, 08:07 AM
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2. I guess this confirms that one or more neighbors' service is using my grounding electrode (water pipe), GEC and neutral to return to source?
Related to this point, I checked with a neighbor who is on the same transformer, and his GEC to his water pipe has current on it.
 
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Old 08-31-20, 10:00 AM
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How far from the transformer are you? Longer means more neutral Resistance and losses, and more likely the ground current will be more significant. Its now really a "networked" return system, with all the secondary customers returning a collective neutral current. But, not the case for L1 and L2; those lines are actually independent for each customer. But, saying all that, the real issues surface with the piping supplying return current that should be supplied by a healthy neutral wire. So, if the neutral actually broke, these currents may be greater than the pipes can handle. Or, your neighbors are relying on your copper pipes more and more as they go PVC, carrying that fault.
 
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Old 08-31-20, 10:14 AM
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How far from the transformer are you? Longer means more neutral Resistance and losses, and more likely the ground current will be more significant. Its now really a "networked" return system, with all the secondary customers returning a collective neutral current. But, not the case for L1 and L2; those lines are actually independent for each customer. But, saying all that, the real issues surface with the piping supplying return current that should be supplied by a healthy neutral wire. So, if the neutral actually broke, these currents may be greater than the pipes can handle. Or, your neighbors are relying on your copper pipes more and more as they go PVC, carrying that fault.
I'm near the end of the run for this transformer. And yes, from what I can tell, we are all using each others grounding electrodes (namely the water pipes, not necessarily the ground rods) and neutrals to return current to transformer.

When people replace existing water pipes in their homes with PVC, are they changing the buried copper supply pipe that runs into the house? If not, then what difference does PVC piping in the house make to this 'networked' neutral effect? Isn't the current running from GEC to the water pipe and then outside the house? There is no place for current to go if it were to move along copper water piping inside the house. Meaning, it can't run from GEC bond at water pipe to my shower or sink and get to neutral. It has to go from GEC bond to water pipe outside house to water main to neighbor's water pipe to his GEC to his neutral and then to transformer, or to nearest water pipe to transformer and then through earth to ground rod for transformer. So as long as the underground pipe from water main serving this street to the individual houses is copper, it doesn't matter if the piping inside the house is copper or pvc because the piping downstream of the GEC bond isn't a path back to source. Unless I'm thinking about this incorrectly?
 
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Old 08-31-20, 10:36 AM
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Copper to PVC.... Two houses ago, I had a new septic drainfield put in. The house had all Cu tubing. Over the new field, they replaced a 15' length of 3/4" Cu with 3/4" PVC. Viola; there can now be no house to house ground current through my water system into the meter, into the mains. This one action could have resulted in a measurable increase in Neutral drop to the pole, especially at the longer distances to the transformer.
But, not likely in my case with only a 50' run of 4/0 Al neutral conductor to the actual pole transformer.

summary: the metallic underground water system is a conductor system, ultimately connecting all the neighbors neutral's together. btw, still very useful in limiting surge/lightning damage.
 
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Old 08-31-20, 11:29 AM
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If the homes share the very conductive piping without PVC breaking the path, then there is a low impedance path from house to house via the piping, which is likewise connected into the power neutral system. So, don't expect zero Amps of ground current in these cases with unbalanced loads. So, the real question is how much is too much. I have not seen a spec, but I would raise a flag if more than 10 or 20% of neutral current is returned via the piping system.
This makes sense.

Doesn't current running through a copper water pipe corrode the pipe?

Taking your point a step further, if the service neutral line was not connected to my panel, then all my unbalanced current would need to use the GEC to water pipe to neighbors water pipes to neighbors neutrals to get back to source. Now suppose all my neighbors except for one all left their service neutral lines disconnected. Now all of our unbalanced current would try to use his neutral to return to source. I suppose his GEC would get overloaded and melt down, severing the connection. And if he upsized his GEC, then maybe his neutral line would overload and melt down?

Practical limitations of wire's current capacity aside, if all the houses' unbalanced current were returning on low impedence path of copper piping to one house's neutral line, none of the houses would experience fluctuating voltage, despite having their own neutral line disconnected, correct?
 
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Old 08-31-20, 12:06 PM
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Pretty much true.

On the corrosion issue; I would not expect current THRU the tube to corrode it, just like wire. However, if there is a voltage delta from tube to ground/dirt, there could be electrolysis damage. I'm not a chemist, but I treat electrolysis as different from corrosion. Both are destructive though.

3/4" type L water tube is about 1/2 pound per foot; this gives a good measure of electrical current capability/resistance. That's close to 3/0 copper! Just so happens that 200 Amp service uses that size copper for L1, L2, and N.
 
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Old 08-31-20, 06:42 PM
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Clamp on ammeters work on the principle of a magnetic field around the wire carrying current. With the home main breaker open, there is no current, hence no magnetic field, hence zero current. Either your clamp on ammeter has inaccuracies or there is a magnetic field sourced somewhere else but strong enough to affect the ammeter. I still have concerns. with Joed's response in post 17. The diagram in post 21 shows the pole grounding rod connected to the pole transformer neutral is needed to complete the electrical circuit created by the hot wire shorting to the grounded part of the load. While the pole grounding rod connected to the transformer's neutral can provide a path for a lighting strike, it is not the only purpose as shown by diagram in post 21.
 
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Old 08-31-20, 07:18 PM
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The diagram in post 21 shows the pole grounding rod connected to the pole transformer neutral is needed to complete the electrical circuit created by the hot wire shorting to the grounded part of the load
This is not entirely accurate. The circuit is completed because the ground wire inside your house is connected to the neutral wire. When the hot touches the grounded metal parts of the device it is in effect touching the neutral and creating a short hot to neutral. Thus tripping the breaker. It has nothing to do with the rods pounded into the ground.
 
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Old 08-31-20, 07:40 PM
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POCO ground rod connection has no effect on your power supply. It is just for lightning protection.
That's not entirely correct. The power company neutral will be floating because it's derived from a transformer and needs to be earthed. It is not unacceptable to see a slight current flow on a house ground as the Poco ground may not be perfect. The problem usually occurs when the transformer has lost its ground completely and relies on the connected houses earth ground(s).

The Poco is well aware of this problem and they will come immediately and check it out.
This video explains it well...... Video
 
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Old 08-31-20, 08:17 PM
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There are transformer faults that could cause some primary to secondary voltage conduction. Fixing the secondary winding to earth reduces that risk. Nobody wants 13kV on their clothes washer cabinet. 😳. That and providing a heavy path for lightning are the big reasons for earthing the secondary side.
 
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Old 09-01-20, 11:03 AM
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The power company supplies you with 120/240v power. You should be able to connect that directly to your panel with no ground connection needed. The power company neutral is supposed to be at 0v potential. Your neutral is not at 0v potential. Your ground is attempting to bring the neutral to 0v. .

This is a vicious problem. I know an electrician that got hurt changing his own service. His cold water ground was supplying his house and his two neighbors with neutral. When he pulled the ground he got walloped. Young guy.... knows better now.

There is supposed to be a ground rod at every telephone pole where there is a transformer. There are many that are missing the ground rods or the wires have broken off.

Don't mess around..... call the power company.
I called PoCo first thing Monday morning. The guy I was speaking with said he's never heard of a situation like this. His initial reaction was that my neutral connection was bad, but then I told him I have current on my GEC even with my main breaker off, and that my neighbor also has current on his GEC. Then he was stumped. So he has created a ticket and they'll send someone out within the next several days.
 
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Old 09-20-20, 08:21 AM
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Following up on this, a few weeks after I reported the issue, PoCo sent their contractor out. They figured it was my neutral connection to the pole (which had some corrosion and wasn't great mechanically either) so they replaced the aerial drop (which was fine by me since they replaced the old bug nut connections wrapped in tape with the newer style connectors). Of course that didn't resolve it, since I reported current on my neutral even with the main breaker off, but they have their checklist of possible culprits to go through so I was happy to let them do their thing. So they were able to confirm current on my neutral even with L1 and L2 disconnected from house (i.e., no drop connection except for the neutral).

Once they reported that back to PoCo, the utility sent another crew out the next day - these guys checked the transformer and found a corroded connection (very old transformer), which they replaced. Still have current on my neutral with meter out, so they suspect it is internal wiring in the transformer, so it sounds like once they report back to PoCo, the transformer may get replaced.

For this explanation to be correct, I guess the ground rod at the transformer is connected to the transformer neutral internally, not at the external connection used by the neutral wire that runs out to the houses. That's why the water pipes provide a competing low impedance path back to source. If the ground rod was connected to the transformer at the same point as the neutral wire that runs out to the houses, it would seem that the water pipe/earth path would be significantly higher impedance path (since the current has to flow through the earth between closest water pipe and transformer's ground rod).
 
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Old 10-08-20, 01:34 PM
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Following up on this, a few weeks after I reported the issue, PoCo sent their contractor out. They figured it was my neutral connection to the pole (which had some corrosion and wasn't great mechanically either) so they replaced the aerial drop (which was fine by me since they replaced the old bug nut connections wrapped in tape with the newer style connectors). Of course that didn't resolve it, since I reported current on my neutral even with the main breaker off, but they have their checklist of possible culprits to go through so I was happy to let them do their thing. So they were able to confirm current on my neutral even with L1 and L2 disconnected from house (i.e., no drop connection except for the neutral).

Once they reported that back to PoCo, the utility sent another crew out the next day - these guys checked the transformer and found a corroded connection (very old transformer), which they replaced. Still have current on my neutral with meter out, so they suspect it is internal wiring in the transformer, so it sounds like once they report back to PoCo, the transformer may get replaced.

For this explanation to be correct, I guess the ground rod at the transformer is connected to the transformer neutral internally, not at the external connection used by the neutral wire that runs out to the houses. That's why the water pipes provide a competing low impedance path back to source. If the ground rod was connected to the transformer at the same point as the neutral wire that runs out to the houses, it would seem that the water pipe/earth path would be significantly higher impedance path (since the current has to flow through the earth between closest water pipe and transformer's ground rod).
Further followup. Utility sent guys out today. They said it didn't look like last crew did anything at the transformer neutral connection, so they redid that connection. That dropped current on my neutral (which they were measuring with my meter pulled out, but there was still between 1 and 2 amps. They checked a couple of houses on the same transformer, and said that when the pulled the meter on one of them, the current on my neutral dropped to zero. So they redid that house's connection to the pole. When they said they were done, I read 0.3A on my GEC to water pipe (meter still out). They said it will never get down to zero and said my ammeter probably isn't very accurate in measuring very low current; I guess the reasoning is that the copper water piping provides a decent alternate path to the transformer, so some current will take this path even though there is a lower impedance path.

I checked after they left, and with power restored to house, I saw ~1.3A on the GEC. I shut off the main breaker, and saw ~0.8A. I'll check again in the evening when everyone is home.

What is an acceptable level of current on the GEC to water pipe? Wondering if I should call utility to come back out and check other houses or maybe there's an internal issue with the transformer.
 
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Old 10-08-20, 02:12 PM
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As I mentioned previously..... it is not uncommon to see a small amount of current flow at your end. I'd say around an amp or so is acceptable. Certainly much better than it previously was.
 
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Old 10-10-20, 05:55 AM
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Hi from Norway. We live in an area with an old supply system that luckily for you are banned in north America.
We have no neutral at all, so the voltage between the live wires and ground varies. That shows that the wires acts as capacitors, and that may explain that you just measure almost 0 A whit breakers off. If one of my neighbors get a ground fault the live wire of the fault drops to close to 0V to ground. If I get another fault with one other wires that may cause the his breaker, or mine trips, or in worst case we get a fire here or there. Please be careful if you suspect a missing ground in the transformer area. You may get some hints by measuring voltages between each live wire and ground and live and neutral.
 
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Old 10-13-20, 07:55 PM
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Measured current on the GEC to water pipe a few minutes ago, and it was ~2.5A (fluctuating around that figure). As we might expect, there is more electricity usage in the evenings among the houses on the transformer than there is during the day, so greater potential for larger imbalances that need to return on the neutral.

By redoing connection at transformer and a neighbors aerial drop, they definitely reduced average current flow through the copper water pipes, but seems like they should check the neutral connections of other houses on this transformer.
 
 

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