Current on GEC and Bonded EMT

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ardmi

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Im not sure on what degree any of this is normal and if its something I need to refer to someone at our shop with more experience.

Yesterday I had to replace a jumper around a water meter in a house.

I put my clamp meter on the GEC and the water pipe prior to the meter and I was getting somewhere in the range of .50-.75 ... so less than an amp. Nothing on the other side of the meter nor on any of the water pipes.

At the meter socket outside, they had a new ground rod sunk, the old ground rod was disconnected but next to it. I was not getting any current at the new ground rod however, I was getting about 1 VAC between the old a new rod.

Inside the house I went around clamping the various conduits (all emt) and some of them were also showing current in the the same less than an amp reading. Turning off any of those circuits had no effect on the reading. I also noticed the reading on the conduits fluctuated a bit from 0 to almost 1A in the span of the hour I was there. When the homeowner used a microwave in the kitchen, the readings on the conduit and the gec also fluctuated ... never going about 1A.

I was perplexed as usual and not sure if I am seeing phantom voltage or something else and was concerned there was a neutral issue at play here. A little reading online suggests some of this is normal but I am unclear as this is the first time I ran into something like this in the field.

Does this sound like an issue needing further investigation?
 
Further testing shows

With the main off at the residence, their is still the less than 1A of current on the water pipe and the gec. I would assume that is normal from the municipal water supply being in parrell to the trans.

However, the current on the conduit has been narrowed down to a circuit with a refrigerator. With the fridge on the conduit it was in was showing close to 1A of current. A nearby conduit on another circuit was showing about half that. With the fridge removed from the circuit, the current readings disappear.

Does that mean the fridge is faulty leaking to ground? Or am I seeing normal EMF noise or non zero current, inductance or something? Please excuse my ignorance.
 
Its the circuit not the fridge. A 1500 heat gun puts about 5 amps on the conduit.

What am I likely seeing here? Am I actually reading a flow on the conduit or some non-zero current from the conductors?
 
140417-1002 EDT

ardmi:

If you have a conduit with some internal current carrying wires, this conduit and its wires go into a black box with some sort of internal load, and there are no other conductors to the black box, then all the magnetic fields from the conduit and its conductors should cancel. Meaning read 0 current when your clamp-probe encompases all the conductors (the conduit is one of the conductors).

Does the refrigerator have a copper pipe connected ice-maker? If so measure the current on that copper tube with and without the refrigerator plugged into the wall. Be careful when unplugging the refrigerator. Do not touch anything else while doing this operation. If there is current flow on the copper tube this could be from a low voltage source, but it could also be a high voltage source (meaning a shocking level). Don't work alone in a situation like this.

Also to what other conductive path might the refrigerator be connected?

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140417-1025 EDT

ardmi:

Assume the heat gun is a two prong device (no EGC), then it is likely that neutral or hot has alternative parallel paths that produce an unbalance current in the conduit and its wires. It is possible there is no current in the conduit itself, just an unbalance in the current between hot and neutral.

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Assume the heat gun is a two prong device (no EGC), then it is likely that neutral or hot has alternative parallel paths that produce an unbalance current in the conduit and its wires. It is possible there is no current in the conduit itself, just an unbalance in the current between hot and neutral.
Click to expand...

And does this indicate a serious problem? Ans your correct the heatgun load does not have an egc.

So in other words the conductors inside the conduit are not balanced, there isn't a return for every ungrounded conductor.... So I have a inductive heating issue then correct?

Or is this normal EMI or EMF (not sure what to call it)?

Is my method of clamping around the entire conduit with a basic ammeter a correct method of measurement?
 
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Clamping around the entire conduit is a useful measurement. You just have to realize that what you read is the total (vector sum) current in the conduit and the conductors inside it, not just the current flowing in the raceway EGC itself.
The heat gun test is telling you that the line and return current of the heat gun are not flowing in equal magnitude through the grounded and ungrounded wires in that conduit.
Nor is the return current flowing in the conduit itself.
There is a serious problem with the wiring of that branch, possibly involving parallel paths caused by bonding neutrals from different circuits.
Once you have resolved that you can return to investigating the EGC current issue. So more on that later.

Tapatalk!
 
I guess I should note that there is no voltage detected on these conduits when I am getting current readings.

From what I describe does this sound hazardous?
 
It certainly might be. You have not presented enough information to tell for sure.
By itself the .5A on GEC and the 1V to a disconnected ground rod do not prove anything dangerous or even unusual.
More information would be needed to make that determination, and the effort needed may not be justified.

PS: No voltage on the EGC just means that the resistance is low, as it should be, and does not tell you what the voltage would be on exposed surfaces if the ETC were to be interrupted for any reason.

Tapatalk!
 
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I should note that the conduit with the current readings contain many wires from 2 or 3 different circuits. Its only one of those circuits that when open makes the current reading disappear.

I was told that two of those circuits were once MWBC. When a new panel was installed, the installers ran a separate neutral for the shared circuits back to where I assume the circuits split. Hopefully that wasn't monkeyed up.

More information would be needed to make that determination, and the effort needed may not be justified.
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Please advise on any other information I can provide.... I assume you mean there would be extensive detective work needed in just about every box. If there are no signs of malfunction otherwise, I wonder if this is warranted?
 
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Whoever split up the MWBC apparently goofed. The current readings you got with the heat gun pretty conclusively demonstrate a Code violation. Whether it also created a hazard is another question.
At a minimum, there will be a hazard if someone opens a neutral thinking they have turned off the corresponding feed breaker and that they are working with an individual neutral.
Are there handle ties on the breaker for the circuit to the heat gun?
If not, then I would say it could be a safety problem for sparkies, if not for the occupant.

Tapatalk!
 
They added a neutral wire somewhere for the shared circuits. Do you think this is proof that it wasn't done correctly. Keep in mind I have no idea if this was occurring prior to this and there are also conductors from a third circuit in this conduit.

The two circuits are still on opposite legs but they don't have handle ties or double poles.
 
If they added a separate neutral, the Code requires it to be in the same raceway as the associated ungrounded conductor(s).
I would call what was done a violation, yes.

Tapatalk!
 
I guess I didn't clarify that, they pulled an additional neutral in that raceway (with the ungrounded conductors) that I am getting the current reading.


If they did goof up when they pulled it, would it be possible for a mwbc with two returns back to the bus in parallel cause what I am describing?
 
140417-1420 EDT

ardmi:

GoldDigger has given you good information, but you should have provided more complete information at the beginning.

My heat gun is labeled 8.3 A and at 123 V after a short run time measures 7.6 A. Typical 1500 W space heaters I have used and tested run about 10 A at 123 V.

In your test situation we can guess that there are at least two neutral paths from the refrigerator socket to the main panel. If your gun is actually 10 A, then about 1/2 of its neutral current is flowing thru the neutral in the conduit, and the remainder in other paths.

One way to search for stray magnetic fields is with a several thousand turn air coil shunted with a 1 ufd capacitor and using an AC voltmeter that resolves 10 microvolts. Basically the coil inductance and the capacitor should be resonant at 60 Hz.

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Whatever they did, there appears to be a parallel neutral which is not in that conduit and that other neutral us carrying half of the load current. That violates the parallel conductor rules.
(Or maybe the problem is actually a parallel hot wire oath not in that conduit.)
When you pull a new separate neutral you may have to find and open a place where several neutrals are wire nutted together to make it proper and legal.

Tapatalk!
 
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gar said:
140417-1420 EDT

ardmi:


In your test situation we can guess that there are at least two neutral paths from the refrigerator socket to the main panel. If your gun is actually 10 A, then about 1/2 of its neutral current is flowing thru the neutral in the conduit, and the remainder in other paths.


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Click to expand...

That leads me back to one of my initial questions. Am I reading actual flow on the conduit as the conductor or am I reading an unbalanced return on one of the conductors inside the conduit?

One thing I assume is unbalanced returns cause inductive heating. Heating causing fire. Does this sound like a fire hazard to the residence?

And if the two of the three circuits inside the conduit are still a MWBC, but now have 2 neutrals in parallel as the return, could that cause what I am describing or further more, pose a fire/overheating hazard?

Whatever they did, there appears to be a parallel neutral which is not in that conduit and that other neutral us carrying half of the load current. That violates the parallel conductor rules.
(Or maybe the problem is actually a parallel hot wire oath not in that conduit.)
When you pull a new separate neutral you may have to find and open a place where several neutrals are wire nutted together to make it proper and legal.
Click to expand...

You were posting as I typed but your response generates the same questions above. Would that neiutral in parallel cause my current readings and are my current readings values that are on the conduit or the conductors inside?
 
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ardmi said:
That leads me back to one of my initial questions. Am I reading actual flow on the conduit as the conductor or am I reading an unbalanced return on one of the conductors inside the conduit?

One thing I assume is unbalanced returns cause inductive heating. Heating causing fire. Does this sound like a fire hazard to the residence?

And if the two of the three circuits inside the conduit are still a MWBC, but now have 2 neutrals in parallel as the return, could that cause what I am describing or further more, pose a fire/overheating hazard?



You were posting as I typed but your response generates the same questions above. Would that neiutral in parallel cause my current readings and are my current readings values that are on the conduit or the conductors inside?
Click to expand...


1. Your clamp on ammeter readings are telling you the total net current flowing in the combination of the conduit and the conductors inside. There is absolutely no way that it can measure anything else since all of those current paths pass through the clamp.
If you want to know the net current in the conductors you will need to clamp them where you can break them out separately, as in a j-box.

2. The neutral in parallel (following a different conduit path!) could easily cause the readings you saw with the heat gun. Probably no relation at all to the other EGC/GES related currents you are looking at though.

3. There is no heating/fire hazard from inductive heating with such low currents. No inductive heating hazard at all if you use non-ferrous raceway.

4. The danger, IMHO, is that you have a wiring setup that is not what the next person to work on it has every right to expect and so they may be injured or create a hazardous situation themselves when working on it. It might even end up killing a plumber. :(

5. The unequivocal objection is that it is not code now and almost certainly was not code at the time it was done. But the owner may or may not want to spend the money to have you fix that.
If you end up modifying the circuits in question for some other reason, there is a strong argument that you now own that problem too.
If you fix it in a half-assed way, then you also own the problem.
 
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