Maybe a stupid question

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joeyww12000

joeyww12000

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Location
Chatsworth GA
Ok today I checked a panel where the grounded conductor was bonded to the can by a bonding screw and there was a little over .30a on the EGC going back to the MDP which fed this panel. I told the boss, and told the boss not to bond at the service disconnect and at the panel but he did not listen...so I waited till they energized one circuit of lights and got out my meter to show him this. My question is can you have amperage without any voltage? I connected my meter in series with the EGC and the can to read amps... I couldnt test for voltage on the can with the meter and I could touch everything without any shock. Would it have made any difference if every circuit in this panel were energized? Would that have been enough load to get zapped by touching the can or would you have to be in series with the EGC and can just like testing with the meter? Sorry if this is an amateur question
 
As far as the .30 reading, that's probably your meter. Without current on the hot conductor you won't read current on the neutral.

As far as your shock question goes, as long as your neutral is solidly connected, why would you get any type of shock from the egc...even if it is illegally bonded.
 
joeyww12000 said:
My question is can you have amperage without any voltage?
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Well, no and yes. A potential difference between two points is required to create a current, but a conductor can have a low-enough resistance to bring that voltage to just about zero.

For example, a shared neutral keeps the load neutral point at or near zero by conducting current. And, just like your current-carrying EGC, would show the current-driving voltage if it were disconnected.

I connected my meter in series with the EGC and the can to read amps... I couldnt test for voltage on the can with the meter and I could touch everything without any shock. Would it have made any difference if every circuit in this panel were energized?
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Again, no and yes. If the various line-to-neutral loads happened to be balanced enough to minimize neutral current, their presence would be moot. You could maximize the current by energizing everything on only one phase.

Would that have been enough load to get zapped by touching the can or would you have to be in series with the EGC and can just like testing with the meter? Sorry if this is an amateur question
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Again, if the conductor in question is of low-enough impedance to carry the current w/out appreciable voltage drop, its existence is preventing such a shock. Just like the neutral of a service, it defines the system's zero-voltage point.


Bottom line, you're correct: no normal load current should be imposed on an EGC.
 
steelersman said:
For some reason I always thought you were supposed to bond them together at the service. I guess I've been taught wrong and been doing it wrong all these years.
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The service stops at the OP's MDP, where feeders supply the (sub)panel in question.
 
Ok Larry... wouldnt the amperage raise on the EGC everytime there was another circuit energized in this panel? What would it take to get hurt here is what I really want to know? Its against code to bond the grounded conductor at the service/disconnect and at a panel fed by the service for some reason...??? I have some on here saying even if its illegally bonded why would you get shocked......? There was amperage on the EGC because one circuit in this panel was energized and I measured with the bonding screw in and with it out and could watch the current fall when I took it out and rise as it was replaced.
 
The illegal bond is causing a parallel return path back to the MDP. Most of the current is going back on the neutral. With the illegal bond you could lift the neutral and still would not get shocked because it's returning through the egc(DON'T DO THIS!). Since you know it's wrong why don't you take it out(bonding screw).
 
joeyww12000 said:
Ok Larry... wouldnt the amperage raise on the EGC everytime there was another circuit energized in this panel? What would it take to get hurt here is what I really want to know? Its against code to bond the grounded conductor at the service/disconnect and at a panel fed by the service for some reason...??? I have some on here saying even if its illegally bonded why would you get shocked......? There was amperage on the EGC because one circuit in this panel was energized and I measured with the bonding screw in and with it out and could watch the current fall when I took it out and rise as it was replaced.
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I was mis-understanding your scenario before. So it wa bonded at the service as it should be, but the problem is that it was also boded again at one of the sub-panels fed from an MDP. You are supposed to keep the neutral and EGC seperated at the sub-panel so that there isn't a parallel return path on the ungrounded (neutral) conductor. Because it is theoretically possible that some current could be present on all parts that are intended to be grounded by the EGC and that a person could be shocked by simply touching the grounded parts of equipment.

This is why you are supposed to keep the neutral and EGC seperated at the sub-panel. Neutral of course should be insulated from the can with the plastic spacers.
 
Joey, in a couple of posts you've mentioned disconnecting the ground and getting a reading in series with your meter. This is poor practice in my opinion. A basic Ideal Meter is rated for only 10amps. If there is more load that that on the conductor your meter could fail and or have some arc flash issues. Along with that, doing this introduces the oppurtunity to shock yourself. Get a clamp on meter for checking amperage on circuits.
 
HotConductor said:
The illegal bond is causing a parallel return path back to the MDP. Most of the current is going back on the neutral. With the illegal bond you could lift the neutral and still would not get shocked because it's returning through the egc(DON'T DO THIS!). Since you know it's wrong why don't you take it out(bonding screw).
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Because noone up to this point would listen, and Ive said from day one before the utility company hooked up the service that this install wasnt right. The company I work for has men in charge that dont need to be in charge, but I cant help that....I dont do the hiring and Im not in charge right now..I know safety comes first, but what do you do???? Im tired of working for this company because of issues like this, but the economy is slow and I cant afford to switch companies now. This makes the second job in a row in which the boss has no concept of bonding and grounding...which in my opinion is the most important part of the install.
 
Good to see you hear along with the rest of us learning! If I were you I'd cool it a little with the people you work for. Let the person responsible for the work or who did the work know you saw something you think is wrong and drop it. If you do the work then you can do it to code but spotting code violations in others work then letting the boss know isn't going to help you at this position. Just some words of wisdom..
 
joeyww12000 said:
Because noone up to this point would listen, and Ive said from day one before the utility company hooked up the service that this install wasnt right. The company I work for has men in charge that dont need to be in charge, but I cant help that....I dont do the hiring and Im not in charge right now..I know safety comes first, but what do you do???? Im tired of working for this company because of issues like this, but the economy is slow and I cant afford to switch companies now. This makes the second job in a row in which the boss has no concept of bonding and grounding...which in my opinion is the most important part of the install.
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I've seen lots of guys that are good mechanics but lousy at knowing and following the code. The only way you learn is watching, listening, reading or making mistakes(that can be costly). I have eight guys working for me but I'm the only one that knows the code book inside and out. They're good troubleshooters and mechanics but I design everything and inspect everything before I call the local inspector.

Get involved with your local IAEI chapter, go to the meetings and start making connections. Invest in yourself, go to seminars, buy books and dvd's...and always work hard at your job. In the future look for a position with a company that cares about doing things right...not one that's just in it for the money.
 
joeyww12000 said:
Ok Larry... wouldnt the amperage raise on the EGC everytime there was another circuit energized in this panel?
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It would as long as each circuit you energize is on the same phase. When you energize a circuit on the other phase, it reduces the neutral current. That was my only point.

What would it take to get hurt here is what I really want to know? Its against code to bond the grounded conductor at the service/disconnect and at a panel fed by the service for some reason...??? I have some on here saying even if its illegally bonded why would you get shocked......?
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Because of simple voltage drop, the neutral of a sub-panel may rise away from zero volts to ground. This voltage should not be imnposed onto exposed, normally-considered-grounded enclosures and surfaces.

In the extreme, an open neutral would impose all of the neutral current onto the EGC or conduit. Because the EGC may be smaller than the neutral, the same current would cause even more voltage drop, resulting in effectively energizing what should be grounded surfaces.

There was amperage on the EGC because one circuit in this panel was energized and I measured with the bonding screw in and with it out and could watch the current fall when I took it out and rise as it was replaced.
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That's all the proof someone who understands electricity should need to see. The condition that results in the least current on the EGC is the correct one. If the boss doesn't grasp this, you may not be able to convince him.


Added: Ask him why we bother to run separate neutrals and EGC's if they're connected together at both ends.
 
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090223-2018 EST

joeyww12000:

Prompted by your starting this thread I decided to make some resistance measurements.

What Larry and others have said basically answered your question.

On to my experiments.

The goal was to measure both 60 Hz and DC resistance of a number 12 stranded copper wire and a 1/2 EMT conduit. DC resistance of copper wire is something readily available on the Internet. That or other sources serve as a reference.

In particular Belden lists the resistance of #12 stranded copper wire as 1.77 ohms per 1000 ft.

My experimental setup consisted of 4 terminal resistors. This is where voltage test points are separate from the current injection points and inboard of the current injection points. Look at how DC shunts are made. They work on AC as well.

On the #12 wire the voltage points were spaced 121" apart, 10.08 ft. On the conduit the spacing was 114", 9.5 ft. Insulators were made so the wire could be inside the conduit for some tests.

Resistance measurements were made at about 5 A for both AC and DC. Low voltage sources were used and a Powerstat was used to adjust input voltage to adjust output current.

The conduit was new and came from Home Depot. Its OD is 0.707" and ID is 0.620" for a wall thickness of about 0.043". The calculated cross sectional area is 0.6635*Pi*0.043 = 0.090 sq-in. The wire area is 0.00513 sq-in for solid. This is a ratio of 17.5 to 1.

My DC measurement of the wire produced 1.63 ohms/1000 ft. In the ball park of Belden's value. Multiple measurements on different days produced the same result. The AC measurement was within 1.5%, but lower. The experiment needs further refinement to be sure this is a valid difference.

DC conduit measurement produced 0.70 ohms/1000 ft.

Over a 10 length this corresponds to about 35 MV drop at 5A for the conduit, and about 81 MV for the #12 wire.

How does this relate to your problem. Suppose there is a conduit running between the main panel and the sub-panel, there is an EGC also between the two, and the neutral is connected to both main and subpanel enclosures. Any neutral current will be divided between the neutral, the EGC, and the conduit. Maybe half or more is thru the conduit.

A separate EGC and the conduit are expected to be in parallel. If the application includes conduit then lightly clean a spot on the conduit close to the main panel, and one close to the subpanel. Use a millivolt capable meter to measure the voltage between the two points. Activate the loads that produce the maximum neutral current. If there is no bonding of neutral to EGC in the subpanel, then the voltage across the conduit should be virtually zero. You must make good electrical contact at the voltage test points.

If you suspect stray magnetic fields are producing part of the reading, then remove the meter leads from the test points and connect a wire between the two meter leads but keep the geometry approximately the same. If the reading is approximately 0, then stray fields are insignificant.

Larger conduit will require greater current for the voltage readings I described.

.
 
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