Code related Theory question

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Re: Code related Theory question

This one has been fun guys. And believe it or not, I do have some direction here and I want to, at some point, relate this back to the code and some thoughts I have, some thngs I want to hear y'alls view of.

But first, let me throw this one out there:

Take the same situation as we have been discussing above (guy in parallel with a phase conductor and guy is perfectly isolated and insulated from all other conducting paths.

Compare it to a guy who puts four D cell flashlight batteries in series and then completes the circuit by touching the positive and the negative ends at the same time.

Who is likely to be shocked the worst?
 
Re: Code related Theory question

Paul, please explain how you were inadvertently shocked. Seems to me that the body is full of water and salt which forms a nice electrolyte similar to the acid in a battery only not so corrosive.

Whenever I have been shocked, there was no noticeable time delay.
 
Re: Code related Theory question

are you saying that you can notice the delay in a sine wave that occurs at 60 hertz by feel? now i know that you don't know. or is it all bs.

:D
 
Re: Code related Theory question

Crossman

This was a good example of how people precive what is written as to how a circuit seems to be rather then thinking out the circuit as to how it really is. As Charlie B. Has said in another thread "when it gets too tough. go back to the simple basic's" and many times it will click in.

The bird on the wire example with the one strand broke was a very good basic example of this circuit.
 
Re: Code related Theory question

I'm going to make an assumption. Based on you're changing the source from AC to DC I am going to assume your human to behave like a capacitor. Where current would flow only long enough to charge it.

I don't know how capacitive people are. I know Rattus used to walk around campus in his hush puppies at up to 16kv. :D

And I think your guy has to be dry for that.
 
Re: Code related Theory question

Sam, electrolytes, like salt water and sulfuric acid conduct in either direction. So the human can be only one plate of a capacitor. Seems that DC was used to kill an elephant way back when or was it AC? Anyway the perception grew that one form of electricity was more dangerous than the other.

Whatever, neither AC nor DC would create a perceptible shock at such low voltages.
 
Re: Code related Theory question

Whatever, neither AC nor DC would create a perceptible shock at such low voltages. [/QB]
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This was my point about the battery comparison.

The 2.7 volts across the cut conductor is, in of of itself, not that dangerous. Obviously the potential for being grounded and getting a shock from the 480 is there and we certainly don't want to be playing around with this stuff.
 
Re: Code related Theory question

Okay, here we go with some good practical stuff. These are things I have thought of in the past and would enjoy getting some input on it. My mind is open and thirsty for knowledge.

Let's think about this parallel voltage thread in relation to parallel paths of the neutral (grounded conductor) that come up so often when talking about grounding.

There is no doubt that parallel paths through waterpipes, conduits, and other equipment exist when the neutral is bonded in subpanels, or anywhere on the load side of the service.

And generally, parallel paths exist around the neutral at the service and back to the utility secondary. These paths could simply be the earth itself or they could be through the water main to other electrical services and back on the neutrals to the common of the utility grid, or many other scenarios.

So what are the dnagers here? You hear the stories of the plumber who got shocked when he cut the copper pipe, or a fire was started because neutral current was flowing in the enclosures of equipment, etc. I do not doubt that these things happen.

But there are literally millions of installations with parallel paths all over the place... they have been in existence for years and years and there have been no problems.

It is absolutely feasible that, depending on the compared impedances, a neutral could be carrying, say 40 amps, and a parallel path in a copper water pipe could be carrying 30 amps. So how dangerous is this 30 amps on the water pipe? If a plumber cuts this pipe, does the 30 amps complete a path through his body when he touches both ends and he gets in series with the pipe?

And what about a parallel path through a run of EMT? Let's say the neutral is carrying 40 amps and the EMT is carrying 30 amps. But then one of the locknuts gets loosened... does the 30 amps cause arcing and a possible fire?

So when do the problems with parallel paths arise? It is my contention that these parallel paths do not create a hazard in and of themselves UNLESS the neutral conductor itself is compromised i.e. loose connections, corroded connections, broken wire, somehow the neutral is damaged and has a high impedance.

As long as the neutral is intact and is within the Code allowed voltage drop rules, things seem pretty safe to me.

Yes, there is that thing about EMI and the "gauss" issue...

What yall think?

Disclaimer: I totally agree with the code rules and am not implying that these parallel paths are a good thing. I just want to know under what conditions they actually become a hazard.
 
Re: Code related Theory question

If the neutral is in good condition, the ground will not carry significant current, and the voltage will be limited to a couple of volts if you cut into a pipe connected to the neutral.

If the neutral is open, then the neutral voltage is determined by the imbalance between the two hot legs. This could be as high as 120V after the pipe is cut.
 
Re: Code related Theory question

How about a conduit that is in parallel with the neutral... high imbalance, say 70 amps. And the conduit has a pretty low impedance.

Perhaps the neutral is carrying 50 amps and the conduit is carrying 20 amps. If we loosen one of the locknuts on the conduit, will it arc? Could it cause a fire? Hey, it is 20 amps ya know....
 
Re: Code related Theory question

How about a conduit that is in parallel with the neutral.
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This condition should not exist in a code-compliant installation.

It would result from an illegal neutral-to-enclosure bonding connection downstream from the main bonding jumper.

Ed

Service17.gif
 
Re: Code related Theory question

I agree that a conduit should not be in parallel with the neutral on the load side of the service disconnect.

So my scenario could occur in two ways:

1)On the line side of the service.

2)in a non-code-compliant situation

The question still stands. Is there an arcing or fire hazard when the locknut gets loosened?
 
Re: Code related Theory question

I can throw in a real world, and probably more common than most would like to think, possibility.

You know if you've breached a hot conductor's insulation in a grounded box or conduit.

What if it's a grounded conductor?
 
Re: Code related Theory question

The question still stands. Is there an arcing or fire hazard when the locknut gets loosened?
Click to expand...
Well, now you've got me thinking. The arcing voltage would be limited to the voltage drop across the neutral conductor that is in parallel with the "open in the conduit.

Ed
 
Re: Code related Theory question

Exactly. So I am thinking that the fire hazards and shock hazards of the parallel paths are minimal UNLESS the neutral itself has a problem like loose and corroded connections, a break in the wire, or perhaps a misguided electrician has inadvertantly disconnected it.

A lot of people would look at my scenario of 20 amps on the conduit and say "yes, 20 amps through a loose fitting is going to be a big problem with arcing and fire hazards" but I am thinking that when the fitting gets loose, the resistance of that path goes up and the majority of the 20 amp current shifts back over to the neutral conductor. There really isn't a fire hazard, an arc hazard, or a shock hazard here.

Now, if the neutral has a problem, then that is when all the problems of the parallel paths are amplified because now the conduit, water pipe, etc, are the only available path for the neutral current. The voltage drops on the parallel paths will potentially sky-rocket when the neutral goes bad.
 
Re: Code related Theory question

One note: I am totally in agreement with the Code that the parallel paths are bad news.

I just want to see if yall agree with my thinking about what the hazard actually is.
 
Re: Code related Theory question

I've always thought it would be pretty easy to build in indicators and annunciators to monitor operation and condition of most of the power system. With all the rules and minute detail I'm surprised that's not mandated. The only thing I can figure is we might get a false sense of security. Like we don't already have that.
 
Re: Code related Theory question

Ok Crossman in your first quizmo (new word) you had a known fixed resistance with your equation. Which lead to a fixed known amount of voltage that would be at the point of contact of the person.

The problem with this question is you now have thrown in a variable that cannot ever guarantee that the voltage drop across this parallel path will be of a low enough resistance to be a safe installation. and as such it would be dangerous to think so. This is why it "could be" a shock hazard and not allowed by the NEC.
 
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