Neutrals, connecting all branch circuits neutrals together

[George Stolz]

Awesome illustration. I never thought someone would ever illustrate this. Thankyou.

No problem. There were a lot of different designs being thrown around, sometimes a picture is the only way to really clear things up a bit.

Would there be a possiblility that if something was plugged into say, outlet 5 and or circuit 5, that when I lock out and test circuit 1's ungrounded conductor at the jct box or device, I could get voltage and or shocked at that point from the grounded conductor?

Yes, if someone gets between the circuit 5 load's neutral and the panel neutral, current will travel through the person to get back to it's source.

If the neutrals stay together, then no, a voltage will not be detectable.

 

[realolman]

Another way of saying illigitimata noncarborundum, but singular, I think.

That's cool ... what does it mean?

Our old union rep used to say something to that effect re: contract negotiations.

He said it meant "Don't let the bastards wear you down."

I always got a kick outta it , but not too many verification sources for dead languages.:lol:

 

[tallgirl]

Not the fields we are talking about, only distance protects us from those.

Distance makes them less strong, it doesn't make them go away. The electromagnetic force has an infinite range ...

I agree and don't know the reason why, I suspect the tic tracer is not looking for the same thing.

The EMT acts as shielding, the same as braided shielding over coaxial cable keeps the signal from interferring with anything around it. The signal that the tracer is looking for isn't escaping from the EMT, much like the signal in a piece of coax isn't escaping.

Steel tube will shield conductors from some types of interference from the outside just like the shield on shielded cable.

This subject is not one I have a lot of knowledge about.

They form a Faraday cage around the conductors, except wherever the conduit ends in a box and the front of the box is open.

Read the article in the URL.

 

[iwire]

Distance makes them less strong, it doesn't make them go away.

Did I say it made anything go away?

Just mentioned distance is what matters.

The EMT acts as shielding, the same as braided shielding over coaxial cable keeps the signal from interferring with anything around it. The signal that the tracer is looking for isn't escaping from the EMT, much like the signal in a piece of coax isn't escaping.

Well yeah....

The issue George and where having was that it keeps the tic tracer from working but the magnetic feilds are not stopped by the EMT.

 

[George Stolz]

Distance makes them less strong, it doesn't make them go away. The electromagnetic force has an infinite range ...

Come to think of it, my wife's in the front yard roasting a hot dog from the heat from Alpha Centauri right now...

I think Charlie B was the one that first introduced me to the electric field and how a tick tracer works, I think I'll go hunting for that thread.

 

[tallgirl]

Did I say it made anything go away?

Just mentioned distance is what matters.

Field strength at the origin and distance. The field goes on forever, how strong it is at any distance depends on how strong it is to start with.

Think about arc flash -- the radiant energy in an arc flash doesn't go away or become safe at some fixed distance. It falls off by the original amount divided by the square of the distance. An arc flash that's four times more powerful requires twice as much distance before the amount of energy is the same, no?

The issue George and where having was that it keeps the tic tracer from working but the magnetic feilds are not stopped by the EMT.

Okay, I don't claim to understand how that could be possible, but I'll take your word for it.

 

[tallgirl]

Come to think of it, my wife's in the front yard roasting a hot dog from the heat from Alpha Centauri right now...

"First, assume a frictionless pulley".

I think Charlie B was the one that first introduced me to the electric field and how a tick tracer works, I think I'll go hunting for that thread.

I'd like to see that. Or perhaps Charlie B will be kind enough to explain again? I've studied TEMPEST quite a bit over the years and I'd think that if there's a magnetic field "leaking" out of a Faraday cage that the NSA would have found ways to exploit that, along with just about everyone else in the intelligence community.

 

[George Stolz]

I found a thread about how tick tracers work, but I don't think it was the one I was recalling. Still looking.

Found it: Transmission Lines.

 

[RayS]

Would I be correct in the stating that if the connection to the panel at the first junction point and all neutrals from there on were in parallel and connected to each other. There would be a possiblility if something was plugged into say, outlet 5 and or circuit 5, that when I lock out and test circuit 1's ungrounded conductor at the jct box or device, that I could get voltage and or shocked at that point from the grounded conductor.

yep. Thats the problem I mentioned. You'd have to lock and tag all the circuits to be safely deenergize the neutral you want to work on.

 

[George Stolz]

I think what confuses me about this topic is that the Steel Tube Institute touts shielding from Electro-Magnetic Interference in their literature.

The tick tracer does not detect magnetic fields, it detects the electric field in the conductor. No current has to flow for the tick tracer to detect the voltage, it's detecting the voltage via the electric field that is always present when the conductor is energized.

So, does the bonded MC sheathing (or the bonded EMT) swallow up that field?

Edit: I'm currently following some of the links provided in the Faraday cage link Tallgirl posted, towards Electromagnetic Interference and Electromagnetic shielding. Maybe it will sink in, who knows?

 

[realolman]

yep. Thats the problem I mentioned. You'd have to lock and tag all the circuits to be safely deenergize the neutral you want to work on.

Although I think it's unrealistic and impractical ...isn't that what you're supposed to be doing?

(and I get the impression from reading these posts that many must not be )...

 

[tallgirl]

Thanks for the links to the old threads. Very informative stuff, especially the discussions about how tick tracers actually work and the schematics.

Those of y'all interested in how serious some people are about detecting and eliminating these stray fields should read the TEMPEST link I provided.

(Now, would someone tell me why my DigiSnap clamp-on tester is broken?)

 

[Bob NH]

(Now, would someone tell me why my DigiSnap clamp-on tester is broken?)

Can't tell you why it's broken but it has a lifetime warranty if you have the receipt.

 

[tallgirl]

Can't tell you why it's broken but it has a lifetime warranty if you have the receipt.

Don't have the receipt -- it was turned in for reimbursement for electrical materials that were on it

Looks like it goes in the trash

 

[iwire]

Field strength at the origin and distance. The field goes on forever, how strong it is at any distance depends on how strong it is to start with.

Think about arc flash -- the radiant energy in an arc flash doesn't go away or become safe at some fixed distance. It falls off by the original amount divided by the square of the distance. An arc flash that's four times more powerful requires twice as much distance before the amount of energy is the same, no?

I have no idea what you think I am missing or have misstated.

 

[dsteves]

That's cool ... what does it mean?

Our old union rep used to say something to that effect re: contract negotiations.

He said it meant "Don't let the bastards wear you down."

I always got a kick outta it , but not too many verification sources for dead languages.:lol:

Yep! That's what it means. Jeez, go eat for 24 hours or so and look how the thread grows!

I'm going to help a neighbor violate 310.4 now; maybe I'll check in later to read the rest of the thread and catch up.

Old rule of thumb at Clarkson College in 1977:
"The object is not to be the furthest ahead, but the least behind."

Dan

 

[iwire]

I'm going to help a neighbor violate 310.4 now;

Now why would you intentionally do that when there are so many ways to avoid it?

 

[winnie]

Please note that when people discuss 'EM' fields in the lay literature, they are lumping together lots of different related effects. Different aspects of electricity and magnetism will have different effects, over different distances, and will be shielded in different ways.

I am not enough of a teacher to write up a complete and correct synopses of the entire discussion, for this I'd suggest the Hyperphysics web site, in particular:
http://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#emcon
and then looking at magnetic field, electric field, and Maxwell's equations and EM waves.

EMT will do a fine job of shielding the magnetic field caused by _balanced_ current flows in a proper circuit, where the supply and return path are in paired conductors in the same pipe.

A 'floating' EMT carrying a single line to neutral circuit will be capacitively coupled to both conductors, and will have an induced voltage equal to half the line to neutral voltage. Ground the EMT (even with a very high resistance ground) and this capacitive coupling will mean very slight current flow, and thus nothing detectable on the outside of the EMT.

_Unbalanced_ current flows will cause magnetic fields that encompass the entire 'loop area' of the circuit. Any EMT around the circuit conductors will interact with this magnetic field and magnetic flux will be induced inside of the EMT, but this will not have any significant shielding effect. The only thing that will shield the magnetic field is a balancing current flow; if the EMT forms a closed circuit, then induced current in the EMT will tend to balance the current flow in the conductors; if the EMT were superconductive then this current flow would exactly balance the inducing current, and you would have effective shielding.

If you have an unbalanced current flow inside of an EMT conduit, then a clamp meter on the _outside_ of the conduit should detect this....though now I think I need to set something up to test this out Might be useful for detecting induced current flow across motor bearings

-Jon

 

[dsteves]

Thanks for the link, Jon. I remembered it like that, but I left both Halliday & Resnick and Sears, Zemansky and Young texts back at the office...

Now why would you intentionally do that when there are so many ways to avoid it?

How else can we speak from experience? ;-)
Dan

 

[tallgirl]

I have no idea what you think I am missing or have misstated.

You stated that "only distance is what protects us". Distance may not protect you. Electromagnetic fields -- and "arc flash" is an electromagnetic field -- obey inverse square law behavior. So while distance is important, it's only half the answer. The other half is the amount of energy at the origin.