"Ground rod" use clarification needed

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RICK FITZPATRICK

RICK FITZPATRICK

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Hello everyone. For those of you whose feet are firmly "grounded" in electrical theory, would you care to comment on the following scenario?: I post this because of my existing residential electrical system does NOT meet the NEC code for subpanel ground, described in another current thread regarding "ground".

Here is what "exists"
Shop is 65 feet from Main Supply panel.

Studio is 25' beyond shop.

Shop has sub-panel connected to Main Supply by (3) #8 conductors, AND #12 bare ground conductor from Main Panel ground connection at water pipe, connected to Neutral buss at subpanel. Shop outlet circuit grounds connected to Neutral buss also.

I personally ran one Studio dedicated audio equipment 20 amp circuit, from its own circuit breaker at shop sub panel. The Studio dedicated circuit ground conductor is connected to the Neutral buss at Shop subpanel.

Information given here on another thread, states that a subpanel, to meet current NEC recommended code must have it's own ground rod(s) connected to subpanel chassi/(ground buss?), with no bond to the Neutral buss.(correct?) In my existing Shop subpanel, there is NO seperate circuit ground buss to bond chassi, circuit grounds, or anything to. No mention is given of whether sub-panel grounding rod and ground buss/chassi should be also connected by conductor from Main Supply "ground", which would seem redundant to me anyway. But I'm not an electrician.

However, having been advised in the past by an electrically enlighted member of another audio forum , that connection to a seperate ground rod at a subpanel, for studio "ground", creates potential "current differentials". He mentions it also creates ground loop possibilitys for audio, since the Neutral buss at the Main Panel is grounded, the Neutral buss at the subpanel would be at the same potential as "ground" at the Main Panel. He further explained, IF, a "ground" rod is used at a subpanel, and the grounded buss at a Studio star grounding point is connected to a seperate ground rod via a grounding buss at a sub-panel , then a "differential" may exist between neutral terminals and ground terminal at the DEDICATED STUDIO OUTLETS.:confused: To say the least. IF the forum from which I received this information, were still in existance, I would not hesitate to try and get a response from this person addressing this new information, as it conflicts with the information given here regarding sub-panel grounding.

So, where does this leave me? I don't know what to believe anymore. Any thoughts?


fitZ:)
 
Fitz,

I do not have my copy of the NEC here - it is sitting in my office.

That having been said - a typical installation of a sub panel includes a ground rod dedicated for that panel - with seperate ground and neutral buss bars.

The ground and neutral buss bars are not to be bonded.

HOWEVER - there are cases where the restriction is not applied - depending on the distance of the run for example.

Steve (Knightfly) has probably explained the requirements for this better than anyone i have ever know - and much better than i ever could - it's very possible (based on what i've observed) that s7 probably can put this into words as well....... without my code book i cannot however -

If this is still an open issue - i will drop back in tomorrow.

Rod
 
The NEC requires subpanel grounding rods at a specific distance, I am going out on a limb here and saying 50' sounds about right. I have observed from my EC days that some inpectors make an issue about this detail, others do not.

My studio's subpanel in the crawl space is grounded via the steel conduit I ran the power feeds in, which grounds the main panel and the subpanel together. I'd guess they are 40 feet apart more or less.

I probably should find my codebook and see if I need another stake. Though, directly below my studio is a garage, with a poured floor, that will be fun.
 
Thanks guys, your too kind to inquisitive old farts.

So, that sounds like I need to change the sub-panel, as there is NO seperate grounding buss in the existing sub-panel. Is that what I'm reading here? Or are existing older sub-panels simply in a state of a possible "hosing the whole load" as you put it? :D

fitZ
:)
 
In a sub panel, the neutral buss bar does not attach directly to the subpanel, tying it to ground, it has to be isolated and brought back to the main panel's neutral buss bar.

The sub panel's ground (the enclosure, and the ground buss bar) should be tied to conduit, or a ground conductor, back to the main box, appropriately.

If there is a large distance between the two, then the ground on the subpanel can float at a volt or two due to the resistance of the metal conduit between the two, or the ground lead, which of course is not a good thing, so a local grounding stake/pipe does the job at the subpanel.

All wire, and metal, increases in resistance as distance increases.

This concept was the initial selling concept behind "monster cable" speaker wire - thicker gage meant lower resistance per foot, meaning you can run it longer distances before noticing a change in resistance.

For my studio, current and prior, I've always ran much higher gauge wire than was necessary, partially to make sure I have the voltage I expect, but also in case I want to upgrade the circuits in amperage later, all I have to do is swap out breakers to whatever I want.

My home studio goes like this:

main box --> 60A breaker --> isolation transformer --> subpanel --> (2) 15A breakers.

The wiring is such that I have 100A wiring to the isolation transformer on the primary side (which is hard to bend BTW), and the wiring from the subpanel post transformer, to the studio switches I have in the wall, can carry 50A each based on the gauge.

For what it costs per foot to install the thicker gauge wire, it was a no brainer for me. And it doesn't hurt anything, but allows flexibility for future upgrades. No rewiring necessary, just swapping out breakers, and the switches in the wall (all eight of them!).

The transformer I have is capable of providing two 120V legs at 40A each, which I seriously doubt I'd ever use.

And yes, the transformer core is grounded to the mains as well.

Safety first!
 
Hello frederic, man thanks for the extended info.


The wiring is such that I have 100A wiring to the isolation transformer on the primary side
Click to expand...

Hey frederic, when you say isolation transformer, is that one of those "toroidial" transformers? IF so, is it just a transformer by itself, or are there other "goodies" with it? And could you tell me a little about it? Like where you get them and such. I've wondered about that for a long time. Does it clean up the power, or ....you know, what the heck does it do besides "isolate". I don't understand the implications. Doggone its tough being electrically ignorant. But your replys are helping to "enlighten" me. Thanks

fitZ:)
 
I don't think you need to swap out the subpanel. Just add a ground buss and land your ground wire from the main panel and the grounds from your devices to the new ground buss.

You may need to add a ground rod at the main panel, because cold-water grounds are to be supplemented by a ground rod (or other acceptable means) at the service.

Also, the #12 AWG copper ground you have should probably be bumped up to a #10.

I'm assuming from the #8 feeders that your subpanel is fed from a 40 amp breaker in your main, thus a #10 ground.
 
Hey c7sus, I'll help your "3000+" ,cause I have at LEAST that many questions left.:D

Anyway, thanks for the suggestions. I don't know why I didn't think of adding the ground buss bar. DOH! I have one. Double DOH! Yea, this is an existing panel in the house I just moved into.
I do believe the previous owner did the subpanel work. So you say I should ADD a ground rod in ADDITION to the waterpipe ground? OK, then where do I connect the conductor from the rod? To the water pipe, or parallel to the conductor from the water pipe, to the neutral buss in the Main service panel? With #10?
Give him an inch and he asks for a fucking mile. Ha! ok, so NO rod for the sub-panel, just upgrade the #12 to a #10 from the neutral buss at the Main panel, gottcha..hmmm, that oughta be fun.

But I have another question.

I swear, for the life of me, I don't understand the principal of "alternating current". I have searched and searched the net for a REAL answer to this question. But the answers I find do NOT tell me what is really happening. In fact, one site, when reaching this final explaination kind of said...."beat it kid, your bothering me" HA! GIVE ME A BREAK!! What do you have to be, a physics major to ask questions like this?
General electrical FAQ' sites are so simplistic, and yet answer nothing. They do give round about answers that lead you down a path to nowhere though. In fact, some seem downright stupid. AND if you really tried to use the nomenclature such as "hot" or neutral, the way they explain it, you'd probably fry yourself. Some help they are.
Anyway, heres the question whether it gets answered or not here.

IF, current is the flow of a valance electron from one atom to another, then with alternating current, electron flow changes direction, right? Well if it does, from what I've read, or understand, then current, when positive is the flow of electrons down the hot lead, through the load where if resistive creates heat, or if inductive creates fields, but then what.....and then where? WHERE do the electrons go if not down the neutral conductor? But then it changes direction.. 60 times a second....right? So doesn't that imply that 60 times a second, the electrons flow FROM the neutral as well? And wouldn't that be the negative side of the waveform? Shit. Its fucked up being stu.....well, lets say unenlightened.

Damn, nevermind. I knew I should have taken physics. But NUUUUUUU, I had to pick up a fucking guitar. Hey, speaking of guitar, doesn't the pickup create alternating current?:D Don't answer that.

fitZ
 
AC (thank God, Fitz, ya had me worried fer a while, bein' from Califernya an' all... :=)

Here's an easy experiment that may make it all click, or not -

Grab your pant leg with your left hand, just below the knee, while sitting down, and pull the slack out of the cloth so you have a smooth tight cloth covering over your upper leg.

Now, put your right thumb down against your upper leg, like you're trying to squash a bug.

Now, rub your thumb lengtwise up and down your leg (humor me here) in about a 4 inch long pattern, back and forth, really quick. (No, damn it, this isn't a perverted sex joke, just stay with me here)

Do that til you feel pain and want a cold ice cube for your thumb.

Questions to answer - 1. Did your thumb travel very far? 2. Did your thumb (and your leg) get pretty warm? 3. What do you think produced all that heat, if not ENERGY being converted from motion/friction to heat? OK, that's AC - All the little electrons need to do to accomplish useful work is to run back and forth (through the load) really fast, and not for that great a distance. Not sure, but it sounded like you weren't sure that electricity needs a COMPLETE path before current will flow - it DOES. In the case of lightning, though, or other higher voltages - a high enough difference of potential (voltage) will cause a current to "jump" the air gap - once that happens, the air gets ionized which lowers its resistance, so the distance between hard conductors can be less once the arc starts, and current will continue.

This is part of why lightning does so much damage - if ionized air were the same resistance as regular air, the split second the lightning arced from ground to cloud it would reduce the voltage and stop. The damage is magnified because the ionized air allows tons more current to flow during the strike before the voltage difference is lowered enough to stop arcing through the ionized air.

On the grounding thing, here's a 4 page long thread from RO that explains pretty much everything you want to know as far as code, etc - partway down on page 2 is interesting -

http://www.recording.org/ubb/ultimatebb.php?ubb=get_topic;f=34;t=000831;p=1

If you don't have a NEC book, you might want to bookmark that thread - if I remember correctly, I quoted half the friggen book before we were done... Steve
 
Doggone Steve, are you a glutton for punishment or what? Hehehe! As if you don't have enough to do already. Hey thanks buddy. 'Preciate it.


BUUUUUUT, it still doesn't confirm or fry my thought about current moving in the neutral leg. DOES IT OR DOESN"T It? You said the electrons don't t have to move very far, but they do move in BOTH directions. RIGHT? I'm just trying to find out if in fact, the neutral becomes"hot" 60 times a second. Thats the part I don't understand. When the electrons MOVE in the negative direction(if thats the right term), isn't that the same thing as the neutral becoming the "hot"? Thats all I'm trying to find out?

Not sure, but it sounded like you weren't sure that electricity needs a COMPLETE path before current will flow
Click to expand...

Steve, I may be from Californ-I -A, but come on....hahaha! Even you use the term
"flow", which gives the illusion that the electrons move the whole distance of the circuit as if it were water. And that analogy is all over the net. Thats what throws me. If ALL the electrons in the circuit move.....HOW FAR? And if only SOME of them move....which ones and where? Dig? Only the ones within the load? Only the ones on the hot side of the generator? Only one at a time.......Or is it as one friend of mine told me.?

He explained it like this. It is the LACK of ONE electron, which he called a "hole" in the circuit. Once that "hole" is created in the generator, another electron trys to "fill" that hole, which in turn, moves the next one, and the next one.....he said we're paying the power companys for moving a hole. Ha! A "hole" lot of money. Any way, that "hole" is somewhere.....but where? And if it "moves" in both directions, then the electrons must move in both directions too! To my way of thingking, that means they move in the neutral side of the load also. BOTH directions. But, his "hole" analogy may be a brain fart. THAT is why I am asking this stuff.

See, what I mean is, ALTERNATING to me, means what ever happens on the hot side of the load, MUST happen on the NEUTRAL side of the load as well. Make sense? Maybe not, but that is the question no less. And till I get a logical answer, I'll keep looking.
Well thanks for takeing the time to hit me up side the head with logic Steve. This ole thick skull takes a lot of whacks some time. Ok, I'll go read that thread.
Steve. Your TOO patient.

fitZ:D
 
FitZ,

try this:

http://www.pbs.org/tesla/ins/ins_acdc.html

and this:

http://www.coastalskills.com/PDF/ELS002-WKB.pdf


These give you some basics.....

One point - the neutral does not become hot due to the alternating circuit design - (at least not in the sense you are picturing it - it can carry enough current though to kill you if you became a part of it's path way - ) it's job is to create a pathway for the left-over residual electricity that is not consumed during the process of "lighting a bulb" or operating a piece of gear. That current is returned to the electic company through that leg.

The alternating flow concept creates a phase reversal of the electrical current in the line - not a push/pull effect. The current flows from a hot leg to the neutral - as opposed to flowing in one directin and then changing direction. It just changes it's phases from a positive to negative phase while doing so.

Or maybe it's just magic............. :D :D :D

Rod
 
"what ever happens on the hot side of the load, MUST happen on the NEUTRAL side of the load as well." -

Yes, no, and maybe.

If you understand DC theory (forget "hole" theory, all it will do is complicate things further for now) then you know that there are three basic ingredients to an electrical circuit (momentarily ignoring frequency-dependent factors like Inductance and Capacitance effects) -

In a DC circuit, you have a Difference of Potential (Voltage), a resistance to current flow (Ohms) and the Current flow (Amperage) - One Ampere is defined as a current in which 6.28 x 10^18 electrons move past a given point in one second.

A complete circuit is necessary from source through load and back to the source (think of the source as the DRIVEN pulley on a ski lift, it's just making the rope keep moving) in order for current to flow.

The wires to and from the Load, while they do have a finite resistance and therefore do have a slight voltage drop, are purposely designed to be large enough in cross-section NOT to be a SIGNIFICANT factor. The MAIN voltage drop in this circuit is the LOAD - if wires were perfect, a 24 volt source connected to a load would result in only two possible voltage measurements, 0 volts or 24 volts.

As far as current flow, yes - Kirchoff's Law states that, in a series circuit, the CURRENT (NOT the Voltage) is the same EVERYWHERE in the circuit. This can be easily proven with a clamp-on Ammeter, if you can isolate the wires to a circuit physically (not always easy in a panel) - just turn on the Load, put the clamp-on around the "Hot" lead to the load, and if you get 14 Amps there you should ALSO get 14 amps of CURRENT, (not voltage) on the RETURN or Neutral wire. If not, you have a ground problem and current is leaking off through the ground. See Kirchoff's Law, above.

Now, just because we have the same CURRENT flow everywhere in a circuit, does NOT mean we have the same voltage - in fact, it's just the OPPOSITE. By definition, if you pass an electrical current through any resistance, you will get a voltage DROP. This is where Ohm's Law comes in - it states that E=IR - E stands for Electromotive force, or Volts - I stands for Induced current, or Amps - and R stands for Ohms, or Resistance.

By that formula, you can see that if EITHER the Current (I) or the Resistance (Ohms) = ZERO, then the Voltage ALSO must = Zero.

Ideally, our circuit would have wires that had ZERO resistance so that ALL the energy we pass through the circuit would be available to the Load, where we actually WANT things to happen - Real life says that there is going to be some Relatively small resistance in the wires to and from the Load - we purposely size the wires to compromise between cost/flexibility and waste of energy. Therefore the wires (both the Neutral and the Hot) will have a slight Voltage drop when the circuit is working.

If we were still talking about DC, this would mean we have a Source of 120 volts DC, which would measure 0 volts on one terminal and 120 volts on the other. As we travel up the wires toward the Load, we would see a slight voltage drop that's calculable using Ohms Law, based on the current that's flowing in the circuit and the small amount of resistance found in the wires.

If we were to measure the Voltage right at the Load, we would NOT see the full 120 volts, but a slightly smaller amount - assuming that our wires to and from the load are the same size, material and length on both Neutral and Hot side, if we lost 1 volt on each wire due to the wire's resistance/voltage drop, then the load would only see 118 volts difference.

Now, let's switch to an AC circuit, operating at 60 hZ, 120 volts (standard USA wall plug stuff) -

First, the 120 volts isn't really 120 volts, it's an AC voltage whose ABILITY to DO WORK = the same as if it were 120 volts DC - but obviously, if this current is going one direction for a while, slowing down, stopping, then going the OTHER direction for a while, etc, then when it IS moving it would have to have MORE power at its peaks than the DC does, in order to be able to do the same amount of work over the same period of time. This "Fudge Factor" is called RMS, which stands for Root Mean Square - this post is already too long to get into all that, so for now let's just say that 120 volts RMS AC will do the same amount of WORK as a 120 volt DC current will do.

If you think of electricity as having to move (one direction or another) through a Load in order to perform Work, then the concept of Current remains the same - back to the Coulomb, or moving 6.28 x 10^18 electrons past a given point in one second (One Ampere) - As long as that AMOUNT of electrons moves in the circuit, it DOESN'T MATTER which way they go, or even if they "stop and take a break", as long as it's AVERAGE movement is the same as the CONSTANT movement of DC current.

To visualise this, go back to the "thumb rubbinb the leg" analogy - If your leg was LONG enough, you'd still get a hot thumb by continuing the same direction (DC) for the same amount of distance traveled, factoring in the varying SPEED caused by changing directions regularly.

Now that nearly everyone's asleep, here's the bottom line - if you measure the Voltage in a Neutral (and yes, there IS CURRENT there) it should be close to ground at any point in the wire, or your circuit has a problem. Measure the Voltage on the OTHER side of the load, and you should see almost the entire supply voltage (minus wire losses) - if you measure the CURRENT, NO MATTER WHERE in the circuit, it should be EXACTLY the SAME EVERYWHERE. If not, you have a ground leak and it is NO LONGER just a SERIES circuit.

The other factors that make AC circuits different than DC circuits are irrelevant here - Inductance and Capacitance, which combine with the frequency of the circuit to cause extra "resistance" known as Impedance (the AC version of Resistance) can be looked at and calculated as simple resistance as long as you operate the circuit at the same frequency. Measure the DC resistance of an AC motor or relay some time - if you were to connect a DC voltage source to these that was the same as the AC voltage rating, you'd be calling the fire department - AC devices are DESIGNED around a Specific Frequency, and their Inductance/Inductive reactance, Capacitance/Capacitive reactance are all factored in. Connect DC to this unit and ther IS NO RESISTANCE other than the DC resistance in the wires, once the circuit has reached a stable state of current.

'nuff of this for now, chew on that for a bit and see if it helps... Steve
 
nuff of this for now, chew on that for a bit and see if it helps... Steve
Click to expand...

CHEW? Ha, how 'bout CHOKE! :D Your right Steve. And btw, I know this subject is WAY beyond the scope of this forum, and you guys have gone WAY past the point I was trying to make. OK? So, my thanks, I'll chaw on this stuff for the next 20 or so years but...uh....wait, about that boundary/soundwave stuff..? Ha! Nevermind. You know me. Thanks guys. Your efforts to enlighten me will be rewarded. I promise NEVER to post anything here regarding electrical that might confuse someone, so YOU don't have to clear it up EVER AGAIN! How's that? Ok? OK.

Well, thats about it for this stuff.......whats next....hmm.... lets see....hey, whatcha know about rainbows....Just saw the most beautiful one I've ever seen. Got to wondering...... What causes the change in colors:p nevermind... I know.....SHUT UP RICK!

fitZ:eek:

ps Thanks guys!
 
Whoa.......... check out the big brain on Steve!:D

I started to attempt to begin to answer this question and thought better of it..............

BTW Steve, do you know how they get Teflon to stick to the frying pan???
 
Hey, 7 - all brains are similar size, mine's just had a LOT of time to absorb stuff - Why, I remember back when I was perfecting the formula for DIRT... :=)

Actually, used to TEACH electronic theory and troubleshooting years ago in the military, guess I haven't forgotten EVERYTHING. Plus, been doing industrial instrumentation/control for the last 25 years, and this state requires two electrical licenses for that...

Unfortunately, I did NOT teach Teflon theory :=( but I do deal with really wierd stuff on my "DDJ", so my totally un-informed "SWAG" (Scientific, Wild-Assed Guess) is that it isn't pure teflon, but a copolymer composite with a PTFE additive - the "binder", or glue, part would need to be inert at temps up to at least 450 degrees C, since Teflon is only good for about that range. It's NOT actually commingled with the metal, because you can scrape it off using metal implements.

Short form: Dunno...
 
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