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What's the purpose for isolated ground?

WillieWonka's picture

I've been asked to do a job that I think I'm going to pass up on for safety reasons. While I have a lot of electrical experience, this particular job makes me uncomfortable. In light of that, however, I had some questions arising from this experience.


The job is to install Neon tubes in a window of a pizza shop. I have to install the power unit with a dedicated 20A 120V circuit. The label on the power unit says it takes in 120v and increases it to well over 15,000 volts before sending it thru the Neon tubes. I saw that on the label and immediately decided that I felt I was in over my head. I believe it's not the volts that will kill you, but the amps, right? or worng?  Because I wasn't sure....well here I am writing to inquire before I do ANYthing.


The installation instructions specify the power unit MUST have it's own ground connection not shared with anyting else. I've heard of this before in other things and now I'm wondering, what really is the purpose of an isolated ground wire? I mean, why can't you have anything else grounding to this same ground wire? Why does it have to be a "dedicated" grouind wire not shared with anything else?


I'm asking because I'd like to tap into an existing circuit nearby that has a Neon power unit, to save me the cost of running a  whole new circuit. But the manufacturer says while I can do that, I MUST run a separate dedicated grouind wire to the new unit and not share the grouind between units. Why not?


If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME
If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #72074, reply #1 of 30)

Willie, if you're an electrician and need to ask these questions it's time to look for a new career.


If you're not an electrician, it's ILLEGAL for you to do electrical work for hire in every state.


In either case, stop playing sparky before you kill yourself or someone else.


DG/Builder

(post #72074, reply #2 of 30)

I know there is some cute phrase about a little knowledge is a dangerous thing but I have a tough time accepting that the world is a better place if we deny inquiring minds answers to their questions.

He already said he isn't doing the work and just wants a better grasp of electrical theory. If you still feel you are threatening innocent lives by sharing the answer to his question, why not recommend a good textbook? Or suggest a good training program.

Karl

(post #72074, reply #5 of 30)

"If you're not an electrician, it's ILLEGAL for you to do electrical work for hire in every state."

ABSOLUTELY WRONG.

Let me ask you this? How could state charge you for not being an electricain when they have no way to identifiy who is an electrican?

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #72074, reply #13 of 30)

Out of curiosity, which states don't recognize electricians as a liscensed trade?

(post #72074, reply #14 of 30)

http://forums.taunton.com/tp-breaktime/messages?msg=74107.13

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #72074, reply #19 of 30)

Cool.


Doesn't mean that there ain't liscencing requirements within the state.  :)

(post #72074, reply #20 of 30)

No.

In a lot of cases local cities/counties have licensing requirements.

In others they only depend on inspections.

In others (mostly the more rual areas) there are no codes or inspections at all, and thus no licensing requirements. I know that is true for MO and IL.

And you will notice that NY is one of the no license states.

I used to know a guy with a manufacturing plant, on Long Island, IIRC. He did all of his own work at the plant and hired a private inspector for approval.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #72074, reply #21 of 30)

Do "isolated" and "dedicated" mean the same thing with regards to a ground? And is that what the little green dot on some outlets means? I was noticing all the different outlets and markings when I was in the hospital. They had orange and red outlets, which I figured were probably dedicated circuit and backup power supplied, but I was just guessing. And some had a little green dot near the ground.

(post #72074, reply #22 of 30)

"Do "isolated" and "dedicated" mean the same thing with regards to a ground?"

Let me give you an exact answer. You, no, maybe, and who knows <G>.

The idea that of the isolated ground is one that goes directly back to the common bonding point. The idea is that other systems won't induce noise on the EGC. That was a big when the offices started getting PC's. I think that it has been learned that the grounds wheren't the cause of the problems and have they aren't being used as much.

All I know about hospitals is that they have very, very specialized requirements.

And in some cases electrical equipment is in direct contact with the flesh, which has much less resistance than flesh. Thus the standard GFCI's don't provide adequate safety.

http://www.leviton.com/sections/prodinfo/surge/sheets/8280_8380.htm

Now there are HOSPITAL GRADE receptacles and I don't know that means. But the grades are residential, spec, commercial, hospital. There may be an industral grade, but that might be part of commercial.

This series includes surge protection and also comes in both isolated and none isolated grounds.

BTW, if I understand it correctly, the recetpacle frame is ground through the box and conduit. And the isolated ground is a separate connection that only connects to the ground pins on the receptacle.

http://www.enginova.com/iso_ground.htm

"One explanation is that some manufacturers of sensitive electronic equipment "require" that their equipment be supplied by an isolated ground system. This explanation is a little weak–first, because such a system is certainly not required by manufacturers of personal computers and, second, because equipment manufacturers are not necessarily the sole authority on power distribution.

(An example comes to mind: some equipment manufacturers once "required" that their equipment be grounded to a separate building ground rod, isolated from the building’s regular electrical ground–an unsafe practice that is prohibited by the NEC. In my opinion, equipment manufacturers should themselves be "required" to design their equipment to be compatible with any power distribution system design that meets the NEC.)"

"The final argument, and the only one sanctioned by the NEC, is that an isolated ground system may reduce electromagnetic noise interference from appearing on the branch circuit. (In fact, the NEC permits the use of an isolated ground system only where required to reduce electromagnetic noise interference; thus, anybody who insists there is any other reason for installing isolated grounding is caught in a Catch 22–and prohibited by the code from installing an isolated ground.)

Large currents in nearby circuits can induce small, unwanted 60-Hz voltages in the grounded raceway of another circuit and the grounded cases of any plug-and-cord equipment. Possibly, some poorly isolated equipment might be sensitive to this–certainly, old-fashioned AC-DC tube-type radios, whose filaments were connected across the AC line, were prone to an annoying 60-Hz hum.

But for most situations, this theoretical concern should be negligible, unless you happen to be located next to an arc welder. To the extent that a separate, isolated ground conductor will be shielded by its steel raceway, it logically follows that current-carrying conductors in another, adjacent circuit would also be shielded. Further, induced voltages between separate circuits are unlikely to occur when the conductors of each circuit are tightly bundled, which will cause induced voltages to be self canceling. In any case, if a redundant ground conductor is pulled inside the steel conduit, and bonded to the receptacle and box, it seems likely that any 60-Hz hum would be suppressed."

"Another explanation is that an isolated ground system affords greater personnel safety against shock–which is why the orange receptacles are seen in hospital rooms, right? However, the NEC does not require an isolated ground system in hospital rooms. (The NEC does require a redundant ground conductor in the hospital’s raceway but not an isolated ground. Interestingly, the NEC allows an ungrounded system in hospitals, which is the Gold Standard of shock protection, at least for the first ground fault.)"

I believe that orange face plate was the old designation for IG, but now a orange mark is also used so that other colors can be used.

And the green or green mark indicates hospital grade.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #72074, reply #23 of 30)

PS

HomeDumpo has a demo board for home video/phone distribution system.

The board has an IG receptacle. And plugged into is a two prong wall wart with 2 wires powering a cable amplifier.

Even if the IG was usefull, it ain't needed in a home installation. And even more so it ain't needed where there is nothing connected to the ground pin.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #72074, reply #24 of 30)

Just sharing my ignorance...

I just bought a Leviton ProGrade isolated ground receptacle at Home Depot for use with my computer in a new office in my shop. Besides the fact that it is orange, cost $13.99 and requires a separate ground wire back to the subpanel, I really do not understand what magical properties this will give my PC. This was made clear when I tried to explain to DW why I needed it. ;-)

Our PCs have been getting along fine without benefit of this isolated ground for years. Oh, well... Can't hurt.

(post #72074, reply #25 of 30)

"Oh, well... Can't hurt."

Except the cost.

Return and buy a couple of beers.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #72074, reply #26 of 30)

Hospital Grade.....is designated by the green dot....

the devices are built to specs that require higher pull-out force on the contacts within a device..... a larger weight ( 5lbs. I think ) is DROPPED from a height ...horizontally and vertically , and the electrical connection MUST be maintained ........the spec pertains
to ALL non-locking cord connected devices....

the colors...

....Red is used for circuits that are sometimes on "normal power "and stay on, or they are energized only during an outage by the standby Generator(s), red is further used on both the Life Safety and the Critical branches, which are separate systems and cannot be interconnected, and most likely will have their own Gens. and transfer switches
these two circuits are inspected very closely, and they are not allowed to be in the same conduits or junction boxes with normal power

sometimes the designers or the facility will specify lighted face receptacles on these circuits in place of Red

Orange, is for IG circuits supplying power for data / comm, or other sensitive gear .....as speced by the equipment suppliers like that Dialysis machine some of us may be hooked to someday

also the grounding in a Hospital or other large facility is very very extensive , intricate and everywhere ,
...even the floors in almost all ORs must be grounded, to prevent static build-up.
in fact the grounding may even be installed by a single EC working only on grounding

once I had to install some HG lighted face 20A GFI in Red ,...I thought I would see them in a month or two

those were on the shelf..................who knew?

.
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'Wer ist jetzt der Idiot?'

Edited 5/24/2006 6:43 pm by maddog3


Edited 5/24/2006 8:12 pm by maddog3

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(post #72074, reply #28 of 30)

Interesting.

So does a dedicated circuit, assuming a plastic junction box and no other metal (such as conduit) qualify as an isolated ground? Or would there have to be TWO grounds running back to the panel?

(post #72074, reply #29 of 30)

. your method would seem to meet the requirement.. in a house of course

its been my experience that two grounds...one of which is marked with a yellow trace is used....

I have routinely pulled two grounds through pipe (and this method is becoming more commonplace as society modernizes.).....where the isolated ground wire would terminate on a separate INSULATED groud bus at the panel , which could have its own grounding feeder.....from the main service

.
.
.

'Wer ist jetzt der Idiot?'

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. . . . . . . .

(post #72074, reply #6 of 30)

Do YOU know everything there is to know about electrical? When you encounter something you're not sure of do you stop an ask before proceeding? And then determine if you proceed or not? I doubt you know everything electrical. 99.9% of my work is residential and I been doing it for years and am quite insured in case it matters. I simply encountered a situation where for once I wanted to know why is there an isolated ground. I've been putting in isolated grounds for many things. I just thought for once to finally ask.....why.

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #72074, reply #7 of 30)

I figured that it was to limit noise introduced into other circuits. But that it not it.

Doing a little research it seems that neon transforms have an internal Secondary Ground Fault Protection. This was done to reduce fires (apparently from failing insulation on the high voltage wires and/or improper installion of said wires).

http://www.signweb.com/index.php/channel/14/id/128/

"Until the UL 2161 requirements took effect, "ground" for all neon installations meant an equivalent potential of zero. But this is no longer true. Imagine a small core-and-coil transformer with one end of the secondary grounded (Fig.3).

If this end were directly connected to ground, the neon tubes' normal operating current would pass through the ground, and the protection circuit could not distinguish between normal operating current and fault current.

Therefore, the secondary "ground potential" output terminal is connected internally to the fault sensor, and it must not be earth-grounded. If this terminal is grounded, the protection device may trip constantly when power is applied, or not at all, depending on the type of protection device. Because the primary ground connector is not the same as the secondary ground-potential connector, installers should not confuse these connections.

The same situation applies to midpoint-return transformers. The installer must run an isolated return wire (preferably GTO) to the transformer's return terminal -- not to the ground lug. The return terminal also cannot be connected to the primary ground lug. This can cause nuisance tripping or malfunctioning of the protection circuit."

GTO wire appears to be the high volta wiring.

Reading this I am not sure what "ground" and "return" that they are talking about. Part of it makes me thing that might be an separate terminal on the transform that the any metal on the sign has to be "grounded" to rather than the connected directly to the EGC.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #72074, reply #16 of 30)

I knew they always had a dedicated ground but never really cared why since I am just doing tesla type tinkering.


Talked to the commercial sparkys today they said pretty much any HV transformer needs a dedicated ground.


Do you look to the government for an entitlement, or to GOD for empowerment. BDW

 

(post #72074, reply #3 of 30)

An isolated ground is a ground that runs all the way back to the service to where the neutral is grounded.  If a sub panel is involved you usually have two grounds going to the sub panel, the iso ground is usually green with a yellow stripe and lands on a isolated ground bus in the panel.


A dedicated ground is a ground that run all the way back to the panel where the breaker is and is strictly for a single piece of equipment.


I wish I could tell you why a dedicated ground is required but the directions seem pretty straight forward.  There are others hear that will be able to answer that question... and I'll be listing.


 


LOL Tim

(post #72074, reply #4 of 30)

I'm no electrician and I don't play one on TV, but, here's my guess . . .


Under normal circumstances, if you get a ground fault, you get something equal to, or less than, 120 volts passing over the ground circuit. No big deal because the system is designed for that and the breaker will pop. With a neon tube transformer, if you get a ground fault, you could send 12-15KV over the ground wire with the possiblilty of not having enough amperage to pop the breaker, leading to the possibility that someone touching the toaster on the same ground circuit will get *themselves* toasted. While the sting from one of these transformers might not kill you, it will toss you clean across the room! (DAMHIKT)


Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #72074, reply #8 of 30)

Beyond the safety issues, here is some input on the technical side.


We manufacture and service electron beam systems, and have similar design methods. The 15KV for the tubes is normal. This is the potential between the interior plates (inside the tube vacuum) to get the neon gas to a charged state.


Why the separate grounding? All HV (high voltage) systems should avoid what are termed as "ground loops" and should be independently grounded. The reseasoning behind this is that if you get an arc in the one tube, it will likely travel down the ground wire. If there are other tubes in the ground path,  they will catch the arc. If they have analog control, this is not usually a problem. If they are digital, they will get fried as well. I am assuming most newer units have some level of digital control.


Good luck,


TTF


 


Edited 5/23/2006 1:25 pm ET by ttfweb


Edited 5/23/2006 1:26 pm ET by ttfweb

(post #72074, reply #10 of 30)

Wow, what a great explanation that I can understand. Thank you very much, I appreciate your taking the time to provide this for me.

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #72074, reply #11 of 30)

WillieWonka,


For INFO only.....   Don't try this at home.


I have a transformer from an old demo job, the tubes were gone but the approximate 8 inch long leads were still attached.  Real heavy unit, about 4"x8"x10".  Didn't do anything with it at the time.  Stuck it in the barn.  Years passed.


Well.......ran into this winter cleaning things up.  Was curious about how much (length of jump) spark it would produce.


The weather had fairly high humidity (light fog in the area),  The insulation looked like it was in good shape, but just in case, out came the rubber gloves, safety glasses always....Plugged the unit in,.....slowly brought the leads together, six inches, five inches, WHAM "FFOJ show" (4 july) about 18 inches from my lips.  What a show!


I figured it was about 4.5 Jump, I call my brother who works at Lockhead Missles &
Space gave him the stats, he said NFW 4.5 inches, bla bla bla, you know how much potential you'd need etc...  I informed him of the very high humidity, he said, it could be possible.  He stated the obvious, be very careful if I repeated the "test". 


I've NOT repeated the test, 15,000 volts 18 inches from your lips need only be experienced once, but what a show.  The spark was twisting and flowing and that grurguling crackling sound, it was great.  It looked alive.


On second thought, I may have to get this on the digital video recorder, I think there is another test coming up....


 


 


  


 


  

(post #72074, reply #12 of 30)

We used to make a Jacobs ladder with used HV transformers. Screw two lengths of coat hanger wire to a board to form a V, attach the leads to the screws and plug it in. Nice hot arc that traveled up the wire until breaking and then starting over again.

(post #72074, reply #15 of 30)

>>"We used to make a Jacobs ladder with used HV transformers. Screw two lengths of coat hanger wire to a board to form a V, attach the leads to the screws and plug it in. Nice hot arc that traveled up the wire until breaking and then starting over again.


I used to do the same.  Neon transformers and oil burner ignition transformers were gold in those days.  Makes me wish I was a kid again.  ;-)


 


"Let's get crack-a-lackin"  --- Adam Carolla

 

"Let's get crack-a-lackin"  --- Adam Carolla

(post #72074, reply #27 of 30)

Same here, 12 - 15 KV neon sign transformers.  The screw terminals on the big ones would support the coathanger wire.  The starting gap would be about 1/2", from there it would climb to span about 8" before the ionized path resistance exceded the unionized gap resistance. 


Another fun thing, we used to rub carbon from old D-cell batteries on the pitted coathanger wire.  For a while, that would add carbon to the plasma, producing a much brighter and longer arc. 


 


 


-- J.S.


 

 

 

-- J.S.

 

(post #72074, reply #17 of 30)

I've NOT repeated the test, 15,000 volts 18 inches from your lips need only be experienced once, but what a show.  The spark was twisting and flowing and that grurguling crackling sound, it was great.  It looked alive.


Don't worry, I WON'T be trying that at home. Sounds quite dangerous.


I have to wonder what 15KV would do to a person, though. I thought 120v could kill. Imagine 15KV. But then someone said it was the amps that kill, not the voltage and that one would survive a 15KV charge.


If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME
If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #72074, reply #18 of 30)

I have to wonder what 15KV would do to a person, though. I thought 120v could kill. Imagine 15KV. But then someone said it was the amps that kill, not the voltage and that one would survive a 15KV charge.

I think you orginally talked about a 20 amp 120V circuit. Doing the math that becomes 15000V at 160mA; more than enough to kill. It just takes a few milliamps to interfere with the heart. Static electricity is called that because the currents are very small (microamps) and short duration but the voltages are large (kilovolts).

Erich

(post #72074, reply #9 of 30)

Electronics labs often have isolated grounds on power connections for electronic equipment. The main reason is to isolate noise paths. Neon bulb systems generally put out a tremendous amount of electrical noise. The isolated ground will limit the spread of the noise to other equipment. This is especially important if you have computers or other electronic equipment in the same area. In modern computers the difference between a 1 and a 0 is less than 2 volts. And the difference between a 1 and a 0 may be the difference between your computer crashing or not.

Erich

(post #72074, reply #30 of 30)

"to save me the cost of running a  whole new circuit."


 


here's the only thing I have a problem with!


I thot this pretend job was for a customer?


 


aside from running the whole new sounds like the right way to do it ...


 


what's with the "to save me money"?


 


save who? Bid the job ... the whole freaking job ... and let the chips land where they may. Stop trying to save the customer money ... things cost what they cost.


Jeff


    Buck Construction


 Artistry In Carpentry


     Pittsburgh Pa

    Buck Construction

 Artistry In Carpentry

     Pittsburgh Pa