Greetings all, I am planning to move a subpanel in my utility room.
It is single phase panel which feeds a electric dryer,and 4 outlets.
I plan to move it and have a pro sign off on it and energize it when I am done.
Inside the panel I find that the neutral bus also has all of the grounds from the
dryer and outlets attached to it, plus a ground wire running to a strap on a cold water pipe.
Is neutral/ground bonding common now? I recall panels I have seen in the past had a separate ground bus.
Any thoughts comments?
Replies
In general a subpanel should have neutral and ground isolated from each other, with the ground being run back to the main panel ground. There are a few exceptions, but none that would seem to come into play in the current circumstances.
(Note, however, that the 3rd wire in a 3-wire electric dryer circuit is considered to be neutral, not ground.)
No, that is wrong.
For the sub-panel the ground and neutral should be isolated.
They are only bonded at the service entrance, which is at the main disconnect. Usually that is the same as the main panel. But in some cases there is a separate disconnect in which case the "main panel" is wired as a sub-panel.
And grounds should not be picked up off of local water pipes.
They need to go back to the grounding electrocde system. Which usually means main panel.
Sounds as if the sub panel was installed under an earlier iteration of the NEC, maybe 9 to 12 years ago, or more.
Moving it will now will mean meeting current code requirements. Leaving it where it is means it is still "granfathered" under the earlier version of the code.
Wouldn't want him to think he has an illegal situation that is dangerous. It is just not current code compliant.
Dave
"Sounds as if the sub panel was installed under an earlier iteration of the NEC, maybe 9 to 12 years ago, or more."And I almost added the comment that picking up local grounds was common practice years ago, but no longer allowed.I have been wondering about that. In fact I think that I ask about the history of 4-wire sub-panels at one time and got replies to the fact that isolated ground as been required as long as they remember.The reason is that I have such a panel that was in installed when the house was built in 79. And I have found a few "issues" with the wiring. And we had miniumum code inspections at the time.And a friend of mine's house also had a such a panel, about the same era. But that had so many code problems you could not use that as a standard. One of the LEAST was the use of a plastic coffee can lid for a coverplate on octagon j-box.And I looked at a house built in 80 in an area that I am guessing did have good inspections. Now this was a custom house, well built. And it had 320 amp service with dual 150 amp main panels. And one feed a 100 amp sub on the other side of the house.A 4-wire cable was run and isolated neutral bus bar. BUT the ground wire as just left unconnected in the main panel. There was a water circulating pump on the hot water tanks and connections for 2 gas furances off that panel. So all of it's "ground" was what was being pickup by "reverse bonding" on the gas and water lines.
Bill, I recently put in a subpanel and ran a ground back to the main. No problem.
I was wondering why. I know it is hard to explain sometimes, but I would like to know the reason. I haven't put alot of thought into this. So it's no big deal. What is the scenario that dictates it? If you don't mind.
Have you read the rest of this thread.Specially my messages to Luka.
I'm on it!
Hello to all, I've been lurking on this site for a long time - time to jump in!
Subpanels were explained to me as simply very large wall boxes. Namely, hots and neutrals isolated from the actual box and each other, grounds are connected to each other and to the box via a ground bar. I have installed several sub-panels over the years and the local inspectors (Delaware) always accepted this method without question.
I suspect the original panel installer did not bother to buy an auxillary ground bar and install it, just used the existing neutral bar instead probably working on the assumption that "this is how a SEP is wired". The ground strap to a water pipe may or may not do anything ( assumes that the water system is grounded by continous metal piping to the earth). Ground strap= belt and suspenders ground on a job which is already compromised.
Never underestimate the value of a sharp pencil and good light!
The simple way to remember it is: Bonding neutral to ground is *required* at the service entrance, and *forbidden* everywhere else.
If you have more than one building on the same service, like a detached garage more than 5 ft. from the house, the outbuilding may require its own ground rod and bonding neutral to ground if it has a panel of its own. IIRC, you can run one branch circuit to the outbuilding, but if you want more, it has to have a sub panel. But for the simple case of one house, all you have to know is: *required* at the service entrance, and *forbidden* everywhere else.
-- J.S.
Thanks for the info - I will have exactly the outbuilding situation you described on an upcoming project in the spring. Will seek clarification from "local authority" before doing anything foolish - I hate to tear out!
Daves measure brings up another point.
"I find that the neutral bus also has all of the grounds from the
dryer and outlets attached to it,"
If that dryer has 3 wires on it then the 3rd connection is a Neutral and not a ground. But the code allows (for existing instalation) the use of the neutral to ground the drier.
Usually that is a technicality, but not when you are working through a sub-panel.
You need to also upgrade the drier to 4 wire connections.
Im gonna hop in and reply to you. I was going to reply to daves post and second it .
Ive looked at a bunch of panels over the last year inspecting. You are right on, no question there . My problem with looking at panels is that the old ones always have the neutral and the bond on the same and only bar. I looked at some very old panels. Most of them are old is the deal. Most of my problem in understanding it is why GFCIs work on the old systems. They do and it seems to me it would be the same as jack legging one at the recepticle which my testers will detect.
Off my tiny rant . Your information was right on and the same as I would inspect the job. Also the recomendations.
Tim Mooney
Most of my problem in understanding it is why GFCIs work on the old systems.Why wouldn't they? They compare incoming current on the hot and outgoing current on the neutral.Our testers don't work on ungrounded circuits because they use the ground to simulate a ground fault.
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Sojourners: Christians for Justice and Peace
Our testers don't work on ungrounded circuits because they use the ground to simulate a ground fault.
You wanna try that again? My testers 'do" work on ungrounded circuits. They will tell me its ungrounded.
Use the ground to simulate a ground fault? Mebbe thats where Im missin it.
Tim Mooney
I should have said the GFI test button won't work - pop the GFI -on an ungrounded circuit, even when the GFI itself is operableMy understanding is that the GFI is only lookinmg at the hot and neutral, but the GFI testor needs the ground to doi its thing.
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Sojourners: Christians for Justice and Peace
"My understanding is that the GFI is only lookinmg at the hot and neutral, but the GFI testor needs the ground to doi its thing"
Thats my understanding too. Although it will work , the tester will catch it . Thus turning it down in my case.
Tim Mooney
>>Thats my understanding too. Although it will work , the tester will catch it . Thus turning it down in my case.I don't understand.A GFI on an ungorunded circuit will trip when there is a ground fault.The test button in a GFI tester will not cause the GFI to trip on an ungrounded circuit becasue the tester needs the ground to operate properly/.My understanding is that it is perfectly acceptable to put a GFI on an ungrounded circuit, but it supposed to be marked as such.
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Sojourners: Christians for Justice and Peace
"The test button in a GFI tester will not cause the GFI to trip on an ungrounded circuit becasue the tester needs the ground to operate properly/."
Bob, we just went over that earliar. The tester works off the neutral and positive. Your last sentence reinforces it and is true.
"My understanding is that it is perfectly acceptable to put a GFI on an ungrounded circuit, but it supposed to be marked as such."
Your first above is incorrect. That is also backed up by you second sentence I copied.
The tester will trip it off the neutral as Bill said earliar . Er somebody did! LOL. That caused me some serious confusement believe me when my tester said faulty ground , but I tripped it ! Dadgum sure did it. Had me seriously stumped. Then to add to confusement I started thinking about the bootleg ground at the meter can and in the old service panels. But as you wrote above, GFCIs still work "ungrounded". Its because as I learned in this thread , its working off the damn neutral.
Ive never passed an ungrounded circuit.
Tim Mooney
Lets be clear of our terms.A GFCI without a ground will trip with the SELF-TEST on the unit.However, a separate testing device will not trip it. That needs a separate path to bypass some of the current. In an installation with a ground it uses the ground for that purpose.Code does allow for the use of GFCI's to replace existing ungrounded receptacles as one of the ways of upgrading the circuits.And it allows the use of ground style receptacles, but without a ground, downstream of a GFCI.But these are only for upgrading existing ungrounded circuits.I think that are cases where unground GFCI's are allowed on new installations, but they are very specialized medical and industrial applicants.
Thats a very clear clarification thank you and on part of it I stand corrected . I had a case where an ungrade was needed on a two wire system and I didnt allow it . I should have researched the code . Thanks . I did make a mistake which caused the electrician to rewire it . Bob was right on that too. Messed up.
Tim Mooney
The GFCI's have a small transformer in them. Both the hot and the neutral wires to the load go the transformer, but in oposite directions. Thus is the exact same current is flow out the hot as in the neutral it does not generato a signal.If there an unbalance of current then it generates a signal and trips.That can be caused by a person between the hot and a ground, for which it is designed. But the imbalacne can also be caused by miss wiring such as the neutral being connected to another neutral downstream of the GFCI.The self test on the GFCI works by connecting a resistor for the hot on the load side to the neutral on the line side so it simulates a ground fault.Now none of this requires a ground to work. That is why GFCI are allowed to replace ungrounded receptacles on older wiring without a ground.However, while the self-test will work, an external tester will not trip the GFCI because they need a ground so that they place for the "fault current" to flow. And without the ground then there is no place for it.
Thanks for all that .
My testers were pretty fancy as they detected several different things. They werent for electricians. Had one light on there , if it came on said bootleg ground or false ground. If someone tried to jump the ground to neutral buss or if they were touching anywhere it would detect it.
They are touching at the meter can is what always confused me . The tester wont detect that . Is it because of the little transformer?
Tim Mooney
Edited 1/20/2005 5:24 am ET by TIMMOONEY52
Tim, are you using one of the "SureTest" analyzers?I've heard that they have a tendency to give false positives for bootleged grounds if the receptacle is close to the panel.I don't know how close "close" is.
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Sojourners: Christians for Justice and Peace
I don't know how close "close" is.
Thats the deal right there . It depends how close. In the same box , it will detect it . But why not at the panel? My under-educated guess is its too far .
But like Bill said , GFCIs will work on an unbonded circuit. They work off the neutral .
Tim Mooney
I would assume that the fancy tester detects a "bootleg" ground by measuring the impedance between neutral and ground. If it's real low, then either the ground is bootleg, or the outlet's real close to the panel. The tester can probably make some guestimate as to how close the panel is, based on high-frequency impedance and/or (getting really fancy) time-domain reflectometry. (If it can do TDR, it can probably tackle the whole job with just that, and not have to do the ground-to-neutral impedance measurement.)
"Now none of this requires a ground to work. That is why GFCI are allowed to replace ungrounded receptacles on older wiring without a ground."
On a circuit with 5 unbonded receptacles could I use one GFCI for the whole circuit when replacing the receptacles?
"On a circuit with 5 unbonded receptacles could I use one GFCI for the whole circuit when replacing the receptacles?"Yes. That is specifically allowed in the code.You are suppose to label them. I forgot the exact working, but I something like UNGROUNDED PROTECTED BY GFCI.But if you buy the individual GFCI's (vs the 3-pack or bulk) they have the labels with them.
On my main panel...Power comes from the road on three wires. (Aluminum, and VERY small, which pisses me off, but ya lives with what they gives ya, right ?)The ground is TWO 10 foot rebars driven in the ground, all but 4 inches. (I used two 12 footers.) 1/4" solid copper from bar to rebar.The ground buss bar and the nuetral buss bar are separate. But they are both bolted directly to the metal box. This is exactly the way the box comes from the manufacturer, and passed very stringent inspection. (Since I installed everything myself, they inspected it out the wazzoo, before they would hook it up. I passed, and THEN SOME....)Now...If I wanted to put in a sub-panel...3 wires from the main. Getting power from a 60 to 100 amp 220v breaker, instead of just tieing into the main. Aluminum cable, basically the size that comes from the road.At the sub-panel... Separate buss bars again. Both bolted directly to the box. And exactly the same ground type as at the main box. 10 foot rebar, driven into the ground, all but 4 inches. 1/4" solid copper wire to the ground bar from there...Why would the sub-panel be any less safe than the main, if both are set up EXACTLY the same ???The sub-panel is fed from the first panel, instead of from the road... being the only difference.Seems to me the sub-panel, being fed from a breaker at the main, is even safer.For the life of me, I can't see why a setup that is identical to the main is any less safe, just because it is called a sub-panel. If I bypassed the main, and tied directly into the meter, it would be a main panel, and it WOULD pass inspection. (Pretend the first main is disconnected, or the power company allows a second main tie to the meter. Or there is a whole new power feed from the road. Don't sidetrack on that point.)
The person you offend today, may have been your best friend tomorrow
"The ground buss bar and the nuetral buss bar are separate. But they are both bolted directly to the metal box."They are only "separate" in the way that you connected the ground and neutral connections to the load.As you said the are both bonded to the case so they are one in the same. It would have been just a correct to mix the ground and neutral connection at the main box.Now for this purpose the term Ground is just an illusion. (For lightning it is a different story). But the ground is a poor conductor and if you measure between the "ground" at one place and aother a couple of miles away (or even less, much less in some cases) you can measure a voltage difference.Now voltage is always defined as the potential between two point. Take a simple battery, you have 1.5 volts between the two terminals. Measure between one end and the "ground" and you won't get any meaningfull measurement.Starting at the generator or at the transformer again you have two terminals. And the only measurement is between them. It is not until you connect one terminal to ground do you have anything that you can measure with respect to ground.Ground is only the local reference voltage.Taken to extermes there are lineman that work on very high tension lines (150 kv and higher) from buckets that are hanging from helicopters. The first thing that they do is to "ground" there bucket to the high tension line. When they do that they are at the same potential as the line.Now how does that pertain to your sub-pannel.If you sub-panel is "away" from the other circuits. Then you can do exactly what you suggest. This is an allowed option for sub-panel in detached buildings IF THERE IS NO METALIC CONNECTION BETWEEN THE TWO BUILDINGS.Now the ground is not a good conductor. So you can't assume that the local reference at the sub-panel is the same as at the main panel.If you have no metalic connections between the two then when you are at the sub-panel you are just like the guy in the helicopter bucket.But if you have a common metalic connection (water pipe, phone line, cable, etc) then you need to make sure that the "grounds" are the same at both places.Otherwise you can get between the "ground" at the outbuilding and the "ground", via the water pipe, to the main panel.Even operating properly there can be a couple of voltags difference because of the current through the neutral.But if there is bad connection on the neutral you can have as much as 120 v difference. BYE, BYE Luka!
Totally separate building.The ground is as good at one place, as at the next. It's not like they are a mile apart. That's kind of a red herring anyway. If the "sub" had been put in as the main, the ground would have been driven in the same place it will be, and would have been just fine. Just because there is a hundred feet or so between the grounds, does not make one ground a good ground, and the second a bad one. They are identical grounding setups. No one goes all over a property to determine the "best" grounding spot, and then sets up their panel right there. The code for the ground is what it is, so that you can be pretty much guaranteed a good ground in almost any soil conditions... Just the luck of the draw where the first one was driven, vs the second one. Either one, all by itself, would be exactly right, according to code.You set up a box, you drive a ground, that is the ground for that box. You set up the next box, you drive a ground, that is the ground for THAT box... The only "connection" between the two boxes is the two power feeds, and the nuetral.Sounds to me like the fact that it is a separate building makes the biggest difference. And that, only because you are not "grounding" back to the original ground source...My hunch here already was that the hoopla was because everyone was assuming the ground went back to the original ground source. (Or to a pipe.) I still say, same building or not, if you are not running a ground back to the original box, and you drive a new ground for the sub box, identical to the ground you drove for the main, there should be no problem whatever.As far as the separate bars might as well be one, because they are both bolted to the box... That is exactly what I have said many times, myself. What the heck is the difference ???In my setup, the ground and nuetral bars are separate bars at the main as well... But are both bolted to the metal box. What's the difference ? Just some code writer's anal "interior designer" side coming out...The only real benefit that I can see is that it is easier to keep the two separated visually, thus possibly making it easier to work on.:)I guess the bottom line here is that we are basically talking about at least two separate kinds of setup. Those types of setup should be delineated, instead of just making a blanket statement that just because it is a sub-panel, it MUST be set up such and so...If you are relying on the original ground, back at the main box, then all the stuff in the rest of the thread applies. If you are driving a new, separate and equal or better ground, for the second box, then most of that stuff makes no difference.
The person you offend today, may have been your best friend tomorrow
"The ground is as good at one place, as at the next. It's not like they are a mile apart. That's kind of a red herring anyway. If the "sub" had been put in as the main, the ground would have been driven in the same place it will be, and would have been just fine.Just because there is a hundred feet or so between the grounds, does not make one ground a good ground, and the second a bad one. They are identical grounding setups. "I might not have been clear.Typically there is NO GOOD GROUND. In the sense that you are using it.The earth is a pi$$ poor conductor.So it is very easy to voltage difference.There are a number of reports of people with swimming pools where they get out of the pool and steping from the wet concrete to the grass and getting "shocked". Mostly it is just a tingle, but it can be worse. The problem is caused by a faulty neutral someplace and current is flowing through the ground. It is often a problem with the power company lines, but it can be a problem with an outbuilding (or a neighbor's outbuilding).The pool and all of the metal in the pool is bonded (grounded) with copper back to the main panel. But if there is a bad neutral and current is flowing through the ground trying to return there will be a voltage drop across ground. Thus the "ground" next to the pool can be different then the "ground" at the main pannel (& and the immediate location where the ground rods are).Cattle are particular sensitive to this and cattle barns often need extra grounding to protect them.The basic idea is that everything that you can come in contact with needs to be at the same potential. Think back to the lineman in the helicopter bucket. He might be 150 kv with respect to the "ground". But he, the bucket, and all of his tools are at 150 kv and thus there is no problem.Whenever you have current flowing in a conductor you have voltage drop. And with the earth you can have a significant voltage drop.So the only way to guarantee that the voltage is zero is to have a conductor ("the ground wire") that normally never carries any current.Thus it is isolated from the neutral except at one magic point.
Ah.And I have obviously taken the thread in a different direction as well.Or tried to.;)I should have started my own.Sorry about the hijack, guys.
The person you offend today, may have been your best friend tomorrow
"The earth is a pi$$ poor conductor.
So it is very easy to voltage difference.
There are a number of reports of people with swimming pools . . ."
I concur. In several locations, I've gotten a slight buzz off an chain-link fence. When measured, it is a few volts AC. Not sure of the source, maybe a neutral-ground connection nearby or maybe picking up the magentic/electric field from overhead lines. But that is in a METAL fence with METAL fence posts in the ground every 8 feet! I've never noticed the effect on a rainy day, for obvious reasons.
A friend worked for BART, the San Francisco area electric train/subway system. If you are standing in the yards where they have their grounding connections, you hair will stand on end. That's from dumping 10,000s of amps into an imperfect ground.David Thomas Overlooking Cook Inlet in Kenai, Alaska
David,What would be a good ground ?Better yet, how can I achieve the best possible ground here at home, using things that should be at hand...Do I gotta pound some kinda rod to the center of the earth ?;)
The person you offend today, may have been your best friend tomorrow
Luka,A good ground?Maximize conductivity x surface area.Conductivity goes up with soil moisture and dissolved solids. Drive a stake into a salt water beach. Or at least put the copper rod into wet ground OUTSIDE the drip line of the roof (almost never done). Adding salt occassionally would help a lot but no one seems to be that sophisicated.Surface area is helped by longer rods (as you have done, and it also gets you into wetter soils). And larger diameter and multiple rods.A buried metal pipe line that runs for miles would be ideal.An item mentioned in FHB about 4-6 years ago was that the resistence of the copper wire to rod connection can be very high. There is a exothermic reaction weld kit (think highway flare plus powdered metal) that welds the copper wire to the grounding welded and drops that resistence to near zero. And it ages very well compared to the standard installation.Current practice with grounding rods seems to be very much weighted towards what is easy to accomplish rather than what is effective. When did a county or private inspector ever measure resistence to ground on a ground rod?! And yet, if it is a high resistence, it isn't there for you when you need it.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Code for rods here is 5/8" x 10' I use 12 footers.Two rods. 1/4" or larger solid copper running to it.Water table here is less than two feet. No matter where you are on my property. I don't know if that is good or bad ??? Looks like good...In the driest part of the driest summer here, you had to dig down maybe 4 feet to find water. But on the back of the property, even at that driest of times, it is so wet that you sink in when you walk back there.Lots of iron in the water here, as well. (Most wells here are hand dug. Hand dug or not, they always have a lot of iron. But the hand dug wells have the most.)Soil conditions are mostly clay. Underneath.But lots of soft moist dirt on top of it, most places. High organic content in the cover layer, down to the water table.I'd like to find out about that weld kit.
The person you offend today, may have been your best friend tomorrow
Luka, it sounds like your soil conditions are about as good as they can be, short of a beach cabana on the Dead Sea. You probably have a 1/10 or 1/100 the resistence of a lot of homes.
Here's one supplier of those exothermic weld kits for grounding rods. Reusable. Maybe someone makes a one-time kits for less.
http://www.erico.com/products/GNkits.asp
Cheaper would be to periodically inspect that grounding nut and tighten occassionally. If you see oxide or darkening, disassembly, sand clean with emery cloth, hit it with a little anti-oxidation paste ($3 for the smallest tube), and reassemble.
You're welcome.David Thomas Overlooking Cook Inlet in Kenai, Alaska
P.S...Thank you.:)
The person you offend today, may have been your best friend tomorrow
>>OUTSIDE the drip line of the roof (almost never done).Is that required or just the best practice?
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Sojourners: Christians for Justice and Peace
>>OUTSIDE the drip line of the roof (almost never done).
Is that required or just the best practice?
Bob, Good practice, not required. And, considering only physcial protection, most people put grounding rods close to the building / pole. But with a nice overhang and properly sloped grade, that's the driest soil around. More so because it gets some heat from the house.David Thomas Overlooking Cook Inlet in Kenai, Alaska
I've put in the first rod for my new service, 30 ft. of 1" K copper pipe sunk vertically by washing it in with water from the hose. It took four hours to do. My plan is to put an identical rod about 50 ft. away at the far corner of the building. I'll run a test lead and check for voltage between them when I get the second one in. (I learned the method from a friend who used to do TV transmitters and recording studios.)
The nearest government monitoring wells are a couple miles from here, and they all show water to be well over 100 ft. down. What washes up out of the hole is adobe at first, and then mostly coarse sand. The rods are outside the drip line, and I'm using those plastic irrigation valve boxes to keep them accessible without making an obstacle to trip over. The first one is in the middle of a walkway that will eventually get concrete.
-- J.S.
"I'm using those plastic irrigation valve boxes to keep them accessible without making an obstacle to trip over"
That's a nice touch.
"30 ft. of 1" K copper pipe sunk vertically" by washing it in with water from the hose"
Went gonzo on the rod depth? That helps.
"by washing it in with water from the hose"
Drill rig?! We don't need no stinking drill rig!David Thomas Overlooking Cook Inlet in Kenai, Alaska
> Went gonzo on the rod depth? That helps.
Up on Mt. Wilson, Pete used to sink rods 60 ft. for TV transmitters. He found some little prehistoric seashell fossils washing up out of the holes. He used to stop and solder on another stick, but I don't have enough water pressure to do that. 30 ft. is as much as I can stand up against the two story house without danger of bending it.
-- J.S.
So sink ten feet, solder on another ten feet, sink that, add another ten footer... etc.
The person you offend today, may have been your best friend tomorrow
So sink ten feet, heat the pipe for ten minutes to boil away the water, solder on another ten feet, sink that, heat another ten minutes, add another ten footer... etc.
The sticks of pipe are actually 20 ft. each. So, Pete used to sink the first to a comfortable working height about 3 ft. above grade, then stop, blow water out to make it easier to heat, and solder on the next stick.
-- J.S.
That's what makes sense to me. And I agree, a heckuva lot more fun than reading code books.:)It's really too bad that I need a ready source of water for this, as it does seem like the ideal way, given the soil conditions here, for me to put in a well. LOLNow if I had about 700 feet of hose, and a great big old pump, I could just get the water out of the river, to do the drilling with....It is possible to get a permit here to get your water from the river. But I have two problems with that. Access and quality.I would have to cross the road, and another property or two, to get to the river. Including the railroad property. It would probably take a couple years just to get all the permission slips I'd need. And it would be no easy task to get to the water... OR to get it pumped all the way up here. As well as the maintenance of something like that in a river that floods, and washes away boulders a quarter the size of a car, and bigger... More costly than a well, overall, most likely.As for quality, well, to be honest, I know there are a lot of septic fields that flood and effluent gets washed into the river. Grandfathered outhouses within feet of the river, as well as just plain dumping of sewage into the river... Plus agricultural chemicals, animal droppings, etc... All told, I'd rather just get my water from a deep hole in the ground.
The person you offend today, may have been your best friend tomorrow
Yeesh, too bad you need a good source of water for that.It would have been a perfect way for me to... Drill a well.:|
The person you offend today, may have been your best friend tomorrow
30' of Cu? It might be less tedious to read Article 250 of the NEC.
The uniformly accepted rule is that if you get more than 25 ohms resistance, then you simply install a second 10' ground rod -- I think 6' away -- and be done with it.
There is a lot of confusion between grounding and bonding. The important thing is to have all your ground [should be bond] wires connected properly. Then any short will cause a short circuit and immediately trip thy breaker. Grounding only has to do with dealing with rare lightning strikes, reference 0 potential and an accidental falling of a high voltage line on your infeed wires.
~Peter
Notice that Martha boycotted Georgie Boy's inauguration because. And notice that he told his wife Laura that he wanted to go to sleep at 10 pm? Well Marine One tool off from the south lawn at 10:30 with an unknown destination somewhere in West Virginia.
> 30' of Cu? It might be less tedious to read Article 250 of the NEC.
I guess it's a matter of taste, but to me that NEC book is plenty tedious. Compared with four hours of watching water and sand come up outta the ground, by me it's close to a wash. ;-) Actually, the reason for it is that it's fun to sink rods by this method, and to see how much better I can do than the minimum required by code. From the copper roof down to the ground rods, my goal is to do this house up the best I can.
> The uniformly accepted rule is that if you get more than 25 ohms resistance, then you simply install a second 10' ground rod -- I think 6' away -- and be done with it.
Perhaps I could tell the inspector that I have two ten foot ground rods, ten feet apart. Vertically. ;-) (Does the code actually say they have to be separated horizontally?) What I plan to do is sink a second 30 ft. rod about 50 ft. away from the first.
Ground rods actually don't have anything to do with tripping overcurrent breakers. A dead short from 120 Volts to a 25 Ohm ground would draw 120/25 = 4.8 Amps, not enough to trip even a 15 amp branch circuit. The main reason for ground rods is to get the Voltage difference between true earth ground and the big metal parts of the house, like EMT and plumbing, as close to zero as possible. This keeps you from getting a jingle when you touch conduit or pipes in a damp crawl space, and it keeps down the AC noise in electronic gear. That's why we sink big ground rods right under the mixing board in recording studios, where we're dealing with microphone signals down in the microvolts.
-- J.S.
Another reason for the ground is to minimize electrolytic damage of metal components in and near the house.
Of course, it isn't a "ground", it's a "grounding system", incorporating several features -- ground rods, connection to steel rebar in the foundation, connection to underground pipes, etc.
FWIW, The separation of neutrals and grounds in sub-panels is a relatively recent detail, it is very common to see them bonded together in subpanels in older work.
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Sojourners: Christians for Justice and Peace
Thanks for the input, I moved the panel,isolated the grounds, and should be all set.
Indeed the 3rd leg on the dryer is a neutral-not a ground,I plan to put a 4 wire replacement plug on it so it will be grounded at last.
On the rear of the dryer there is a jumper from the neutral to the chassis of the dryer,
I assume I should remove this jumper once I properly ground the unit.
Having done this, what is the danger of a ground/neutral bond at a sub-panel?
Is there possibility of the ground loading up if the load on the sub is not balanced?
Thanks
Yes, remove that jumper and replace the cordset with a 4 wire cordset.Having done this, what is the danger of a ground/neutral bond at a sub-panel?If the neutral should open up then anything that is connected to that neutral can be as high as 120 volts.That include the case of the dryer which is "grounded" to neutral in the 3 wire system. Also anything with a ground pin that is connected to a metal case will also be hot.