Two ex. carpenters having a ( discussion) about when to put the bonding screw in a load panel. Neather knows beans about wiring. HELP!!!
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Remember, a little knowledge can be dangerous:
The neutral bar should be bonded to the box and the ground bar when it is the main panel; the panel with the first, primary disconnect after the meter.
there's a great combo....carpenters doin electrical work...
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...not much of that around here.......;>})
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...what rjw said.........!
Thats nothing! We also did the concrete work, rough framing, roofing, siding, electrical, plumbing,( sink & floor drain), insulation, and drywall. Left the furnace to heating contractor. We are building MY shop.
I know what you mean ,I don't like HVAC either !romex or conduit?
My first construction job (back in the 70's) I worked for a builder that pretty much did it all. Small company maybe 10 or less. We subbed very little. Most houses where 3000 sf plus. That's some bigguns in the 70's.
Most times he would sub the plumbing and hvac. Every thing else we did and did it good. I have seen times when we where a little slow and would build all the cabinets.
Man did I learn a lot from that guy!!
Yeah, but have you seen how bad "MOST" electricians holes are when they cut into a nice piece of cabinetry??? Most, not all and that's not an exaggeration. (Can you say exaggeration, I can't)
Just shaking my head thinking about some of the ones I've seen over the years.
well it cant be worse than when the carpys decide the electric is in THEIR way.......
migraine, ...I'm teasin' these guys...I tried to do most everything around my hooch, only to find out ....I DON"T KNOW JACK
Ahh, Another jack of all trades... master of .. maybe one??? Welcome to the society of "I'll just do it myself"
Actually, If I sold all my tools/machinery, there probably be enough money in the kitty to pay someone to finish our own home. Then I'd have time to go shopping with her
I just tell the wife, "you get what you pay for". Some day I hope she takes me up on it. I always need a little motivation
take out one of the screws where all the neutrals com in. in my panel (square d) mine was in the right side at the top. the screw will go through the nuetral bar and through the bow bonding the box.
i changed my service from the incoming to the ty in off all the original piping even tyed the service drop in and i'm a carpy.
when to put the bonding screw in a load panel.
Only the main panel, no sub panels, none of them.
I think what you meant to say was that the ground is tied to the neutral in only one place: the main panel. In any sub-panels, the supply cable's ground wire must be bonded to the panel case and NOT tied to the neutral.
If (like me) you bought one of those main entrance panel kits c/w breakers to use as a sub-panel, you must remove the installed tie-bar which grounds the neutral and you must install a bonding terminal large enough for the incoming feed wire's ground.
There's different conditions that determine whether you do or don't bond ground and neutral (aka the equipment grounding conductor and the grounded conductor).
You bond--electrically connect--the neutral and ground at the service.
The service is defined as the point at which the utility company wire ends and the premises wiring begins. It may be at the meter base, or at the main disconnect. This may be a separate cutoff box or the main breaker in the main panel.
Out here in the West and on the Pacific Coast, we usually use a combo meter socket and main panel, mounted on the outside of the house. It's called a service entrance panel or "all-in-one".
So, where you install the "main bonding jumper" to link the ground and the neutral depends on what your serving utility defines as the end of their wiring.
The other posters are right, you do not bond the ground and the neutral in any subpanel in the same building as the main panel/service. This has been an NEC rule for decades. And it's been ignored for about as long. The systems wired this way present a small but real risk of shock or electrocution, and if something goes wrong with the ground and neutral pathways back to the main panel, the risk is very serious. As in, the metal tool or fixture case becomes energized.
There was a recent tragedy in a Southern church where the pastor was in a baptismal font and was electrocuted when he touched a microphone to adjust it. Turned out someone had cut a ground connection to reduce "hum" in the audio system, a fault developed, and the pastor got caught in the circuit between the grounded metal floor drain and the energized microphone.
It's a different case if the subpanel is in a different building than the service or feeder panel, and there are no metallic pathways (metal water pipe, phone or TV cable wires, etc) between the buildings. You can get away with running a three-wire feeder (hot-hot-neutral) and bonding the ground and the neutral in the subpanel.
Good luck.
It's a different case if the subpanel is in a different building than the service or feeder panel, and there are no metallic pathways (metal water pipe, phone or TV cable wires, etc) between the buildings. You can get away with running a three-wire feeder (hot-hot-neutral) and bonding the ground and the neutral in the subpanel.not really, you still got to add four wire and not bond the netrual and ground but do add a ground rod at the bldg only connected to the ground side.also in any subpanel the netrual cannot be grounded to the box itself. Must have the plastic isolater bewteen the bus and the box.. 2+3=7
No, really. If a three-wire feeder is OK (no metalllic pathways), then you bond G to N and both to the panel housing at the subpanel. It's sort of like a new "service" for the separate structure.
On ground rods--if the subpanel is in a different structure (detached) than the main panel or service, you have to have a grounding electrode system. If your area is using the 2005 NEC, that means a concrete-encased electrode for any new construction where footings are being poured, or 2 ground rods if not. Doesn't matter whether it's a 3-wire or a 4-wire feeder, a separate structure has to have a grounding electrode system.
You could look it up--see the 2002 NEC Sections 250.32(B)(1) and (2).
Cliff
Edited 1/18/2006 12:06 am ET by CAP
<<The other posters are right, you do not bond the ground and the neutral in any subpanel in the same building as the main panel/service. This has been an NEC rule for decades. And it's been ignored for about as long. The systems wired this way present a small but real risk of shock or electrocution, and if something goes wrong with the ground and neutral pathways back to the main panel, the risk is very serious. As in, the metal tool or fixture case becomes energized.>>
Cap,
I know that it's the rule for sub panels, but I don't understand the purpose. I try to run possible scenerios through my brain but I can not find an example where the danger would be any different if the ground and neutral were bonded or not at a subpanel. The only time it made sense to me to keep neutral above the ground was on a shore power situation where parasitic voltage to ground caused electrolisis. What am I missing?
First of all, within a struction the term "ground" is missleading.It does not matter what the "ground" is referenced to.On high tension powerlines they some times work on them from buckets suspended from helicopters. The first thing that they do is to "ground" the bucket to the hot line. The bucket and hot line are now at the same potential so there is no problem.The same idea WITHIN the house. All grounds and and all metal that is bonded to the ground (directly or indirectly) such as equipment with metal caes, water pipes and heating ducts are at the same potential.However, whenever you have current flowing through a conductor you will have a voltage drop. Thus if you allow neutral current to flow through the ground it all of the "grounds" won't be at the same potential. And if you lose a neutral connection you can have a full 120 volts on the "grounds".For example you have a kitchen serviced by a sub-panel where only 3 wires are run and the neutral is bonded to the ground. If neutral contect is lost between the sub and main panels then everything that is connected to the EGC from that sub-panel will be hot. One item might be a refigerator that is near a sink which has a faucet that is bonded to the ground at the main panel.
QUOTE
However, whenever you have current flowing through a conductor you will have a voltage drop. Thus if you allow neutral current to flow through the ground it all of the "grounds" won't be at the same potential. And if you lose a neutral connection you can have a full 120 volts on the "grounds".For example you have a kitchen serviced by a sub-panel where only 3 wires are run and the neutral is bonded to the ground. If neutral contact is lost between the sub and main panels then everything that is connected to the EGC from that sub-panel will be hot. One item might be a refrigerator that is near a sink which has a faucet that is bonded to the ground at the main panel.
END QUOTEBill, doesn't there _also_ have to be a short somewhere within that system?That is, if you "just" lose the neutral connection, won't the connected fixtures/appliances just stop working, _unless_ there is also a voltage leak (short circuit) somewhere in that system, in which case the grounds become energized as you described?
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Sojourners: Christians for Justice and Peace
Yes, the appliacne will stop working.But you have have say all of the loads connected from hot to neutral. It is easy to leave one one and others like the frig are automatic. When anyone is one then the neutral (and thus the ground bus) will be at 120 volts.
I didn't follow that, and this is an area I'd really like to understand better.
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Sojourners: Christians for Justice and Peace
<<For example you have a kitchen serviced by a sub-panel where only 3 wires are run and the neutral is bonded to the ground. If neutral contect is lost between the sub and main panels then everything that is connected to the EGC from that sub-panel will be hot. One item might be a refigerator that is near a sink which has a faucet that is bonded to the ground at the main panel.>>
Bill,
In the problem you posted here, the problem is the failure to run a 4th wire, ground conductor, to the sub. Which I thought was required. Or am I still being dense.
"In the problem you posted here, the problem is the failure to run a 4th wire, ground conductor, to the sub. Which I thought was required. Or am I still being dense."Well the 4th wire is required when you don't bond the neutral to the ground. My basic assumption is that if one does not know what they are doing t hat typically they will violate both rules.However, even if the 4th wire is run then there can still be a problem.EGC's are sized ONLY to current current long enough for a short to clear a breaker. In the larger sizes (like a sub-panel feed) they are smaller than the current carrying conductors. Thus in you have 4 wires and bonding the neutral and lost the neutral you could have excess current going through the EGC. That could generate a larger than normal voltage drop. But it would also overheat the EGC leading to possible failure of that also.
Yeah, I’m still being dense!!! You ain’t gotta draw me no picture …but it helps. I can now see where a dropped neutral would end up using the ground wire as a conductor---and because of voltage drop create a potential to earth ground. I gotta quit drinking in the morning;)
There may be an electrical reason or it may be just the preferred practice which is code. If you go to Australia, the ground and neutral are bonded together everywhere possible. This include electrical boxes, subpanels, all junction points. The idea is to reduce ground loops I beleive but that's code in Australia. I've always wondered why as well. The best answer I can come up with is that the ground potential will always be 0v because no current is flowing in a normal condition. The neutral may be off by a few volts at 100'+ but that's because the neutral carries current, so there's gotta be a voltage drop. The idea of a ground is to protect in a fault condition and I would assume that only one circuit would fail it's hot to ground at a time. This means only one circuit worth of current is carried to force the breaker/fuse to trip when the exponential current is carried through.Clear as mud? Me too.
Hey boats,
Bill H. hit the nail on the head.
If the ground and the neutral are connected at a subpanel in the same building as the main panel or service, both the ground and the neutral will carry the return current back to the source panel. How the current divides between the ground and neutral depends on the relative impedances of the two paths. Why is this a problem?
First, as Bill laid out, if the neutral is compromised (if it's partly or completely cut, or a connection at a terminal loosens up), the ground will carry more or all of the neutral current. The system still works, BUT, depending on how much impedance ther is on the grounding path (now the partial or full current return path), the equipment grounding conductors won't be at zero voltage or very close to it, like in a normal system. So the metal parts of that sawzall or other tool or appliance or fixture with a three-prong plug are going to be carrying a voltage. How much? Depends on how good the equipment grounding path is. Could be a tingle, could be death.
Things like a partially cut conductor or a loose connection at a terminal do happen. I just did a system evaluation at an old house and found a very loose connection at the feeder neutral terminal at the main cutoff (the neutral going to the main panel). Voltage drop under load in the house branch circuits went from 15-16% @ 15 amps to 10% after I tightened it up. That's still high, there may be other poor connections, but feeder and branch circuit runs are long and the house is at the end of the secondary, a long way from the transformer, so I don't think VD will ever reach the suggested 5%.
If the EGC and neutral are bonded (at a same-building-as-main subpanel), and the neitral is open, and the equipment grounding conductor in the feeder is compromised as well (high impedance), then it's a very dangerous situation--the voltage in the equipment grounding conductors of the branch circuits supplied by the subpanel goes up, maybe to 120V. Unlikely? Yes. Possible? Yes, especially in a poorly installed or maintained system, or one that's been mucked up (through modifications by a hack, or inadvertant damage).
Then there's the point that the equipment grouding conductor in the feeder may be an uninsulated conductor (like if you're using large gage NM cable as a feeder), that's not meant to be a current carrying conductor under normal conditions.
This last point is much more of an issue with systems in metallic conduit. If the feeder ground is carrying current, that means that the conduit is, too. The conduit may be the sole equipment grounding conductor, and so depending on how much current there is on it and it's impedance, it may have enough voltage on it to present a danger of shock or electrocution. Even if the conduit has an insulated grounding conductor in it, the conduit is still going to carry some current and have some voltage on it.
There's one side issue here that's worth mentioning--how do you know if the equipment grounding conductor (EGC) on a branch circuit is good--that is, has low enough impedance to do it's job of carrying fault current back to the source to trip the breaker?
Those little outlet polarity testers, you say? Well, those will tell you if there is a break in the EGC, ir if the impedance is extremely high. But they'll show "Ground OK" even if the impedance may be high enough to cause a serious problem.
How about testing resistence of the EGC with the ohmmeter feature of a multimeter? You could check the resistence looped through the neutral and EGC, or use a test cord connected to the panel ground bar to test resistance of the EGC. But that's just DC resistance and at only a few milliamps current. The impedance of the EGC path will be different at 10 amps AC, a not-unreasonable fault current (and one which won't trip a 15 or 20 amp breaker for quite some time).
What I use to check EGC impedance is a tester that checks impedance under a heavy load. There are a couple out there that do this, but I use the Ideal SureTest most often. It's amazing to see a polarity tester show "OK", then find that the EGC impedance under a 12 amp load is several ohms.
There's more info on the Fine Homebuilding website under "online extras" and "old house wiring".
Best,
Cliff
p.s. So you'e involved in shore-to-ship power systems? Oh, man, that's a minefield. Way too many cases of electrocutions at marinas where badly designed, installed, or maintained power systems (and boat electrical systems) have caused deaths by electrocution. Or are you involved at shipyards? CP
CAP: good description.There does not need to be a neutral failure for problems to arise with ground loops.If the neutral and the ground (EGC) conductors are tied together at two or more points, then they form a parrallel circuit. Current can flow in either or both conductors. It is just like two resistors in parrallel, both resistors carry current based on ohm's law E=IR, I=E/R. In a 120 volt circuit, we know the neutral carries current. Lets say you plug in an iron (1000Watts). The neutral will carry (watts=I*E for resistance loads or I=W/E) 1000/120=8.333 amps if the neutral is used alone. If someone connects the neutral and ground conductor together, then the neutral and ground conductors share this 8.333 amps. If the ground and neutral conductor are the same size and length, then each conductor will carry 8.333/2 = 4.1666 amps. A ground wire carrying 4.1666 amps is no longer a ground wire due to voltage drop ( E=IR voltage drop= 4.1666 times resistance of the wire). This is also known as a ground loop, and can lead to very dangerous voltages on "grounded" objects.The quote :
"There may be an electrical reason or it may be just the preferred practice which is code. If you go to Australia, the ground and neutral are bonded together everywhere possible. This include electrical boxes, subpanels, all junction points. The idea is to reduce ground loops I beleive but that's code in Australia. I've always wondered why as well. The best answer I can come up with is that the ground potential will always be 0v because no current is flowing in a normal condition. The neutral may be off by a few volts at 100'+ but that's because the neutral carries current, so there's gotta be a voltage drop. The idea of a ground is to protect in a fault condition and I would assume that only one circuit would fail it's hot to ground at a time. This means only one circuit worth of current is carried to force the breaker/fuse to trip when the exponential current is carried through."
makes no sense, as to connect neutral conductors to ground conductors everywhere makes many ground loops and lots of ground current possible. I have used a clamp on ammeter on ground wires and seen over 10 amps of current flowing due to ground loops. Luckily the wire runs were short so voltage was not lethal. But, given wet hands and feet, lethal voltage does not have to be 120.Remember, bond everything metal to everything metal ( that is not at working voltage!), only bond neutral to ground at one point (typically service entrance-definition varies by locality), and check for ground current (rarely done).Frank DuValYou can never make something foolproof because fools are so ingenious.
Thanks for the education fellas-- I now be smarter-- and my kid can have his crayons back.
CAP
<<p.s. So you'e involved in shore-to-ship power systems? Oh, man, that's a minefield. Way too many cases of electrocutions at marinas where badly designed, installed, or maintained power systems (and boat electrical systems) have caused deaths by electrocution. Or are you involved at shipyards? CP>>
Yeah, a little of both. On the recreation side.
I used to own a marina where we had a nightmare sometimes identifying stray currents and voltages. Not so much from our equipment but from our customers-- improper wiring on boats causing corrosion and electrolysis-- both AC and DC.. and have seen too many hack job electrical services at shrimp and crab docks in our area. No GF protection in wet service areas-- painfully true where service exceeds 115V ie 3 phase motors for conveyers or processing equipment. too expensive to be safe is the excuse. A kid got killed a year ago while swimming at a marina outside N.O. from stray current on a conveyor with no gfi protection - a judge owned that marina believe it or not.
On the industrial side.
I'm a commercial diver by trade and water and electricity obviously don't mix too well. We constantly have 440V motors in the water with us powering tools, pumps and the like. So GFI protection is paramount-- actually more for the topside personnel handeling the umbilical on live equipment. So insulation and shielding is a trade by itself.
Edit I did SC 3 times and I still got it wrong
Edited 1/18/2006 11:39 pm ET by Boats234
Boats,
You're very welcome.
Whoa! A commercial diver--that takes some real cajones.
Using 440V motors in salt water--holy crap! I thought you guys used air powered tools. I was in a tool store once which had a bunch of pneumatic sawz-alls, supposedly for underwater work.
Best,
Cliff
More of an underwater ditch digger ;) I did it for 18 years -- now I just do a little consulting and alot of fishing
Air tools only work in very shallow water---30' and less
Hyd. tools are the norm--- using elec. over hyd. to shorten umbilical length on most applications-- its easier to push electrons then hyd. fluid.
clear me up a little on this. i have a main panel and 2 subpanels[ 1 in basement and 1 in garage] both subpanels are fed with hot,hot, netural, ground,both subpanels are not bonded. now i'm getting ready to come off the garage subpanel ,go underground in 3" plastic 150' to another 100 amp panel in the barn. are you saying i can run this with a hot,hot,ground,then bond the panel? is this to nec?i had planned on four wire,but it would save some bucks to be able to go 3. thanks larryhand me the chainsaw, i need to trim the casing just a hair.
Larry,
Yes, if there is NO metallic pathway between the buildings, you can run a three-wire feeder. That means no phone wire, no CATV, no galv iron or copper water pipe, no intercom, no nothing. With a three-wire feeder, you bond the ground and neutral at the subpanel. And install a grounding electrode system, of course.
Do yourself a favor and run a four-wire feeder. It's safer.
Cliff
there's a fhb article in the last year or so on the topic of sub-panels and ground-neutral ties.
Y'know, it's interesting how many people think they know electrical, even simple electrical like residential, because when they hook it up, it works.
But there's a lot of stuff, especially system grounding, that can be pretty well screwed up, but won't matter until something goes wrong, or two things go wrong at the same time.
Like-- a high-energy pulse on the secondary power lines (from lightning or a high voltage line contacting the secondary); or a conductor being damaged or cut, or a terminal coming loose in combination with a fault condition in an appliance, light fixture, or tool.
Then maybe there's a fire, or someone gets shocked or electrocuted.
So like an earlier poster said, a little knowledge is a dangerous thing.
There was a case a couple of years ago here in Sacramento, very close to my home, where a little girl was electrocuted at a self service car wash. An unlicensed and unqualified general contractor installed the lighting poles and didn't run a grounding conductor to each pole, instead driving a ground rod at each pole.
It worked fine for years, until a ground fault developed in one of the poles. There was no equipment grounding conductor to convey the fault current back to the breaker and trip it, so the pole became energized. The little girl touched the pole while standing in a puddle. It killed her.
I've seen some scary bad wiring done by unqualified people who probably thought they knew what they were doing. Would you believe an outdoor receptacle (15 years old, a non-GFI) with a hot-ground polarity reverse? All it would've taken for an electrocution is for someone to plug in a grounded, metal-cased tool.
And I'm not saying that a non-electrician can't become qualified sufficient;y to safely do some basic things, but it takes a lot of effort to learn enough to do it right.
Cliff