440 foot run #2 Alum. sub-panel question

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  #1  
Old 01-19-08, 07:28 AM
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440 foot run #2 Alum. sub-panel question

Ok here is my layout, I have a 200 amp main panel in house with a 60 amp double pole breaker feeding #2 aluminum running 440 feet to a sub-panel in garage. Its #2 3-wire so i will have to drive ground rods at the garage. At that distance Im only good for 20 amps per leg so I plan on putting 2-20amp breakers and dividing the load betwwen them. Now the sub-panel I got has just 2 lugs for the wire and not another main breaker so to speak. Also only one grounding lug. My questions are:

Is this Ok to have direct lines feeding the panel and not have another main breaker to be able to shut off at the sub-panel?

Also I assume i will have to add a grounding lug for my grounds that will attach to my ground rods. correct?

The lug thats in the panel now is insulated from the panel itself so this is for the neutrals and the grounding lug i will install will be solid to the back of the panel itself. correct?

My 200 amp main panel has just one grounding lug that has all the neutrals and grounds in one and its insulated from the back of the panel. Why wouldnt something ground the panel itself?

mike
 
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Old 01-19-08, 08:25 AM
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I'm not an electrician, but if your subpanel has less the 4 breakers, it might even be 6, you do not need a main disconnect at the subpanel. The inidividual breakers in the subpanel serve as the disconnect.

You will though, have your main disconnect in the main panel where you are tapping power out of.

Someone will correct me if I'm wrong, so hang in there.
 
  #3  
Old 01-19-08, 09:34 AM
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You need a ground rod at the garage regardless of whether it is a three wire or four wire feed.

If you have any other metallic path to the garage (water pipe, phone line, etc.) then you must have a four wire feed to the garage.

A three wire feed to the garage requires that ground and neutral at the garage are one in the same. A four wire feed has them as separated. The ground always gets bonded to the panel.

Install the proper number and size circuits you need at the garage. Do not limit yourself to two 20 amp circuits, unless that is all you need.

I would install a larger panel than what you have.

The main panel should be bonded to the buss bar(s) for the ground and neutral wires. If it not then make it so.
 
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Old 01-19-08, 10:29 AM
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The main panel should be grounded no matter what, but depending on if you have a service disconnect outside the neutrals may be isolated for a reason. If you just have a standard meter setup then yes it should be bonded.
 
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Old 01-19-08, 11:10 AM
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The math says that the most i can have with a 5% voltage drop is 20 amps per leg because of the distance so that is why i will have 2-20 amp breakers. i doubt i will need more then that anyway.

So your saying the Neutral and ground will be in the same bar at the garage? I did not know that and again I am surprised from the factory that the bar is isolated from touching the panel itself. Why do they do that? I have to make a jumper wire or something to ground the panel cover itself? I guess i will have to do that in My house too and every other panel around here i dont get why they dont do that from factory. That subpanel holds 8 single breakers any more thoughts on having the wires feed it directly versus having a seperate main breaker?

Also the only other metal going that 440 feet besides the electric is a coax cable that i will use for security camera and that camera will get its power from the garage and only send an RF signal through it to the house. That may not be code but its too late now the 3 wire is buried and in conduit.

mike

mike
 
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Old 01-19-08, 11:22 AM
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You need a four wire feeder to the garage. Period. That coax wire is a metallic ground path.

Pull the wires out of the conduit and the re-pull with a ground. You should have figured this out first. Your installation will be unsafe and will not pass inspection. You pulled the wires through the conduit, you can pull them out. At least I hope you pulled them through the conduit. If you pulled the wires as you assembled the conduit the you ruined the wires, and need to replace them anyway.

Wire the garage properly. If you only need two circuits then put in two circuits, But do not let the voltage drop issue get in the way. The breakers in the panel have nothing to do with the maximum current feeding the panel.

As for the ground/neutral issue, the neutral buss is NOT bonded to the panel so that it can be a neutral (only) buss. A neutral buss does not connect to the panel. Instead the panel is connected to the ground buss. A green bond screw is provided when it is proper to connect the neutral buss to the panel, that is when the neutral buss and ground buss are on in the same.

In your case you need a four wire feed and separate neutral and ground busses. Use the provided neutral buss without the bond screw as the neutral and add a ground buss.

Do the job right, or don't do it at all.
 
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Old 01-19-08, 11:32 AM
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ok so in my house on the 200 amp entrance with no seperate grounding bar i will jump a wire to the panel itself to ground that. Correct?

As far as pulling out 440 feet of wire........aint happening. Its direct burial #2 alum. and i ran the wire first on top of the ground and slid the conduit over it and assembled and then buried. How can you ruin the wires by not pulling them through? Now with 2 ground rods at the garage, how in the heck can ground jump into the shielded coax cable and run all the way to the house? if i dont put a grounding block on the coax cable would that be better or worse?

mike
 

Last edited by rotomike; 01-19-08 at 12:07 PM.
  #8  
Old 01-19-08, 12:14 PM
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If your main panel is not bonded to the ground wires, it should be.

You ruined the cable. The glue and/or cement on the conduit destroys wire insulation.

You do not understand grounding. The ground rods at the garage have nothing to do with the ground between the house and the garage. You are going to see current traveling over the coax for your security camera, possibly destroying the camera or the receiver at the other end. Further, your grounds at the main panel and the house will have current on them, providing the possibility of someone getting shocked.

You setup will fail inspection and it jsut might kill you or someone else.

Please fix it. You should have planned it first, and then only done the work AFTER you learned what was proper. You will have a very unsafe situation. It;s a hard lesson to learn, but it;s better to learn a lesson and do more work than it is to die because you were too lazy to fix your improper installation.
 
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Old 01-19-08, 12:32 PM
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Im just doing what my electrician said to do and he supplied me the stuff. When he runs long runs like that he does the cable first and then slides conduit over it and says he has done it hundreds of times. Your saying that PVC cement will eat through direct buriel wire? I will be amazed at that. That casing has to be about 1/8" thick and i am going out to garage and load up some pvc cement on en extra piece of direct burial #2 alum. and see what happens.

" You are going to see current traveling over the coax for your security camera, possibly destroying the camera or the receiver at the other end. Further, your grounds at the main panel and the house will have current on them, providing the possibility of someone getting shocked."

where is this current coming from? Your saying its going to go through the 100% shielded coax from the #2 alum?

Mike
 

Last edited by rotomike; 01-19-08 at 01:05 PM.
  #10  
Old 01-20-08, 08:55 AM
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I don't know about the grounding but as for the coax.


Coax and Category cables (networking/phone) cables are recommended to be at least 12 inches from the nearest electrical cable if they are running in the same direction.

You can cross the cables at 90 degree crossings if they have to touch but that should be limited to only if you have to.


The reason for this is the direction of current and how it works. The current will cause interferrence in your coax cable and can definately destroy circuits in any devices you have plugged into it.




I don't think you have done enough research to start this project and I don't think you are taking very logical advice from the people you are asking help from.




A simple book from Home Depot will tell you to fish the wire regardless of length because the cement can deteriorate the shielding/insulation. You aren't going to be able to sit there and watch it because it is something that happens over time and is speed up with heat. It hardens cracks and eventually breaks.




From the sounds of it your electrician friend doesn't know the safety guidelines or read up on current codes from the NEC though. I am studying up on how to add circuits and recepticals in my garage and I know not to do the pipe run, pvc or metal conduit, AFTER the cable. And I got that information from a 15$ book from home depot.



Coax is supposed to be a minimum of 12 inches away from electrical cable when running parrellel. There are no codes for this, but it is the recomendation because of the damage the interferrence causes on devices plugged into the coax. Same with Cat5e Cat3 Cat5 Cat6 cables. Coax and Networking cables can be run together but not with electrical.


You can doubt it all you want, doesnt make it any less true.
 
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Old 01-20-08, 10:04 AM
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well after doing lots of research on the cement Im not at all worried as it will not eat through it. The odds on it eating through 2 wires big enough to let the 2 wires touch in the same spot is a million to 1. There is no documented proof anywhere on the internet that i could find and the only thing i saw was that its the acetone that is harmful and it wont eat the HDPE coating on the wire. Also i did the same wiring run 6 years ago with my barn and it still is fine and I called my electrician today and he just laughed and said they have been doing that for decades with pvc and never had a problem. Our state inspector recommends using 3 wire almost all the time with seperate groud rods at the subpanel. As far as that coax goes, again im not worried i run coax all the time parallel with electric and even though its not recommended it works fine and i never had a problem. Its juts a cheap camera feed and if it has a little interference its no big deal but i doubt it will. All the cable is shielded.

Im confident now on everything working and i think its a bit overkill to say "its all ruined and you must pull it out" And things like "you could get killed" That is just overkill and on another forum an electrician moderator said i would be fine.

mike
 
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Old 01-20-08, 10:32 AM
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You won't pass inspection the way you have things.

Why did you start this job before learning how to do it properly?
 
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Old 01-20-08, 10:34 AM
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and on another forum an electrician moderator said i would be fine.
Was this about possible cement problem? Can you provide a URL for the thread?
 
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Old 01-20-08, 10:49 AM
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you asked why i started this job without learning how to do it properly. The answer is "I DIDNT" I asked my electrician and he supplied me the stuff and told me how to do it. He is not worried at all about the pvc cement. he did say that the coax probably isnt code. In My town we have no code enforcment officer or anybody that comes around and looks at anything. Small town with barely a town office. There wont be anybody coming to look thats for sure. Worst case scenereo is that i can cut the coax cable on one end and possible pull that out of there but the electric is staying.

Mike
 
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Old 01-20-08, 11:13 AM
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PVC cement melts PVC to form a weld. PVC cement also melts the insulation on wires.

You didn't ask a qualified electrician. No qualified electrician will apply conduit AFTER the wire has been pulled through.

I also doubt that a qualified electrician will tell you to pull a three wire feed to an outbuilding when the newest codes will require a four wire feed , and when he knows that you will be running something else metallic.

Rem,ember this, you have only saved money until it fails. Ans it will fail. Maybe not for you, but it will fail.
 
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Old 01-20-08, 11:18 AM
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our state electrical inspector says to run 3 wire and not 4 wire to an outbuilding and to ground it at outbuilding is safer and better the 4 wire. Pvc cement does not melt HDPE which is the outer casing of the wire. Show me the proof on that! you wont find it.

Mike
 
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Old 01-20-08, 01:26 PM
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Regardless of whether you run three or four wires, you still need a ground rod at the building. The ground wire serves a different purpose than the ground rod.
 
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Old 01-20-08, 01:47 PM
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With the coax, I believe the biggest concern isn't interference from being too close to electrical lines, but rather current that may be carried on it. It doesn't matter how many layers of shielding there are, the metal in the coax will still conduct electricity. There could be a different voltage potential for the ground at the house and garage. You are interconnecting them when you connect the cable to devices that are then connected to the electrical systems at each building. I don't think the coax is the only problem with your project, but I wonder if you could use a wireless (or fiber-optic) link from the garage to the house.
 
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Old 01-20-08, 03:44 PM
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Originally Posted by racraft View Post
Regardless of whether you run three or four wires, you still need a ground rod at the building. The ground wire serves a different purpose than the ground rod.
i was told with 4 wire your not suppose to drive ground rods at other building and that is the reason for 4 wire.

mike
 
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Old 01-20-08, 03:51 PM
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Originally Posted by Strategery View Post
With the coax, I believe the biggest concern isn't interference from being too close to electrical lines, but rather current that may be carried on it. It doesn't matter how many layers of shielding there are, the metal in the coax will still conduct electricity. There could be a different voltage potential for the ground at the house and garage. You are interconnecting them when you connect the cable to devices that are then connected to the electrical systems at each building. I don't think the coax is the only problem with your project, but I wonder if you could use a wireless (or fiber-optic) link from the garage to the house.

there may be some sort of wireless but 400 feet through woods may not be easy. This camera will be sending an rf signal which is very low voltage and its not like satellite sending 18 volts. also you should be able to plug into 2 different spots its all tied to same transponder and it shouldnt be different voltage or enough to bother. Like i said this is like extreme low voltage going through the cable and the electric lines will be under no load most of the time unless i put lights on in building. I have ran coax several times in houses through the same hole with electric in ceiling hundred feet right beside several electric wires and never had a problem. Im not saying it cant happen but i never have seen a problem but we will see when i fire it up.

mike
 
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Old 01-20-08, 04:07 PM
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You miss the point entirely, and you do not understand electricity.

It is dangerous and against code.

Bottom line. Your setup is against code, a life threat, and you are risking more than you realize by using it.
 
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Old 01-20-08, 05:07 PM
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Originally Posted by racraft View Post
You miss the point entirely, and you do not understand electricity.

It is dangerous and against code.

Bottom line. Your setup is against code, a life threat, and you are risking more than you realize by using it.
Only way its a life threat is if the neutral breaks somehow and current jumps and one way or the other there is ground rods and breakers on both ends so i aint worried about it. The chances are way better of me getting struck by a falling 747 jet. I do understand electricity and My electrician who has been one for 20 years says i will be just fine and dont listen to the internet _________!!

I will be back in 10 years to give you my report on how good things are working. Again, my barn is setup the same way with no problems for 6 years and that has phone and coax in same conduit and a 12/2 with it also hehe and my other garage has several wires in the same conduit including entrance wire and that has been since 1989 so about 20 years so yeah you can say code this and code that but its not life threatening unless some major freak accident which could happen even if there were 4 wire instead of 3 wire.

Mike
 
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Old 01-20-08, 05:23 PM
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Originally Posted by racraft View Post
You miss the point entirely, and you do not understand electricity.

It is dangerous and against code.

Bottom line. Your setup is against code, a life threat, and you are risking more than you realize by using it.
racraft, if i pulled the coax out of the conduit all together then you would feel better about the 3 wire and no metalic path and all that and your only worry would be the cement possible eating the wire. even at that, its in conduit all the way and breakers on both ends and ground rods so how can that kill you?

mike
 
  #24  
Old 01-20-08, 05:52 PM
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The conduit will fill with water. It will eventually get into the cables due to the damage done to the insulation by the PVC glue. This will cause premature damage to the electrical wires. It may cause line voltage (ie 120 volts) to get onto the coax. Someone touching the camera or the receiver could get a nasty shock, or get killed.

Yes, I would feel better if you removed the coax. Low voltage cables are expressly forbidden in electrical conduit, regardless of how many wires are in there, so your placing the coax in the conduit was wrong from the beginning. You will still have premature failure of the electrical cable, but at least you won;t put high voltage on the coax cable.

You should have run two conduits, separated by at least one foot. Then you should have run four THWN wires in one conduit for electrical power and your coax in another.

ANY book on home wiring and any competent electrician would have told you this. It sounds like you had neither of those for assistance, which is a completely avoidable mistake that you made.
 
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Old 01-20-08, 06:50 PM
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early on you said i would be fine with 3 wire and ground rods at the sub-panel if i didnt have a metallic path. Now your saying 4 wire but anyway, how in the heck is that conduit going to fill with water? every joint is cemented and it goes from building to building.

if i leave the coax in place i will be sure to have it run through grounding blocks which should keep someone from touching it to get a shock.

Mike
 
  #26  
Old 01-20-08, 08:16 PM
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A three wire feeder is allowed by old code rules to a detached building. It is, however, not as safe as a four wire feed, which is why it is no longer allowed by new code rules.

Underground conduit fills with water. The conduit leaks and there is condensation due to the warm air from the building(s).

You still aren't understanding. Grounding the coax won't make a difference. Doing so will actually increase the current flowing on the coax shield.
 
  #27  
Old 01-20-08, 09:02 PM
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racraft is fond of saying 'will fail' when the reality is 'probability of failure is increased and expected life is reduced'. He can rub people the wrong way when calling them out on errors, but the reality is that 99% of the time when he calls you out on an error, you've done something wrong.

He has pointed out very real code issues with your installation.

Code _requires_ than conduit systems be installed complete from one pull point to another, and then the conductors installed. This requirement applies both for metal and plastic conduit systems. The _potential_ of conductor damage caused by glue is only one of the reasons for this requirement, and I don't know the others. I simply know that this is a code requirement. The PVC cement produces a solvent weld, and must soften the PVC conduit in order to do the job. The same solvents (and solvent fumes) can potentially soften the PVC insulation. This is not to say that they _will_ do this, just that it can happen, and that the risk is high enough that this is not code compliant.

Code has specific restrictions for 'low voltage' cables sharing a conduit with power cables. Most low voltage systems are not designed to deal with the voltages and currents available from power systems, and low voltage systems are not built with the same safety protections built in to the system. Any sort of short between power conductors and a low voltage conductor will be _much_ more dangerous than a similar short from one power cable to another.

The specific code requirements with respect to 3 wire versus 4 wire to a detached structure talk about _bonded_ metallic paths, not _any_ metallic path. The reason for this requirement is to prevent neutral current from flowing on the 'parallel path' associated with that alternate bonded metallic path. In a 3 wire installation, for safety you _must_ bond neutral to ground at the detached structure. This means that any bonded metallic path will be electrically in parallel with the neutral. If this happens, then whenever you have current flowing on the neutral (in other words, most normal use of electricity), then some significant fraction of that current would flow on the parallel path.

Coax usually has a _grounded_ shield. It prevents noise from getting to the central wire, but the _shield_ is the problem here. That grounded shield could become a parallel path and cause serious issues. (In fact, this is a recurring problem in a place that the NEC does not control: cable tv outside lines. The cable line coming in to your house gets its shield grounded at the house...but it is also grounded at the cable company box outside. Sometimes you find enough current flow on the shield conductor to melt the cable.)

Code has recently changed to prohibit 3 wire feeds to detached structures. My _hunch_ is that for longer outdoor runs without conflicting parallel paths, the 3 wire feed is potentially safer, but the code making panel decided that the very significant risks of conflicting parallel paths was sufficient to prohibit that practice. 3 wire feeds may still be legal in your area if the latest code has not be adopted; this is especially likely if the local inspectors feel that 3 wire feeds are safer.

Underground conduit is considered a wet location, even if it is very well sealed. If nothing else, air movement will cause condensation which can fill up the conduit. This is not to say that all underground conduit will be soaking wet, just that enough underground conduit is wet enough that code requires that it be treated as a wet location.

Finally, IMHO any electrician who advises someone to do something that explicitly violates code is not a qualified electrician. They may very well be hired out and paid to do electrical work, but they are missing something in the form of basic continuing education.

-Jon
 
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Old 01-21-08, 06:28 AM
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Winnie, I didnt know there was some nice guys on here. Thank you for your remarks. very informative and reasonable explanations. Well the local state inspector does in fact believe that 3 wire is safer and i think what i will do is pull out the coax to make everyone happy but leave the electric. This is run in 2-1/2" conduit and it would take a lot of condensation to fill it. I will have it sealed on both ends. Like i said i did my barn that way 6 years ago and all is good so i will wait this one out until a failure (if any) happens.

Mike
 
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Old 01-21-08, 10:57 AM
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There are lots of nice guys here. Anyone who donates their time to competently helping others is a very nice guy.

Don't let the fact that the 'personality' of the advice that I give is different from racraft's; I am in absolute agreement with racraft that your installation is not code compliant and advise you to re-do it. It is my personality to describe shades of grey, his personality to say 'code' or 'not code'. But I do not advise anyone to violate code.

I cannot compel you to dot every 'i' and cross every 't', though I do hope that I've helped you make an informed decision.

Best of luck
Jon
 
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Old 01-21-08, 05:53 PM
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I worked at a guys house today and co-incidentally he is a master electrician and trains or teaches electrical and is very smart and had the 2008 NEC book out. Anyway he said 3 wire is the best way to go and he wasnt sure about the 4 wire deal so he looked it up and its not concrete about using 4 wire and he highly recommends i stay with 3 wire and its much safer and better then 4 wire. Especially at 440 feet!! he said go 3 wire for sure. I asked about the pvc cement and he just chuckled and said people have done that for years and he never heard of any problem nor could I find anywhere on the internet anybody that ever had a problem with pvc cement and wire. I told him someone said it will fill with water and again he chuckled and said there we be condensation in there but it wont fill up. He again said dont worry about the 3 wire just run it like it is. he didnt like the coax cable in there and i have decided to pull that out at least.

Mike
 
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Old 01-21-08, 06:10 PM
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Mike,

I find everything you said hard to believe. It doesn't matter what version of NEC is out (i.e. 2008). Local authorities dictate what NEC they follow.

This "Master" electrician had to look up what a 4 wire setup was?
 
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Old 01-21-08, 08:16 PM
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i am not lying and the guy didnt believe that the 4 wire is the new NEC code like you said earlier. He knows what the heck a 4 wire set-up is he teaches this stuff. He looked it up and he didnt see where it said that 4 wire is the current NEC standard for a situation like mine running 440 feet away. He indeed said that along with the other electrician i talked to. Both say 3 wire is way better and safer.

our local inspector says 3 wire so that is what it will stay. just like i was told to do in the first place. Only thing i really did wrong was the coax in which i will pull. I am not lying at all about what both of these guys say. I will talk to 2 more electricians that i know and i bet they say the same. i think your going a little over board here.

Mike
 
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Old 01-21-08, 10:28 PM
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It would be interesting if one of the electricians here who is a member of the Mike Holt forum post over there about the major points of contention here.
 
  #34  
Old 01-22-08, 09:11 AM
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The original poster has his answer.

He had three code issues. 1) The coax in the same conduit as the feeder, 2) the three wire feeder with the parallel path, 3) the glued in sections conduit. He has solved 1 and 2, and chosen to leave 3...which IMHO has far more to do with performance and reliability than safety. If it were my house I would change it; if I were visiting him I wouldn't lose any sleep.

With regards to a master electrician not knowing the latest and greatest code, that is not a question of skill or workmanship, but a question of continuing education. More than likely, a group of DIYers who use these forums will be more aware of current changes than a professional who doesn't hunt down continuing education. If the local inspectors push three wire feeders, then it is quite possible that the electrician has not come up to current code on that topic.

(History: for a long time, code provided the _option_ of a three wire or four wire feed to a detached structure. All 'services' are essentially done with three wire feeds, so it makes "sense" that detached structures be wired in the same way as the original structure. However there are real safety issues with three wire feeds, in particular the parallel path issue. In the 2008 code the rules have changed to eliminate the 3 wire option, though many localities have not adopted the 2008 code yet. )

You can read the relevant code sections yourself. Go to http://www.nfpa.org/freecodes/free_a....asp?id=7005SB
agree to the license, then 'open national electrical...' (This gets you the 2005 code)
http://www.nfpa.org/freecodes/free_a....asp?id=7008SB (This gets you the 2008 code)

The part about the conduit being continuous prior to putting the cables in is 300.18(A) (the general section) and 352.30 (the section specifically dedicated to Rigid Nonmetallic Conduit)

The part about 3 wire and 4 wire feeds is in article 250 "Grounding and Bonding", in particular 250.32 "Buildings or Structures Supplied by Feeders or Branch Circuits. In the 2005 code, 250.32(B)(1) describes the 4 wire feed, 250.32(B)(2) describes the requirements for a 3 wire feed. In the 2008 Code you will note that this section has changed, and you only have 250.32(B) for the 4 wire feed.

I should note: we are using the terms 3 wire and 4 wire feed. Really the issue is one of having a combined neutral and equipment grounding conductor (3 wire) or separate neutral and EGC (4 wire)...the code talks about the separate or combined neutral and EGC, to be general for single and 3 phase service.

-Jon
 
  #35  
Old 01-22-08, 01:55 PM
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Very Good Winnie and your right i have chosen to leave the wire even if it got a little glue on it and we are talking a storage building really with most likely only lights and maybe an outlet or 2 for plugging in something but real minimal use so if something fails then i re-run new wire no big deal but i will keep a eye on things. No need to throw away $500 worth of cable because it MIGHT by some fluke of a possibility (none ever reported) that it may go bad somehow when i can use it for maybe 10 years maybe 20 or maybe till i die. My other system done the same way has 6 years going strong and guys have dont it this way for years around here and never a problem so why throw away wire with such a remote chance of getting damage.

As far as the 3 wire goes well maybe the code writers feel 4 wire is better but the inspector around here will let 3 wire fly no problem and if there were "real safety issues" like Winnie said then they would make people re-due the current set-ups in which there are thousands or millions all over the US with 3-wire and i havent seen it on the evening news for everyone to pull them out and re-due them with 4 wire so i dont think its a "real safety issue".

i am going to make a sample piece of conduit closed on both ends maybe 4 feet long and put some 3 wire in it and gob some pvc cement on it in a few places and set it underground and maybe another sample above ground and check it from time to time year to year and see if anything happens. I can come back and post my results years from now if this thread is still kicking around.

Mike
 
  #36  
Old 01-22-08, 03:06 PM
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I understand that this is an academic discussion at this point, and that I will not convince you to change your mind. I am proceeding on the basis of reducing any remaining minsunderstandings.

Electrical systems are _very_ safe. Not perfectly safe, but pretty darn close. What this means is that something can be less safe than code mandates, but still pretty safe. Imagine if you will some sort of installation which, when done properly to code, has a 1 in 100,000,000 chance of failing and burning down your house in any given year. Now imagine that someone does a 'hack' job; this version doesn't meet code, and has a 1000x greater chance of failing and burning down your house. The most likely event is that the failure won't happen and the house won't burn down...but the hack job is 1000x more dangerous than the proper job.

The _known_ safety issues with '3 wire' installations are all pretty much associated with the 'parallel paths' issue that I discussed above. If your local inspector understands the parallel path issue, and is pushing for '3 wire' installs but is making sure that there is no parallel path, then that is IMHO just fine.

The issues with parallel paths are ones that need to be resolved, and they _are_ causing problems. Unfortunately one of the issues is that you have different code making bodies who make different rules, and the NEC does not have jurisdiction over the majority of parallel path problems: the service entrances from the power company to the building. Parallel path issues show up here as neutral current flowing on CATV shield conductors (causing them to overheat and melt), and neutral current flowing on plumbing systems (which has killed plumbers working on water pipes).

The NEC eliminated the option to use '3 wire' installations, but considers them safe enough to be 'grandfathered'. As I said previously, if there are no parallel path issues, then IMHO the 3 wire installation is probably safer for long outdoor runs. However this is just a hunch, not backed up by any sort of studies.

I look forward to the results of your experiment! My best guess: the worst risk for the glue is that the cable gets glued to the side of the conduit, and that if something fails you will be out there digging up the conduit rather than simply pulling in more conductors.

If your research turns up no problems, then you might consider writing up a proposal to change the code to permit your installation approach

-Jon
 
  #37  
Old 01-22-08, 04:14 PM
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hahahaha i dont think i can convince them to rewrite the code. They will always want the conduit to be done first because the wire has to be pullable. It must be able to be pulled in and pulled out so they want conduit done first mostly for that reason and not because cement might ruin it.
I would love to see a case where the cement did ruin cable but havent heard of any on the internet. if you find one post it.
I dont think the cement will stick to the side. Im going to try to get it to stick to outside if i can just to see if it does. I got extra pieces and extra wire so can do lots of experiments.

So if I pull the coax out of there all together and get rid of it then i will have no parallel path and the 3 wire will probabbly be fine. It was done in 2007 so it was done according to NEC recommendations at that time (if they changed in 2008.)

Winnie, I actually enjoy reading your post and very informative and educational even though you dont agree with some things I enjoy it. Very professional and makes sense.

Mike
 
  #38  
Old 01-23-08, 05:15 PM
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going to start my test project tomorrow with pvc cement and conduit.

Another question, this 3 wire has 2 lengths of #2 alum. and one #4 i for neutral. The stripe lead is smaller and Im quite sure its #4.

Question 1: Is there a code on the size of the neutral in this case?
Question 2: If there is a code and this is too small why do they make wire like that?
Question 3: If this is against code what harm will there be on a balanced load at 15 amps per leg. No answers like "it might kill me" but just real "most likely" answers.

Mike
 
  #39  
Old 01-23-08, 06:04 PM
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There are many codes that come in to play for sizing wire...I am pretty sure that you are kosher with those sizes and breakers.

Cables are made this way because in most circumstances where you are running feeders that large, the maximum load on the neutral will be less than the load on the hot conductors. Cables are generally made for the common power requirements of shorter runs.

With long runs you can run into circumstances where the 'normal' difference in conductor sizes results in a code violation, but I don't belive that you have a problem with that here. The worst issue that you have is that if you load a single 120V circuit fully without loading the other circuit, you will get more voltage drop then expected.

-Jon
 
  #40  
Old 01-23-08, 06:43 PM
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yeah i will try to balance as much as i can. If i get a compressor i will make sure its 220 and i may even break the lights up to 2 -10amp breakers. Not sure just what im going to have for lights but 40x80 building basically storage building but i will have about 10 amps maybe at the most so i may break it up so the load is always equal and i guess that means the Neutral cancels out or something to that effect so there is no load on the neutral. not sure exactly how it goes but I know to balance the load as much as possible especially in my case with a long run.

thanks again for very informative answer.

mike
 
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