Electrical

[dail(Guest)]

Well, I tried to "login" before posting this but, as usual, I forgot my "password" again. ...sigh. To much stress in my life I guess. Anyway...

For those who are savey on electrical, I found a problem the other day that has me puzzled.
Need some idea on where to begin looking for the answer to it.

As some of you know, I'm building a 167 sq foot cottage for my sons to use while we live in our rv. (Drawings posted elsewhere at this site.) At the moment, the exterior is sheathed in black board with waffer board on the corners. I just slapped paint on it, to help protect from the weather, as this is a temporary structure.

I wired the building for 30 amp service. Now, mind you, I am a "Jack of Trades" which means, "Master of None." But I do try to be careful and study up on everything I do.
The main floor, has two circuts; a 14 plus ground for lights, 15 amp breaker, and a 12 plus ground 20 amp breaker for appliances. It is the same for the second floor.  

All wires are sheathed (Romex) and run through the center of studs with metal gaurd plates on the studs to prevent accidental nailing through from the interior walls.

The panel box, feeds off a 30 amp wire, that is connected to a 30 amp plug, and then runs to a 30 amp service outlet off the RV pole. I think the box at the RV pole, is "bonded" to the ground from neutral. The panel box, is "grounded" to the ground wires in the circuts.

Here is the problem; I happen to touch one of the sheathing nails on the outside wall, which was damp, and got a mild shock. It is near the breaker box on the inside.

I got my multi meter, and sticking a probe in the dirt, then on  several nails (galvanized 1&1/2 roofing nails) that show, got a reading of about 110 volts. Yet...
When I use my circut checker, it says every thing is wired correctly.
Infact, no breakers "throw" durring service. Everything works fine.

I'm stumped. Is there something I'm missing here?

The only thing I can figure, is that since neutral is tied to ground at the RV pole, and the panel box is grounded, that a low current is drifting back due to moisture, to the wall sheathing and framing in that area.

Is that possible?

Photos and schmatic can be supplied if that would help.

Thanks guys....dail

[JRR]

From your description, I'm not sure if you have wired a two-wire or three-wire system.  

Many years ago most houses were wired two-wire ... then codes were upgraded to three-wire.  "Hot", current carrying "neutral, and non-current carrying (isolated) "ground".  A special rod is to be driven so far into the earth to provide "ground" connection for the house.

The "ground" is to be available in each outlet and all boxes are to be connected.  (I believe) the "ground" and the "neutral" are only to be brought together by the utility company on the pole ... if then.  Nowhere else are they to be connected.

I'm a novice, so you need better advice than mine.

[manhattan42]

Couple problems.

First, a utility structure must have at minimum a 60amp service according to the National Electrical Code. A 30 amp service is a code violation and illegal in most locations.

Second, if you have framed using metal studs, you can have a potentially deadly situation on your hands.

It is possible to electrify the entire metal frame of the house if a fastener penetrates the insulation on an ungrounded (hot) conductor and it becomes energized.

This killed a man recently in Florida:

http://www.local6.com/money/7302637/detail.html

Even if you have wood or other non-metal studs, you may have penetrated your wire bundles as they enter the service panel and created a similar problem.

Could be the result of a number of other issues as well.

The bottom line is you have a very serious electrical problem and one that could be deadly.

No other recourse at this point but to call a professional electrician to eliminate the danger.

[dail(Guest)]

Thanks! I appreciate the info.
I've shut down the power to the utility building until I can figure out where the problem is.
It is not metal framing. Conduit is used to the main box. I think, since no plates were put on the outside of the walls, that a nail must have penetrated the wiring through one of the pass throughs.
I am going back and pull exterior sheathing to check all boxs and wiring.

[n74tg]

Question for Manhattan42

I read the Rafael Ugalde electrocution article on Local6.com.

It seems right now everyone is trying to initially place blame on the electrical code violation of not "bundling" the wires.  However it seems to me that bundling wouldn't necessarily have prevented electrocution; as even if bundled the wire could still be located in such a location as to allow a dry-wall screw to still penetrate both steel stud AND wire insulation such that studs could still become hot.

Maybe I don't know all the requirements of bundling from the NEC, such as exactly where wire must be placed in relation to steel studs (ie directly in the middle of the stud, so that maximum distance from flanges is maintained). Do you (or anyone else) know any more info about this?

I ask this because it seems to me that even if we use wood studs AND place all wire runs in the middle of the stud, that an errantly placed long nail could still penetrate wire insulation and make at least the nail hot.  While this isn't nearly as bad as electrifying the entire (metal) stud house frame, it still could result in electrical shock.

[dail(Guest)]

That is an interesting question.
His reply though, and then reading the article he referenced, did make me realize one thing I will deffinently do when I have the opportunity to work with metal framing again. I just didn't think about it until that article and his comments. That is, I will run all wiring in pvc conduit through the cutouts on the studs, rather than just the romex itself. And, all framing, walls, floors, trusses, etc. need to be bonded then "grounded to earth."
I just never thought about that before, till reading that article.

In this situation though, on wood framing, each "pass through" (hole in center of wooden stud.) has to have a barrier plate nailed over it, (on application edge.) to prevent accidental nailing through the wire passing through it. I did that. Which is normally done durring the rough wiring phase of a project. Which makes me wonder about an oversight on my part about something inside the panel box.

The 60 amp thing, well, this little project was somthing I've done out of necessity, and couldn't aford alot of cash to spend on. I estimated my loads and odds of use as per time of day, and figured for that. When code wants you to assume someone forgot and turned everything on in the house at "once," and the wiring needs to be able to handle maximum capacity thats going to pull. Which is, I admit, the smarter route to go....it just costs more.

[manhattan42]

Caveat:

Although I am a builder and do electrical work incidental to my jobs...
And although I certify as a residential construction and plumbing inspector...and even license locally as an electrician...

My knowledge of electricity and electrical codes is limited and my opinions on the subject of electricty should not be considered 'expert' by any means.

I may know a bit more than the average person, but that should not be mistaken for having equivalent knowledge of an electrical professional.

So please take what I say with that understanding and have what I say verified by bona fide code and electrical trade experts.

Try the  http://www.mikeholt.com code forum for some real electrical help if you need it.
-----------------------------------------------------------------------------------------------------------
OK, that said,


N74tg asked:

"I read the Rafael Ugalde electrocution article on Local6.com.

It seems right now everyone is trying to initially place blame on the electrical code violation of not "bundling" the wires.  However it seems to me that bundling wouldn't necessarily have prevented electrocution; as even if bundled the wire could still be located in such a location as to allow a dry-wall screw to still penetrate both steel stud AND wire insulation such that studs could still become hot.  

Maybe I don't know all the requirements of bundling from the NEC, such as exactly where wire must be placed in relation to steel studs (ie directly in the middle of the stud, so that maximum distance from flanges is maintained). Do you (or anyone else) know any more info about this?"

The NEC as well as the Electrical provisions of the International Residential Code (which is just the NEC in condensed form) recommends that cables be placed as close to the center of studs, joists, or rafters as possible whether they are run through bored holes or run parallel to the framing member.. This applies for metal, wood, or other framing materials.

The purpose should be obvious: to protect the cable from penetration from fasteners.

However, the Code does not mandate that cables be run in this location. They can be placed closer to the edge of  framing members, or even on the finished surface of a wall, ceiling, etc...

When cables come closer than 1 1/4" inches (32mm) to the edge of a framing member, however, the cable must be protected either by being run in an approved conduit or by having protective metal plates at least  1/16" (1.6mm) thick placed in such a fashion as to cover the cable to protect it from nail or screw penetration. Alternately, one can use shielded cable (BX, MC, etc) to achieve the same purpose.

If one is seriously interested, they can find protection of cables treated in section 300.4(A) of the NEC or Table E3702.1 of the IRC.

"Bundling" is not really the correct term for centering cables as close to the middle of studs, joists or rafters. "Bundling", for electrical purposes, refers to cables run closely together through the same hole or closely together vertically through plates and the effect of creating 'hot spots' from increased resistance. But "bundling"  will serve us to mean 'keeping cables as far from the edges of framing members' for purposes of this discussion.

The point is, that cables should be run as far from the edges of a framing member as possible to avoid penetration by a fastener whenever possible.

The effectiveness of this "bundling" is relative to the thickness of the framing member, however.

(I am going to herinafter call all studs, joist, rafters, plates and framing members "studs" for simplicity sake)

2x4s studs are nominally 3 1/2" thick. 2x10s studs are nominally 9 1/4" thick.

1 1/4" in from the edge of 2x4 stud leaves only 1/2" in the center to be bored for a cable that can be run there without protection. That doesn't leave a large margin for error. For a 2x6 stud (5 1/2" nominal thickness) you can bore a hole or keep your wires 'bundled' in the center 3" of the stud and not have to protect them.

So the 'thicker' a stud the safer it can be when penetration from a fastener is a concern.

Building codes also regulate the length that fasteners can or must be for wall coverings to further protect them from penetrating electrical cables or plumbing pipes.

For example, Table R702.3.5 of the IRC indicates that when hanging 1/2" drywall, the maximum nail or screw length for both metal and wood studs can be 1 5/8". For a 2x4 stud, this should allow a maximum penetration of no more than 1 1/8" from the edge of the stud when the fasteners are properly installed and the wiring cables are centered on the studs. (1 5/8" screw - 1/2" drywall = 1 1/8" stud penetration)

However, using longer than approved  fasteners (a building code violation) could cause penetration of an even properly centered cable...and why coordination between code inspectors and the builders and electricians and plumbers is such a crucial element of proper construction.

So you are right, using the 'wrong' fastener; One too long for the designated purpose can cause penetration even when the cable is properly located.

In the article, improper 'bundling' is but one of the 'mistakes' that led to this tragedy.

Not having the metal frame of the house grounded is another, but Florida Code will soon change that.

[Dberry]

Well, I tried to "login" before posting this but, as usual, I forgot my "password" again. ...sigh. To much stress in my life I guess. Anyway...

The main floor, has two circuts; a 14 plus ground for lights, 15 amp breaker, and a 12 plus ground 20 amp breaker for appliances. It is the same for the second floor.  

All wires are sheathed (Romex) and run through the center of studs with metal gaurd plates on the studs to prevent accidental nailing through from the interior walls.

The panel box, feeds off a 30 amp wire, that is connected to a 30 amp plug, and then runs to a 30 amp service outlet off the RV pole. I think the box at the RV pole, is "bonded" to the ground from neutral. The panel box, is "grounded" to the ground wires in the circuts.

Here is the problem; I happen to touch one of the sheathing nails on the outside wall, which was damp, and got a mild shock. It is near the breaker box on the inside.

I got my multi meter, and sticking a probe in the dirt, then on  several nails (galvanized 1&1/2 roofing nails) that show, got a reading of about 110 volts. Yet...
When I use my circut checker, it says every thing is wired correctly.
Infact, no breakers "throw" durring service. Everything works fine.

I'm stumped. Is there something I'm missing here?

The only thing I can figure, is that since neutral is tied to ground at the RV pole, and the panel box is grounded, that a low current is drifting back due to moisture, to the wall sheathing and framing in that area.

Is that possible?

Photos and schmatic can be supplied if that would help.

Thanks guys....dail

I would try and narrow it down to what part is causing it.  First with the main breaker off is the voltage still there?  no?  2nd power one circuit on first.  Check.  Then turn it off and check the other.  narrow it down to the 15 amp or 20 amp leg.  Did you use stranded wire by any chance?  Could one strand have contact with the siding?  Do you have an aluminum foil type radiant barrier installed with the insulation?  If you can narrow it down to which leg is the problem, you can disconnect the wire from the service connect and check again.  Perhaps the box has a faulty insulator?  

Just use your multimeter to do the checking and make any connections with the main breaker off.  Post on what you find out as this is an interesting puzzle.  One other idea.  Are you building near any buried lines?  

Good luck

[manhattan42]

Here is a picture of nailing plates as used to protect electrical cables and plumbing pipes from nail penetration:

http://www.tlc-direct.co.uk/Images/Products/size_3/TLSP1.JPG

[Amanda_931]

shhhh!  

don't tell anyone,

it's not that safe

[size=11]But I tend to stick the convenience--as opposed to security--type passwords in a folder at the ISP or the portable email.  Here, or the New York Times, for instance[/size]

[dail(Guest)]

I appreciate the discussion on this paticular subject. I learn something new all the time from others. I have a very broad background of experiences to draw upon when working on projects but, I'm not a real expert at any of them.  

Sometimes I do not know which is better; being "handy" or being "specialized."

My son and I, went out last night and ran some tests. I stuck one probe in the ground, then setting the volt-ohm to AC voltage, tried to test for leakage while he flipped breakers, by touching the nail heads on the exterior sheathing with the 'hot' probe. (1/2" black board on 2 x4 studs. And yes, the 2 conductor with ground vinyl clad cable is run through 1/2 dia. holes in center of studs width.) The black board was damp from a previous day's rain storm.

Starting with all breakers off, we got very low voltage readings (+/- 0.34 volts. The test area is near the panel box on the inside.) until he flipped one last breaker. Then I got a reading of 84.3 +/- varible. Less than the other day. (But I had pulled those nails that gave me the 110.)
I think now, I know what is happening. Based on my limited knowlege of the subject. Since no breakers have tripped, and the circut tester shows no shortage to ground on any of the circuts; an additional sheathing nail (galvanized 1 & 1/2 inch roofing) must have nicked a "neutral" wire. (hole may be off center.) I had gone back and added some later once we 'threw up' the basic wall and did the rough wiring. (We've been in a hurry on this project.) No plate gaurds where put on the outside, just the inside walls.
Since no sideing is on yet, I plan on pulling the sheathing and seeing what "gives" in that area. (Black Board, is just "glorified cardboard. When it rains hard, that stuff gets soaked like a sponge.)
This utility building, is meant to be temporary, hence the hurry in construction.

Hopefully it will be a simple fix...

[glenn-k]

I have to disagree with you, Dail.  One of your nails hit the hot wire.  Neutral or ground shouldn't give you any reading as they are tied together at one point or another, especially if you are gettiing 84 volts if I read rignt.

Now you could probably read voltages on nail heads noting differences in voltage, and locate the one with the highest voltage as resistance through the wood should lower the rest - maybe.  Wear your rubber boots and don't touch anything except the test lead.  Keep your helper there to turn off the breaker if you get stuck to the wall.

If reading neutral to ground your reading should be zero.

[dail(Guest)]

Thats ok. That was my best assumption based on my limited knowlege and what I was seeing at the time.

At the moment, that breaker is "off." So I am getting no reading. I'm going to pull the sheathing and insulation out and try to figure out exactly where the hot spot is. There are four "pass throughs" in that location. (Under a window.) All power will be off at that time.

[Jimmy_Cason]

A little basic electrical safety for those like me that are unaware.

http://www.cdc.gov/elcosh/docs/d0400/d000467/d000467.html


Does anyone know the dangers of using a portable generator in a light mist? I would assume it would be just as bad or worse than a regular outlet. I am sure I will need to tell my wife one day soon that I cannot work on the house because of the weather. I need a little info to give her when it happens.

[Daddymem]

shhhh!  

don't tell anyone,

it's not that safe

[size=11]But I tend to stick the convenience--as opposed to security--type passwords in a folder at the ISP or the portable email.  Here, or the New York Times, for instance[/size]

A couple different, easier solutions.

1.  Passphrases not passwords.  "Ilovevanillaicecream" is an example.  More here: http://en.wikipedia.org/wiki/Passphrase
It goes deeper than what wikipedia has, but don't wanna bore ya but basically phrases are a lot easier to remember and the length makes it a lot harder to crack, even without number and letter combinations.

2.  Common password with site variant: add letters to a common password based on what site you are on.  For example, say rutabaga is your standard password.  For countryplans, think CP and make your Countryplans password rutacpbaga, for gmail rutagmbaga...etc.  Of course, rutabaga is pretty non-secure by itself anyways so try a common word with number, symbol and letter combination like ru7@b@g@.  Again, this can get pretty in depth - or you could just use this to generate a good common password to begin with: http://www.winguides.com/security/password.php

[glenn-k]

Maybe I'm stupid, Jimmy, but we were working on the 6 acre warehouse in the rain water 1/2" to 1" deep using GFI equiped outlets or our welder generator.  Never even got a tingle.  We always carried around a 8' 4x4 to throw at our partner to knock him free of the wires if he should become stuck to it.  OK -I was exagerating there a little but we didn't have a problem and do watch out when we are doing it. :-/