Wiring from load center to attic

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  #1  
Old 06-09-01, 06:21 PM
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I was looking for suggestions and advice for electrical circuits going into my attic. Here is the present equipment:

Exterior surface mounted load center with meter socket (100amp Zinsco yuck) and one 1/2" emt running around house and into wall. Only two 20 amp circuits currently installed. Almost all of the wiring in each room begins at a ceiling fixture and drops from there to receptacles and switches. 50% flex conduit, 50% 2-wire romex currently installed.

I would like to rewire the my single story house a little at a time and I need to start by bringing conduit into the attic from the surface mount panel and for aestetics I'd really like the least number of pipes running up the wall. I will use a big enough junction box(es) for all conductors to separate the circuit runs once in the attic

Questions:
1. If I run thhn/thwn in conduit for less than five feet on the exterior, must I use the 75 column to derate ampacity because it is considered a wet location.

2. If I decide to run cable in conduit on the exterior, must I use UF rather than NM

3. How do I figure how many cables can fit in a conduit and does the sheathing lower the temp. rating or does NM-B derate like THHN at 90

4. Are there any tips or tricks of the trade that I can use to bring circuits from a surface mount panel into the attic and distibute from there.

Thanks in advance
Phil H
 
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  #2  
Old 06-11-01, 12:23 PM
RickM
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1. If I run thhn/thwn in conduit for less than five feet on the exterior, must I use the 75 column to derate ampacity because it is considered a wet location.

The de-rating of these conductors will be based on the number of conductors in the conduit. Start in the 90 degree column, and de-rate down from there. You may have to run #10 in order to get a de-rated conductor to handle 20amps.

2. If I decide to run cable in conduit on the exterior, must I use UF rather than NM & 3. How do I figure how many cables can fit in a conduit and does the sheathing lower the temp. rating or does NM-B derate like THHN at 90

You do not have to use UF cable. The size of the cable is based on it's physical size (width), and is treated as one conductor. If the cable is flat, use the largest measurement (see note 9 to Tables, Chapter 9, 1999 NEC). Add up the sizes, and select a conduit which will handle that size, according to code. The de-rating is based on 90 degree, just like THHN. However, when you are through de-rating, the ampacity of the wires cannot be more than the rating of the 60 degree rated conductor.

4. Are there any tips or tricks of the trade that I can use to bring circuits from a surface mount panel into the attic and distibute from there.

I would suggest running seperate THHN conductors, thru conduit, to a j-box in the attic. Base the size of the box on the size of conduit you run to it. Run your cables to this j-box, and make up all your conductors with approved wire nuts. Remember, if metal, this box will need to be grounded. You can run 1 ground from the panel to this box, based on the largest overcurrent device, and land it to an approved bus. This will allow you a location to land the equipment grounding conductors from the cables.

Hope this helps.

Rick Miell



 
  #3  
Old 06-11-01, 02:14 PM
resqcapt19
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Rick,
I don't agree about the derating. If it is THHN/THWN wire and installed in an outside raceway it is only 75C wire and any required derating must be from the 75C column. An outside raceway is a wet location. If it is THWN-2 then it is 90C wire even in wet locations.
Don(resqcapt19)
 
  #4  
Old 06-11-01, 07:22 PM
Wgoodrich
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Rick I agree with resqcapt19 concerning the wet location requirement both due to location and starting point of derations.

However he mentioned running the conduit up the wall from the top of the panel. If he places that panel high enough without violating the 6 1/2' max on the main breaker in the panel the conduit may be less that 24" in length therefore derating would not be required.

I do agree with your conduit fill thoughts. The cable must be calculated concerning conduit fill according to the maximum width and as a round conductor. This would make it about equal to the demensions of a #2 insulated conductor considering fill of the conduit.

I agree with changing the wire to THWN due to the fact of the difficulty of limiting the number of conduits as he wishes.

I don't think either of you answered but if he ran nonmetallic sheathed cable instead of THWN it would have to be type UF cable due to the wet location. Type NMB cable is allowed only in dry locations.

If it were me and if he is intending to rewire the structure, I would check into upgrading the service at this time and install the new panel inside the dwelling. Two things would benifit. The Romex then could go inside the wall directly into the panel and the panel should increase in life expectancy substantially.

Hope this helps

Wg
 
  #5  
Old 06-11-01, 10:39 PM
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Thank you all for your responses. I like the idea of using a bus in the junction box for the grounding conductors. I have thought about upgrading the service, but I had not thought about moving anything until now. Another good reason for replacing my panel is the cost of Zinsco breakers.

Thanks
Phil H
 
  #6  
Old 06-12-01, 09:31 AM
RickM
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Don & Warren,

Why do you consider a conduit, run on the surface of a structure, as a wet location? If it is because of the fact that it is outside, then why are you allowed to install overload devices in the panel, directly below it? If the interior of a metal conduit is a wet location, is not the interior of the panel? (See Defination of "Wet Location" in Article 100)

The inside of a conduit run underground is in a wet location, but a conduit run up a wall? The conduit itself could be in a wet location, but the interior? I don't think so.

I also don't know where you come up with the statement about using only the 75 degree column, instead of starting with the 90 degree column, for derating.

As long as the results, from derating, starting from the 90 degree column, are not larger than the ampacity of the 75 degree column( or the 60 degree column, if terminations are rated 60 degree, only), you are still ok. We are talking about 15 and 20 amp circuits, most likely, so as long as the resulting figures are above this figure, the wire will still handle the required load, without undue heating.

Section 310-15(b) give the modifications to Table 310-16. Also see Section 110-14(c)(1 & 2).

Rick Miell
 
  #7  
Old 06-12-01, 11:45 AM
resqcapt19
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Rick,
Lets start with your last point first. If it is a wet loaction then the wire is only 75C wire and this is the ampacity that you would derate from.
As far as if exterior conduit is a wet loaction, I too look at Article 100. I think that we can agree that any conduit installed on the exterior of a building exposed to the weather is in a wet loaction. Now the question becomes; is the interior of a conduit that is installed in a wet location also a wet location? I can only look at my experience with outside conduit. It gets wet on the inside. The only code that I can cite is 225-22 and 230-53. The second one doesn't apply here because we are not talking about service raceways, but the first one implies to me that the interior of the conduit is a wet location.
As far as the panel I assume it is listed for use outside. If it is a NEMA 3R enclosure you will find drain holes in the bottom to let the water that enters drain away.

Phil,
If you run the conduit, I would strongly recommend that you come out of the side of the panel near the bottom to limit any addional water from entering the panel. I try to avoid conduit entries into the tops of wet location enclosures.

Don(resqcapt19)
 
  #8  
Old 06-13-01, 07:44 PM
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Thanks for the tip on not exiting through the top of the panel. It's a moot issue with my panel since the meter is on the top. I would probably avoid exiting the top anyway. Right now, wg has me thinking about an interior panel.

Phil H
 
  #9  
Old 06-13-01, 08:25 PM
Wgoodrich
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RickM; Other than possibly breaker lugs, do you have specs showing a terminal or device connection that is rated for more than 60 degrees that is by a testing lab., that are designed for #1 or smaller conductors?

If you will look at Table 310-16 you should find that THWN is listed in the 75 degree column and only THWN2 is lited in the 90 degree column. If resqcapt19 and I are right about our thoughts concerning the wires in that conduit being in a wet location, and considering the requirements for drainage in panel approved to be installed outdoors and rated as weatherproof the the w in the THHN/THWN wire would put you in the 75 degree max setting.

Now to support your challenge look at Article 100. The definition of a dry location allows for an area that may occasionally become wet. This definition may cause grounds for an argument that inside the conduit the wires may occasionally get wet but not expected to become wet therefore the THHN rating would be allowed again therefore allowing the 90 degree start on your deration calculations.
Here we go again in that gray area. Which would it be wet or dry location. Really could be argued either way. Thus affecting the starting point of your deration calculations.

Below expands on what resqcapt19 said that might help;

373-2
(a) Damp and Wet Locations. In damp or wet locations, surface-type enclosures within the scope of this article shall be placed or equipped so as to prevent moisture or water from entering and accumulating within the cabinet or cutout box, and shall be mounted so there is at least -in. (6.35-mm) airspace between the enclosure and the wall or other supporting surface. Enclosures installed in wet locations shall be weatherproof.

What ya think?

Wg
 
  #10  
Old 06-13-01, 09:47 PM
rickoh
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can i ask a dumb question? if there are knock outs on the back if the breaker box why cant he knock ine out and go up threw the wall?
 
  #11  
Old 06-13-01, 10:09 PM
Wgoodrich
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Rickoh, I see nothing wrong with your suggetion. However I took him to be set on installing the conduits outside, I suspect in his opinion for ease of installation. Peronally I suggested moving the panel to face inside also.

Wg

 
  #12  
Old 06-13-01, 11:19 PM
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Rickoh, Thanks for the suggestion, The panel is on stucco,is opposite my tub enclosure, and its located in the corner of the house and that portion has a shallow pitch hip roof. I really dont like the thought of trying to drill through the top plate nor do much work in the attic above the panel. Plus I have conduit stuck on my brain because I was looking for an easy way to do a little at a time. Good idea though. I'll give it some more thought tomarrow.

Thanks,
Phil
 
  #13  
Old 06-14-01, 07:13 PM
Wgoodrich
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One suggestion that may jump in your thoughts on installing the panel inside but also find an easy way to get down the wall from the attic. A common trick is to locate a wall in the area that is next to a corner or other object such as a shower or cabinet or closet that creates an outside corner. Build a short wall of about 2 or 3 studs nailed to a top plate and bottom plate about 1/2" short of the finished floor to ceiling. The nail that false wall against that existing corner thus making a short offset. Then you can go from attic to crawl space all you want. Once you finish your wiring you can scew a plywood piece to it and paint it same as the existing wall or drywall it and finish it out without melting in the attic. No fishing of wires would be needed with that false wall trick and you can easily place the panel inside out of the weather and solve most concerns you had.

What ya think?

Wg
 
  #14  
Old 06-19-01, 02:40 PM
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I've found that in alot of places (esp. older homes) it is relativly easy to fish a few cables beside the soil stack. It usually runs from basement to attic, and is run through a series of square holes. If you go up into the attic with a roll of string, and a lead sinker, you may be able to drop a line down in one of the corners of the hole, and pull up your snake.
 
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