Running wires from main panel to attic

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  #1  
Old 10-03-06, 07:36 AM
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Running wires from main panel to attic

I've been trying to figure out a way to get all of my wires from my main service panel, up the wall into the roof attic area above my kitchen. I was told all the wires need to be clamped at the panel & then stapled to a piece of plywood up to the attic. Most of my knockouts are in the side of the panel, which means I can't have any studs along side of the box. I'm not real fond of this idea as I need to frame my wall differently to make this work well.

I believe the wires in my last house just ran up the wall in a big bundle, not even in conduit. It was built only 5 years ago, so it's a pretty recent wire job. Can't remember for sure, but I think is how it was done. So, can I just run the wires up through some 2" conduit up to the attic & then branch them out to where they need to go?

What might be some other options? I need to have this figured out by this weekend when I plan on doing this work.

Thank in advance.

Dan
 
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  #2  
Old 10-03-06, 08:35 AM
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I am breaking this down into two parts for clarity.

Danno,
You are bringing up one of this industries hotley debated topics.

If you do decide to put all the wires in one conduit, or bundle them together, you will need to make ampacity adjustments to each circuit (called de-rating). Basicly you will need to run a larger wire size or limit the allowed load on each circuit. De-rating starts when you have more than two cables in any hole in a stud or more than three bundled together.

The debate is about how long the conductors can be bundled together before de-rating is requred. Is it needed for just one hole or do the conductors need to bundle for so many feet. Another part of the debate is the big question of If this type of bundling actually causes a problem, or if it is a not needed code requirement.

The current rules 2005 code say that if the cables are bundled for more than 24 inches or if they pass through a hole that will be fire stopped you need to de-rate them.

I have seen enough old work that I believe had problems due to bunding and IMHO there is a real problem here, and that the code just needs to be re-worded to be easier to understand it this regard.
 
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Old 10-03-06, 08:49 AM
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Part two

Danno,
You mention that you have a panel with factory KO holes.

What I have done in the past is to run as many as possilbe of my cables in the wall cavity next to the panel. Drill holes in the stud below the panel, and bring the circits in from the bottom of the panel. Leave just one or two holes in the bottom incase someone wants to fish an extra circuit later and leave more spare holes at the top since this is more likelly where a person will want to fish the wires.

Since this is your house, You may want to run a 3/4 conduit to the attic and crawlspace under the house, put an empty box and cover on the pipe and leave it incase you want to add more later. This way you will not need to fish the walls to add a circuit.

The only way to get this many wires into a stud space and secure all of them at least 1 1/4 inch from the face of the stud, is to add a support between studs and secure the wires to that support. They make brackets for this, but I have always just picked up a bit of the carpenters scrap wood and used it as dead wood at the panel.

Remember that most 3/8 romex connectors. (the ones that fit in a 1/2 trade size KO) are rated for two 12-2, two 14-2 or one 10-2 cable. You can save holes buy doubling up the cables in a connector.

Since local building codes vary, it is a good idea to have a talk with the building dept. inspector prior to doing the work to find out what his/her opinion on the installation is. Most of the time these people are very cooperative, and if you can just look past the sharp edge that they show, you will have excellent results by enguageing them in your decision making process.
 
  #4  
Old 10-03-06, 10:30 AM
wgc
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clarify firestopped 1 cable or 3?

Originally Posted by jwhite
...De-rating starts when you have more than two cables in any hole in a stud or more than three bundled together.
...
The current rules 2005 code say that if the cables are bundled for more than 24 inches or if they pass through a hole that will be fire stopped you need to de-rate them.
Could you please clarify that? If cables pass through a hole that is firestopped, do you need to de-rate them every time, or when more than three are bundled together?

I've been considering running around with a tube of fire-stop caulking to plug all the holes I've fished wire through. One hole probably doesn't make a difference but filling all of them might slow the spread of any fire. I haven't seen any support for that idea though so if there is a real penalty in ampacity, I don't need to do that.
 
  #5  
Old 10-03-06, 10:37 AM
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Quote from the 2005 nec: "Where more than two NM cables containing two or more current-carrying conductors are bundled together and pass through wood framing that is to be fire- or draftstopped using thermal insulation or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a)."

If or not to fire stop the holes is not covered in the nec. Under most building codes, if the wires pass through a floor or ceiling they must be fire stopped.

The code says that if they are fire stopped then the ampacity of the conductors needs to be de-rated.

Just leaving out the fire stop, so that you do not have to de-rate the conductors is NOT an optioin.
 
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Old 10-04-06, 10:53 AM
wgc
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thanks

I apologize if my request for clarification seems to hijack this thread, but once more .... hopefully this applies to the original poster as well ... correct me if I'm still wrong ...

It sounds like you are telling me (and the original poster) not to fish more than two cables through each hole at the top or bottom of a wall (if possible). Then I can fire stop and do not have to de-rate.

Thanks for the building code reference about fire-stopping the holes being required in most places. I didn't know that and have never seen it done in any house, I just thought it was a good idea.
 
  #7  
Old 10-04-06, 11:24 AM
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wgc,
This is where explaining this gets a little more complex.

When de-rating wires we need to count the number of current carrying conductors. For a regular 120 volt two wire circuit there are two. So a 12-2 romex is two conductors. With a MWBC there are still only two since the neutral only carries the imballance it does not need to be counted.

Next the table I posted above gives us percents to de-rate the wires depending on the number of wires that are in the same raceway (conduit) or bundled together. From 4 to 6 wires is 80 percent from 7 to 9 is 70 percent.

Next we have to look at the allowed ampacity of the wires from table 310.16 Most romex is made with type THHN wire. This wire has a 90 deg c rating. Table 310.16 has two other colums for 60 deg c and 75 deg c.

Now we cannot put #12 wire on anything larger than a 20 amp breaker, or #14 wire on anything but a 15 amp breaker. But, for the purposes of de-rating we can use the 90 deg c columb if the wire carries that rating.

The 90 deg C rating of #14 wire is 25 amps. 70 percent of 25 is 17.5 amps. So the de-rated amperage of the wire is still higher than the max breaker that you could use anyway.

The result of a #12 wire at 70 percent is 21 amps.

After you have read this post for the tenth or so time, it will become clear that you would need 10 current carrying conductor bundled or passing through a fire stopped hole before de-rating is a problem that must be addressed. This applies for wire sizes 14 and 12. For larger wire sizes the exact math is different. But, in residential work, you will probably want a seperate hole for the larger wire sizes anyway.

The last thing to consider is that you can only bore so big a hole in the top or sole plate to start with. 1 1/4 is about max. Only so many wires will fit in that size hole.

The short answer is that if you have a bunch of bored holes you are probably ok. If you want to use one large coduit for all the wires you will have a problem.
 
  #8  
Old 10-04-06, 11:28 AM
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I just want to add that if the romex you are buying is only rated 75 deg C then the math changes a bit, but I would suggest buying the better wire, since most light fixtures and such are listed to be used with the 90 deg c rated wire anyway.
 
  #9  
Old 10-04-06, 11:37 AM
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Sorry to be so long winded, but I want to add a note on firestopping.

It has only been in the last few years that firestopping has been required in all holes that go through the floor or ceiling. This is not electrical code, but we are requred to follow all building codes, not just the ones that have our trade in the title.

The reason is that it has been proven that firecalking the holes does slow the spread of fire.

It may not seem at first to be that big a deal. Firecalking a hole may slow that blazing inferno for a matter of a minute or two. However, like smoke alarms, these measures buy use that precious minute or two that are criticle in a fire.

The difference of just a few seconds can be the difference between someone lying in the door way passed out when the fire department gets there, or someone making it safely outside and to neighbors house to get help.
 
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