conduit fill for romex in PVC sleeves

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robbione

Member
Location
Tampa, FL
We will be doing a mega single family home that is a total of 4 floors.
The garage is poured slab on grade, but the others are pre-cast Post Tension slab between floors.
The architect & engineer want me to determine how many & what size conduit sleeves I will need for wiring between floors.
I'm having a very difficult time getting my head around this.
I plan to request 6" conduit sleeves (why not?), but I need to figure out how many 12/2 or 10/2 romex will fit in each. (I'll deal with larger appliance circuits separately)
Most of the panels, including all the lighting control panels are going in the 4th floor mechanical room.
I'm trying to determine how many 12/2 romex are allowed in a 6" sleeve @ 60% fill - (less than 24" between floors).

Is the following correct?
12/2 romex is 5/8" diameter (.3125 radius)
.3125 squared =.09765
.09765 x pi 3.1416 = .3068 sq. in.

6" PVC sched 40 @ 60% fill = 17.140
will allow fifty-five 12/2 cables?!?

That can't be right... is it?

Any other suggestions to keep me out of trouble on this are greatly appreciated.
 

SEO

Senior Member
Location
Michigan
There is a little more to it than that also look at section 334.80 and the ampacity adjustment factors in section 310. I would be careful applying note 2 in your case.
 

robbione

Member
Location
Tampa, FL
So help me out...
How can I figure out how many 12/2 cables I will be able to pull through a 6" sleeve?
The job was permitted prior to the code update here in Florida so I believe that the derating per 334.80 is not required.
That being said, I am concerned about the heat.
There has to be some mathematic way of getting to my answer?
 

SEO

Senior Member
Location
Michigan
I think that the key is if your cables are bundled less than 24" you may be able to use note no. 2 or you could use your calculations. There may not be any adjustment factors that you would have to apply. I would check with your AHJ and get his input.
 

kacper

Member
Location
Islamorada
We will be doing a mega single family home that is a total of 4 floors.
The garage is poured slab on grade, but the others are pre-cast Post Tension slab between floors.
The architect & engineer want me to determine how many & what size conduit sleeves I will need for wiring between floors.
I'm having a very difficult time getting my head around this.
I plan to request 6" conduit sleeves (why not?), but I need to figure out how many 12/2 or 10/2 romex will fit in each. (I'll deal with larger appliance circuits separately)
Most of the panels, including all the lighting control panels are going in the 4th floor mechanical room.
I'm trying to determine how many 12/2 romex are allowed in a 6" sleeve @ 60% fill - (less than 24" between floors).

Is the following correct?
12/2 romex is 5/8" diameter (.3125 radius)
.3125 squared =.09765
.09765 x pi 3.1416 = .3068 sq. in.

6" PVC sched 40 @ 60% fill = 17.140
will allow fifty-five 12/2 cables?!?

That can't be right... is it?

Any other suggestions to keep me out of trouble on this are greatly appreciated.

When calculating and designing the number of sleeves keep in mind Table: 310.15(B)(2)(a)
10 x 12/2 romex in one sleeve between floors (20 current ? carrying conductors) will reduce the ampacity of the wires by 50%.
One of the options you should look to it distribute locations of the subs (panel boards).
If possible try to avoid feeding wires between floors or at least reduced to option to minimum.
Also keep in mind Arc Fault changes in NEC 2008:)
 

iMuse97

Senior Member
Location
Chicagoland
Any large house is deserving of one (or several) well-placed subpanels...

In this case, put one on each floor. I've done beach houses that were very
compact, but four floors high, and had a sub panel on each floor to deal with this issue.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Given the design parameters of this house (4 floors, post tension slabs, 4th floor mechanical room) I don't think that robbione has much flexibility to add sub-panels where it's convenient for him or to change the wiring method.
 

robbione

Member
Location
Tampa, FL
Regarding sub-panels, Yes I agree that is ideal, however, the architect did not allow much usable space for panels on the 1st or 2nd living floors and the ground floor is under BFE.
I managed to squeeze a couple of sub panels in 1st & 2nd floor mechanical closets, but the real problem is the ligthing control homeruns. There are 10 lighting control panels with approx. 300 lighting loads. No place to put those panels except the large 4th floor mechanical closet. Now I have to feed 300+ switch legs from the 4th floor down.
Going to meet with the inspector to discuss the bundling/derating issue.
 

elohr46

Senior Member
Location
square one
Regarding sub-panels, Yes I agree that is ideal, however, the architect did not allow much usable space for panels on the 1st or 2nd living floors and the ground floor is under BFE.
I managed to squeeze a couple of sub panels in 1st & 2nd floor mechanical closets, but the real problem is the ligthing control homeruns. There are 10 lighting control panels with approx. 300 lighting loads. No place to put those panels except the large 4th floor mechanical closet. Now I have to feed 300+ switch legs from the 4th floor down.
Going to meet with the inspector to discuss the bundling/derating issue.

regarding your romex question, someone posted a chart a while back that had the cross sectional area of 12/2 nm listed at .132"
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
I've been on the road you're traveling. You are gonna have miles of cable running from each light to the controll panel, most of them loaded 3 to 7 amps max and the derating still applys. ughh!!

There is a pic on this site of a grocery store ran in romex. That is what this house will look like I bet.

IMO pipe and THHN are still your friend. You gotta get creative though. Think about places you can squirrel away J boxes that will not be a problem come service work time.
 
We will be doing a mega single family home that is a total of 4 floors.
The architect & engineer want me to determine how many & what size conduit sleeves I will need for wiring between floors.


Any other suggestions to keep me out of trouble on this are greatly appreciated.


I do not mean to be rude, but....


You are wiring a MEGA single family home.

There is an ARCHITECT & ENGINEER attached to this project.

And they are asking you to engineer the job? Are they paying you to do their job?

My "other suggestion" is to ask them to provide the calculations and you will review them. Remember, if you engineer the job, you are responsible for the engineering if something goes wrong. I have experienced just how bad it is for an electrician when he engineers and things go south.
 

buldogg

Senior Member
Location
Green Bay, Wisc.
I do not mean to be rude, but....


You are wiring a MEGA single family home.

There is an ARCHITECT & ENGINEER attached to this project.

And they are asking you to engineer the job? Are they paying you to do their job?

My "other suggestion" is to ask them to provide the calculations and you will review them. Remember, if you engineer the job, you are responsible for the engineering if something goes wrong. I have experienced just how bad it is for an electrician when he engineers and things go south.

Well said Pierre
 
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