Romex in smurf tube?

[snakevargas]

I preinstalled some 3/4" blue smurf tube from panel to attic, about a 6ft run. At some point I'm going to try to run 6ga hot tub wire in there. I'm a little confused about conduit fill ratio and what is permissible. I read something somwhere that led me to believe the fill ratio only matters if the conduit is used in an and-to-end (i.e. box to box) manner and doesn't matter for short risers like this that are only terminated on one end. However, I'm skeptical of this as I don't recall seeing an official source.
 
I suppose if it's an issue, then I could always terminate the smurf tube in the attic to a box, run THHN in the smurf tube, and splice to romex in the box in the attic.

 

[JimS]

This sounds like an issue you have to ask the local AHJ (authority having jurisdiction).  In my area it is common to use a couple large conduits from the main panel to contain all the runs of romex to the ceiling and they don't seem very concerned with fill.  But this is PVC conduit.  I don't know about smurf tube.

 

[Del91574]

Without me getting the NEC out, I'll assume you're going to have 4 conductors in the 3/4" flex, which by any stretch is going to be very tight, NM cable or THHN. Conduit fill is a factor, otherwise the conductors will need to be derated, generally meaning oversized.
 
Smurf is ENT as far as the code is concerned.

 

[snakevargas]

My assumption is two 6ga conductors and an 8ga ground. I *think* that's the way my last hot tub was wired. I don't have the hot tub yet, haven't even picked one, so I don't know for sure. Just thinking ahead.
 

Without me getting the NEC out, I'll assume you're going to have 4 conductors in the 3/4" flex, which by any stretch is going to be very tight, NM cable or THHN. Conduit fill is a factor, otherwise the conductors will need to be derated, generally meaning oversized.
 
Smurf is ENT as far as the code is concerned.

 

[Del91574]

It depends on if the unit is 120 or 240, so that would be the variable. Wire is cheaper than rework, unless you're going 100% copper these days ^_^

 

[sda]

This is one of those gray areas.
 
For example, from the NEC
Chapter 9, Table 1 (the conduit fill percentage table), Note (2)
"Table 1 applies only to complete conduit or tubing systems
and is not intended to apply to sections of conduit
or tubing used to protect exposed wiring from physical
damage."
 
The ENT you have isn't a complete conduit system, its open at one end.  That makes it a sleeve, or not.
Then again, its not being used to protect exposed wiring, and ENT is useless against protecting wiring from physical damage.  The NM Is probably tougher than the ENT.
 
6-2 or 6-3 will fit physically in 3/4 ENT, probably a bit tight and won't be real easy to pull.
 
If you consider the ENT segment a conduit system, even though it doesn't meet the critera, then 6-2 or 6-3 will overfill the ENT.
 
If you want to do the math, the cross sectional area of the cable must be less than 53% (one conductor) of the cross sectional area of the ENT.
A cable is considered a single conductor for fill purposes.
 
3 #6s and a #10 ground will barely fit within the 40% (more than 2 conductors) fill limit of 3/4 ENT.
You don't really want to add an extra splice (in a large box in the attic) for a high amp circuit unless you have to.
 
If you really want to do it right, crack the wall and run the cable direct into the panel.
 
I would just run the NM though the 3/4 ENT "sleeve" and call it good.
 
Even if you only need 6-2 to the spa, run 6-3.  You never know when you might need a neutral.

 

[Neurorad]

I'd have several long talks with the AHJ, but that's just me.

Agreed, most people would just get it done, and not be too concerned.

 

[snakevargas]

I don't plan on the AHJ ever seeing the inside of the attic, so I probably won't ask if the smurf tube is my only question. I'm mostly concerned with doing what's smart and safe, and it sounds like running romex a short distance in the smurf tube riser could be characterized as such.

Thinking through the next phase of the problem, I have two more questions. The wire is going to have to come down a garage wall, hop across a stud, and then go under the crawlspace.

1) The stud, actually a double stud, is directly beneath a large GLB beam that supports the second story over the garage. Of course I know not to touch the GLB itself, but is there anything wrong with drilling through the supporting stud using the limits (40% ?) for holes drilled in a load bearing stud? Given the choice, I'd rather not, but don't know a good alternative.

2) Now for the big controversial question... What about running 6/2 or 6/3 romex in the crawlspace? Much googling leads me to code references that this is allowed by NEC, stapled to the underside of the floor joists, for dry crawlspaces. The controversy I find in forum threads is whether a crawlspace is considered "dry" or "damp" or "wet". I've found 75-post-long flame wars in other forums on this very point.

Running 6/2 or 6/3 UF would eliminate the concern, but damn that stuff seems expensive and would be a bear to work with. I'd really like to just run conduit in the crawlspace, but that certainly means no romex in that conduit and I'd therefore need to transition with a splice somewhere.

I realize that #2 in particular might only be answerable by the AHJ, so that might be where I have to take it.

 

[apostolakisl]

I will profess ignorance on the specifics of your situation.  
 
However, I do know that at least in some situations running jacketed wire inside of conduit is not allowed or you have to down-rate it.  The reason is heat.  I have dealt with this before in the situation of yard lines, but never for smaller gauge stuff in walls.

 

[Del91574]

If you're really concerned about the NM cable, legalities, etc, then I'd suggest going conduit through the space then run to a suitable JB or up to the unit itself. THWN and PVC is cheaper than UF cable usually.

 

[snakevargas]

I might end up doing just that. I hate having to throw a big junction box (I'm assuming a 6x6x3 box to leave adequate room to splice the 6/3? or could I get by with a standard double-wide junction box?) in the wall, but it's probably the best way to go.

 

[Del91574]

I don't have my copy of the NEC handy, so I can't give you the box volume calcs off the top of my head.