Raceway Fill Calculation

[shortcircuit2]

What size EMT tubing is needed for two Southwire 12-2 NM-B (romex) cables?

Here is the manufacturer's specification on NM-B...

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6

Please show the formula used to figure this out.

 

[Dennis Alwon]

multiply the mils given then use a converter from mil squared to mm squares.

Go to chapter 9 Table 4 and use fill at 2 wires 31% single a multiwire cable is considered one wire Note 9 table 1 in chapter 9

 

[wwhitney]

What size EMT tubing is needed for two Southwire 12-2 NM-B (romex) cables?

Here is the manufacturer's specification on NM-B...

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6

Please show the formula used to figure this out.

The relevant information from the spec sheet is "approximate cable dimension (mils)" 410x179. Chapter 9 Table 1 Note 9 says to treat the cable as being circular with a diameter 410 mils.

Now I'll take a shortcut and look at Chapter 9 Table 5 and note that RHH #4 has a diameter of 0.412 mils. That's close enough (and not smaller) that the answer will almost certainly be the same for RHH #4 and 12-2 NM-B. Annex C Table C.1 says that 1" EMT is the smallest size for (2) RHH #4 wires. So the answer is 1" EMT.

Cheers, Wayne

 

[Dennis Alwon]

What size EMT tubing is needed for two Southwire 12-2 NM-B (romex) cables?

Here is the manufacturer's specification on NM-B...

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6

Please show the formula used to figure this out.

How long a run is it? Is it a sleeve. If it is a sleeve then 1/2" emt is fine IMO

 

[jeff48356]

How long a run is it? Is it a sleeve. If it is a sleeve then 1/2" emt is fine IMO

Yes, I've always used 1/2" EMT for two 12/2 cables when running outlets onto basement/garage walls, and no inspector has ever cited me for it. EMT is only about 4' long or so. As long as the cables are flat up against each other, they will slide through with no problem for that short a run.

 

[ramsy]

The relevant information from the spec sheet is "approximate cable dimension (mils)" 410x179. Chapter 9 Table 1 Note 9 says to treat the cable as being circular with a diameter 410 mils.

Now I'll take a shortcut and look at Chapter 9 Table 5 and note that RHH #4 has a diameter of 0.412 mils. That's close enough (and not smaller) that the answer will almost certainly be the same for RHH #4 and 12-2 NM-B. Annex C Table C.1 says that 1" EMT is the smallest size for (2) RHH #4 wires. So the answer is 1" EMT.

Cheers, Wayne

That was an amazing illustration of NEC-Table navigation.

NFPA copyrighted, cross-referenced Table chaos is not user friendly. Its an overwhelming Chapter and Annex of idiot-table adjustments, exceptions, notes, and errors & omissions (if you catch them).

NFPA-Table chaos inspires people to beg for internet help, demand spreadsheet hacks, or stupid-phone Apps. All usually unreliable, much less accurate at NFPA Load Calcs, Ampacity adjustments, Conduit/Box fill, or Voltage Drop, etc..

Further, no such expert system would be useful without warning the user of NEC 334.12, Uses Not Permitted for NM cable (ie) outdoors, etc..

 

[dm9289]

Not sure why you are using the romex perhaps availability, if you have a need for smaller conduit for your bender you can strip jacket that way you wont cause heating or fill problems.

In my situation in industry with no specs on cable I use a micrometer to measure diameter. basically area sqin= (diameter^2)(.79) and look at the fill tables.
If your cable is not perfectly circular use the largest dimension

 

[MAC702]

...NFPA-Table chaos...

Loved it!

 

[shortcircuit2]

In this area we have basements and garages with concrete walls. So, one method to install receptacle outlets on the concrete walls is romex is run along the sill and then sleeve the romex down the concrete wall in EMT to a box with receptacle.

I was trying to see the formula for converting the "mils" in Southwires specs to a dimension in Table 4 of Chapter 9

wwhitney's shortcut gave the result of 1-inch EMT for 2 cables.

Here is Encore's specs on type NM-B cable...

https://www.encorewire.com/wp-content/uploads/EncoreWire-NMB.pdf

Encore lists the 12-2 NM-B cable at (0.160 x 0.450)...what's the formula for this romex with 2 cables in EMT?

 

[Dennis Alwon]

As I send earler if you have a sleeve then the fill doesn't count so whatever the 2- 12/2 nm cables fit into. Personally I like to use pvc and I use 3/4" because it is easier then 1/2"

As Whitney stated early .160 x .450 then you would use the larger dimension (.450) as the size then do as whitney stated in the earlier post

 

[infinity]

In this area we have basements and garages with concrete walls. So, one method to install receptacle outlets on the concrete walls is romex is run along the sill and then sleeve the romex down the concrete wall in EMT to a box with receptacle.

Sounds like a sleeve to me similar to this:

 

[MAC702]

...romex is run along the sill and then sleeve the romex down the concrete wall in EMT to a box with receptacle. ...

Info that should have been in the OP.

No formula for this. Use what fits. If you don't want to stuff them down a 1/2" tube, use a 3/4". It would be ludicrous to use 1" because some Chart Party told you to.

 

[MAC702]

Remember that the formula for a raceway (not a sleeve) takes into account that you might have up to four 90º bends to pull through.

 

[shortcircuit2]

Another practice with romex in a raceway is when an addition is done and the panelboard is in a finished plastered garage so the homeruns are sleeved in EMT or PVC through the garage area over to the panel.

Would you apply the raceway fill rules on this or the sleeve rule in Note 2 of Chapter 9?

Thanks for the replies.

 

[Dennis Alwon]

If it is a sleeve then there is no fill however, you will have to derate based on the number of current carrying conductor's in the sleeve.

 

[mgawat]

I know this is an old thread but how lkong of a pvc conduit raceway would constitue a 'sleeve' vs a raceway. I came across an incomplete job that I am having to take over., the previous contractor installed 10/2 times 2 cables in 3/4" conduit for a lenth of about 25. Now,' to me this would be a raceway and the requirments of chapter 9 table 1 would seem not to allow this. My second questiuon has to do with a connector on the conduit required when the nm cable enters the conduit. isn't one requitrred at the the point of connection?

 

[LarryFine]

The general consensus is that a box-to-box run is a conduit, and open-ended is a sleeve.