A snowy day here in Tulsa, I will show how to do the math for this cable or any cable.
It will get kinda long, sorry.
The NEC don't give a lot of assistance here on how to do the calculation, however does provide rules which will yield an answer. Then some common sense should be applied as not to possible damage to the cable from frustration of the installation. What be worse is a non code compliant installation or AHJ red tag.
I have to pipe across a garage and then enter an attic, will #4 SER cable fit in a 1" conduit by code? I believe #4 SER is 3-#4's with a bare #4 so 4 #4's total plus insulation I hate to have to set a j box, splice than switch to SER if I were to use THHN in the conduit. The conduit will have 2 90's plus a kick. Thank you in advance
So let's start here with the OP.
What we know:
#4 SER cable ( 4-4-4-6)
J- box in Attic
Straight run section with 2-90's and a kick
What one (I) would assume.
Based on the kick, I would say EMT.
Based on 90's,kick and j box it may or may not be a sleeve. Most likely not a sleeve so a calculation should be done to be compliant as well not damage the cable during installation if in a sleeve.
The OP question is 1" compliant.
So I would ask 1" what, assume EMT.
This is where we head to chapter 9 tables.
Table 1, number of conductors or cables. *Read entire heading
1= 53% of cross sectional area.
Then look at note 9 for tables. Attention to the words based on diameter. Again read the entire note.
Still no clear way of calculation. The clue is the tables for percentage of fill. There in mms² or in². So the note says use diameter of the cable and the fill is in in². At this time I will just say take note of table 2 for later in the discussion as it related to article 338 (SE cable).
This means we must take diameter and turn it into in² or area in square inches. Since we're electricians we pretty familiar with a circle the whole 360 thing. If not here is a reference.
As you can see the diameter is the measurement straight across the circle. This means we can simple measure this or use the mfg OD (outside diameter) of the cable. The mfg for one of these cables is .757 inches. Remember we're calculating in inches. So if we were to measure this cable as noted in note 9 it measures 3/4" that would be .75 (3 divided by 4= .75) however we're going to use mfg listed OD.
Now we need to change this OD to Area in square inches or d ( diameter) to in² (area square inches. There is couple different ways to do this, π r² or d²*.7854.
For the first one π r². It pie x.radius² ( radius x radius). Radius is half the diameter as shown in the circle picture. The d listing for the cable is .757 divide that by 2 or .3875 and times it by its self or square the number.(²).
Pie(π) is 3.141592653589793 or just use 3.141592. now you can use you calculator and this is what it looks like.
So you area in Square inches is .45 with this can go the tables for your raceway choice look at 1-wire 53% to size. Since we're using EMT arrival 358. It would be 1" at .458 allowed. A short cut I like is take that .45 and dives it be the % or .53.
This give you the area for minium size of race way at 100% in in². Which is .864 for a 1" emt.
Now for the second way, d²*.7854. diameter squares or d x d x .7854
You may ask where did the .7854 come from it's π/4.
Now you can size the minium raceway required for any cable. If your using a NM flat cable as noted 9 says measure the diameter of the fastest part and use that for d. You can also use this for multiple cables of the same or different sizes.
For fun fact now about the table 2 noted at beginning. In 338 it states five time diameter for bending radius inner edge for a minimum of .757*5= 3.78. 1" in table 2 is 5.75 center line for one shot. Just a fun way of seeing how the code articles work together.
So choosing the size depends on what is compliant and how easy you want the job to be. I would never us 1" for that job even though you can. Hope this helps others if so I would put the 2 formulas in you book on chapter 9.
Please some one check my math. Thanks.
