I need Help with a bending radius

[Smart $]

I would add one thing, in this thread I'm simply thinking out loud. I'm not 100% convinced that what I've hypothesized is completely accurate although in my mind it makes perfect sense. :slaphead:

Well let's see if we can make your sense a little less perfect

314.28 Pull and Junction Boxes and Conduit Bodies.
Boxes and conduit bodies used as pull or junction boxes
shall comply with 314.28(A) through (E).
Exception: Terminal housings supplied with motors shall
comply with the provisions of 430.12.
(A) Minimum Size. For raceways containing conductors
of 4AWG or larger that are required to be insulated, and for
cables containing conductors of 4 AWG or larger, the mini-
mum dimensions of pull or junction boxes installed in a
raceway or cable run shall comply with (A)(1) through
(A)(3). Where an enclosure dimension is to be calculated
based on the diameter of entering raceways, the diameter
shall be the metric designator (trade size) expressed in the
units of measurement employed.

So, IMO, Type TC 3C/12AWG cable does not have to comply with 314.28(A)(1) though (A)(3).

 

[weressl]

I used NEC 336.24 and then a table from Appleton that shows bending radius for their condulets

Here is a part of the table:

LB125-M, -A	K125150-CM, -CA	GK125-150-N	GK125-150-V	LB-125, -A	BC-125G	SGN-125	SG-125	1-A	1-1/4	1.250	2.625
LB150-M, -A	K125150-CM, -CA	GK125-150-N	GK125-150-V	LB-150, -A	BC-125G	SGN-125	SG-125	1-A	1-1/2	1.312	2.812
LB200-M, -A	K200-CM, -CA	GK200-N	GK-200V	LB-200, -A	BC-200G	SGN-200	SG-200	1-A	2	1.500	3.500

In am aware that I could have been installing this incorrectly over the years, but I have never seen this done by other contractors either and have been to dozens of plants over the last 15 years with these types of installations.

Yep, you and 85%+ of the US installers. I congratulate you of being a thinking member of your trade! (I have been fighting this battle for three+ decades, so needless to say my delight in your post.)

Tray cable was NEVER intended to be installed in conduit:

• Conduit is designed to be a raceway, a completely closed system
• Conduit is intended for single conductors,
• A conduit is designed to ENCLOSE multiple single conductors,
• Hence conduit bodies designed to accommodate the bending radius's of conductors, a minimum of TWO of the larges conductor that fits the specific corresponding conduit size,
• TC cable has the extra jacket to be installed on a - more or less - support system, such as cable tray
• Cable tray is designed to SUPPORT multiple cables that are provide with an extra protection, namely the jacket, over the insulated single conductors,
• There is a support system designed to branch off single or 2-3 tray cables off of the cable tray, it is called cable channel, or the lately introduced but used elsewhere on the world for decades, the cable basket systems.

 

[Smart $]

Thanks for all the help so far...Maybe you guys could show me what size TEE fittings you guys come up with for these size cables:

a 3/c #14 TC with a diameter of .34"

a 3/c#12 diameter is .49"


Using a standard size TEE condulet (not Mougul)


THANKS!

3C/14AWG: 4 ? 0.34" = 1.36"​

.
If we go by outside bend radius and the table you posted earlier, you're looking at 1/2" here, assuming a Tee has the same R2 as an LB.
.

3C/12AWG: 4 ? 0.49" = 1.96"​

.
Same conditions as above, you're looking at 1" here.


If we go by inside bend radius, 2" for the 3C/14, and the table doesn't go high enough for the 3C/12.


If we go by centerline, we have to allow for half the diameter and use outside bend radii.
.

3C/14AWG: 4.5 ? 0.34" = 1.53"​

3C/12AWG: 4.5 ? 0.49" = 2.21"​

.
Then you'd need 3/4" and 1-1/4" Tees, respectively.

 

[infinity]

Well let's see if we can make your sense a little less perfect

So, IMO, Type TC 3C/12AWG cable does not have to comply with 314.28(A)(1) though (A)(3).

I knew that I had to be missing something.

 

[don_resqcapt19]

Since the cable diameter is larger than a #4 AWG conductor then IMO you need to use the 6X formula for an angle pull.

Rob,
I don't think that there is anything in 314 that even suggests that you use the OD of a multiconductor cable for the purposes of 314.128 box sizing.

314.18 (A) Minimum Size. For raceways containing conductors of 4 AWG or larger that are required to be insulated, and for cables containing conductors of 4 AWG or larger, the minimum dimensions of pull or junction boxes installed in a raceway or cable run shall ...

It seems clear to me a that the rules in 314.28 only apply when the conductors are #4 and larger, no matter what the OD of the cable assembly may be.

 

[Brian Donlon]

Its my understanding the the word RADIUS always means inside (dictionary definition).....


It is Garbage that the code requires such am impractical installation..


THanks everyone!

3C/14AWG: 4 ? 0.34" = 1.36"​

.
If we go by outside bend radius and the table you posted earlier, you're looking at 1/2" here, assuming a Tee has the same R2 as an LB.
.

3C/12AWG: 4 ? 0.49" = 1.96"​

.
Same conditions as above, you're looking at 1" here.


If we go by inside bend radius, 2" for the 3C/14, and the table doesn't go high enough for the 3C/12.


If we go by centerline, we have to allow for half the diameter and use outside bend radii.
.

3C/14AWG: 4.5 ? 0.34" = 1.53"​

3C/12AWG: 4.5 ? 0.49" = 2.21"​

.
Then you'd need 3/4" and 1-1/4" Tees, respectively.

 

[weressl]

Rob,
I don't think that there is anything in 314 that even suggests that you use the OD of a multiconductor cable for the purposes of 314.128 box sizing.

It seems clear to me a that the rules in 314.28 only apply when the conductors are #4 and larger, no matter what the OD of the cable assembly may be.

Nevertheless it is still in violation to the MANUFACTURERS restriction on bending radius which the Code adresses elsewhere.

 

[Brian Donlon]

Are you saying the manufacture supplies the required Bend radius for their cable on multi conductor? Where does the code reference this?


Thanks !



Thanks

Nevertheless it is still in violation to the MANUFACTURERS restriction on bending radius which the Code adresses elsewhere.

 

[Smart $]

Its my understanding the the word RADIUS always means inside (dictionary definition).....

Not the word radius, but I agree the combined form bend radius is typically to be measured to the inside curvature, as the minimum radius one can bend a pipe, tube, sheet, cable or hose without kinking it, damaging it, or shortening its life. There are some examples in the NEC which state to use the centerline, but those are regarding the bending of conduit and tubing.

Also, I may have made a mistake in my determination using the inside radius, which I compared the minimum to R1 of the table. You could actually use 5 times the diameter (4 times for minimum radius and 1 extra diameter to outside of cable) and compare to R2.

3C/14AWG: 5 ? 0.34" = 1.70" -------> 3/4" conduit body

3C/12AWG: 5 ? 0.49" = 2.45" -------> 1-1/4" conduit body

...
...

Nevertheless it is still in violation to the MANUFACTURERS restriction on bending radius which the Code adresses elsewhere.

Are you saying the manufacture supplies the required Bend radius for their cable on multi conductor? Where does the code reference this?

Yes, and it could be greater than the Code required minimum.

110.3 Examination, Identification, Installation, and Use
of Equipment.

...

(B) Installation and Use. Listed or labeled equipment
shall be installed and used in accordance with any instructions
included in the listing or labeling.

 

[Smart $]

FWIW, I am somewhat suspect of the table values for R1 and R2, not having the exact method to determine these values. If we use the example of the linked documentation for "mogul" bodies, the diagrams indicate the R1 and R2 values are determined using a cable width the full inside diameter of the conduit. We all know that such a cable would be a violation of the Code fill requirement. Consider the following comparison depiction. The top image is captured from the "mogul" doc. The bottom image is my evaluation.

 

[weressl]

Are you saying the manufacture supplies the required Bend radius for their cable on multi conductor? Where does the code reference this?


Thanks !



Thanks

For example: http://okonite.com/engineering/bending-ratios.html

In Article 110, if my recollection is correct is where installation according to manufacturers instruction is stipulated. (I am sure we get somebody supply more accruate reference.)

 

[Smart $]

...
In Article 110, if my recollection is correct is where installation according to manufacturers instruction is stipulated. (I am sure we get somebody supply more accruate reference.)

Already did in Post #32... 110.3(B). Even quoted it.

 

[weressl]

Already did in Post #32... 110.3(B). Even quoted it.

...and I thank you!

 

[mivey]

OK, I'll accept that for the purpose of discussion... short of producing the exact document

Getting back to the OP issue, 336.24 doesn't stipulate using inside, centerline, or outside bend radius as other Articles do. Which should be used?

Inside would be standard AFAIK.

 

[mivey]

I appreciate everyones help. I would like to see what you guys come up with as far as sizing the correct TEE size for these size cables:

3/c #14 TC with a diameter of .34"

For a 3/c#12 diameter is .49"

#14:
R1 >= 4*0.34" = 1.36"
R2 >= 4*0.34" + 0.34" = 1.70"

so 2.0" fitting according to your table

#12:
R1 >= 4*0.49" = 1.96"
R2 >= 4*0.49" + 0.49" = 2.45"

so >2.0" fitting according to your table

 

[mivey]

Since the cable diameter is larger than a #4 AWG conductor then IMO you need to use the 6X formula for an angle pull.

4X. See 336.24

 

[mivey]

So that means for me to route a 3/c #12 awg TC cable with a diameter of .49" I need to use a 2" TEE???


A standard 2" TEE fom appleton has a 1.5" inside radius (Training R1) and a 3.5" outside



This cannot be correct??

Yep. That's why they make a UB fitting. In the mogul case, if you have a 0.9" TC cable you would need:
an R1 of at least 4*0.9 = 3.6" and and R2 of at least 4*0.9 + 0.9 = 4.5". So you need a 2.5" LB but only a 1" UB (or even smaller).

For a 1.4" TC cable you need:
an R1 of at least 5*1.4 = 7.0" and and R2 of at least 5*1.4 + 1.4 = 8.4". So you need a >4.0" LB but only a 1.5" UB.

 

[mivey]

FWIW, I am somewhat suspect of the table values for R1 and R2, not having the exact method to determine these values. If we use the example of the linked documentation for "mogul" bodies, the diagrams indicate the R1 and R2 values are determined using a cable width the full inside diameter of the conduit. We all know that such a cable would be a violation of the Code fill requirement. Consider the following comparison depiction. The top image is captured from the "mogul" doc. The bottom image is my evaluation.

R2 less R1 is not the cable diameter. R1 and R2 are mins and max values. If the cable has a min bend radius of R_min, then R1 must be equal to or greater than R_min (and R2 equal to or greater than R_min + diameter, which I think is usually the case).

 

[weressl]

4X. See 336.24

Wouldn't manufacturers requirement for greater bending radius would override that for multiconductor cables?

 

[weressl]

Well let's see if we can make your sense a little less perfect

So, IMO, Type TC 3C/12AWG cable does not have to comply with 314.28(A)(1) though (A)(3).

But it has to comply with the manufacturers instructions.

[h=4]Power and control cables without metallic shielding or armor[/h]
Thickness of Conductor Insulation Inches​	Overall Diameter of Cable, Inches​
1.000 and Less	1.001 to 2.000	2.001 and over
Minimum Bending Radius as a Multiple of Cable Diameter​
.156 and less	4	5	6
.157 to .315	5	6	7
.316 and over		7	8