conduit fill ratio for conduit with two bends

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thekingtut

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Dear mike Holt friends
for conduit filling what is the filling ratio for conduit with one and with two bend assume any conduit with 3 three conductor , i need an answer from code , how to calculate it for one bend and for 2 bends, someone till me for straight length i can consider it 40% , for one bend it will be 36% and for two bends it will be 32% fill ration but he did not mention the reference.
 
You will find the fill limits in the specific raceway article in the code, which generally refers you to Chapter 9, Table 1. The number of bends are irrelevant (as long as you are at 360 degrees worth of bends or less).
 
thekingtut said:
Dear mike Holt friends
for conduit filling what is the filling ratio for conduit with one and with two bend assume any conduit with 3 three conductor , i need an answer from code , how to calculate it for one bend and for 2 bends, someone till me for straight length i can consider it 40% , for one bend it will be 36% and for two bends it will be 32% fill ration but he did not mention the reference.
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With the exception of the 2 ft "nipple rule", conduit fill limits as prescribed by the NEC are not a function of bends, length, or complexity of the pull. For any raceway longer than 24 inches or with at least one bend, the limits are 53% for 1 wire, 31% for 2 wires, and 40% for 3 or more wires. In general, it represents about 3/4 of the diameter of the raceway that can be filled with wires. And if you draw it to scale, you'll see why we have the exotic 31% limit for 2-wires.

If you do learn to subtract a fill percentage to anticipate bends, this is a rule of thumb from experience, rather than a formal required rule. It is a good idea, because raceway fills at the NEC limits can be much tighter than you really want to do.

The 2-ft "nipple rule" allows filling up to 60%, when the raceway is 24" or less, and straight. I would measure the 24" from opening to opening, so it would also need to account for the length of the bushings or hubs at the ends. This represents about 90% of the diameter fill. Obviously you cannot fit 60% with 2-wires, because the maximum they can fill is 50%, so you might want to follow a more practical limit for 2-wires in a nipple.
 
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1964element said:
There are s lot of good apps for pipe fill

Sent from my E6782 using Tapatalk
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Are there any that advise you on best practices for sizing conduits above and beyond the NEC limits, to account for practical experience?

I don't want to look like the ignorant fool who puts a 20A circuit in a 4" raceway (I'm exaggerating). But at the same time, I don't want to specify feeders that will be impossible to pull, even if NEC compliant.
 
Carultch said:
Are there any that advise you on best practices for sizing conduits above and beyond the NEC limits, to account for practical experience?

I don't want to look like the ignorant fool who puts a 20A circuit in a 4" raceway (I'm exaggerating). But at the same time, I don't want to specify feeders that will be impossible to pull, even if NEC compliant.
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I rarely size my conduits larger than what is required by the NEC and see no reason to do so. Changing the size of the raceway does little to reduce the required pulling force.
 
Carultch said:
I don't want to look like the ignorant fool who puts a 20A circuit in a 4" raceway (I'm exaggerating). But at the same time, I don't want to specify feeders that will be impossible to pull, even if NEC compliant.
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If you are a specifier, it is typical to specify the NEC minimum conduit size and the EC will increase it as they see fit to make it easier for them. As long as it is physically doable, the minimum per NEC is what you show.

You are not going to the site and laying out the pipe run for them, where they might need to adjust anyway. If they choose to run in some weird way, were they run onto a roof or buried in the dirt and you didn't expect that, it is just another time where the EC needs to know the code too. Similar to if you intended a raceway per circuit, but they find some method of combining circuits and run in a common raceway, you wouldn't be able to guess that and derate as would be needed for extra CCC
 
Carultch said:
The 2-ft "nipple rule" allows filling up to 60%, when the raceway is 24" or less, and straight. I would measure the 24" from opening to opening, so it would also need to account for the length of the bushings or hubs at the ends. This represents about 90% of the diameter fill. Obviously you cannot fit 60% with 2-wires, because the maximum they can fill is 50%, so you might want to follow a more practical limit for 2-wires in a nipple.
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Where does it say that to qualify as a nipple that the raceway needs to be straight?
 
thekingtut said:
Dear mike Holt friends
for conduit filling what is the filling ratio for conduit with one and with two bend assume any conduit with 3 three conductor , i need an answer from code , how to calculate it for one bend and for 2 bends, someone till me for straight length i can consider it 40% , for one bend it will be 36% and for two bends it will be 32% fill ration but he did not mention the reference.
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...you are from Egypt, do they follow the National Electric Code (NEC) from the USA?
 
don_resqcapt19 said:
I rarely size my conduits larger than what is required by the NEC and see no reason to do so. Changing the size of the raceway does little to reduce the required pulling force.
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I have had good luck with this same practice with feeders.

ron said:
If you are a specifier, it is typical to specify the NEC minimum conduit size and the EC will increase it as they see fit to make it easier for them. As long as it is physically doable, the minimum per NEC is what you show.

You are not going to the site and laying out the pipe run for them, where they might need to adjust anyway. If they choose to run in some weird way, were they run onto a roof or buried in the dirt and you didn't expect that, it is just another time where the EC needs to know the code too. Similar to if you intended a raceway per circuit, but they find some method of combining circuits and run in a common raceway, you wouldn't be able to guess that and derate as would be needed for extra CCC
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:thumbsup::thumbsup::thumbsup:

Bingo, show me what the minimum you want is, I will bump it up if I see the need. :)
 
Carultch said:
Are there any that advise you on best practices for sizing conduits above and beyond the NEC limits, to account for practical experience?

I don't want to look like the ignorant fool who puts a 20A circuit in a 4" raceway (I'm exaggerating). But at the same time, I don't want to specify feeders that will be impossible to pull, even if NEC compliant.
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can you give us an example of a compliant NEC conduit fill that is impossible to pull?
 
jusme123 said:
[/B]

can you give us an example of a compliant NEC conduit fill that is impossible to pull?
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One example would be when 3-conductors jam, as they arrange themselves in a line, instead of a triangle. This typically happens when your fill is close to the 40% limit, specifically for 3 wires.

Another example is offset nipples. I recall trying to fit 4/ #8s + 1/#10 through a 3/4" offset nipple of the curved Bridgeport type, with a coupling on both ends. This meets the NEC at 31% fill. The wire did not make it through when I built a practice assembly. I ended up replacing the offset nipples with the angular RACO type, and it worked much better. The angular changes in direction help the wire bend the right way, much better than the curved changes in direction.

I commonly see the advise that conduit sizing directly from the NEC requirements alone can be tighter than practical. Naturally, the question becomes, objectively, how should one anticipate how to oversize conduit?
 
iwire said:
I guess you are just that awesome. :D

I doubt it is easy for you as you are making it sound.[/

I have constant disagreements with my guys about bigger wire pulls. As soon as they hear anything ending in MCM, they start looking for the tugger. I told the guys that we're doing a secondary pull on Monday and immediate the question was asked, "when are they delivering the tugger?" Granted, we have seven sets of 4-wire 750 MCM AL, but the runs are only 30' long. By the time you account for set up the equipment, making the ends, the pulling rate of the tugger, a 1/4" rope, a half hitch, and one extra guy on the other end makes for a much quicker go of it. I rarely break out the equipment for anything under 75'.

I guess my point is, that sometimes "easy" isn't the quickest way. That being said, I would never attempt to pull the run you mentioned.
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Carultch said:
One example would be when 3-conductors jam, as they arrange themselves in a line, instead of a triangle. This typically happens when your fill is close to the 40% limit, specifically for 3 wires.
...
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Informational Note 2 to Chapter 9, Table 1, tells you to check for this problem. Of course that is not an actual code rule, but it is a possible issue.
 
iwire said:
I guess you are just that awesome. :D

I doubt it is easy for you as you are making it sound.
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I am far from awesome. I'm scrawny. Got cut from the high school basketball team, never even tried to play football. I have pulled a lot of full boats through 1/2" emt and not had to visit the training room after the job was done.

Actually, I'm a little embarrassed to admit, I'm sure you can get eleven 12AWG solid in 1/2" emt. Office furniture job, the specs called for an isolated ground and neutral. Boss had already told us to use 1/2" before he found out about that part. I just did what I was told.
 
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