How to Calculate Conduit Fill

#accesstopower #conduitfill #NEC2017
accesstopower.com
Many Electricians carry around an Uglys book, which contains tables on conduit fill. Actually, these tables come from the National Electrical Code Annex C. While these tables are very useful, they are limited in that they show conduit fill for a number of only one size conductor.
What if you have multiple wire sizes that you need to install in that conduit? How do you determine if your conduit can legally handle the amount of conductors you want to install. Now keep in mind that if you install 3 or more current-carrying conductors in a conduit you will also need to derate those conductors, but that is a lesson for another day. Today we are discussing how to size the conduit for the number and size of conductors we want to install. And if the conductors are different trade sizes, then how to determine that fill.

[@joedematteo3144]

You’re probably gonna get me through this school appreciate it hope to see more in the future

[@AccessToPower]

Joe, thanks for commenting on our video. I’m glad the content is helping you. Let me know if there are any specific topics you are most interested in. I’m always looking for helpful topics to create future content.

[@joedematteo3144]

AccessToPower yes actually load calculation would be pretty nice, and a quick question for it, what are 3 parts of general lighting load

[@4abettaworld]

Awesome brotha, you really simplified that whole process for me. Your time is greatly appreciated. Excellent explanation, thank you

[@jamesurquhart5410]

Now this is one of the best visual explanations I've seen regarding how to use chapter 9 of the NEC. Great job and thank you.

[@AccessToPower]

James, Thanks for the comment on our conduit fill NEC video. I appreciate the positive feedback.

[@mlcarter138]

Demand factor and load calculations. Everyone struggles at explaining these two. You seem to be very good at explaining things. This video was very helpful. Keep em coming.

[@bobsplace4114]

I took my 06a Hvac limited test recently and a conduit fill question was on the test, among others questions I had no clue on, never do such wiring and don't plan on it with an 06a license , but on watching this video my rescheduled test I might have a fighting chance to get this one right. Ty Bob

[@DanielinLaTuna]

Thank you! I sent this video to my brother who was wondering how many branch circuits he could fit into 3/4” EMT. I told him it depends on wire size. This video answered his questions, and explained “why”

[@RodLogan1]

THANK YOU SO MUCH for explaining that step by step. I was just issued a permit to install a subpanel and a few branched circuits in my garage. I already had the numbers from the Uglys book, but really wanted to better understand how to use the NEC tables to calculate this on my own as I plan my layout for conduit. After watching this video, I'm not really sure why it didn't make sense right away when I looked at the tables before because it's very straightforward. Liked and subscribed for sure!

[@CanitJayce]

You explained this very well I was getting super frustrated because I couldn't get the right answer and it was because I was overcomplicating it I appreciate the help

[@aaronfidelisrecine]

Thank you so much. I'm doing the self paced WECA and this is a great help!

[@jgoddard0757]

I really like the spreadsheet idea!!! Thanks!

[@chrisbyrge2188]

Very informative and simply explained. Good job!

[@KevinCoop1]

Southwire has an App for this. It works extremely well! It also calculates the probability for Jambing or getting them stuck in the conduit. Fine points to this video. Exceptions to what was shown are, you are allowed to use manufacturers information for your specific conductor. NEC uses Southwire data. Also, the percent fill can be 40.5% and allowed to round down. It's all in the NEC.

[@slaughterhousejazz]

Awesome! Thanks for the derating blurb. Good to know!

[@jasonokane496]

Great video sir,, very informative and good presentation

[@salvadorochoa6465]

Good stuff boss I was stuck on my HW for a sec I think I got it down ! Thanks law dog

[@jarrydee2799]

Taking my J-man test at the end of Nov. Thank you for this!

[@fetahmorina]

How did it go?

[@jakobsime4190]

how was it

[@SouthwestIndustrialElectric]

Great details! Thanks for sharing this breakdown.

[@ralphramsey82]

Thank you for taking the time to explain this 👍🏻👍🏻

[@robertochavez6221]

Thanks for sharing! Should I count ground as a conductor too?

[@carultch]

For sizing conduits, yes. This is entirely a question of what geometrically fits in the conduit. Application of the conductors is irrelevant.

[@LJ_828]

Thank you for sharing this, it is very helpful.

[@israelolugbemi9412]

This is very insightful

[@brucelehman6353]

Great explanation, thanks

[@johncoyote6755]

Very good. Thank you sir.

[@danielvargas3292]

Ty. Testing out tomorrow.

[@johntopham3]

When you are talking about conductor size, does this include the insulation? Or do you just mean the actual conducting copper portion? Thanks

[@AccessToPower]

This is the OD or outside diameter of the wire including the insulation

[@johnny3ce]

Thank you! 👍😎

[@armondcooper1548]

How do I get a PDF version of the code book? Great Video THHN!!!

[@connorchamsarian-soule1633]

So I have a question, Why don't u have to account for the cross-section area when u put all the numbers in. Was it because it was already account for in the code book?

[@Howeezy92]

Hi Walter! How would I apply this chart to RTRC Conduit (Fiberglass conduit). I can't seem to find this type of conduit on the chart. For example: Figuring out if I can fit 2+ 750 MCM into a 5" FRE Conduit

[@NicholasTheGreat]

So how does adjustment factors play into this? I had a Jman tell me that you can’t do 10 #10’s in 3/4 because you still need to derate, but isn’t that the whole point of annex C?

[@AccessToPower]

This video was on conduit fill only. You will need to derate your conductors if you have more than 3 current carrying conductors in a raceway. You could have 10 #10’s in a raceway, but you will need to derate them by 50%. Table 310.15(B)(3)(a)

[@lh98]

So I can run 2 Romex 12/2 in a 1/2” pvc conduit if I remove the sheathing and just run the 2 black 2 white and 2 bare conductors legally? I could even drop one bare conductor and just use the one?

[@Robert-qw7ex]

Can you do a video on derating so many people don’t understand it’s of the wire insulation not the device terminal ratings electricians don’t understand you can use the 90deg column when derating

[@nayivisdenis1401]

profesor.we need to remember the ampacity when we fill the pipe

[@AccessToPower]

Thats correct. That will be a subject for a derating video. In this video I was only teaching about how to know when you have max fill in a conduit. Derating is super important and needs its own explanation. Thank you for commenting and helping others to be aware...

[@nayivisdenis1401]

thankyou profesor for your videos!!

[@ameershalabi2024]

How do I know if I have enough room in the conduit to fit the section area of the 9 wires or 12 wires?

[@turbotubesteak]

good stuff. do you have a derated fill video ?

[@AccessToPower]

mozart601 not yet. I will be making one soon

[@chrisworst8353]

Nicely done!

[@vnesmuonnam]

What is reason 2 wires only allow 31%? Should be some where between 40-53%? Thank you

[@pld8993]

If you install 2 conductors only, the largest ones that you can get in there, they will sit side-by-side in the conduit, from wall to wall. That will leave a whole lot of empty space in the conduit. Draw a circle and then two equal circles inside the first circle that sit next to each other and touch the walls inside the first circle, you'll see what I mean.

[@andresariaslondono7003]

Very good explanation.

[@Repackrider84]

How do calculate what size SOW submersible cable O.D fits in a certain size I.D. conduit?

[@britaniaduran3080]

Thank you so much you earn my subscription, my respect and a like.

[@JohnSmith-vq4oe]

in my case it is total 2 cables. 1 cable is multi core say 4 core 10mm and other is 1 cable single core 10mm as grounding as this is street lighting cables buried under ground in conduit from pole to pole, these are pulled in one conduit and the conduit fill is 45% and this is already done on the site. will it work

[@masteresayson8689]

Good afternoon, hello how to buy ugly's book 2017

[@andyguedea6239]

Good video.

[@CaliArbuckle]

How many 4-pair UTP cables (1/4-inch diameter) can be pulled through a 2-inch (inside diameter) conduit?

[@AccessToPower]

What is the outside diameter of your cable in inches squared (in2)?

[@CaliArbuckle]

@@AccessToPower I am not really sure how to answer that. I found the area of the pipe of 3.1416 in2 and the area of the wire 0.0490875 in2. I divided the area of the pipe by the area of the wire 3.1416/0.0490875 =64. I need 50% fill so my guess was 32 wires at 50% fill. I am not sure I have this correct but it is for a test for work so they did not give the diameter of the cable in inches squared. Thank you so much for trying to help!

[@AccessToPower]

If 50% fill is what you need then your answer is correct. I took the (area of the conduit / .5) / area of the wire.

[@CaliArbuckle]

@@AccessToPower Thank you so much for the help!! I feel better!

[@oscargarcia8159]

Great video!!

[@JohnSmith-vq4oe]

do we have to consider grounding cable as one cable with one multi core power cable during conduit fill calculation knowing that only one cable dissipating heat and for one cable it is 53 percent conduit fill. in my case it is 4 core 10mm2 as three phase and neutral and another cable is 1 core 10mm2 as grounding conductor.... Please replay on this Question.

[@AccessToPower]

When you are trying to determine conduit fill, you are considering the Outside Diameter of each of the cables, or conductors in a conduit and comparing that to the inside diameter of your conduit. You need to stay under your 40% fill for a standard conduit run. Weather the conductors are current carrying or non-current carrying does not matter when it comes to conduit fill. Now when it comes to derating, (adjustments and corrections for the number of current-carrying conductors in a conduit, (see TABLE 310.15(B)(3)(a) Adjustment Factors for More Than Three Current-Carrying Conductors) as well as ambient temperature (see TABLE 310.15(B)(2)(b) Ambient Temperature Correction Factors Based on 40C (104F)), you will definitely need to adjust the size of your conductors, or maybe increase the number of conduits to avoid excessive derating of the ampacity of your conductors. Derating will be a topic for a separate video. We did not discuss it in this video.

[@JohnSmith-vq4oe]

@@AccessToPower in my case it is total 2 cables. 1 cable is multi core say 4 core 10mm and other is 1 cable single core 10mm as grounding. so i should calculate it 31 percent conduit fill

[@glasshalfempty1984]

4:18 ...I'm very confused. 1 conductor 53%...okay, I'm with you. Add another conductor, 2 conductors now, 31%....okay, the volume of conductors has increased, so therefore, the fill has decreased to 31%...still with you. OKAY, so the more conductors, obviously the less you can....wait...over 2 conductors ....40%?! Huh? That makes no sense. I just can't wrap my head around it. Can you help shed some light on this inconsistency please?

[@hamzasadat3943]

I am also confused ,If you got an answer please share with me it .👍👍👍

[@glasshalfempty1984]

No answer yet unfortunately :\ everybody seems to just be going with it so I can't help but think I'm overthinking it... But even so, I never figured it out and would like to understand.

[@hamzasadat3943]

@@glasshalfempty1984 thank you ❤

[@KevinCoop1]

Draw a circle for a conductor and a larger circle for inside conduit. Now draw two circles touching conductors and circle for conduit. Now draw three conductors and a conduit. The shape is the reason. Think of more like six. Remember this is only fill percentages, not number of conductors or size discussion.

[@crack1270]

Like kevin coop said it has to do with the way the 2 conductors wrap around each other when pulled together through a raceway

[@DanBurgaud]

Bends make for a harder pull. How does it compute when the conduit contains multiple bends?

[@carultch]

The Capstan equation. T2 = T1*e^(mu*theta), where mu is the friction coefficient, theta is the angle in radians, and e is Euler's number. This determines how much tension multiplies as you pass through each bend.

[@rezzle2457]

Hypothetical question , if there’s 10 grounding (green )wires , do they all count? Thank you

[@carultch]

Yes. All conductors regardless of application count.

[@pld8993]

Yes, but there'd almost never be a need for that many ground wires in a conduit. A single ground wire can be used for multiple circuits, though it must meet the sizing requirements for the highest rated conductor of the group.

[@yourstruly4864]

and how do i make a spread sheet ?

[@AccessToPower]

@@yourstruly4864 you can use Excel or Google sheets, or you can use Numbers on a Mac to create spreadsheets

[@rickyt281]

Thanks you are awesome!

[@morffi1123]

whats the page?

[@Josh-mh3kl]

Can I pull 16 awg through ¾"pvc conduit? approx 50ft and two 90 degree turns?

[@AccessToPower]

How many 16 awg conductors

[@Josh-mh3kl]

@@AccessToPower 3 conductors. hot, neutral and ground

[@AccessToPower]

@@Josh-mh3kl yes you can. No problem

[@AccessToPower]

Although #16 wire isn’t rated for that many amps. What size breaker is protecting that circuit?

[@Josh-mh3kl]

@@AccessToPower I am running three Pentair Intellibrite 500W pool lights to a pump house. (each into their own 3/4" pvc conduit) I have not installed any circuit panel as of yet. They recommended i run 1" conduit but it was too late. Koi pond is back filled already. (0.46 amp per light. Total of 1.38 amps)

[@JohnSmith-vq4oe]

Please tell me why its set for one cable 53 percent fill, for two its 31 and for three or more its 40 percent why is the reason behind this percent set

[@AccessToPower]

hello John. Thanks for posting on one of our videos. According to Note 2 of "Notes to Tables" in Chapter 9 of the NEC, the conduit fill requirements are required to keep the conductors from suffering physical damage. While that is the only note, I am sure that a secondary reason is to dissipate heat from the current carrying conductors. Also, the inside diameter to of the conduit walls and the outside diameter of each of the conduit fill stays very consistent from 1, 2, and 3 conductors. For one conductor the ID of the conduit is roughly 1.37 times the wire diameter. For 2 conductors the ID of the conduit is roughly 1.27 times the wire diameter. and for 3 conductors the conduit ID is also roughly 1.27 times the wire diameter.

[@glasshalfempty1984]

@@AccessToPower Thanks for answering this question but...that still doesn't make sense. If 1 conductor is 53% and 2 conductors are 31%....then logically...MORE than 2 should be NO MORE than 31%...yet it says 40%? 2 conductors would be less restrictive than 3, provide more air space for heat dissipation, more room to keep the conductors from suffering physical damage...etc. It's very confusing.

[@AccessToPower]

@@glasshalfempty1984 the following graphic should help you visualize why the fill is more with 3+ conductors as opposed to 2. images.app.goo.gl/ghPAMDMRjbqbAncC6

[@michaelkeith5178]

If you were to look into the conduit with the two wires in it The way the round wires lay in the round conduit is more conformed to the perimeter of the conduit

[@packinaglock]

@@glasshalfempty1984 🤣 Because the guys making up the code book have a God complex and sit around discussing "what kind of crazy insane sh*t can we get them to do this year."

[@antoniohernandez7171]

Stupid question but when I do the math for 8 (10 AWG) conductors it gives me a bigger number.. I’m confused

[@ThreePhaseHigh]

Can too many wires in conduit from the transformer to the breaker box on an 800 amp service make your meter read high on high usage days. ( 8 wires total 4 250 aluminum wires for each leg 240 Single phase all wires cut same length) 30 ft From transformer to breaker box. C T metering.

[@AccessToPower]

hello ThreePhaseHigh. the current passing thru the meter, or the current transformers in the case of the 800 amp service you described, is what causes the meter to run. So even if there is induction onto your 800 amp feeder from the other conductors, unless there is a load, I don't think it will have any effect on the meter.

[@JohnSmith-vq4oe]

Guys I have problem, total 2 cables. 1 cable is multi core say 4 core 10mm which is 3phase, Neutral and other cable is single core 10mm as grounding as this is street lighting cables buried under ground in conduit from pole to pole, these are pulled in one conduit and the conduit fill is 45% if i consider 2 cables and this is already done on the site. will it work. i want Justification that it will not create problem as the Electrical Consultant is asking me to replace it with higher size conduit which allows 31% conduit fill. please i want to know any exception in the code regarding this matter.

[@AccessToPower]

John. there is no exception besides a 24" or less conduit. In that case you can have 60% fill. But you application would be a standard pipe run with 2 cables for 31%.

[@oscar27ization]

I thought after 3 current carrying conductors you have to derrate. I keep getting confuse. Can you please help me?

[@AccessToPower]

You do have to derate conductors after 3 current carrying conductors. This video was about calculating conduit fill, not about derating. I will make a derating video as well, but this video was meant to show you how to calculate fill.

[@oscar27ization]

@@AccessToPower thank you , but does that mean in reality you can’t put all those wires in a single pipe? Cause the code book says u can but then u have to derrate???

[@AccessToPower]

@@oscar27ization not necessarily. It depends on what the load is. And example is what if you have (3) 1 hp motors at 480 V. You would have a minimum of (9) current carrying conductors and a ground. A 1 hp motor @ 480 volt 3 ph only draws about 1.5 amps. So even after you derate the wire (say #12 AWG) it still has plenty of current carrying capacity for that load.

[@oscar27ization]

@@AccessToPower ohhhh is see, right that makes sense. If I have a 3/4 emt pipe and it can fit 16 number 12# in it, but every circuit load will be for a house like outlets, lights, and small appliances then there is no need to derrate there cause maybe Most of those circuits won’t draw a lot of amperage

[@rupe53]

@@oscar27ization ... you say MOST circuits would not be carrying full load, but if they are not dedicated circuits (hardwired to the end use) you should consider full branch rating as the load. Shit happens. OTOH, you could cut down on the number of wires by feeding 2 branches with a double breaker so there's only a single neutral to a pair of 120 volt circuits. The only issue is the shared breaker will give you a common trip with a fault. OTOH, code would allow the shared neutral and a shared 2 pole breaker. You'd save 2 wires on 4 branch circuits so now only 14 conductors instead of 16.

[@bryanzavala3119]

What spread sheet do you use ?

[@AccessToPower]

Hi Bryan, I am just using a google sheets spreadsheet that I created for the video.

[@JohnSmith-vq4oe]

in my case it is total 2 cables. 1 cable is multi core say 4 core 10mm and other is 1 cable single core 10mm as grounding. so i should calculate it 31 percent conduit fill

[@AccessToPower]

Yes. With 2 cables 31% fill is correct

[@michaelkeith5178]

If you were to look into the conduit with the two wires in it The way the round wires lay in the round conduit is more conformed to the perimeter of the conduit

[@2424jhg]

Don’t forget you have to derate for number of current carrying conductors.

[@AccessToPower]

Josh Ghacemi absolutely need to derate based on the number of current carrying conductors. That will be the subject of a different video.

[@JohnSmith-vq4oe]

i want to know why for one cable it is 53 percent, for two cables it is 31 percent and for three or more cable it is 40 percent? please anybody Answer

[@glasshalfempty1984]

What I want to know is why NOBODY IS ADDRESS THIS?! It makes NO sense. I'm relieved to find somebody else asking but I'm shocked that you're the only other one.

[@elmasbuscado909]

Ask mike holt

[@rupe53]

@@glasshalfempty1984 ... actually the "1 conductor = 53%" is to keep you from filling the pipe to 106%. (not possible) If 2 conductors = 31% then adding a 3rd conductor would be an additional 15.5%, which is well over the 40% fill. I know it sounds a bit nutty but the math is simple.

[@carultch]

@@glasshalfempty1984 It has to do with how well circles pack in a circle. Generally, these area fills correspond to approximately 70% to 80% diametral fill. Since a round wire fits perfectly in a round raceway, you get to fill it to 53% by area, to get it to this diametral fill. Since two wires at maximum, can pack to 50% of the raceway by area, if you jam them in there wall-to-wall, the allowable percentage is limited to 31%. 3 wires and higher, worst case scenario, will pack like a triangle stack of 3 circles. If you work out the typical packing efficiency of 3 or more circles, you'll get between 70% and 80% diametral fill, if you fill it to 40% by area. You do need to be concerned with jamming for 3 conductors specifically, which is very likely around 40% fill exactly, so you generally want to shy away from the 40% for 3 conductors. That's where they end up lining up instead of triangle-packing.

[@crack1270]

Don't forget you will have to derate by 50% for ten current carrying conductors Table 310.15(B)(3)(a)

[@AccessToPower]

shawn the don absolutely. I’ll make a separate video on derating. This video was strictly dedicated to conduit fill. Thanks.

[@nonplus2op879]

Someone swing their notes from this

[@hernandezrene46]

Minus 5

[@Imwright720]

They make it way to complicated. If the wire will go through, good to go. Once you get above to much fill it wont go. It’s easier to use a larger conduit. It’s self regulating. Like most things they want to make it more complicated than necessary. The same people who wrote it probably wrote the tax code.

[@ClickinChicken]

wire in metal electric conduit so no one can screw into it or pound a nail into it. if it fits. Why's it so darn tooten important? heat? gas escape?

[@carultch]

@@ClickinChicken The reason conduit fill is important, is to keep the pull practical, so you don't damage the conductors. You fill the conduits to about 70% to 80% by diameter, and these area percentages roughly correspond to that diametral fill.

[@edwardsmith4353]

too bad you dont do ambient calculations

[@masteresayson8689]

Good afternoon, hello how to buy ugly's book 2017

[@gusc6785]

Home depot has them in electrical aisle