Conduit Fill Calculations for Low Voltage Wires

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minesh21

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I have a project dealing with hundreds of cables, mostly all low voltage. We have existing conduits and I need to calculate conduit fill. Typically, I work with AC power so I use the standard 40% for over 2 wires. But I don't believe this applies to low voltage (coax, cat 5, etc.) wires. What percentage fill should I be using for IMC (NEC table 4)? I am looking at past projects and see a different company used 60%, but I'm not sure what the justification was.
 
Is no NEC requirement here that I am aware of. But consider length of run, type of raceway, how full you intend to fill it, number of bends, and what kind of stress you may put on the cables you are going to pull as it may effect their performance if you pull too hard. Cat 5 and 6 cables if only slightly compromised may still function but you may not get maximum data speeds the cable is capable of either.
 
There is no conduit fill for comm wires, see 800.110, 820.110, and 830.110.

That said, EIA/TIA specs are more restrictive than the NEC, and some mfg will not honor a warrantee unless installed by those specs.

In the real world, what kwired wrote. Basically follow Chapter 3 installs: no more than 4 quarter bends in a run (or between pull boxes), and the less bends you can do, the better. and you cannot use too much wire glide (clear lubricant). Also make sure your payouts are smooth and dont try to force it or pull a kink/knot thru a conduit.

What size is your conduit? What type? (EMT, ENT, RPVC, etc). How long are the pulls? How many degrees of bend?

You can put up to 210 cat6 thru a straight 4" sleeve, but you'd be hard pressed to pull a third that many cables thru a 170' run with 4 quarter bends in it. Maybe not at all; I remember one job we did here where we had a 3", 170' long EC installed conduit that we needed to get a 100pr Cat3 and about 20 cat5/cat6 thru. The cables would not go past the 3rd quarter bend. EC wound up disassembling the conduit there.

EIA/TIA specs are pull boxes every 100' and after every two quarter (90*) bends.

eta: here is a chart that seems pretty accurate by memory:

https://www.belden.com/resourcecent...uit-Capacity-Chart-Conduit_Capacity_Chart.pdf
 
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JFletcher said:
There is no conduit fill for comm wires, see 800.110, 820.110, and 830.110.

That said, EIA/TIA specs are more restrictive than the NEC, and some mfg will not honor a warrantee unless installed by those specs.

In the real world, what kwired wrote. Basically follow Chapter 3 installs: no more than 4 quarter bends in a run (or between pull boxes), and the less bends you can do, the better. and you cannot use too much wire glide (clear lubricant). Also make sure your payouts are smooth and dont try to force it or pull a kink/knot thru a conduit.

What size is your conduit? What type? (EMT, ENT, RPVC, etc). How long are the pulls? How many degrees of bend?

You can put up to 210 cat6 thru a straight 4" sleeve, but you'd be hard pressed to pull a third that many cables thru a 170' run with 4 quarter bends in it. Maybe not at all; I remember one job we did here where we had a 3", 170' long EC installed conduit that we needed to get a 100pr Cat3 and about 20 cat5/cat6 thru. The cables would not go past the 3rd quarter bend. EC wound up disassembling the conduit there.

EIA/TIA specs are pull boxes every 100' and after every two quarter (90*) bends.

eta: here is a chart that seems pretty accurate by memory:

https://www.belden.com/resourcecent...uit-Capacity-Chart-Conduit_Capacity_Chart.pdf
Click to expand...

We are using IMC conduit (ranging from 1" to 4"). These will all be straight pulls that goes from above ground to underground via existing penetrations and conduits.

Basically I will be using a various number low voltage cables, varying in size and type. I have the O.D so I can calculate the areas. What I need to know is the percentage fill I should use given these are straight vertical pulls in IMC conduit. Does the EIA/TIA reference this somewhere? Can you please provide a link? I was thinking of just using 60%.
 
Cables and conductors that are covered by Article 725, require compliance with the standard conduit fills. See 725.3(A). Ethernet cables are covered by Article 725.
 
don_resqcapt19 said:
Cables and conductors that are covered by Article 725, require compliance with the standard conduit fills. See 725.3(A). Ethernet cables are covered by Article 725.
Click to expand...

Now I'm really confused. This contradicts the previous posts that reference 800.110, 820.110, and 830.110.
 
minesh21 said:
We are using IMC conduit (ranging from 1" to 4"). These will all be straight pulls that goes from above ground to underground via existing penetrations and conduits.

Basically I will be using a various number low voltage cables, varying in size and type. I have the O.D so I can calculate the areas. What I need to know is the percentage fill I should use given these are straight vertical pulls in IMC conduit. Does the EIA/TIA reference this somewhere? Can you please provide a link? I was thinking of just using 60%.
Click to expand...

I've never pulled comm cable thru IMT, tho it should be the same fill wise and ease of pulling as EMT. Straight pulls with no 90s would let you pull more cable than if there were 4 90s in it.

BICSI has released the 13th edition of the Telecom Distribution Methods Manual; it's a 2 book set, each 2x the size of a 2014 NEC. I can check to see if they have any recommended fills for conduit. I have the 11th edition but something like recommended fill wouldnt have changed since that printing. I will check after dinner and post what I find later tonight. I'll also look to see what article(s) internet cabling falls under, tho I believe it is 830 as all Cat6 cable Ive seen is rated CM, CMX, CMR, or CMP, not CL2 or CL3.
 
don_resqcapt19 said:
How is there a conflict?...they are different articles and cover different things.
Here is an article that discusses Ethernet being covered by Article 725 and not by 800.
Click to expand...

After reading this article and digging a little deeper I see your point. I guess there is a discrepancy of applying article 800 or article 725. If you apply article 800 there is no fill requirement. If you apply article 725, it refers you to 300.17 which references the conduit type for fill calculations. So I guess we should technically be applying the fill calculations included in Chapter 9 Table 4. Is this correct?
 
minesh21 said:
After reading this article and digging a little deeper I see your point. I guess there is a discrepancy of applying article 800 or article 725. If you apply article 800 there is no fill requirement. If you apply article 725, it refers you to 300.17 which references the conduit type for fill calculations. So I guess we should technically be applying the fill calculations included in Chapter 9 Table 4. Is this correct?
Click to expand...
If the cables are covered by Article 725, you are required to apply the fill calculations.
 
How is there a conflict?...they are different articles and cover different things.
Here is an article that discusses Ethernet being covered by Article 725 and not by 800.
Click to expand...

Another article about what the author thinks the NEC is saying rather than looking at the facts. If anything the reverse should be true. Telephone wiring should be 725 CL2 because it carries 48VDC and 90VAC (capable of knocking you on your butt). Ethernet only carries a signal. But we can debate this until the cows come home until the codemaking panels understand it themselves and clarify it.

As far as I'm concerned ethernet is communications and Art. 800.

As for the OP, with multiple types of cables what I do is consider for myself how many I can comfortably pull given the size of conduit, length, number of bends and how much lube I could dump in there so as not to stress the cables. Without stressing the cable is the key. Unless I had cables of a similar size and type I wouldn't even think about standard fill requirements because I would probably be well below the maximum anyway.

-Hal
 
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hbiss said:
Another article about what the author thinks the NEC is saying rather than looking at the facts. If anything the reverse should be true. Telephone wiring should be 725 CL2 because it carries 48VDC and 90VAC (capable of knocking you on your butt). Ethernet only carries a signal. But we can debate this until the cows come home until the codemaking panels understand it themselves and clarify it.

As far as I'm concerned ethernet is communications and Art. 800.
-Hal
Click to expand...

Agree, and telephone over coax can tingle too. If there is PoE, it might be an article 725 install; PoE injectors and PoE switches are class 3 power supplies.

It doesnt matter what the catx is used for when it comes to conduit fill as the cables are physically the same. Heat build up is a non-issue. in researching this topic, supposedly the 2017 NEC will have some new material re: comm cable classifications.

minesh21 said:
After reading this article and digging a little deeper I see your point. I guess there is a discrepancy of applying article 800 or article 725. If you apply article 800 there is no fill requirement. If you apply article 725, it refers you to 300.17 which references the conduit type for fill calculations. So I guess we should technically be applying the fill calculations included in Chapter 9 Table 4. Is this correct?
Click to expand...

300.17 does not refer you to the fill tables; only the FPN mentions those code sections and FPN are not code.
 
Here's the EIA/TIA specs:

https://www.bicsi.org/uploadedFiles...entations/Caribbean/TIA-569UpdateOverview.pdf

they are way more restrictive than the NEC. Here's what they say on conduit fill:

Conduit
Sections between pull points shall not exceed 30 m (100 ft)
 in runs that total more than 30m (100 )’ , insert pull boxes so that no
segment between pull points exceeds the 30m (100’) limit.
No section shall contain more than two 90 degree bends
Conduits with internal diameter of 50 mm (2 in) or less, inside
bend radius of a bend in conduit shall be at least 6 times the
internal diameter
Conduits with an internal diameter of more than 50 mm (2 in),
the inside radius of a bend in conduit conduit shall be at least 10 times
the internal diameter.
Bonded to ground, in accordance to national or local
requi t remen s
 Has reference table for pull box sizes
 Maximum f ll i for furniture pathways is 40%

Conduit (RIGID, EMT, ENT, PVC, HDPE)
‐ Must be a minimum of 3/4”
‐ 40% Fill‐Ratio (NEC) applies

Note that EIA/TIA specs are NOT enforceable code, tho they may be required by contract.
 
hbiss said:
Another article about what the author thinks the NEC is saying rather than looking at the facts. If anything the reverse should be true. Telephone wiring should be 725 CL2 because it carries 48VDC and 90VAC (capable of knocking you on your butt). Ethernet only carries a signal. But we can debate this until the cows come home until the codemaking panels understand it themselves and clarify it.

As far as I'm concerned ethernet is communications and Art. 800.

As for the OP, with multiple types of cables what I do is consider for myself how many I can comfortably pull given the size of conduit, length, number of bends and how much lube I could dump in there so as not to stress the cables. Without stressing the cable is the key. Unless I had cables of a similar size and type I wouldn't even think about standard fill requirements because I would probably be well below the maximum anyway.

-Hal
Click to expand...
A new section was added to 725 for the 2017 NEC that addresses the concern of excessive heat in POE cables. Based on that I would say that CMP considers ethernet cables to be covered by Article 725.
 
The following Bicsi power point agrees that Ethernet Cables are covered by Article 725. The key is that the ethernet cables are not extended from equipment owned by a communications utility.
Click to expand...

I'm no fan of BICSI. I suppose they would agree with the poor wording that could make it appear that wiring not extended from a communications utility is not communications wiring. Why would that make a difference? What about ethernet wiring from a cable modem or telco ONT? That originates from a utility. What about the station side of a PBX? That doesn't and it's communications.

It's not about where it originates it's about the voltage and current it carries. IMO if it's less than CL2 it's communications.

A new section was added to 725 for the 2017 NEC that addresses the concern of excessive heat in POE cables. Based on that I would say that CMP considers ethernet cables to be covered by Article 725.
Click to expand...

Yes. If Ethernet wiring carries power as with POE then it should come under 725. However, I don't know how much heat CL2 wiring would generate and if there is CL3 POE I don't know where you would find a listed CL3/CM CAT5e or CAT6 wire.

-Hal
 
That BICSI page makes no sense, sorry. Someone tell me why who owns the PBX changes the circuit to a 725 install or an 800 install? Electrically, are they not identical? Also, if I run cat6 from a patch panel (or 110 block)to a keystone, there is no telling what IT guy is going to hook to the backbone cabling. Yes, chances are high it will be IT equipment but as Hal can tell you, if it's 110 to keystone, it might just be POTS. I've never had an inspector ask me the purpose of my cabling. Maybe they dont know, dont care, or it just doesnt matter. From experience, if you use the correct cable type (CM, CMR, CMP) for the app and support/firestop it correctly, that's about all you need to pass an inspection. Sad but (mostly) true.

Also, they write that POTS is 800 but a VoIP install is 725. As Hal wrote above, that's bass ackward too.
 
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