Long Conduit Telephone Cable Capacity

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Old 08-05-10, 10:02 AM
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Long Conduit Telephone Cable Capacity

We have a local bridge with empty, 4" metal conduits hung underneath. The total length is about 400 feet. It is exposed to the sun and outdoor thermal environment in Northern California. We would like to know the maximum percentage of the available conduit area we can fill with telephone cable to meet code.

I have seen 53% (single cable), 31% (2 cables) and 40% (3 or more cables) as the NEC code. However, the code is limited to a length less than 50 feet. Where can I find a code or guideline which deals with our length of 400 feet?

Thanks.

Mel Amato
 
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  #2  
Old 08-05-10, 10:48 AM
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I have seen 53% (single cable), 31% (2 cables) and 40% (3 or more cables) as the NEC code. However, the code is limited to a length less than 50 feet.
There is no 50' length limit in the NEC -- it applies to conduit systems of any length greater than 24". A fill limit of 40% of the cross-sectional area of the inner diameter of the conduit is the NEC requirement for 3 or more cables. Generally, however NEC is not used when dealing with communication systems so it may not apply to your situation. Because of the distance and perhaps small cable, you may need to consider pull tension on the cable when deciding what materials are appropriate.

If this is a public roadway you'll almost certainly need an engineer's stamp on the plan anyway, regardless of the code articles.
 
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Old 08-05-10, 12:03 PM
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Why isn't the phone company and their enginners involved in this?
 
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Old 08-05-10, 05:58 PM
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Originally Posted by ray2047 View Post
Why isn't the phone company and their enginners involved in this?
my thoughts exactly

who owns the conduit and do you have permission to use it ?

what is the pair count and type of cable are you using ?

that would certainly enter into the fill ratio
 
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Old 08-06-10, 10:19 AM
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Long conduit telephone cable capacity

This is not a proposed installation. We are trying the estimate the actual fill for an installation made in 1979. Neither the phone company or the bridge owner (city) will help us.

Mel Amato
 
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Old 08-06-10, 10:34 AM
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Originally Posted by melamat View Post
This is not a proposed installation. We are trying the estimate the actual fill for an installation made in 1979. Neither the phone company or the bridge owner (city) will help us.

Mel Amato
Still not making sense. Why are you involved? Why do you need the info? If this is some kind of dispute with the TelCo you are going to need more then an opinion here. An assessment by an independent communications engineer and a filing with the appropriate state regulatory agency may be the correct path.
 
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Old 08-06-10, 01:46 PM
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Rays right again that is all regulated and has nothing to do with you .

if your having service issues file a complaint with the PSC

as to NEC most telcos are exempt from the NEC so any fill ratio you can comer up with is meaningless anyway
 
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Old 08-06-10, 07:44 PM
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That kinda puzzle and with commuation cable the NEC code not really in effect at all and what more that you have city / Telco to deal with this.

You should check with the state codes they have pretty strict guideline with conduit on pubic bridge .

That all I can able say for time being due there is a bit of red tape to get involded even with exsting installment.

{ I allready went thru with street luminaire circuits it was pain in the rear end }


Merci.
Marc
 
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Old 08-06-10, 10:59 PM
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Long conduit cable capacity

There is a move to demolish the bridge. The structural rating of the bridge is a function of its dead weight which includes the telephone conduit. We believe that the weight has been estimated high simply to lower the rating and thereby allow funding for a replacement bridge. The rating on the margin so that even the conduit weight including the cable is a factor.

Neither the city or the state will help us in this regard because they are trying to justify a bridge replacement.

We simply need to know the applicable code so that we can estimate the total weight.
 
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Old 08-06-10, 11:04 PM
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Ray,

Any idea who the appropriate state regulatory agency is. If its the state DOT, they won't help since they want to demolish the bridge. The county also does not want to get involved. AT&T claims they cannot speak with me because of homeland security considerations.
 
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Old 08-07-10, 06:08 AM
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Just curious ... Are you against replacing the bridge because of historical reasons or cost?

In your first post you said the 4-inch conduits were empty?

In any case, I believe that structural engineers use 100% fill when calculating the load, then add a safety factor. The safety factor is added to everything, which would explain why the weight rating seems so high.

I know that when we fly speaker cabinets our riggers use safety factors of 4x to 10x to calculate the potential on the fly points.

If I were you I would ask an independent structural engineer and not a political entity.
 
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Old 08-07-10, 11:51 AM
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Rick,

The cost for rehab is about 1/2 the cost of a replacement. In addition the bridge is eligible for listing on the National Register of Historic Places. On July 30, it was nominated by the State Historic Commission for actual listing. So my answer is yes and yes.

The bridge rating equations already include AASHTO established safety factors. Its not required to add an additional safety factor on the weight calculations. The conduits are not empty. We simply need to determine their contents.
 
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Old 08-07-10, 01:46 PM
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Don't try to estimate the weight of what's in them for sake of arguments without knowing what's in them...your position won't hold water. You won't know what percent of fill is there - you'll just have a bunch of assumptions.

You might be able to determine what kinds of cable are inside based on what can be seen at either end, unless they continue to AT&T equipment and can't be seen.
 
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Old 08-08-10, 07:21 PM
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We are not trying to estimate an unknown. We are trying to determine the total number of wire pairs and the gauge size. This is a simple question which AT&T refuses to answer based upon homeland security excuses. There is a manhole accress but accuss is illegal and possibly dangerous because of potential gas in the manhole.

I am not interested in a debate on our motives. I am simply interested in how we can obtain basic facts on the contents of the conduits. This should be public information which should be available from a public agency.

If anyone has any supportive suggestions, they would be appeciated.
 
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Old 08-08-10, 08:40 PM
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This should be public information which should be available from a public agency.
AT&T is not a public agency they are a private concern and I doubt that their is any "public agency " that knows or cares what if anything is in the conduit

I do agree with the homeland security issues and don't find it to be a Excuse I don't thnk they really need a excuse to not divulget the contents to you

I do credit you with showing the sense not to try the manhole .
 
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Old 08-08-10, 09:41 PM
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It appears that I will not obtain any practical suggestions on this website. I am a conservative and do support the rights of private business.

I certainly am not a terrorist. AT&T simply does not want to get involved. They would be willing to provide this info to our city who owns the bridge. I am not confident that our city would pass on the correct info to me since they have an axe to grind.

Hopefully, someone on this site will provide me with a usefull suggestion rather that engage in a debate as to my rights and business rights.

My question is simple and not threatening.
 
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Old 08-08-10, 09:57 PM
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I do not believe there is any way for you to accurately gauge the contents of the bridge conduit without actually looking at what's in there. It probably does not even follow the original plans as existing wiring is often abandoned when new is installed or upgrades are made. The telecom companies are under no obligation to follow electrical code, so even calculating based on maximum fill limit is not particularly useful as they may or may not have followed it. Furthermore, it is reasonable that there may not even be copper twisted pair wire in the conduit; it could be a single fiber.

Nonetheless, I can't imagine the weight of telecom cable is really even a factor in the bridge structural rating. It has to be nearly insignificant compared to the other loads placed on the bridge.
 
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Old 08-09-10, 12:47 AM
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Your comment has convinced me that this website is of no practical value and that no one has any real interest in providing any practical advice.

The bridge rating equations are a very sensitive funtion of the weights. In this case, the conduit weight with cable is a major factor in determing the elibibility of our bridge for federal funding.

We will obtain data necessary to determine the actual total weight of the conduit including the cable by other means.

There is no need for any one else to respond with uniformed and biased comments.
 
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Old 08-09-10, 04:24 AM
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This website and the answers you've read only means that no one here has any definitive answers for you. The only real answer to your question is, "Low voltage cabling does not fall under NEC guidelines for conduit fill."

If those conduits have been there since 1979 you can bet they're stuffed with copper -- or were at some point if they have since been replaced with fiber.

That's why I suggested using 100% fill to get your calculations. A typical 100-pair outside plant telephone cable is one inch in diameter and weights about 500 pounds per thousand feet. One 400-foot conduit stuffed with four cables (if you could get four in there) would weigh 800 pounds plus the weight of the conduit itself.
 
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Old 08-09-10, 09:35 AM
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Rick,

Thanks. You have provided an answer to the fill question in your first sentence.

The conduit itself is aluminum EMT. OD is 4.25". Wall thickness (I measured with a rented ultrasonic gauge) is 0.090". Empty conduit weight is about 1.36 lb/ft. Contents unknown to us at this time.
 
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Old 08-09-10, 08:15 PM
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Originally Posted by melamat View Post
The conduit itself is aluminum EMT. OD is 4.25". Wall thickness (I measured with a rented ultrasonic gauge) is 0.090"..
They make scanning tools to scan concrete many inches thick for cables, broken water pipes, and other obstructions. Maybe one of these tools can be used to scan the pipe to see how full it is.
 
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Old 08-09-10, 08:45 PM
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Originally Posted by melamat View Post
Rick,

Thanks. You have provided an answer to the fill question in your first sentence.

The conduit itself is aluminum EMT. OD is 4.25". Wall thickness (I measured with a rented ultrasonic gauge) is 0.090". Empty conduit weight is about 1.36 lb/ft. Contents unknown to us at this time.
If what you have is aluminum EMT, the OD should be 4.5" and weight should be 159 lbs/C plus the fittings.

http://www.atcelectrical.com/literat...-1751_Alum.pdf
 
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Old 08-09-10, 09:22 PM
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They make scanning tools to scan concrete many inches thick for cables, broken water pipes, and other obstructions. Maybe one of these tools can be used to scan the pipe to see how full it is.

start scanning the pipe and you could be interrupting data transmissions

what would the scan tell you as to weight anyway

bottom line is the OP is sticking his nose where it doesn't belong demanding info he has no right to
 
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Old 08-09-10, 09:30 PM
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Read on next section

Merci.
Marc
 

Last edited by french277V; 08-10-10 at 11:35 AM. Reason: reopen up the thread
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Old 08-10-10, 11:28 AM
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Ok Here is the OP's quote:

Unfortuately, you closed the long conduit post before I had an opportunity to report good news. I finally got through to the correct person at ATT and they provided the complete cable descriptions which includes not only copper of various sizes and bundles but a 216 optical fiber cable.

I also wanted to clarify the dimensions of the aluminum EMT conduit. This is a style no longer manufactured. There are no connectors. The sections interlock and are glued. The carefully measured OD is 4.25" as I noted. Conduit is sized by ID so that with a will thickness of 0.090" as measured, the ID is 4.07" which is close to the ID for present aluminum or steel conduit which are a nominal 4.5" OD but heavier. For the dimensions measured, using the density of aluminum the weight is 1.36 lb./ft.

Sorry about that.

The thread is open now.

Merci.
Marc
 
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Old 08-11-10, 07:55 AM
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Congrats on your successful persistence. As previously alluded to, be aware that regardless of the actual dead weight of the existing cables, the licensed PEs making these determinations may be estimating high because they will need to account for any future reasonable use of those conduits regardless of what is in there now.

Granted the only thing that will probably be added by the company is fiber, but without a legally binding document or statutory requirement restricting what is placed in the future, the engineer's viewpoint will be that the heaviest currently-manufactured cable may be placed in the conduit at some point in the future.

If you want anything measured with a safety margin, a civil engineer is the person you want. Obviously political forces know that. So, as you are probably aware, for your argument to simply gain a toehold, you will probably need opposing opinions from one or two licensed PEs with a lot of experience in this area. Good luck.
 

Last edited by ArgMeMatey; 08-11-10 at 07:56 AM. Reason: typo
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Old 08-11-10, 09:54 AM
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Many thanks to the moderator for reopening this thread.

We are already seeking a licensed structural engineer to support our case. Finding one to work pro-bono is proving to be a challenge.The present weight analysis is for the bridge as it is. If it is rehabilitated (about 1/2 the cost of a replacement), it will receive a modern, lightweight deck which will allow for a subtantial future expansion for underbridge utilities.

By highballing (lower bridge sufficiency rating) the weight now, the city's engineering consultant is assuring that the bridge's sufficiency rating is in the lower range which will make it eligibile for the federal funding of a replacement bridge. This definitely skews the objectivity of the bridge alternative evaluation process.
 

Last edited by melamat; 08-11-10 at 09:55 AM. Reason: typo & add
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Old 08-11-10, 09:25 PM
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Sure I am glad to get the thread reopen up and thanks for your time here.

I know this is pretty instering discussion what we normally don't see this in the fourm at all.

Note: to the rest of readers this topic is montered pretty closely so just keep it neat here.

Merci.
Marc
 
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