COAX cable in 3/4" and conduit fitings

[NotreDave]

All,
I need some help please. I am sort of lost. I am running a coax cable (see attached) in a 3/4" conduit. It will fit in the conduit with no problem at all, my question is looking at the minimum bending radius of the cable, which is 2.5 inches, I don't think a regular crouse-hinds 3/4" LB27 will work due to the max. bend radius of that fitting. I will use a 1" crouse hinds BUB3 for the 90 degree bends. I have a problem and need guidance when specifying a "TEE", because "tee" fittings are required for this installation. According to the chart (link below), I would have to go to a 1-1/2", mark 9 T59. The plant (ExxonMobil) uses Form 7 fittings. I am so confused on this issue and would love someone to enlighten me on code or rule of thumb. The manufacturer told me I could wrap the coax around my finger, lol. i would love to hear what you all have to say about this! Are there other charts out there, excel spreadsheets, calculators, that could help me in the future? I thank you much in advance.
David
http://www.cooperindustries.com/con...trial-fittings-bend-radius-cubic-capacity.pdf

 

[K8MHZ]

I guess my first question is why you are running coax in conduit?

The min. radius is important. If that is not kept, the center conductor of the coax will migrate toward the shield and create an impedance bump. If the bend is too sharp, the center di-electric will become damaged.

You may have to substitute a box for the T in order to maintain your radius.

Whoever designed a system with coax going through a small T-condulet should think about some refresher courses.

 

[ADub]

Anybody ever terminate a coax receptacle in a single gang 20 cu/in nail on box? Probably about the same result as running it through a conduit body. And I bet it even works when you're done.


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[K8MHZ]

Anybody ever terminate a coax receptacle in a single gang 20 cu/in nail on box? Probably about the same result as running it through a conduit body. And I bet it even works when you're done.


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But will it pass a data rate test?

I am pretty sure that the 93 ohm cable that is being pulled won't be used for cable TV.

RG-62 is a 93 Ω coaxial cable originally used in mainframe computer networks in the 1970s and early 1980s (it was the cable used to connect IBM 3270terminals to IBM 3274/3174 terminal cluster controllers). Later, some manufacturers of LAN equipment, such as Datapoint for ARCNET, adopted RG-62 as their coaxial cable standard. The cable has the lowest capacitance per unit-length when compared to other coaxial cables of similar size. Capacitance is the enemy of square-wave data transmission (in particular, it slows down edge transitions), and this is a much more important factor for baseband digital data transmission than power handling or attenuation.

 

[gadfly56]

I guess my first question is why you are running coax in conduit?

The min. radius is important. If that is not kept, the center conductor of the coax will migrate toward the shield and create an impedance bump. If the bend is too sharp, the center di-electric will become damaged.

You may have to substitute a box for the T in order to maintain your radius.

Whoever designed a system with coax going through a small T-condulet should think about some refresher courses.

My guess is that it's for physical protection. It was probably just spec'd to run in conduit and no one actually "designed" anything.

 

[NotreDave]

COAX cable in 3/4" conduit

COAX cable in 3/4" conduit

All,
This application is for a GE model GF868 ultrasonic gas flow meter with 4 transducers at Exxonmobil. I have to run the coax in conduit. Each transducer head requires one coax cable to the electronics console which will be remotely mounted 75 feet away. I am running a 3/4" conduit from the console and branching off with 1" BUB's for the 90 degree fittings, but it will require 3 "tees" in the conduit run. It's just hard for me to believe that 1" tees wouldn't work but according to chart, it won't. Since my first post, I have made all the conduit 1". This is my dilemma.
Thanks,
David

 

[K8MHZ]

Be advised that since the instructions for the installation of the coax specify a 2.5" min. radius, installing it with less than such would be an NEC violation, in addition to any performance issues that may incur.

 

[K8MHZ]

All,
This application is for a GE model GF868 ultrasonic gas flow meter with 4 transducers at Exxonmobil. I have to run the coax in conduit. Each transducer head requires one coax cable to the electronics console which will be remotely mounted 75 feet away. I am running a 3/4" conduit from the console and branching off with 1" BUB's for the 90 degree fittings, but it will require 3 "tees" in the conduit run. It's just hard for me to believe that 1" tees wouldn't work but according to chart, it won't. Since my first post, I have made all the conduit 1". This is my dilemma.
Thanks,
David

First, the drawing is in error by noting that T-condulets are typical for coax cable. They are not.

Second, can you replace the T's with boxes? I would have to check, but I am pretty sure you could maintain a 2.5" radius in a 4 11/16" box. Maybe even a 4", but it would be close.

 

[NotreDave]

I will change that note to read "TYPICAL".
What kind of box do you suggest for a Class 1, Div. 2, Class B,C,D area?

First, the drawing is in error by noting that T-condulets are typical for coax cable. They are not.

Second, can you replace the T's with boxes? I would have to check, but I am pretty sure you could maintain a 2.5" radius in a 4 11/16" box. Maybe even a 4", but it would be close.

 

[K8MHZ]

I will change that note to read "TYPICAL".
What kind of box do you suggest for a Class 1, Div. 2, Class B,C,D area?

Sounds like you will need a 'Hoffman' type box rated for the area. They are pricey, but you can get them in any size. I would suggest doing some more sketching. It looks like you could get away with 4" boxes if going corner to corner, but a 6" for the one where all 4 cables come in and would need to be fed on one side from the center.

Hoffman is a brand name, and slang for boxes meant to be used in environmentally particular areas.

 

[zbang]

How close are the sensors actually? Why not run a 1" to a single 6" box and individual 3/4" to each sensor? Seems like that would be easier and more reliable.

 

[ADub]

Yeah I'd do 4 pipes for 4 cables, each ran to precisely where it's needed, field bends only


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[petersonra]

Sounds like you will need a 'Hoffman' type box rated for the area. They are pricey, but you can get them in any size. I would suggest doing some more sketching. It looks like you could get away with 4" boxes if going corner to corner, but a 6" for the one where all 4 cables come in and would need to be fed on one side from the center.

Hoffman is a brand name, and slang for boxes meant to be used in environmentally particular areas.

Its div 2. Probably won't need anything special like explosion proof.

I would personally be inclined to not use conduit boxes at all. I think you could install a larger junction box (for lack of a better term for it) and just run conduit from there out to the sensors and just bend it as needed. You can't bend the conduit any tighter than what the coax can take.

or long sweep elbows?

 

[NotreDave]

I am looking for cable bend radius for crouse-hinds tee TB57, which is a deeper fitting. Does anyone know where i can get this information? Can someone tell me on how to calculate this by using the fittings dimension? TB57 wasn't listed on the chart I attached earlier.

 

[K8MHZ]

I am looking for cable bend radius for crouse-hinds tee TB57, which is a deeper fitting. Does anyone know where i can get this information? Can someone tell me on how to calculate this by using the fittings dimension? TB57 wasn't listed on the chart I attached earlier.

The TB57 is an 1 1/2" fitting. Alone, it looks like it may come close, but if you use reducers in the fitting to get back to 3/4 or 1", that means the coax won't be able to use the entire space, as it would be away from the inside wall of the fitting and it looks like you don't have any room to lose.

I am going with the recommendation by to use conduit all the way to a single box. I don't think you will be able to get your bend open enough using T condulets unless they were way oversized.

 

[ADub]

The TB57 is an 1 1/2" fitting. Alone, it looks like it may come close, but if you use reducers in the fitting to get back to 3/4 or 1", that means the coax won't be able to use the entire space, as it would be away from the inside wall of the fitting and it looks like you don't have any room to lose.

I am going with the recommendation by to use conduit all the way to a single box. I don't think you will be able to get your bend open enough using T condulets unless they were way oversized.

I agree that separate conduits would be best if it lays out right but I don't really understand what you're trying to prove in the first paragraph. The smallest radius of the cable will be in the conduit body not where the pipes terminate. The reducing bushings are inconsequential in my opinion.


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[ADub]

I am looking for cable bend radius for crouse-hinds tee TB57, which is a deeper fitting. Does anyone know where i can get this information? Can someone tell me on how to calculate this by using the fittings dimension? TB57 wasn't listed on the chart I attached earlier.

If you're desperate enough for a definitive answer maybe just buy the fitting and pass a short piece of the cable through it to see if it conforms or not


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[NotreDave]

I downloaded a 1.5" tee, T57, to scale and drew my cables with an o.d. of .239" dia. and a bend radius of 2.5 inches. It works for me, what do you think? What am I missing here? i just don't understand.:?

 

[gadfly56]

I downloaded a 1.5" tee, T57, to scale and drew my cables with an o.d. of .239" dia. and a bend radius of 2.5 inches. It works for me, what do you think? What am I missing here? i just don't understand.:?

Is that radius on the inside, centerline, or outside of the coax? That aside, I'd agree with others that you should just get a large enough box and run directly to each transducer. If this is a Class I Div 2 area, you'll need XP rated fittings, and seals if the devices aren't listed as intrinsically safe. Big box with direct runs will likely be easier to install and cheaper.

 

[tom baker]

I use the T&B Universal LB, 1" size, for fiber optic jumper cables.

http://www.graybar.com/manufacturers/tnb/elbow

Works great, maintains my bending radius. GBE carries.