Fiber Optic cable with CCTV power cable & with 11 kV power cable

[masalah]

Dear all,

I received a query on site based on design drawings. The design drawings are for CCTV site network & 11 kV power cables network (in Doha, Qatar).

1- The CCTV design drawings show a detail that mention the following:

- "Details of CCTV power and fiber optic cable trench in shared path" ; in which one 150mm uPVC duct only is drawn.

2- The 11kV cabling site network design drawings show details in all of which the following is mentioned:

- "Details of ducts of concrete encased 11kV+fiber optic cable"

The query of the contractor: Can the 11kV power cbales pass along with the fuber optic cables just like in CCTV detail??

My question also: if yes, isn't there any fear of noise on the signal(s) that can be carried on fiber opic cables??

Thank you in advance for your replies, hope to be referenced with codes/standards references.

Yours,
M.A.Salah

 

[Skogsgurra]

11 kV, 30 kV and 110 kV overhead lines are often used to carry fibre cables. The fibre is then wound around the HV/MV cable and there is no adverse effect. So, you can rest assured that this is accepted technique and will not cause any problems at all.


Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

Typically the fibre will be a non-metallic type with Kevlar armour rather than steel tape in this application. Steel is obviously a conductor and can result in transfer voltages or unexpected fault current paths.

 

[bacon4life]

No electrical noise for nonmetallic sheathed fiber, but a couple other issues to think about: In my region of the USA, fiber splicing technicians do not usually have training to enter medium voltage vaults, so they have to coordinate with a line crew to place the fiber and then to bring the ends of the fiber out of the vault for splicing. Also, verify that the fiber optic cable is rated to operate at least as hot at the electric cable. We have some 85C fiber limiting the capacity of a duct bank with 105C electric cable.

 

[Marmite]

There is no problem with the fibre and 11kV cables sharing the same trench route, but it is bad practice to draw them into the same duct. (Unless you are using it for distributed temperature sensing) The fibre should be in its own duct. For safety reasons it is normal for the power and fibre optic ducts to be colour coded in some counties so that you can easily distinguish between them. If they share the same duct an 11kV cable fault in the duct will probably take out the fibre. One of the benefits of ducts is the ease of installation (or removal/replacement) of cables. With one duct, if you tried to pull one cable in or out, the fibre will probably get trapped and damaged in the process.

Regards
Marmite

 

[masalah]

Thank you all for your replies ...

 

[masalah]

Dear Marmite,

Yes, the contractor was asking about passing through the same duct.

I couldn't get the meaning of your phrase "take out the fiber" ...

To recheck my understanding, Is your point of view is that, it is wrong for the following reasons:

1- A fault in the 11 kV power cable may cause a fault in the fiber optic cable adjacent with it.
2- If we tried to pull the power cable, the fiber optic cable will be trapped.

Or you mean only one point, that if a fault happened to the 11 kV power cable and you needed to pull it, the fiber optic one will be trapped & damaged (i.e. no fault will be transferred to the fiber optic cable, only trapping and damage)...

Thank you for clarification.

 

[Marmite]

It is likely that an 11kV cable fault would damage the fibre, if they share the same duct. Even if the fault itself doesn't damage the fibre, the fault location may do.
If you try to pull out the 11kV cable there is a possibility of damaging the fibre.

When cables are installed in ducts they do not necessarily sit neatly in the bottom of the duct, as shown on duct section drawings. In reality the cables snake in the duct, especially around bends, meaning that the smaller cable can easily get trapped against the duct wall by the larger cable.

Regards
Marmite

 

[waross]

I am a little concerned about:

"Details of CCTV power and fiber optic cable trench in shared path" ; in which one 150mm uPVC duct only is drawn.

If the fiber cable includes power conductors for the CCTV cameras we may have a problem, not with the fiber cable but with the included camera power conductors.

Bill
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"Why not the best?"
Jimmy Carter

 

[masalah]

As a common practice, I know that no problem to put power cables for CCTV cameras with fibre optic cables.

 

[waross]

I didn't realize that the 11,000Volt cable was the power supply for the cameras. Sorry!!

Bill
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"Why not the best?"
Jimmy Carter