IET
Decrease font size
Increase font size
Topic Title: Fibre optic Cable near distribution power cables
Topic Summary:
Created On: 09 October 2012 09:05 AM
Status: Read Only
Linear : Threading : Single : Branch
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 09 October 2012 09:05 AM
User is offline View Users Profile Print this message



mickyb

Posts: 6
Joined: 16 October 2002

Hi all,
I am currently designing a a 33kV cable system which also requires a fibre optic cable. Our approach to date has been to install this in a subduct in a 100mm duct beside the main power cable. What if any are the implications of this? Is there a minimum separation distance we should be keeping the two apart?

any help or guidance would be much appreciated.

Thanks in advance
Michael
 09 October 2012 09:30 AM
User is online View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19457
Joined: 23 March 2004

I guess you won't have EMCissues - the problem being more physical than electrical. Will you need to access the FO whilst the 33kV is still live - if it's all ducted then I suspect not as it could be replaced/repaired without any access to the 33kV line - if you have to dig for it though then that's a different matter.

I suspect if you have segregated ducts and segregated (or seperate) chambers/draw pits for each system there won't be a problem with regards seperation.

Failing that - move it 2m away - that should solve any issues

Regards

OMS

-------------------------
Failure is always an option
 09 October 2012 09:47 AM
User is offline View Users Profile Print this message



mickyb

Posts: 6
Joined: 16 October 2002

Thanks OMS,
Access won't be a problem as its continuosly ducted with separate draw pits and splicing chambers. National grid standards recommend a clearance of 450mm but don't say if this can be reduced for distribution.

Would be nice just to put it 2m away and forget about it but digging a 2.5m trench rather than one 500mm would be hard to justify! Even following National grid standards will have a significant cost inpact.
 09 October 2012 11:28 AM
User is online View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19457
Joined: 23 March 2004

For sure Mike - I guess the question is do you really need to follow NG guidance if this is private network or distributor cabling - and is it adoptable perhaps is the other consideration

I'd be happy to go with a sensible risk assesment, which your pit and duct system is clearly informed by - but I guess it's the framework in which you work is going to have the exact answer for the circumstances.

Get it right though - first time - cos digging that little lot up to shift a control fibre by a couple of hundred mill is going to be a right sod

best regards

OMS

-------------------------
Failure is always an option
 09 October 2012 04:27 PM
User is offline View Users Profile Print this message



ArthurHall

Posts: 735
Joined: 25 July 2008

You can go as close together with the power and fibre cables with no issues, on some multi core cables the fibre is embeded in the packers of the cable. As you are using two seperate cables one question is, is the fibre used for protection or just comms. If just comms I agree with Ohm's comments. If it is for protection there is an argument that the fibre should be above the power cable so that anyone excavating hit the fibre first. This may trip the power circuit or at least raise an alarm. The last time I laid a double circuit 33kv the (metalic) pilots were laid in the middle.
 09 October 2012 06:24 PM
User is offline View Users Profile Print this message



alanjhodgart

Posts: 14
Joined: 11 September 2002

One aspect to consider seperation wise is if there will be a requirement to joint on the 33KV cable in the future, eg fault repair, network/circuit changes. Having them too close would mean moving the fibre to facilitate jointing.

Cira 300mm spacing should be ok to accomodate the joint shell, less if we are talking about single cores in trefoil.


Alan
 10 October 2012 12:32 AM
User is offline View Users Profile Print this message



alancapon

Posts: 5746
Joined: 27 December 2005

What is the construction of the fibre cable? Is it non-metallic, or does it have a metallic armour? We use a fibre cable with a Kevlar armour (non-metallic) and there are no issues running that close to / parallel with power cables.

Regards,

Alan.
 10 October 2012 02:39 PM
User is offline View Users Profile Print this message



mickyb

Posts: 6
Joined: 16 October 2002

Thanks for the comments everyone. Fibre will be non-metallic and is to be used for protection. Power cables will be laid in trefoil. Theres certainly plenty to consider.

regards,
Michael
 15 October 2012 10:59 AM
User is offline View Users Profile Print this message



JonathanM

Posts: 1
Joined: 15 October 2012

We have worked on NG sites, and rather than go to the boher of ducts, a direct buried non metallic cable would be my choice, but make the design a 'ring' in case of failure, i.e. you can patch the active components in either direction between tx and rx. A good example of a highly robust single mode cable which can be directly buried in a sand filled trench or within a duct is the Nexans SP953 which features a unitube containing fibres suspended in a jelly covered by a non-metallic dielectric armour with fibre reinforced plastic (FRP) protection.
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.