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Standard User Rhubarb
(committed) Sat 13-Feb-21 12:22:34
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Mechanical Vibration from Fibre Cable


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Hi.

I'm waiting for the installation of BT FTTP which due to Covid has been delayed a couple of times and has turned into a 2 stage install with a current installation date at the end of March. OR turned up this week and installed the overhead cable from the pole to the house.

I woke a few times in the night last night hearing a low frequency rumble like there was a van engine ticking over outside the house. After a while and a wander around upstairs I realised that the noise seemed to be loudest in the bedroom below where the new cable is anchored on the house. Once it was light I got up and investigated further and noticed through the bedroom window that the new cable was vibrating violently in the wind. The cable is anchored on the facia board and the vibration is sounding through the roof woodwork I assume. I suspect that the cable vibration is due to the uneven profile of the hybrid cable as the other normal round cables from the pole were just waving about in the wind. According to Google Maps the cable span is about 54 metres and we are 500ft ASL and quite exposed.

I cannot imagine how this problem can be resolved but I'm wondering if anyone else has had the same and managed to do something? Does OR have any solutions that might help? I am wondering about some form of damper that could be added near the anchor. Any info appreciated.

Cheers - Andy (A light sleeper hoping for calm weather. grin)

Edited by Rhubarb (Sat 13-Feb-21 12:28:57)

Standard User MHC
(sensei) Sat 13-Feb-21 12:28:40
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Re: Mechanical Vibration from Fibre Cable


[re: Rhubarb] [link to this post]
 
Easy resolution would be to have the fixing point moved to solid brick/block work.


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M H C


taurus excreta cerebrum vincit
Standard User Rhubarb
(committed) Sat 13-Feb-21 12:41:18
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Re: Mechanical Vibration from Fibre Cable


[re: MHC] [link to this post]
 
In reply to a post by MHC:
Easy resolution would be to have the fixing point moved to solid brick/block work.

Yep, that's one thing I thought of but the only problem I can think of is that to get sufficient height they'd have to anchor near the top of the brickwork and that might not give enough strength for the long run given that there'd be little weight on the upper bricks. It's a house with the soffits level with the top of the upstairs windows. It's a long span and the cable sags more than the 'normal' cables and runs partly over a road. Andy


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Standard User MHC
(sensei) Sat 13-Feb-21 12:46:02
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Re: Mechanical Vibration from Fibre Cable


[re: Rhubarb] [link to this post]
 
I have a 55m metre drop too - so it should bot be an issue provided it is correctly tensioned. They should have taken the road into account when specifying the pole originally


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User Rhubarb
(committed) Sat 13-Feb-21 13:01:24
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Re: Mechanical Vibration from Fibre Cable


[re: MHC] [link to this post]
 
In reply to a post by MHC:
I have a 55m metre drop too - so it should bot be an issue provided it is correctly tensioned. They should have taken the road into account when specifying the pole originally

I'll need to try to contact someone on Monday to see if anything can be done. There's another pole that's only 40 metres away that would allow anchoring on the gable end which would be a much stronger anchor point but I doubt they'd move to that. I'm hopefully more likey to get something done now as the installation is not yet completed. Andy
Standard User _Icaras_
(newbie) Sat 13-Feb-21 14:08:29
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Re: Mechanical Vibration from Fibre Cable


[re: Rhubarb] [link to this post]
 
Tricky one.

I’d expect Openreach to accept that this is an issue that needs resolving though.

Using the other pole if possible seems better, you don’t want the cable to be too tightly tensioned, it should have quite a bit of movement in it.

Icaras
Standard User MC31
(committed) Sat 13-Feb-21 14:48:18
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Re: Mechanical Vibration from Fibre Cable


[re: Rhubarb] [link to this post]
 
The cable is anchored on the facia board

Really ? We have not been fixing stuff onto facia boards for years !

these comments are my own and in no way represent any company that i may or may not be linked too.
Standard User dect
(fountain of knowledge) Sat 13-Feb-21 14:57:31
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Re: Mechanical Vibration from Fibre Cable


[re: Rhubarb] [link to this post]
 
In reply to a post by Rhubarb:
a low frequency rumble like there was a van engine ticking over outside the house.
I'm interested to know exactly where the origin of the rumbling is coming from, do you think its from the facia board due to the stress on it (from the cable and its anchor) or from the whip of the cable?


Edit: I've reread your post and think I've go my answer smile

Edited by dect (Sat 13-Feb-21 15:12:07)

Standard User Rhubarb
(committed) Sat 13-Feb-21 18:17:53
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Re: Mechanical Vibration from Fibre Cable


[re: dect] [link to this post]
 
Hi. Thanks all for the replies.

Firstly, re fixing to fascia boards. The houses where I live were built mid 1970s and all had wooden fascias when new. Every house around here has the phone cable anchored on the facia board. About 18 years ago I had the old facias removed and replaced with μpvc. The job was done by a good friend with a little help from me. I was conscious of what I considered to be a long run being supported by the facia (I'd felt the strain when we'd secured the bracket via a strong rope to an eyelet in the brick when the job was being done) so I fitted a piece of 3" x 3" across 2 trusses and fixed it with 2 strong brackets so it was flush behind the new facia. The existing BT bracket was refitted with new longer screws through the plastic into the wood to ensure a strong attachment. Maybe I did too good a job of it! A neighbour recently had an additional line fitted for WFH and that was fitted to the facia.

I'd be happy for it to be anchored to the brick but most of the strength in a brick wall comes from the weight above the bricks and not the mortar between them. Fixing the attachment just below the facia/soffit would likely result in the brick(s) coming loose. Further down would probably result in the cable being too low mid span where it is just over the road. I might be wrong.

Transfer to the other pole would be a nice idea but it would involve crossing a cable from my current pole to a neighbor's house. Also each pole had an 8 and 12 way CBT fitted which seems to roughly equal the number of cables from each pole, I assume these will all be reserved for existing provisions when the PSTN finishes in 2025.

Having messed about when the wind got up again this afternoon it doesn't take much to stop the vibration transferring to the house, I opened the nearest window and rested an aluminium walking pole on the cable about a foot from the anchor and partially closed the window jamming the pole. I suspect this put some pressure on the cable (there was no noticeable deformation) but it stopped the noise. Maybe I need a Stockbridge damper.crazy

Cheers - Andy

Edited by Rhubarb (Sat 13-Feb-21 18:44:50)

Standard User jpm
(member) Sat 13-Feb-21 18:28:36
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Re: Mechanical Vibration from Fibre Cable


[re: Rhubarb] [link to this post]
 
I don't know if this is the correct size to allow you to move the cable to a brick fixing, but Openreach engineers should have access to things like this

https://www.comtecdirect.co.uk/product/dropwire-brac...
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