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How NOT to Fix a Broken Home Fibre Optic UK Broadband Cable

Friday, Dec 29th, 2023 (12:01 am) - Score 11,120
fibre splice outdoor openreach engineer fttp

Some of us may take this for granted, but it’s easy for regular consumers to overlook that fixing a broken fibre optic cable on your property is NOT the same as the old approach for re-wiring network cables. Put simply, in most cases, you should not attempt to correct a broken fibre yourself. But you can learn.

The first and, hopefully, most obvious thing to understand here is that optical fibres are made of glass or plastic and transmit their information via light. This is thus a significantly different medium from traditional network cables that transmit information as electrical signals over strands of copper wire, which are much easier to repair via widely available tools and common DIY methods.

NOTE: Avoid looking directly at the light emanating from the exposed end of an optical fibre. Often the light isn’t powerful enough to fully penetrate your eye / retina during brief exposure (the water in your eyeball will absorb most of its energy), but it could still cause harm to the cornea or lens.

The problem is that as the coverage and take-up of Fibre-to-the-Premises (FTTP) based broadband ISP networks rises, then so too will the number of people suffering accidental cable breakages, which may occur both inside or outside your home – often during unrelated DIY or household maintenance tasks.

However, most regular people are unconsciously hard-wired to think of cables as having metal cores, thus it ends up being quite easy to think they can attempt to repair a broken fibre. Take for example this case, as highlighted by Exascale, of somebody who accidentally cut their fibre and attempted a repair using choc block terminals, obviously without success (“I cut the fibre cable by accident, and I’ve connected it back together, but I’m still without service… Help!?“).

In other cases, we’ve heard of consumers trying to repair broken fibres by taping both ends back together, which obviously didn’t work (signal loss was a bit of an issue).

The Correct Ways to Fix a Broken Fibre

Generally speaking, if you break a fibre optic cable inside your home, then the best “fix” is to call in a trained professional (contact your ISP) to correctly cut, clean and then “splice” the fibre back together at the point of breakage using special fusion splicing or mechanical splicing equipment (fusion kit is VERY expensive, often costing up to several thousand pounds).

Using a splicing machine correctly also requires training to avoid mistakes and to properly understand different scenarios, although with the proper direction pretty much anybody can pick up this skill and often quite quickly (e.g. see all those past pictures on news articles of MPs having a go at it).

UK Prime Minister Rishi Sunak Splices Fibre (B4RN)

Rishi Sunak Splicing a B4RN Fibre

On top of that, you then have to be able to test the cable using an Optical Time Domain Reflectometer (OTDR) or similar device to ensure its integrity / splice loss (e.g. things like tiny particles of dirt could cause signal loss, which may impact performance). Overall, this approach is generally not considered a DIY task, albeit due mainly to the high cost of equipment and the need to understand how to use these devices. But it is still doable.

The alternative is to simply identify the cable used and replace it with a similar pre-terminated one that already has the necessary end connectors attached (this is often what the network operator will do – replace the entire lead-in cable due to the lack of slack and because a mid-span joint can be ugly). The caveat is that such cables will have often been installed through a wall and may also require you to open the operator’s external wall box equipment, which their rules may or may not prohibit (check first).

However, replacing the cable between your internal optical modem (ONT) and the external wall box connectors will require a fair bit of time and effort. Once again, it is safer to just involve a professional, who can fix the cable at the exact location of its break and save you potentially doing further damage to your house. But as usual, this all depends on your own personal confidence and skill set.

Finally, a mechanical splice is potentially within reach as a DIY task due to the lower cost of equipment, but these are more akin to a temporary “fix” and still require a number of tools / kit that the average person will not have at home (e.g. optical fibre strippers, fibre cleaver and the mechanical splicer itself with suitable connectors). Mistakes are likely, and some prior knowledge is required. So once again, it’s best to involve a professional.

Not to mention that a mechanical splice is generally not an ideal method for joining single-mode fibres (they’re better for multi-mode, but can do both) due to the smaller fibre cores that are difficult to align, yet most fibres used for home installs will be single-mode.

Most of the FTTP network operators we asked said that, depending upon when the break is first reported to them and the availability of local engineers, they’d aim to fix such problems by the end of the next working day (sometimes it might be possible on the same working day, but it’s best not to assume) – the work itself normally takes about 1 hour. Businesses with a proper Service Level Agreement (SLA) may get a shorter time to fix.

In that sense, it really is better to just be patient and wait for the professionals to do a proper job. A small charge for this may or may not be levied, depending upon the network, circumstances and ISP. But it’s worth pointing out that most domestic fibre breaks don’t seem to occur mid-line (i.e. along your inside wall), but are often broken splices in a wall outlet or in a joint box at the road, usually in line with sudden cold snaps of weather or decorators moving things. Those are really the domain of your operator and should be left well alone.

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By Mark Jackson
Mark is a professional technology writer, IT consultant and computer engineer from Dorset (England), he also founded ISPreview in 1999 and enjoys analysing the latest telecoms and broadband developments. Find me on X (Twitter), Mastodon, Facebook and .
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17 Responses
  1. Avatar photo NE555 says:

    Mechanical splices are normally only used for multi-mode fibre – and all telecoms fibre is single-mode.

    1. Avatar photo Tom says:

      I also thought this.

    2. Avatar photo Fttx says:

      Fine for SM, 0.1dB is repeatable if you have a semi decent cleaver and good cleanliness. Great option for repairs.
      Mech splice should be of a decent quality though.

      Index matching gel does not mind if multi mode or single mode.

    3. Avatar photo SC-APC Connector says:

      I’ve spliced SM fibre with a mechanical splices (running 10/25GbE through the house). Loss of around 0.1-0.15dB across 10 splices. Works brilliantly in my setup, but with how fiddly it was, likely not something for the average person to do with incoming fibre. Best to just get the ISP out to rectify or if possible, get the right patch lead and use that.

    4. Avatar photo Ad47uk says:

      When Zzoomm connected outside to inside via the splice box, they did not splice, but used a connector, I presume that is a mechanical splice or am I wrong? I was a bit disappointed as I wanted to watch them do the splice LOL.

      Not that having the join make any difference, I still get over 500Mb/s up and down.

      I must admit, I would not like to try fixing it myself, I don’t have the skills or tech to do it.

    5. Avatar photo XGS says:

      A connector isn’t a splice it’s a connector. Splices join two fibres into one, a connectorised fibre either side of a flange connects two fibre cables but they remain distinct fibre cables with no touching of the fibre cores in each cable.

      Could think of it as like using an extension lead: the lead and the power cord of the device are distinct cables connected to each other via connectors and you wouldn’t call them spliced, that’d be cutting the copper cables on both and hard wiring them together.

      Very much hope joining the inside and outside cables didn’t cause slowdown given the inside is where you’re using it. Would only cause performance issues if faulty.

    6. Avatar photo Ad47uk says:

      @XGS, never said it was a splice, I said it was in the splice box, which I admit, may be the wrong name for the box that is on the wall outside my house where the outside fibre meet the inside fibre. But I always seen it called a splice box.

      I know what a splice is,

    7. Avatar photo XGS says:

      You asked a question, an answer was given.

      You’re welcome.

    8. Avatar photo Ad47uk says:

      @XGS, LOL, I see what you mean, but in this world, there are lots of descriptions for things that don’t make sense.

      Just had a look at a video about mechanical splice, and it looks like the same thing they used here, which is maybe why they need such a large box compared to Openreach
      I did not get close enough to see, all I know is that they did not use a splicer.
      Not bothered as long as it works, but would have liked to see them using a splicer.

    9. Avatar photo XGS says:

      Open it up and have a nose. If it’s all connectorised be easy enough to see. The box may be because they use pre-connectorised cable of various lengths and need room for loads of excess if they have to use, say, a 50 metre cable for a 41 metre run.

  2. Avatar photo GG says:

    Nice piece, thanks.

  3. Avatar photo Billy Shears says:

    Reminds me of when I was at school. One of the kids built a radio from a kit and wondered why it didn’t work. He’d used “Plastic Solder”.

  4. Avatar photo Nick Roberts says:

    Like the “Making Good” process is so different between industries and professions . . cut-back the bad until you find good material and then join.

    Surprised they don’t use some sort of “Shot” short-interval portable laser to do a glass weld for the joining.

    1. Avatar photo XGS says:

      Melting the glass together is done. That’s what fusion splicing as opposed to mechanical splicing is.

    2. Avatar photo XGS says:

      I suppose it could be said that producing an integrated circuit with a hundred billion transistors is the same as building a circuit at home.

      Brain surgery can be reduced to some basic steps but I doubt you’d let me loose in your skull.

      Not sure why you’ve disdain for the folks that do these jobs. The precision of the fusion splicing kit is extraordinary, margin for error low and plenty that can go wrong given a speck of dust is more than enough to ruin things.

  5. Avatar photo Daniel says:

    The “splice box” is called a CSP (Customer splicing point) you will find this is where the cable from the network and the cable from you house (in/out cable) is spliced, there is a minimum of 1 metre of each side spooled inside so failed splice can be cut away and enough good cable left to re-splice.

    Tolerance are less than 0.7 degree cut angles and a loss of less than 0.05dBM at the splice joint.

  6. Avatar photo Wayne Reeves says:

    The part about using pre-terminated replacement cables to the CSP ( grey box on outside wall) is incorrect, fttp is spliced in there, so that there is an “endless” fibre from the headed in the exchange, to the ONT (socket in the house). I fit fttp every day.

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