Wiring regulations and there application to optical fibre in the home.

Why would wiring regulations apply to glass fibres that don't even conduct electricity?

well the signals are carried electromagnetically in the glass -it is a waveguide after all, just unlike coax and UTP, not one that goes down to DC. And more prosaically, as the OP notes, being garotted by a fallen bundle of optic fibres is much the same as it being copper,  and CAT whatever and optic fibres are often put in the same routes by the same folk, so a one size fits all approach makes sense.

Now it is less clear if most network installers read or care what is in BS7671, but the authors of the standard think they should.

to the OP, as far as BS7671 is concerned there is no de-minimis cable size below which the rules relax, but the decision to worry about compliance with the standard or not, may involve such a thought.

M,

Why would wiring regulations apply to glass fibres that don't even conduct electricity?

Well they do - see 110.1.2 (vi). I guess the thinking is that entanglement can in theory happen with any kind of cable, so lacking anywhere else to put the requirement, it fell to BS 7671 by default.

I do notice that OpenReach etc still seem to be using plastic clips on the outside of buildings...

I can see an argument that if a cable disintegrates before the fixings in a fire, then it's not liable to collapse as such, so meeting the requirement.

   - Andy.

I genuinely thought I deleted this post. It was the first time using this forum and I posed the question in the wrong box. I reposed the question in the correct boxes here.

https://engx.theiet.org/f/questions-about-iet-engx/30830/wiring-regulations-and-their-application-to-optical-fibre-in-the-home

I hope this clears up the discussion as the full question is available.

Hi Timothy, I've merged the two threads into this one and moved it to the Wiring Regs forum which should clear up any confusion

Simon Barker said:

Why would wiring regulations apply to glass fibres that don't even conduct electricity?

Because Coroner's Rule 43 letter following the inquest into the Shirley Towers fire recommended it?

To quote item 6 (my highlight):

6 It is recommended that Building Regulations are amended to ensure that all cables, not just fire alarm cables, are supported by fire-resistant cable supports. This could be achieved by an amendment to BS 7671 (2008) Institute of Electrical Engineers Wiring Regulations.

A copy of the letter is available in the following Report, and you can see the above item 6 on Page 5: https://www.shropshirefire.gov.uk/sites/default/files/11-coroners-rule-43-letter.pdf

Timothy Durkin said:

ome of the single core buffer fibre I am working with has the tensile capacity of sewing cotton and crumbles in fire.  Even very small metal clips do not offer the clamping force needed to support the vertical runs

That might lead to it being unsuitable for some areas without a suitable support system ... I see the issue, and there's an open question about whether it might (or might not) cause entanglement.

Have you asked the advice of the manufacturer, importer or distributor ?

Thanks all

The supplier provides guidance for installation for compliance edition 18 and from that point of view it is not an issue. We have a compliant solution. My question was broader in the sense that entanglement, as serious as it is, has a lower limit. The fibre I am referring to is 900 microns in diameter and has no strength member, it can be broken by hand with little effort.  As we switch from copper lines to optics would I wanted to know if this had been considered already or might in the future there may be dispensation for single lines with a breaking force of some yet to be defined limit. Mechanical clamping of fibres of this nature can lead to damage of the fibre and intumescent adhesives may offer an alternative.

From my experience at least it's normal practice to run this type of fibre in some sort of protective tube? Probably still an argument that the tube will melt before a plastic clip fails. If there were a large number I can see an argument for support that will not suffer from premature failure. But for one or two i would probably use engineering judgement. There is nothing to say clips have to hold things tightly, they just have to prevent collapse.

Timothy Durkin said:

As we switch from copper lines to optics would I wanted to know if this had been considered already or might in the future there may be dispensation for single lines with a breaking force of some yet to be defined limit.

That's a good question ... individual runs are of course a different beast to bundles.

Are there other safety issues for the public with easily-breakable fibres though?