In a previous post I mentioned the possibility of adding a POF (plastic optical fiber) cable to existing electricity ducts with live power cables. POF is a great yet still expensive (lack of volume) option for a home network. Installing is easy with a 2 x 2.2 mm cable and I have experienced no (“zero”) reliability problems in the last year in my home POF network.
One of the vendors (www.homefibre.at) advocates this particular option and we had a conversation about safety regulations. In my country (and probably many others) the regulations aim to prevent thermal hotspots that could lead to fire, and to prevent crossover (shorts) of power lines to other conductors.
The question was both legal and practical: would pulling POF cable next to live power cabling in the same duct lead to insurance risks (no coverage in case of fire) and/or practical risks (risk of fire or shorts)?
The practical risk would seem at first glance to be very low: plastic is not very conductive preventing shorts. Yet the main material of POF cabling is PMMA aka Perspex, a very flammable material. Fortunately the manufacturers cover the PMMA with a flame retardant material, allowing it to pass the UL-tests (USA flammability resistance tests) (pdf UL Flame retardant tests )
The other practical risk occurs when the ducts are too full, preventing heat (generated by high currents) from escaping. The regulations give clear guidelines for the maximum filling of a duct with powerlines: no more than 33% of the cross section of a ducts may be filled with cabling.
Let’s do some math:
An electrical wire H07V-U of 2.5 mm² conductive cross section measures 3,2 mm diameter on the outside.
Pi r² = 3,14 x 1,6² = 8 mm²
3 wires (including groundwire) : 24 mm²
A POF cable measures (2 x, separate for send and receive) 2,2 mm in diameter.
Pi x 1,1² = 3,8 mm²
2 x = 7,6 mm²
All together : 32 mm²
The diameter of a normal PVC duct is 16 mm, minus 2 mm for the material thickness. The open cross section is 153 mm², 1/3 of that is 51 mm².
So: adding one or two POF cables to an electrical duct would not violate the regulation.
The legal question has no clear cut answer as the regulations have not been written with this application in mind. The lawyers I contacted suggested that if the POF cable would have the same flame retardant characteristics as the electrical cable, and the same isolation voltage as the electrical cable, you would have a good case in court.
My conclusion was that a professional possibly would hesitate to take the legal risk as a company as it is terra incognito, but that the practical risks for a DIY installation are quite limited (provided you would use an UL listed POF cable).
Now the only barrier to take is volume production to get the costs down.
















