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Aaarrrggghhhh! HELP! My builder has cut through Pyro cable!

Discussion in 'off topic' started by kitemap, Apr 19, 2017.

  1. kitemap

    kitemap Immoderate

    I'm in the process of doing up my flat and I wanted to replace the double socket where my stereo is going for 4 double sockets.
    As I had a builder in at the time I asked him to do it for me but as he was channeling out the wall he cut through the Pyro cable that feeds the sockets!
    Neither of us knew the the mains was wired with Pyro before this happened.

    Is this now buggered or is there anything that can be done once the cable has been exposed to air?
    The big problem is that as far as I know all the Pyro wiring runs within the concrete floor (I assume between the floor and the screed along with the under floor heating), so a rewire will be tricky.

  2. blossomchris

    blossomchris I feel better than James Brown

    I would have thought any competent electrician/electrical engineer would be able to answer this.
    From experience I am sure a few contracts I have been involved in have made alterations to existing pyro installations.

  3. kitemap

    kitemap Immoderate

    Thank you. I do have an electrician going there tomorrow but thought I'd post here on the off-chance that there was a competent electrician/electrical engineer that may be able to prepare me for what to expect.
  4. Rug Doc

    Rug Doc pfm Member

    Has he cut through the cable at a convenient place for a socket? would be ideal to re-terminate at this new location.. Hopefully it's not 6 ft up the wall??!!
  5. madmike

    madmike I feel much better now, I really do...

    Looked it up on Wikipedia....Pyro

    Advantages...When used within a tenanted area, carrying electricity supplied and billed to the landlord, for example for a communal extract system or antenna booster, it provides a supply cable that cannot easily be 'tapped' into to obtain free energy.

    Disadvantages...The termination points: While the length of the MI cable is very tough, at some point, each run of cabling terminates at a splice or within electrical equipment. These terminations are vulnerable to fire, moisture, or mechanical impact.
    Vibration: MICC is not suitable for use where it will be subject to vibration or flexing, for example connection to heavy or movable machinery. Vibration will crack the cladding and cores, leading to failure.
    Labour Cost: During installation MI cable must not be bent repeatedly as this will cause work hardening and cracks in the cladding and cores. A minimum bend radius must be observed and the cable must be supported at regular intervals. The magnesium oxide insulation is hygroscopic so MICC cable must be protected from moisture until it has been terminated. Termination requires stripping back the copper cladding and attaching a compression gland fitting. Individual conductors are insulated with plastic sleeves. A sealing tape, insulating putty or an epoxy resin is then poured into the compression gland fitting to provide a watertight seal. If a termination is faulty due to workmanship or damage then the magnesium oxide will absorb moisture and lose its insulating properties. Depending on the size and number of conductors, a single termination can take between 1 and 2 hours of labour (an electrician should be able to make a termination in 10 to 15 minutes on up to 4 core smaller sizes). Installation of a three-conductor MI cable (size No. 10 AWG — about 5 square mm) takes about 65% more time than installation of a PVC-sheathed armoured cable of the same conductor size.[3] Installation of MICC is therefore a costly task. Certain PTFE, silicone or other polymer-insulated cables have been substituted in applications which require similar properties in terms of flame spread, which use less labour to terminate. MICC is still used in applications which are particularly suited to its combination of properties.
    Voltage rating: MI cable is only manufactured with ratings up to 1000 volts.
    Moisture absorption: The magnesium oxide insulation has a high affinity for moisture. Moisture introduced into the cable can cause electrical leakage from the internal conductors to the metal sheath. Moisture absorbed at a cut end of the cable may be driven off by heating the cable.
    Corrosion: The copper sheath material is resistant to most chemicals but can be severely damaged by ammonia-bearing compounds and urine. A pinhole in the copper sheathing will allow moisture into the insulation, and eventual failure of the circuit. A PVC over jacket or sheaths of other metals may be required where such chemical damage is expected. When MI cable is embedded in concrete as snow melting cable it is subject to physical damage by concrete workers working the concrete into the pour. If the 3-5mil coating is damaged pin holes in the copper jacket develop causing premature failure of the snow melting system.
    Repair: If the MI cable jacket has been damaged the magnesium oxide will wick moisture into the cable and it will lose its insulating properties causing shorts to the copper cladding, and thence to earth. It is often necessary to remove 0.5 to 2 metres (1.6 to 6.6 ft) of the MI cable and splice in a new section to accomplish the repair. Depending on the size and number of conductors, a single termination can take between one and two hours of labour.[3]
  6. London Lad

    London Lad pfm Member

    Pyro is relatively easy to terminate and join providing you have the right tool but you will need to 'dig it out' to get access to the ends.
  7. kitemap

    kitemap Immoderate

    It's cut pretty much where the sockets will go. There is about 8 inch
    inches of the two Pyro cables coming up from the floor. Hopefully it will be okay.
  8. kitemap

    kitemap Immoderate

    This could be worrying as I only have 8 inches before it goes into the concrete. Being indoors and totally dry hopefully it will still be possible. Also it's not a spliced repair I want just a termination.

    Thank you for your help.
  9. London Lad

    London Lad pfm Member

    A splice in pyro repair is in fact just two terminations.

    8" on each end? If so that should be enough but it leaves nothing for error.

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