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Panel Wiring Used External to an Enclosure. 400 Volt.

Zoomup
Hello, I hope everyone is fit and well.


I have been doing some work in an intake building that is really an old locked wooden shed at the edge of a holiday chalet park. The original installation dates back to the early 60s. Modern distribution boards exist that may be 30 years old.


The metering is via three current transformers. The single insulated wiring, about 1.5mm2 that runs from the current transformers goes to the metering equipment in a steel enclosure, and is open to touch at shoulder height.


Also, there are three spring loaded test switches and three neon indicators in the metering enclosure that test the presence of three phases.


 Three supply phase cables (6.0mm2)  run in insulated and sheathed cables to three 16 Amp. "slide lok" fuses carriers on the surface outside the metering enclosure. Open to touch, but insulated and sheathed. From the three fuses the wires seem to be single insulated instrument wire, open to touch, that run to the metering equipment enclosure test lamps.


Was this ever normal? Three single insulated 400 Volt wires running at shoulder height, not enclosed, surface run, open to touch.


Z.


  • 0
    Is the building a locked enclosure accessible only by tool or key  ?

    If it really is early 60s (red, white & blue phases, not red, yellow & blue)  then the whole double fault to danger mentality that we have  today had not really developed, and yes exposed single insulated wiring would not have raised an eyebrow, especially behind a locked door.  Actually earthing was also given less importance, (like none at all for lights), so that too may be a bit squiffy in terms of Zs and modern disconnection times.

    (and no electronic loads, so reduced neutrals still in vogue for 3 phase supplies)

    After all, bare busbars behind covers held by knurled brass thumb nuts, and light switches and ceiling roses where the covers span off by hand to reveal eminently touchable bare metal were very much still the order of the day.  The current transformer secondary windings will not (I hope) be handling more than what today we would call ELV, though a primary to secondary  winding short in a current transformer may not be detected if the metering wiring is not earthed on one side....


    Had it been done later  there might have been a removable perspex panel or something if the intention was to leave it visible to show no fiddling with the meter wiring.

    I suspect even back then it was something of a special, but more or less  in the spirit of the standards of the time.

    M.

  • 0
    mapj1:

    Is the building a locked enclosure accessible only by tool or key  ?

    If it really is early 60s (red, white & blue phases, not red, yellow & blue)  then the whole double fault to danger mentality that we have  today had not really developed, and yes exposed single insulated wiring would not have raised an eyebrow, especially behind a locked door.  Actually earthing was also given less importance, (like none at all for lights), so that too may be a bit squiffy in terms of Zs and modern disconnection times.

    (and no electronic loads, so reduced neutrals still in vogue for 3 phase supplies)

    After all, bare busbars behind covers held by knurled brass thumb nuts, and light switches and ceiling roses where the covers span off by hand to reveal eminently touchable bare metal were very much still the order of the day.  The current transformer secondary windings will not (I hope) be handling more than what today we would call ELV, though a primary to secondary  winding short in a current transformer may not be detected if the metering wiring is not earthed on one side....


    Had it been done later  there might have been a removable perspex panel or something if the intention was to leave it visible to show no fiddling with the meter wiring.

    I suspect even back then it was something of a special, but more or less  in the spirit of the standards of the time.

    M.

     


    Hello Mike,

                             yes the intake room is padlocked. Should I get the metering company to improve the exposed single insulated 400 Volt wiring? The main supply tails are insulated and sheathed red, yellow and blue coloured. P.S.C.C. 1.5kA. E.F.L.I. 0.15 Ohms. Earthed by a 16mm2 black single that runs alongside the main underground armoured incommer.


    Z.


  • 0
    Yellow makes it a few years newer than you think. Might be worth sending a pic to the metering company and seeing if they are happy to be responsible for its continued safety, though I suspect the answer will be a toss-up between  'dunno' and 'yes'.

    M.
  • 0
    Are these just the wires from the current transformers? It is not quite clear to me if these are really a supply to something. Current transformer secondaries have no significant voltage present.
  • 0
    Slide-loks were usually employed to protect the CT control wiring if I remember correctly. Some were rewirable and some were cartridge.

    In any case, it is nothing to do with the site/installation owner.

    Probably not worth flagging up to be honest.
  • 0
    davezawadi (David Stone):

    Are these just the wires from the current transformers? It is not quite clear to me if these are really a supply to something. Current transformer secondaries have no significant voltage present.


    No, these single insulated open to touch wires are carrying 400 Volt three phase to the test lamps.


    Z.


  • 0
    whjohnson:

    Slide-loks were usually employed to protect the CT control wiring if I remember correctly. Some were rewirable and some were cartridge.

    In any case, it is nothing to do with the site/installation owner.

    Probably not worth flagging up to be honest.


    The slide locks are in series with the 400 Volt three phase single insulated wires that supply the three test neon lamps. The current transformer output wires are not externally visibly fused.


    Z.


  • 0
    mapj1:

    Yellow makes it a few years newer than you think. Might be worth sending a pic to the metering company and seeing if they are happy to be responsible for its continued safety, though I suspect the answer will be a toss-up between  'dunno' and 'yes'.

    M.


    The main fuse box is a large grey M.E.M. three phase three way unit with large 100 Amp porcelain fuse carriers with handles and 100 Amp.  fuse wire. The original installation was late 50s according to the site manager.


    The large BS3036 fuse carriers are very much like this example, but are not made to take H.R.C. cartridge fuses.

    MEM 100 AMP HRC FUSE CARRIER HOLDER PORCELAIN 440v | eBay


  • 0
    Hello Zoomup

    Be careful with the Slydloks. A colleague of mine had a big fright when pulling out a live rewireable Slydlok fuse on no-load. It flashed to earth and gave his hand and arm a temporary suntan. Make sure they're dead before touching them. Regards, Colin.
  • Former Community Member
    0 Former Community Member
    Zoomup:
    whjohnson:

    Slide-loks were usually employed to protect the CT control wiring if I remember correctly. Some were rewirable and some were cartridge.

    In any case, it is nothing to do with the site/installation owner.

    Probably not worth flagging up to be honest.


    The slide locks are in series with the 400 Volt three phase single insulated wires that supply the three test neon lamps. The current transformer output wires are not externally visibly fused.


    Z.




    You wouldn't see fuses in the CT's as if a fuse were to operate and leave a CT open circuit the voltage would be seriously lethal


    Just as an observation, aren't all fuses "in series" - they wouldn't be much use at all in parallel would they ?


    Regards


    OMS


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