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Dangerous connections?

Discussion in 'Electrical Engineering' started by Arthur, Aug 1, 2007.

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  1. Arthur

    Arthur Guest


    A few months ago i posted a question about connecting a bit of equipment to
    the mains power utility, and the practice of passing 20 Amperes down the
    power plant return (no neutral) in a 3-phase supply. I also dislike the
    practice of shorting the power plant return (PE) to the neutral (N) in the
    user equipment.

    I have since been told to keep my mouth closed. This is the way we do it,
    although still I refuse to put what I call "dangerous information" into the
    BrE installation instruction card for installers in my workshop.

    In this group i was asked repeatedly for the equipment and manufacturer,
    which i refused to deliver. Ok, well here it is. Scans from the manual and
    the source material. i put it all on an site:

    Am i right? Are some of these power connections dangerous?

    Country = England (Bedford) where British and EU laws prevail.

  2. There isn't enough info in those docs to know how the load is
    connected to the terminals. Also, I can't see if the terminal
    block is before or after the supplier's cutout -- is the
    supplier's main cutout in the cabinet?

    In the UK, there is a common supply system called TN-C-S (or
    Protective Multiple Earthing) where the protective earth and
    neutral are shared in the supply network in a PEN (Protective
    Earth and Neutral) conductor. These are separated at the
    supplier's cutout though. However, if the supplier's cutout
    is in the cabinet, then there would seem to be no point in
    separating them at that point, although I'm not familiar with
    supplies to street furniture.
  3. Arthur

    Arthur Guest
    The bit of wire comes from the power companies junction box. The charts
    explain where to connect the wires. The terminal block is inside the user

    The last drawing for example, shows the power company have provided only two
    - PE (PG), Ground, Earth, safety earth, green/yellow wire.
    - Live, single phase, 230v AC

    The drawing shows that inside the equipment we are expected to connect
    together the protective earth/ground (cabinet chassis) and the power
    neutral. In this configuration if the PE (earth/ground wire) becomes
    open-circuit, then the metal cabinet in the high-street will have 230v AC
    live cabinet that passers-by can touch. In normal operation one can expect
    20 to 40 Amperes of current down the protectibe earth/ground wire in this

    Other configurations show that in this user equipment we have to short
    together the power companies protective earth/ground and the neutral
    conductors, which is also illegal by both EU ans UK regulations.

    I can accept the three phases and PE (PG) when configured phase-to-phase,
    BUT when each phase is returned throgh the power supply companies protective
    earth/ground wire then my teeth start to move about, and the hairs on the
    back of my neck stand up: I don't like putting current down the protective
    earth wire, ESPECIALLY on a bit of equipment that is to stand on the high
    street with the general public leaning against it.

    The ONLY configuration I have installed with equipment is L1, L2, L3, N, and
    PE as five seperate conductors, all provided by the power company.

  4. Arthur

    Arthur Guest

    I only looked at the first diagram.
    I included both good and bad drawings - all of them.

    Protective Earth = PE = PG = Protective Ground = Power plant return =
    safety earth = yellow/green wire in the power cable.

    N = Neutral
    L1, L2 and L3 = the three live phases.

    Now take a look at the last drawing that instructs me to connect all 3
    phases together to form a single-phase equipment. the PE and N are also
    strapped together.

    These two connections are then connected to the power companies distribution
    box, and the two wires are connected between PE and L1.

  5. Arthur

    Arthur Guest

    There isn't enough info in those docs to know how the load is
    Take a look at picture #3. The cable from the power companies distribution
    box is only two wires:

    - Protective earth/ground
    - One live phase

    The connection block is in the user equipment, and the power cables comes
    from the power companies distribution box.
    In a system where the power provider has both protective earth and neutral
    at the point of delivery, the user equipment may not later bond the PE and N
    together, if they are provided as seperate conductors. It matters not what
    the power service provider does to provide these two conductors.

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