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concrete pad anchored 24vDC scissor lift and equipotential bonding

psychicwarrior

Hello good afternoon everyone. I'm after an opinion please on a requirement to bond.

A '4 ton' twin scissor lift platform installation to a concrete pad [set in the ground], for raising vehicles, has 2 seperate ground anchored metal base and framework scissors  and each contains a 24V DC motor.  These scissors are connected to a control unit which draws its supply, from the the 240V AC electrical installation.    Other than the case of the control unit (confirmed as exposed parts), the metal work of the scissors is not electrically earthed (or intended to be) I am informed due to the extra-low voltage motors.

It could be (could it) that once the bases of the scissors are anchored into the concrete pad, especially depending on the anchoring arrangement (depth etc),  that this metal work becomes extraneous part.

The detached garage is supplied from a main building with TN-C-S earthing arrangement  (the garage does not have any other extraneous parts).

Would folk agree that  there is/could be a bonding requirement for the scissor parts  and is there any issue with doing this (if it is extraneous) with the 24V DC arrangements contained ?

Thank you.

Habs

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  • 0

    If you bond the equipment won't it then become an Exposed-conductive-part that could become a danger if the P.M.E. installation loses its supply P.E.N. conductor? You don't want a large live metal structure at 240 Volts open to touch do you?

    Well if all the metalwork around it is at the same 240V (exposed-condutive-parts of class I equipment) they you probably do. Principle of equipotentiality and all that.

       - Andy.

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  • 0

    If you bond the equipment won't it then become an Exposed-conductive-part that could become a danger if the P.M.E. installation loses its supply P.E.N. conductor? You don't want a large live metal structure at 240 Volts open to touch do you?

    Well if all the metalwork around it is at the same 240V (exposed-condutive-parts of class I equipment) they you probably do. Principle of equipotentiality and all that.

       - Andy.

Children
  • 0 in reply to AJJewsbury

    This was an interesting discussion from a while back AJJ  -  in fact  this bonding thingamyjig  is always a thought provoker and this discussion you started back then is useful as reading it made me think about what is trying to be achieved in a scenario.

    (it is the old site so the link might not work ... but ive also put an extract of some scenarios you presented where an installation may be present.)

    www2.theiet.org/.../messageview.cfm

    Alright lets start it off .

    1. Inside a house with metallic plumbing.
    Assuming that the supply pipe is metal, or that the metal pipe work system picks up the 'earth potential of the building' - yes

    2. In an aluminium framed greenhouse at the bottom of the garden.
    Either use Class II equipment only, or bond locally to the socket outlet / light etc. This latter action will of course allow the green house to attain a high potential with respect to the surrounding area in the event of a fault - so you might consider a grid - as below

    3. In the aluminium framed car port attached to the above house, with a class 1 light fitting attached to the metalwork and an outdoor 13A socket on the house wall (under the carport).
    As below

    4. In a corrugated steel lean-to shed, earth floor, attached to same house, again 13A socket on the house wall (inside the shed) and class 1 light fitting in contact with the steel.
    You can't bond the floor - so either use Class II, or put a grid in the floor, or put a radial earth tape around the exposed sides of the shed and connect it to the light and the socket outlet cpcs, or rip out the installation and move it

    5. For a class 1 lamppost outdoors, inches away from a run of steel fencing.
    No I don't want to bond the world . If you are worried you could put an earthed (to earth and the supply) grid in the ground around the lamp post base - in an attempt to limit 'touch voltage', or change the lamp to Class II.

    6. As above, but in a children's play area where it's obvious from paint abrasion that the kids use both as an extension to the climbing frame.
    As above.

    7. A class 1 bollard light next to a stand pipe (water tap) fed by copper pipe (as in a camping site).
    As above

    8. As above, class 1 light next to a tap, but this time inside a damp brick-built shed with a damp concrete floor (i.e. the "facilities" at the same camp site)
    Change the light to Class II .

    9. As above, but floor has a DPC and is covered with lino.
    What about the walls .


    Regards

    Geoff Blackwell

  • 0 in reply to AJJewsbury

    But if the lift is not bonded it will not become live. What about live lift to earthed concrete floor dangers?

    Z.

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