concrete pad anchored 24vDC scissor lift and equipotential bonding

Bonding of extraneous-conductive-parts is only required if the method of protecting from electric shock is ADS (although bonding still might be a good idea if extraneous-conductive-parts might import a non-Earth potential from other installations, but that's unlikely to be the case here).

So ignoring the 24V (presumably SELV) motors, the question then becomes are these parts you want to bond within reach of anything that's subject to ADS?

Then there's the question of whether the concrete pads are sufficiently well connected to true Earth potential - if inside a building and above the damp proof membrane, they may well not be. A test of the part to something well connected to Earth (say the supply PE) and see if their resistance to Earth is less than say 23kΩ would be a first step there.

   - Andy.

Thanks for commenting AJJ

I omitted to mention that I was conscious of being an issue really only if there is a within reach situation ... that would be the control panel casing possibly depending on how close it is to the scissors, or perhaps from [faulty] piece of equipment plugged in to near by sockets and used when working under a vehicle. It all seems a bit of a rare risk I agree.

Yes the membrane may affect and I am aware of the testing to establish how 'earthy' the metal work ends up.

that said, let's say it may be best to bond all things considered, is the issue of the 24V DC an issue ... I presumed not as it will be separated one would have thought... for one thought ?

On balance even before I posted, I was leaning to not being inclined to bond, due to the within reach mainly being unlikely, but worth sharing just in case any one spots something to be aware of.

Thank you

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?

Z.

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.

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

A piece of lifting equipment like this is likely to be classified as 'machinery' for the purposes of the Supply of Machinery (Safety) Regulations (see guidance on the Lifting Operations and Lifting Equipment Regulations on the HSE web-site: https://www.hse.gov.uk/work-equipment-machinery/loler.htm)

Downstream of the point of connection of the machinery to the mains supply, BS EN 60204-1 applies to machinery, and NOT BS 7671. (The electrical equipment of machines covered by BS EN 60204-1 is specifically excluded from the scope of BS 7671.)

In certain situations, BS EN 60204-1 has very different requirements for earthing and bonding to BS 7671. If there is any doubt about installation requirements such as earthing and bonding, it would be advisable to seek guidance from the manufacturer, not least because of potential safety issues with controls and electromagnetic compatibility.

If memory serves, the manufacturer of the machinery is required to address this kind of thing in their instructions, according to BS EN 60204-1.

The manufacturer may also require, or recommend, that certain electrical tests are conducted in accordance with BS EN 60204-1, which may differ from those carried out in BS 7671.

good points.   in fact the  manufacturer (which offer an installed or self install package - this setup runs off a 13A socket they said) was contacted and they said they were not aware of any installation that has ever been bonded  as an extraneous part .    it will be interesting to see how earthy the lift part ends up once anchored into the concrete.  :-)

In that case, there are two options to comply with BS 7671:

(a) Ensure the extraneous-conductive-parts are kept out of arm's reach of any exposed-conductive-parts and other conductive metalwork in the building; or

(b) Get in contact with the manufacturer and ask them what to do because the UK national wiring code (BS 7671) requires main protective bonding to be applied in this situation to prevent electric shock due to simultaneous contact with either exposed-conductive-parts or other extraneous-conductive-parts within the installation.

Is this a commercial installation in the UK, that you've been asked to look at a new installation for? If so, the Client also has duties under CDM to resolve this issue, say if it involves other works, or an existing installation . If it's a domestic Client, the Principal Contractor for the works in question undertakes the Client's Duties, and would have to resolve the issue.

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

Z.