Grounding and Aerial Lifts

[mikemac52]

Hi,

I am not an engineer and beg your patients in this request and with the length of the explanation.

In my industry there are differing opinions on the merits/necessity of grounding an aerial lift. Along the lines of the differing opinions of using an arc welder with grounding on a suspended scaffolding. All of the information I can find on aerial lifts deals with lifts approaching high tension wires which we never do. Our issue is with having electrical equipment on an uninsulated lift.

Two main situations we encounter are Single phase 220V or a complete 3 phase 208V Distribution, sometimes run directly to the equipment, sometimes to a distribution box. The equipment could be either tungsten lighting units or metal halide arc units. Cable is run up the outside of the arm and is either #2 or 2/0 welding/ entertainment cable.

The equipment is clamped to the bucket in various ways but is done strictly to mount the equipment with no eye towards grounding. If the bucket is old, it is metal to metal, if new, the paint rules out electrical bonding. With the various mounting techniques used, even with metal to metal contact of the mounting hardware, there is no certainty of a good electrical bond.

Grounding of our generator run power system is astandard. Some folks ground at the generator for the entire system, some like to ground locally at the distribution boxes. The ground points for the system are usually far from where the aerial lifts are used.

So now we have a man (or woman) in the bucket with equipment which is grounded through its connectors but which may or may not be electrically bonded to the lift.

In dry weather we pretty much ignore things since the tires of the lift do a decent (not perfect) job of isolating the lift from ground. In wet weather things get a little dicey with different pieces of equipment leaking more voltage to ground than others. (It is all rental equipment and quality and design vary greatly.)

Would it be better for the technician to isolate the lift as much as possible, going so far as to disconnect the electrical connection grounds? Or should we ground the lift at all times? Or something in-between?

Thank you for your time,
Michael McDonald

 

[rbulsara]

Ground the lift at all times and even at multiple points. Use flexible bonds across moving parts or loosely connceted parts for mecnhanical operations (such as across a hinge between a cover and frame).

Plus the technicians shall follow all safety precautions they do while working on any other electrical equipment on or off the lift. This includes means to isolate the person as much as possible, that what insulated tools etc do. But that is not substitute for effetively grounding a system.

A grounded system will clear a fault (remove potential from other wise non-currenty carrying parts) 'before' a person would even be on the equipment, in most cases. That is its real value.