Proper grounding is the key to maintaining arc stability.
Voltage drop from the act of traveling through ground leads and connections averages 1 volt per 15 feet of travel.
Having undersized ground lead and/or poor work connections amplify this loss in arc voltage.
With a poor ground, you can still strike an arc, but the resulting unstable arc will detrementally affect the weld quality.
Poor grounds often lead to inexperienced welders claiming the welding machine is broken.

Tim

Nalla,

I thought that was what Al had done.  And then provided an excellent example to explain.

But, let me ask a question: Are you referring to the 'Ground', properly termed 'Work' coming from the welding equipment to the project?  Or maybe a 'Ground' that goes from the welding equipment and/or project to the 'Earth'/'Ground' ?  Or am I missing another possible definition of 'Earthing'?

It can be difficult for us to get your translation correctly interpreted at times to know how to properly respond to your questions.

Many larger projects I have worked were very safety concerned and had procedures requiring the 'Grounding' of the work, the equipment, and other items which could in any way be cause for electrical hazard.  We drove 10 foot long copper clad rods into the ground and connected them to the pressure vessels, tanks, etc that were under construction.  We drove more into the ground at the generator trailer that powered a number of welders and grounded that.  The 'Ground' that is included in common electrical lines is not always adequate for the job.  In Oregon all our farm outbuildings had to have the metal skin of the building grounded separately from any electrical ground for power.  Then, the power system had a Ground besides the Neutral that comes through the line.  Many will say, and I am no electrician, that the neutral and ground are the same.  In many aspects that is true.  But there are differences in the safety application between the two.  That is why small 110 volt hand tools with certain housing materials in their design need a grounding lug as well as the hot and neutral wires and all industrial and residential codes changed a good many years ago to include a three wire cord/recepticle instead of just two wires. 

Some projects will require repairmen with portable welders to drive a ground/earth rod and ground their equipment before striking an arc.  Safety, both for the workers and the equipment from stray electrical charges that follow the path of least resistance. 

Hope I have understood your OP correctly and that this is of help. 

Have a Great Day,  Brent

Brent and Al have provided good insight.

I've been watching this thread and cringing... 

Brent has made the most important point in this conversation so far... Which I will repeat.

We don't know what your talking about!

Understanding terms is difficult, and extra difficult when english is not the primary language of one of the persons involved.  It just makes it a little harder  :)

1.   Earth Ground

2.   Work Lead

These two items are both very important and both have a role in welding safety and quality.. But they are not the same thing.

I think you will get the answer you want when you can describe for us in a little better detail what your electrical issues are.

Both Earth grounding and work lead placement are always covered in the welding power supply operators manual... If you have exausted this source of data and still are having problems.. or just don't understand.. there is probably somebody here who can assist you in trouble shooting.

Nalla apologies for some of the responses. The Lincoln Electric's operator manual regarding Electromagnetic Compatibility (emc) quote "Earthing of the Workpiece - Where the workpiece is not bonded to earth for electrical safety, not connected to earth because of its size and position, e.g., ships hull or building steelwork, a connection bonding the workpiece to earth may reduce emissions in some, but not all instances. Care should be taken to prevent the earthing of the workpiece increasing the risk of injury to users, or damage to other electrical equipment. Where necessary, the connection of the workpiece to earth should be made by a direct connection to the workpiece, but in some countries where direct connection is not permitted, the bonding should be achieved by suitable capacitance, selected according to national regulations."
What I believe this is saying is that if emc is problematic "earth" the secondary and machine to prevent emc from damaging printed circuit boards in the welding machine.
Also if two or more machines have different secondary connections (like one electrode positive and one electrode negative) to work piece this places the machines output in series which doubles the voltage versus both machines with the same output (both electrode positive) which would be parallel same voltage.