. Checked cord connections, voltage input
When this was done, was it done while the machines were running? (voltage input)
#1: the "work cable" which is connected to the workpiece and provides the return current path from the workpiece to the welding machine.
Did you test for voltage drop while welding between the welding table and the welder return connection? Also test the voltage drop on the electrode lead between the welder and the electrode.
The votage drop while running is only 2V and 3V on some at worst.
Is this voltage drop at the welder input or welder output? A quick test is to "short" the arc at the table and check for temperature changes on the electrode cable and connections as well as the "ground" cables and connections.
The ground clamp connection is good as well because they are actually permanently attached because the welding tables are so large.
See my comment above and check again!
Both wire feed and stick welders are suffering from the same problems though! I'm really confused on this one.
See kwired's post below.
This next comment is probably a long shot. Is this shop on utility power or a generator?
I have no idea how much impact this may have but is it possible high harmonics can be a problem?
Maybe need to look closely at both voltage and current and see if something is abnormal.
The possibility of harmonics being an issue is very large if all the machines are of newer vintage. When the welding "quality" tests were performed, did you isolate the other welding machines? Both on the input power as well as the outputs? Are there any other non linear loads like VFD's? Have the machines been tested to prove that they might be the actual culprits? I'm thinking some good testing would include taking the existing machines to another site to see if they work correctly and bringing a known "good machine" to the problem site.