WELDER PROBLEM!

whys my wire snapping right at the driveroll b4 it goes into the small spring?? i loosened up the tension alot and played with that for awhile and it will weld for like 10 secs then snaps again... i was gettin shitty voltage in the garage im in i thought that might be the problem cause it seems im not gettin full penetration at all... so when i plugged it in to the main outlet box it snapped again b4 i could try it out and i had to leave the garage for a bit ill be back there l8r to try again...anyone ever experience this??