Specifications

MedWeld 3000 Catalog Revision 8
July 2002 Page 54 of 72
Safety Ground Fault Systems for Manually Operated Transguns
Monitoring and control circuits are required for ensuring the safety of human beings
who operate a welding gun that is integrated with a welding transformer. There is
high voltage cables that come in close proximity to the person who manipulates the
“transgun” hence several designs need to be incorporated into the tool to make sure
that the person does not become the easy path to ground for a primary electrical
short circuits. At a minimum, the following three requirements must be included:
The integrity of the ground cable between the control and the welding
transformer needs to be monitored at all times to assure that the cable would be
capable of grounding out the primary short in the event of occurrence.
Imbalances of current between the control and transformer need to be
monitored at all times. Should the current to the transformer exceed the current
returning from the transformer by 10 mA or greater, it would be presumed that
primary current is finding its way to ground. The control must then isolate the
welding gun from the power lines.
A grounded metallic shield must surround the power cables between the
welding transformer and the welding control. The shield is grounded in the control
and not at the welding gun.
There are additional monitoring and control functions that can be
implemented to ensure safety. Some of these are listed as follows:
An isolation contactor can be included to remove the power line from the
transformer during equipment idle time.
Periodic measuring and verification that the insulation covering the primary
cables is adequate.
Automatic control testing and validation can be incorporated into the design to
ensure that all the safety-monitoring circuits are functioning.