Stray Current Interrupter Device – SCID

Stray Current Interrupter Device – SCID


– The following is a demonstration of the
installation of a device that can prevent stray current damage from an incorrectly set-up
arc welding machine. Previously, we have demonstrated how a simple
operator error can lead to a situation where enormous stray welding current levels can
flow through unintended paths in a facility, including the grounding and bonding wires
in the electrical system. Now we will show you how the installation
of a prototype device that we are calling a stray current interrupter device, or SCID
for short, can stop the damaging current flow. The main SCID control module is added to the
welding electrode lead. The sensor is clamped over the arc welder’s
primary supply cord. The power supply to the SCID device is added
and now we can turn it on. At this point we can press the TEST button
on the unit to check it’s operation and then RESET so that we are ready for welding. Initially, we will demonstrate a correct welding
set-up where the current return clamp is properly located near the point of welding on the steel
down-draft table. Our machine is set-up for SMAW welding using
DC electrode positive. However, the SCID unit is designed to work with both polarities of DC, as well as AC current and the various pulsed current operations. The SCID unit allows the welding operator
to proceed normally. Now, we will change the set-up to simulate
a case where the welder has neglected to properly connect the current return clamp near the
point of welding. As you can see here, the bare current return
clamp has been left in contact with the machine’s chassis through the cart that it is sitting on. This conduit will allow stray welding current
to travel through the table and return back to the machine through the duct-work, the
building structure, and the building’s electrical grounding and bonding conductors. We can see now that the SCID unit has instantly
interrupted the fault condition and sounded an alarm. Once the welder realizes their mistake and
corrects the set-up, the SCID unit can be reset and welding can continue safely.

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