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Voltage Reduction Devices
鈥淲e鈥檙e a millwrighting company and use stick-welding (SMAW) for installation and repair jobs in a variety of on-site work.听 We鈥檝e been told that we should be using a VRD to help prevent electric shocks.听 Please explain this VRD.鈥�
Author: Dave Hisey, is the chair of the T/C for CSA W117.2 and CSA C232 (CSC26) Electric Welding Equipment
A 鈥淰RD鈥� or Voltage Reduction Device 鈥� a specific type of hazard reducing device; a device designed to
reduce the no-load voltage of a welding machine to a safe level. CSA W117.2 -19 Definitions. This device must be used under certain circumstances according to the Canadian national standard for welding safety, CSA W117.2-19 (7.2.1.2 Approved voltage-reducing devices).听 These units can be purchased as an after-market accessory and added to the welding machine, or many modern machines have them built in as a control feature.听
The aftermarket device is installed into the welding circuit and operates from power of the welding circuit while the built-in device is a part of the welding machine. Be careful of the built in VRD units as many machines are shipped with the VRD disabled, and a procedure must be followed to enable it (consult your manufacturer or the handbook). Do not assume that the VRD is functioning because the welding machine came equipped with one built-in. Also, 12 volts is a safe voltage as specified in CSA W117.2-19, so ensure your unit puts out 12 volts or less.
The voltage differential between the electrode and the workpiece in SMAW while the machine is 鈥極N鈥�, and idling is known as the no-load or open-circuit voltage.听 This voltage can be up to 113 Volts (direct current).听 If the welder contacts this voltage, it can drive enough amperage through the human body for electrocution to occur.听 This is a particular concern in maintenance welding applications where the welder may be exposed to wet, damp, or humid conditions or where they may come in direct contact with the workpiece on a large structure. Moisture, sweat or just plain rainwater can lower body resistance significantly, as resistance lowers, current in the form of amperage increases and if your body comes in contact with the electrode, you may not be able to let go. Canadian welders have died this way.听 (See attached Figures.)
A VRD lowers the effective voltage to a safer level and automatically senses the welder striking the arc.听 The device can detect the difference between a weld and a human body based upon the resistance level.听 If the VRD detects the weld, the main voltage turns on almost instantly and the weld continues normally.
It is important to note that the use of a VRD does not eliminate requirements to use other preventative measures, including PPE and using dry rubber mats to insulate the worker from the structure being welded. Do not believe someone who tells you that DC welding machines are safe, and they cannot kill, as the last 2 welders to die of electrode shock electrocution in Canada were killed by DC welding machines. In a review of 18 electrode shock fatalities, I completed in 2016, 8 died from electrode contact with the face or neck, 11 were found lying on the ground or on the metal they were welding 鈥� sound like a familiar position. Think about that the next time you squeeze into a tight space in poor conditions without the protection a VRD provides.
听For more details about all aspects of safety in welding and related processes the Canadian Standards Association has made CSA W117.2 鈥�Safety in welding, cutting, and allied processes鈥� freely accessible to all Canadians.听 (There is more detail on how to access this standard in an article that I co-wrote with my colleague Jonathan Fernando from the CSA in the Fall 2021 edition of the CWBA 鈥淲ELD鈥� journal.)
Dave Hisey, chair of the T/C for CSA W117.2; chair of CSA C232 (CSC26) Electric Welding Equipment. He also represents Canada on Commission VIII Welding Health and Safety with the International Institute of Welding. A volunteer, Dave, is sponsored in this work by the 阴APP导航. Please contact him via email drhisey@shaw.ca with your comments or if membership of CSA W117.2 or CSA C232 technical committees is desired.
Thank you to Professor Jim Galloway for the illustrations
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