VRD stands for voltage reduction device. When a VRD is fitted to a welding machine it reduces the maximum unloaded open circuit voltage across the output terminals of the welder to a safe voltage normally this reduced voltage is about 12 volts (Australian Standards 1674.2 2003 state this voltage must be less than 35 Volts DC and 25 Volts AC). When a load of less than 200 ohms resistance is applied to the output of the welding machine the VRD will sense this and turn the welder to full output then welding will commence.

When the resistance across the output rises above 200 ohms or the electrode is removed from the workpiece then the VRD will turn the output of the welder back to a reduced output state.

The rules pertaining to voltage reduction can be obtained from website www.standards.com.au "Type in Standard no 3195".

Why is this necessary

A lot of new welders and some older units have an open circuit voltage in excess of 105 volts D.C. or 85 volts a.c. This voltage is currently legal and in normal (dry) conditions may be quite safe.

The only trouble is 95% of sites do not have these normal conditions e.g. (damp or wet, caustic, salty, working at height or in a confined space) an electric shock in these conditions can and has proven fatal. (Ventricular fibrillation, falling from heights and inability to escape the power source when in confined spaces) not to mention the serious physical injuries sustained as a secondary result of an electric shock.
Electric shock from a welder power source can also cause serious internal injuries to the human body. These injuries are not always immediately noticeable.

Another safe work practice is to have a Dead Man (Isolation)switch in the electrode circuit, this switch will isolate the power from the electrode should the need arise. This system requires a trained observer to operate the Dead Man switch should the welding operator get into any life threatening situations.

It is also recommended all the above devices be tested regularly. SafeTac manufactures the VRD, Dead man switch and test unit mentioned above. Other VRD and safety devices can be designed to suit special operator and company requirements.

• Welding machine insulation levels should be checked regularly.
• Voltage Reduction Devices are used as an aid in operator safety.

SAFE WORKING PRACTICES MUST ALWAYS BE OBSERVED!