Safety Selection of Welded Wire Mesh Machine

by Kathy Li machine & equipment

Some welding machines are inherently safer than others, for example DC welded wire mesh machines are recognized as safer than AC wire mesh welding machines. Risk controls known as hazard reduction devices (HRD’s) are now commonly used as an effective risk control.

Welding machines can be a source of electric shock and they are widely used.

Further, welding operations are often carried out at mines where the environment can increase the risk of electric shock or electrocution (Most mine situations are Cat C environment to AS 1674.2 -2007). Selection of the safest welding machine and HRD arrangements is critical.

Category C Environment -- An environment where the risk of an electric shock or electrocution by arc welding is greatly increased due to low body impedance of the welder and a significant risk of the welder contacting the work piece or other parts of the welding circuit.

NOTES:

Low body impedance is likely in the presence of water, moisture or heat, particularly where the ambient temperature is above 32°C. In wet, moist or hot locations, humidity or perspiration considerably reduces the skin resistance of human bodies and the insulating properties of personal protective equipment accessories and clothing.

“Uo” is the highest output voltage listed for the welder.

If no formal assessment has been documented for the welding task, it is to be assumed that the environment is Category C.

Covers should be fitted to wire feeders unless Uo is less than 25 V a.c. or 35

V d.c. and there are no exposed control / motor wires above 25 V a.c. or 35 V

d.c.

It is important that the frame of a building or any structure is NOT used as the

return lead to the welding power source.

The welding power source nameplate “Welding power source Output” section should be checked for a.c. or d.c. - shown below at 6) as ~50Hz i.e. an a.c. welding power source. The Open Circuit Voltage Uo (or sometimes OCV) shown below at 9) as 48 V, is too high for an a.c. welding power source in a mine unless it has a HRD.

Where the welding power source has more than one current setting, there may be two open circuit voltages as shown below. This a.c. welding power source would also require a VRD.

It is not acceptable to have a means (eg switch) to defeat the HRD on a welder for use at a mine. Where metal gouging is required, a power source of sufficient size to operate with a HRD needs to be selected.