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Electrical Safety In Arc Welding - Manufacturers' Monthly What Is Vrd In Welding Machine

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Electrical safety in arc welding - Manufacturers' Monthly what is vrd in welding machine

Electrical safety in arc welding - Manufacturers' Monthly

ELECTRIC arc welding has been described by many people as a "dangerous" activity.

Electrical safety in arc welding - Manufacturers' Monthly what is vrd in welding machine

ELECTRIC arc welding has been described by many people as a “dangerous” activity. However it can be performed safely provided all circumstances and components of the welding process are considered.<[ql]>

The most important aspects are equipment and sound work practices.

The WTIA has published Technical Note 22 Welding Electrical Safety Expert Technology Tool that covers all aspects of arc welding electric safety practices.

This document together with the operating manual of equipment should form the basis of all training and information sessions.

Equipment should be designed and manufactured to conform to the requirements of the International and Australian standards (IEC 60974 or AS 60974).

The standard not only covers the machine but also the input cable and plug requirements (most commonly overlooked) and markings that form part of the machine. This standard has superseded the AS 1966 part 1, 2 and 3.

The AS standard also specifies the size of coupling device (plug) that should be used. The size of plug depends on a formula that not only uses the maximum current draw but also the duty cycle of the particular power source. These requirements tie in closely with the standard for the electrical wiring of buildings.

The use of any welding power source will not only cause the power source itself to heat up, but the input cable and plug will increase in temperature as well.

If the input cable that is being used is under-rated (too small) or the construction of the insulation of the cable does not conform to the requirements of the Australian standard AS 3191, it will cause the cable to overheat and serious degradation of the insulation could occur.

The wires may then be unprotected which could lead to serious electric shock. Equally if the plug does not conform to the appropriate standard (AS 3112) a similar situation could occur within the plug.

Another dangerous practice that exists within the marketplace is that people alter the earth pin on 15A plugs to ensure that the power source can be used in the more popular domestic 10A sockets.

This is extremely hazardous as the current draw would normally exceed the protection of the household circuit causing the circuit breaker to constantly drop out.

The state of the altered earth connection pin will in many cases cause increased resistance that would lead to a rise in temperature of the plug and household outlet socket.

Any damage to the input cable of a welding power source (or for that matter any electrical device) must immediately be addressed. In welding power sources where constant operation can cause significant rise in temperature, simply “taping” the damaged area is extremely dangerous and not acceptable.

Electrical shock

The risk of electrical shock significantly increases when welding is undertaken in damp or wet conditions.

This most often occurs in the early morning or in underground mining operations although these conditions can occur at virtually any site from the farm to the workshop.

For Manual Metal Arc (MMA) welding power source to operate effectively with a given type of electrode, it requires a minimum OCV (Open Circuit Voltage).

The OCV of a machine is measured between the output cables (work return lead and electrode holder lead). For general purpose electrodes this has to be a minimum of 50V (as specified by the electrode manufacturers).

However in wet or damp atmospheres, exposure to 30V can lead to serious or even fatal electric shock.

Therefore to ensure that the risk of this happening in these atmospheres is minimised, MMA machines have been fitted with VRD (Voltage Reduction Devices).

These devices act in such a way that once the arc is broken the machine will return to a safer state with an OCV of 15 to 30V.

If power sources are additionally fitted with a Voltage Reduction Device this device must conform to the requirements of AS 1674.2.

It must be noted that fitting a VRD to a welding machine adds to the safety of the machine, particularly in adverse welding conditions, but does not serve as a substitute for good and safe welding practice.

Maintenance of equipment is an important step in ensuring that equipment keeps working safely. The checklist found in WTIA Guidance note 7 “Health & Safety in Welding” should be followed before equipment is turned on.

*Nic Bothma is industrial products technical manager at BOC 131 262, www.boc.com.au.

Electrical safety in arc welding - Manufacturers' Monthly

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