Welding Power Sources - Lincoln Electric RANGER 405D Operating Manual

What are VRD & ROCV Devices?
VRD's are gaining popularity as a "must have" safety accessory
especially where welding applications are being carried out in an
environment with a high-risk of electric shock such as wet areas
and hot humid sweaty conditions.
VRD & ROCV are the abbreviations of two different naming
conventions used to describe safety device fitted to welding
power source to help protect the operator from electric shocks.
VRD stands for 'Voltage Reduction Device' and ROCV stands for
'Reduced Open Circuit Voltage' both devices are either fitted as
an after market addition or part of the integral design of a
machine. They reduce the voltage at the welding output terminals
whilst not welding to a no load voltage of no more than 35V for dc
welding and for AC welding 35V peak 25V a.c. rms, when the
resistance of the output circuit is below 200Ø (ohms). The lower
reactivation resistance is of the device the higher the safety level
but also requires that the welding cable connections be keep in
good electrical condition.
Having good electrical connections also limit the possibility of
other safety issues such as heat-generated damage, burns and
fires.

Welding Power Sources

Welding power sources generally have an Open Circuit Voltage
(i.e. the voltage at the welding output terminals whilst not welding)
in the ranges of 35 – 115VDC. Welding machines for stick
welding (MMAW) and similar constant current (CC) processes,
supply a higher open circuit voltage between the electrode and
the work when the welding machine is switch on and ready to
commence welding. These welding machines have a drooping
characteristic, with the open circuit voltage higher (typically
60-80V) than when the arc is established and welding current is
drawn (20-35V).
Consequently, the greatest danger occurs when handling the
electrodes and the electrode holder between welding operations,
such as when changing electrodes.
Welding machines for MIG (GMAW & FCAW) have a flat constant
voltage (CV) characteristic, generally with a lower open circuit
voltage (30-60V). Also, the current is turned on & off by a gun
trigger, which also controls the wire feed. Therefore, the welder is
not exposed to open circuit voltage, unless the trigger is turned on
and the wire is feeding. Also, electrodes are not changed as
frequently as for stick welding (MMAW).
For these reasons VRD/ROCV's are
incorporated into the stick welding mode (CC) of welding
machines being used in environments with high-risk of electric
shock.
W A R N I NG
All multi-process CC/CV machines which are fitted with VRD's do
not offer low voltage protection in CV modes. If the multi-process
machine has a "WELD TERMINAL ENABLE SWITCH" enabled,
the weld output terminals will be electrically 'HOT' a n d
potentially High Voltage present.
Only 'ACROSS THE ARC' type wire feeders with a internal
contactor fitted should be used in this configuration.
Arc air gouging is not recommended in CV. Due to 'CV MODE'
not offering VRD protection.
Page 4
VRD - VOLTAGE REDUCTION DEVICES
more commonly
This reduction of the voltage supplies a safer level of voltage
when an arc is not being struck or when an electrical resistance
less than the welder's body resistance have been detected.
All VRD's are only an aid to safety and personal protective
equipment and safe working practices must be observed at all
times. The risk of electric shock during welding from a correctly
installed and maintained welding machine is negligible, provided
that sensible precautions are taken by the user and correct safe
working procedures are followed. All parts of the output circuit
should be considered electrically alive, and consequently welders
should ensure that no part of their body is placed in such a
position as would complete a path through it for the passage of
electric current. Safe working procedures should always be
followed whether a VRD is fitted or not.
Operation
Due to inherit low voltage safety features of the VRD's to reduce
the possibility of electric shock to the operator. A very slight delay
during striking of the electrode may be experienced. The high
voltage that is available on units without VRD's allows them to
penetrate and burn through dirty, painted and heavily mill scale
plate. Units fitted with VRD's cannot penetrate and are required
to register the correct resistance, which switches the safety
device into weld mode. Unlike other VRD's Lincoln uses micro
processor control to monitor and establish the arc without the
sticking and shorting of the electrode to the job as seen in many
other VRD installations. Due to the requirement of the resistance
in the circuit to be low for a VRD to operate, a good
metal-to-metal contact must be made between the metal core of
the electrode and the job. A damaged or poor connection
anywhere in the output circuit may limit the operation of the VRD.
Some electrodes form a cone at the end of the electrode after the
welding arc has been broken, particularly iron powder and low
hydrogen electrodes. This cone will need to be broken off in order
to have the metal core of the electrode to make contact.
Safe working procedures should always be followed whether
a VRD is fitted or not.
Ranger 405D IMA 608D