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OPERATION
B-6
WHAT ARE VRD AND 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 and ROCV are abbreviations for two different
safety devices used in a 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 used as an after market addition or
part of the integral design of a machine. VRD and
ROCV reduce the voltage at the welding output termi-
nals when not welding to a no load voltage of less
than 35V for DC welding and for AC welding 35V peak
25VAC RMS, when the resistance of the output circuit
is in the range of 20-200 (ohms). The lower reactiva-
tion resistance of the device, the higher the safety
level and also requires that the welding cable connec-
tions be kept in good electrical condition.
Having good electrical connections also limits the pos-
sibility 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 when not welding) in the range of 35-
115VDC. Welding machines for stick welding
(MMAW) and similar constant current (CC mode)
processes supply a higher open circuit voltage
between the electrode and the work when the welding
machine is switched on and ready to commence weld-
ing. These welding machines have high open circuit
voltage (typically 60-80V) then when the arc is estab-
lished and welding current is drawn the voltage drops
to 20-35V.
Consequently, the greatest danger occurs when han-
dling the electrode and the electrode holder between
welding operations, such as when changing elec-
trodes.
Welding machines for MIG (GMAW & FCAW) have a
flat constant voltage (CV) characteristic, generally with
a lower open circuit voltage (30-50V). Also, the cur-
rent is turned On and 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).
VRD/ROCV’s are more commonly incorporated into
the stick welding mode (CC) of the welding machines
being used in environments with high-risk of electric
shock.
SAFETY
The 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 resis-
tance have been detected. All VRD’s are only an aid
to safety, 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 negligi-
ble, provided that sensible precautions are taken by
the user and correct safe working procedures are fol-
lowed. All of the welding output circuit should be con-
sidered electrically active (hot) and the welder should
make sure that they do not become a part of that cir-
cuit to ground or they could receive a severe electric
shock that could kill. Safe working procedures should
always be followed whether a VRD is fitted or not.
VRD OPERATION INDICATOR
On the front panel of the Air Vantage 500 are two indi-
cator lights. A red light when lit indicates voltage
greater than >30V and a green light when lit indicates
voltage less than <30V.
These lights monitor the OCV at all times. In the CC
mode when the welding arc has stopped the green
light will illuminate indicating that the VRD has
reduced the OCV to less than 30V. During welding the
red light will illuminate indicating that the OCV is
greater than 30V. During welding the red and green
light will flash on and off. This is normal operation as
the welding voltage will produce less than 30V,
depending on the process and type of electrode being
used.
If the red light remains illuminated after welding in the
CC mode, please refer to your local field service shop
for service.
OPERATION
The low voltage safety features of the VRD’s is 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 reg-
ister the correct resistance, which switches the safety
device into weld mode.
AIR VANTAGE® 500 CUMMINS