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GENERAL SAFETY REGULATIONS
Before opening up any machine, always pull out the mains
plug first, or otherwise ensure that the machine is "dead".
Components, assemblies or other units may only be start-
ed up once they have been installed inside a shockproof
housing. They must be "dead" (i. e. without current) while
being installed.
Tools may only be used on units, components or assemb-
lies once it has been ensured that the units are discon-
nected from the voltage supply and that any electrical
charges stored in components inside the machine have
been discharged.
Live cables or leads connected to units, components or
assemblies must be checked regularly for signs of insu-
lation faults or breaks.
If any defect is found in the power supply lead, the unit
must be withdrawn from service immediately, until the
defective power lead has been replaced.
Where new components and assemblies are fitted, atten-
tion must constantly be drawn to the importance of adher-
ing strictly to the characteristic data for electrical quanti-
ties given in the accompanying descriptions.
If the descriptions provided for the non-industrial final
user do not make clear what electrical characteristic val-
ues apply to a component, advice must be sought from a
qualified expert.
ELECTRICAL SAFETY MEASURES WHEN
ARC-WELDING
HAZARDS FROM ELECTRIC CURRENT
Both mains and welding current can be hazardous. It is forbidden
by law for anyone but a qualified electrician to do anything with any
parts which are in contact with mains voltage. The only excep-
tion to this applies, of course, to the power plug and the mains
switch. When repair or maintenance work is being carried out on
the power source, the machine must first be completely discon-
nected from the mains. For all but the most minor jobs on the
machine in the course of which the operator may have to leave the
room, even if only briefly, the plug socket(s) should be un-
mistakeably blocked.
Important note for the TIG welder:
Inside the power source is the HF ignition unit, which operates at
extremely high voltages of several thousand volts. The metal
housing containing the ignition device has a warning label on it
which reads "WARNING! HIGH VOLTAGE CAN KILL!". This
housing may only be opened by a qualified electrician - and only
after the machine has been unplugged from the mains! When
welding is being carried out with assisted ignition, the welding
bench must be earthed.
PROTECTIVE EARTH CONDUCTOR.
Every 3-phase power supply system will have a PE conductor.
This is a non-live, earthed conductor and connected with the
housing of the machine. If an earth fault occurs on the machine
there is an immediate short circuit between the PE conductor and
phase, causing the fuse on the corresponding phase conductor
to blow, and/or tripping the fault-current breaker (FI).
Both the mains and the machine supply leads should be regularly
checked by a qualified electrician to ensure that the PE conduc-
tor is functioning correctly.
OPEN-CIRCUIT VOLTAGE
The highest - and thus the most dangerous - voltage in the weld-
ing current circuit is the open-circuit voltage. The maximum per-
missible open-circuit voltages are stipulated in national and in-
ternational regulations according to the type of welding current,
the design of the current source and the extent of the specifically
electrical danger posed to the workplace.
RECTIFIER POWER SOURCES
A DC welding power source should be constructed in such a way
that if there is a fault in a rectifier (e.g. open circuit, short circuit
or phase fault), the permissible AC values cannot be exceeded.
Below, the open-circuit voltage ratings to IEC 974 (1.1.90) for
working under normal conditions and for working under conditions
of increased electrical danger:
WORKING UNDER NORMAL CONDITIONS
For welding jobs done under normal conditions and using simple
equipment, the following open-circuit voltage ratings apply:
for DC - peak value 113 V
for AC - peak value 113 V, effective value 80 V
These max. voltages may be exceeded on appliances equipped
with an RC circuit, so long as - with the arc unlit - the higher volt-
age does not occur for longer than 0.2 secs.
Exceptions may apply in the case of fully mechanised, automatic
or other special procedures. For welding current sources capable
of delivering either DC or AC, the respective regulations apply to
whichever operational mode the machine is switched to.
WORKING UNDER CONDITIONS OF INCREASED
ELECTRICAL DANGER, meaning:
- welding work in confined spaces, in cramped surroundings, on
or between electrically conductive parts, in damp or hot spaces:
For welding jobs done under conditions of increased electrical
danger, the following open-circuit voltage ratings apply:
for DC - peak value 113 V
for AC - peak value 68 V, effective value 48 V
An AC voltage occurring in the welding circuit may not exceed
48V. This also applies to welding rectifiers being used forwelding
purposes when the equipment is used e.g. inside a boiler or tank
etc. Welding rectifiers for use inside boilers, tanks and the like
must always be clearly marked with the letter
WORKPIECE CLAMP
If the electric flex of the workpiece clamp is shorter than the torch
hose pack or the manual electrode cable - meaning that the clamp
cannot be fixed anywhere immediately near the welding zone -
then the welding current will find its own way back. It may do this
via machine parts (e.g. during repair work), ball-bearings, electric
switches etc. This may then cause certain parts to become red-
hot, make chains and steel cables snap, and even cause the PE
conductor to melt through.
All this can also happen if the workpiece clamp has simply not
been fastened properly, or only laid on the surface of the work-
piece, in which case the course taken by the current will depend
on the presence of "bridges" or angle bars and the like. (Fig. 44)
(R)
L
1
(S)
L
2
(T)
L
3
(MP)
N
PE
Abb. 44
The power source may never stand on electrically conductive ground!
Connection to workpiece: NEVER like this! Use a firmly connected clamp.
PE conductors will be destroyed if the welding current ever has to find its own
way back.
81
("safety").
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