This mandatory classification runs likes a red thread from selection of the smallest
limit switch through to the overall concept of the entire machine, whereby it is necessary to grapple with
the permanent conflict between what is technically feasible and what is permitted on the basis of "pure
Thus: Depending on application, not every technically feasible safety category is also
permitted. For instance, in the case of contactless protection devices (light barriers etc.) only
categories 2 or 4 are permitted. By contrast, in the case of tread mats, categories B to 4 can be used, depending on risk
assessment, provided these categories can be reached at all owing to the design. The 2-hand control C575 would technically also
comply with the lower categories but it cannot be connected in categories 1-3.
1 The categories are not intended to be applied in any specific order or hierarchical arrangements with respect
to the technical-safety requirements.
2 The risk assessment will indicate whether full or partial loss of the safety function(s) as the result of fault is acceptable.
Possible selection of categories pursuant to EN 954-1
Starting point for the risk assessment of the safety-related component of the controller.
S1 - Slight (normally reversible) injuries,
S2 - Serious (normally irreversible) injuries, including death
F- Frequency and/or duration of the risk exposure
F1 - Rare to frequent and/or short duration of exposure
F1 - Frequent to sustained and/or long duration of exposure
P- Options for risk avoidance
(Generally referred to the speed and frequency at which the dangerous components moves and to the clearance from the dangerous
P1 - Possible under certain conditions
P2 - Hardly possible
B1-4 Categories for safety-related components of controls
• - Preferred category
• - Possible category requiring additional measures
- Disproportionately extensive measures by comparison with the risk
Classification of a machine into categories to EN 954-1
Pursuant to the Machinery Directive 89/393/EEC, every machine must comply with the relevant Directives and Standards.
Measures must be taken to keep the risk to persons below a tolerable extent. In the first step, the project planner performs a risk
evaluation to EN 1050 "Risk Assessment". This must take into consideration the machine's ambient conditions for instance. Any overall
risk must then be assessed. This risk assessment must be conducted in such a form as to allow documentation of the procedure and the
results achieved. The risks, dangers and possible technical measures to reduce risks and dangers must be stipulated in this risk
assessment. After stipulating the extent of the risk, the category on the basis of which the safety circuits are to be designed is
determined with the aid of EN 954-1 "Safety-Related Components of Controls". This determined category defines the technical requirements
applicable to the design of the safety equipment. There are five categories (B, 1, 2, 3 and 4) whereby B (standing for basic category)
defines the lowest risk and, thus, also the minimum requirements applicable to the controller.
Possible selection of categories pursuant to EN 954-1
Starting point for risk assessment of the safety-related components of the control.
Scope of application
Potential risks and hazards posed by a machine must be eliminated as quickly as possible in the event of danger. For dangerous movements,
the safe state is generally standstill. All safety switching devices of Series C 570 switch to de-energised state, i.e. standstill for
drives, in the event of danger or fault. Standard EN 60204 demands that every machine must feature the Stop function of category 0. Stop
functions of categories 1 and/or 2 must be provided if necessary for technical-safety and/or technical-function requirements of the
machine. Category-0 and category-1 stops must be operable independently of the operating mode, and a category-0 stop must have priority.
There are three categories of stop function:
Shut-down by immediate switch-off of the energy supply to the machine drives.
Controlled shut-down, whereby the energy supply to the machine drive is retained in order to achieve shut-down and the energy supply is
only interrupted when shut-down has been reached.
A controlled shut-down in which the energy supply to the machine drive is retained.
EMERGENCY-STOP devices must have priority over all other functions. The energy supplied to the machine drives which may cause dangerous
states must be switched off as quickly as possible without further risks or dangers. Resetting of the drives may not trigger a restart.
The EMERGENCY-STOP must act either as a stop of category 0 or as a stop of category 1.
The basic device of the 570 Series of safety switching devices can be used for EMERGENCY-STOP applications up to
maximum category 4 to EN 954-1. Depending on external wiring and cable routing of the sensors, category 3 resp. 4 to EN 954-1 must be
Safety door monitoring
Pursuant to EN 1088, a distinction is made between Interlocked, separating protective devices & interlocked, separating protective
devices with follower. Here as well, the safety switching devices are used for EMERGENCY-STOP applications. Controls up to category
4 to EN 954-1 are possible.
Presses and punches
The two-hand control C 575 is a device on which the operator must use both hands simultaneously, thus protecting him against risks
and dangers. The overtravel monitor C 578 is used on linear-driven presses (e.g. hydraulic, pneumatic and spindle presses) in
accordance with VBG7n52. It checks for the following only once during the test stroke:
- Correct connection of the operating controls
- External cable discontinuity
- Possible failure of the components to be monitored cyclically
The overtravel monitor can be used only in conjunction with a two-hand control. The press controllers and overtravel
monitors are suitable for installation in controls for eccentric, hydraulic and spindle presses. They can be used up to category 4 to
EN 954-1. Type III C to DIN 574 is possible specifically for presses.
The safety switching device C 570 operates internally with several contactor relays. The contacts of the relays comply with the
requirement in respect of positively driven operation to ZH 1/457, Edition 2, 1978. This means that NO contact and NC contact may not be
closed simultaneously. safety relays with positively driven contacts are used in the newly developed safety switching devices C 571-C 574,
C 576, C 577 , the contact expansion C 579 and on the press controllers C 575 and C 578. This series of devices is characterised by an
extremely narrow design (22.5mm and 45 mm). Approvals and test certificates, conventional on the market, have been issued by BG, SUVA,
UL and CSA. The function of the internal contactor relays/relays is monitored in a redundant circuit. In the event of failure of a relay,
the safety switching device always switches to de-energised state. The fault is detected and the safety switching device can no longer be
switched on. Using normally closed contacts and normally open contacts for the same function complies with the requirement in respect of
Enable contacts (FK)
The safety-related function must be controlled via safe output contacts, the so-called Enable contacts. Enable contacts are always normally
open contacts and switch off without delay.
Signalling contacts (MK)
Normally open contacts and normally closed contacts which may not perform safety-related functions are used as the signalling contact. An
Enable contact may also be used as a signalling contact.
Delayed Enable contacts
Drives which have a long overtravel must be decelerated in the event of danger. For this purpose, the energy supply must be maintained for
electrical braking (stop category 1 to EN 60 204-1). The safety switching device C 574 also feature OFF-delayed Enable contacts, besides
undelayed Enable contacts. Delay times of 0.5 to 30 s are available. The sealable cover cap C 560.10 (see Selection data and Ordering
details, Accessories) can be fitted onto C 574, C 6702 to protect against unauthorised adjustment of the set delay time.
If the Enable contacts of the basic device do not suffice, positively driven contactors (e.g. B6, B7) may be used for contact expansion.
One solution for increasing the number of Enable contacts, which is both simple to use and space-saving, is the expansion unit C 579
(only 22.5mm wide). The expansion unit C 579 provides 4 additional Enable contacts.
Expansion unit C 579
Expansion unit C 579 may not be operated separately in safety-related circuits but must be combined with a safety switching device C 57x.
One Enable contact of the basic device is required for connection of an expansion unit. The category of a control with expansion units
corresponds to the category of the basic device.
Snap-on mounting on 35mm top-hat rail to EN 50 022. Screw mounting of the safety switching devices C 57x can be implemented with two
additional plug-in tabs C 560.20 (see Selection data and Ordering details, Accessories).
A User Manual with a device description, connection diagrams and application information in several languages is enclosed with every
safety switching devices of Series C 570 and C 67xx.
"Safety Engineering" Application Manual
You can find further information in the "Safety Engineering" Application Manual. It provides you with the required information on the
relevant safety standards and project planning information. The entire range of components used for safety applications is explained in
this Manual, from the sensor (Emergency-Stop command devices and position switches), through evaluation units (safety switching devices
C 57x and fail-safe control AC 31 S) to the actuator (e.g. contactor for switching motors). All these components must be selected
correctly in order to meet the requirements applicable to modern safety facilities.