9-5
Chap. 9 CONFORMITY WITH STANDARDS
9.6 Compliance with EN954-1, Category 3
9.6.1 General
In FRENIC-MEGA series of inverters, opening the hardware circuit between terminals [EN] and [PLC] stops the output
transistor, coasting the motor to a stop. (EN: Enable input) This is the safety stop function prescribed in EN60204-1,
Category 0 (Uncontrolled stop) and compliant with EN954-1, Category 3.
Note: Depending on applications, additional measures may be necessary (for end-user) to apply such as ‘brake function’ to
prevent movement and motor terminal protection against possible electrical hazard(s).
Use of terminals [EN] and [PLC] eliminates the need of external safety circuit breakers while conventional inverters need
those breakers to configure the EN954-1 Category 3 compliant safety system.
9.6.2 EN954-1
European Standard EN954-1 (Safety of machinery–Safety related parts of control systems) prescribes the basic safety
requirements for machinery categorized according to the requirement level. Category 3 represents the requirements that the
machinery shall be designed with redundancy so that a single fault does not lead to the loss of the safety function. Table 9.3
shows an outline of the category levels and their safety requirements. (For detailed requirements refer to EN 954-1)
Table 9.3
Category Summary of requirements System behavior
B
Safety related parts of control systems and/or their safety
devices and their components shall be designed,
constructed, selected, assembled and combined in
accordance with the relevant standards so that they can
withstand the expected influence.
The occurrence of a fault can lead to the
loss of the safety function.
1
Requirements of Category B shall apply.
Well-tried safety principles and well-tried components shall
be used.
The occurrence of a fault can lead to the
loss of the safety function, but the
probability of occurrence is lower than
for Category B.
2 Requirements of Category 1 shall apply.
The safety function shall be checked at intervals suitable
for the machinery.
The occurrence of a fault can lead to the
loss of the safety function between the
checks.
3
Requirements of Category 1 shall apply.
Safety-related parts shall be designed, so that:
- a single fault in any of these parts does not lead to the
loss of the safety function, and
- a single fault is detected whenever reasonably
practicable.
When the single fault occurs, the safety
function is still maintained.
Accumulation of undetected faults can
lead to the loss of the safety function.
4
Requirements of Category 1 shall apply.
Safety-related parts shall be designed, so that a single fault
is detected during or prior to the next demand on the safety
function. If this is not possible, an accumulation of faults
shall not lead to the loss of the safety function.
When faults occur, the safety function is
still maintained.
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