Secure Disable Applications

Case 1: Simple Start / Stop
Case 2: Interlock to EN 954-1 Cat 2
Case 3: Fail safe interlock to EN 954-1 Cat 3
Case 4: Secure Disable used in EN 954-1 Cat 4
Case 5: Provision of braking through drive
Case 6: Elevators to EN 81-1: 1998

Case 2 – Interlock (previously with feedback) to EN 954-1 Cat 2

The failure mode where the relay closes (or stays closed) when not energised no longer exists, so the feedback contact is not required.The enable input wiring has to be protected in order to avoid the possibility of a short circuit to positive
d.c. supply or digital logic signal which could cause inadvertent enable. Protection is achieved either by ensuring physical
separation from all other circuits or else by the use of a cable with an earthed screen so that a short circuit always
results in an earth fault and a loss of the logic signal (see EN ISO 13849-2).

The benefits of using Secure Disable are:

• Power contactor (with connected movement) eliminated (cost and space saving)
• Feedback checking arrangement eliminated
• No need for drive early-disable arrangement

The additional cost of arranging protected wiring for the drive enable input is small compared with these benefits.