Stop categories 0, 1 and 2 — NEN-EN-IEC 60204-1

A processing line with a sorting machine, conveyor belt and potting machine usually has several stop functions: an operational stop at the end of a cycle, an emergency stop button for hazardous situations, and sometimes an automatic stop triggered by a fault signal. NEN-EN-IEC 60204-1 (§9.2.2, "Safety of machinery — Electrical equipment of machines") makes a fundamental distinction between three stop categories, and not every category is suitable as an emergency stop.

The three categories

• Category 0 — immediate removal of the power supply to the machine's drive elements (an uncontrolled stop: the machine "coasts to a halt" without a controlled deceleration).
• Category 1 — a controlled stop, in which the power supply to the drive elements is removed only after the stop has been reached (for example, controlled braking of a conveyor belt before the motor is made voltage-free).
• Category 2 — a controlled stop in which the power supply to the drive elements remains available during and after the stop.

Which category applies to an emergency stop?

This is the core of §9.2.2: an emergency stop function must always be implemented as stop category 0 or 1 — the actual choice between 0 and 1 follows from the machine's risk assessment (a category-1 stop is permitted when an uncontrolled, immediate loss of the drive itself would create a greater risk, such as a load that would then fall uncontrolled).

Category 2 is never permitted as an emergency stop function — because the power supply to the drive elements remains available under category 2, it does not provide the guaranteed removal of energy that an emergency situation requires. Category 2 is intended for normal operational stops (for example, an end-of-cycle stop), not for hazardous situations.

Note: which category applies to a specific machine/stop function follows from the machine-specific risk assessment (in line with the C-standard/Machinery Directive application) — this is not a choice that can be made independently of that assessment.

Why this is relevant during inspection and use

During a NEN 3140 inspection of an installation with connected machines, the emergency stop function itself is not always assessed in detail (that is largely 60204-1 territory at commissioning/modification of the machine, see the machine safety - 60204 guide), but an inspector or user who notices that an emergency stop button does not actually de-energize the drive (category-2 behaviour on an emergency stop function) should treat this as a serious deviation.

Common mistakes

1. Mistaking a "stop" button on the control panel for an emergency stop function — a regular operational stop (often category 2) is not a substitute for the red, latching emergency stop button.
2. Assuming every emergency stop is implemented identically — categories 0 and 1 are both permitted, but behave differently (immediate versus delayed loss of power); this must be evident per machine from the documentation/risk assessment.
3. Applying category 2 to a function intended as an emergency stop — this does not comply with §9.2.2 and can, during a fault, actually sustain a hazardous situation instead of ending it.

Related

• NEN-EN-IEC 60204-1 — electrical safety of machinery
• NEN 3140 inspection — what, how often, by whom