Lift table in potentially explosive environment

If a lift table is used in a potentially explosive environment, special measures need to be taken. These measures need to ensure that the scissor lift table does not itself become a source of danger and cause an explosion triggered by a spark.

The danger in the potentially explosive environment

As the name of these zones already indicates, there is a risk that an explosion may be triggered in Ex zones. For this reason, it is essential to prevent sparks from occurring in such an area.

The following are the main sources of sparks on a scissor lift:

  • electric sensors that perform a switching operation and
  • the electrostatic charge of components.

Spark generation in electric sensors

When an electric sensor switches, two previously electrically connected components are separated from each other. At the beginning of the switching process, the air gap between these parts is still very small, so that the applied voltage can be sufficient to generate a spark between the switching elements.

There are two common solutions to prevent this problem:

  1. By encapsulating the switching elements.
  2. By reducing the applied voltage.


With encapsulation, the switching elements are separated from the potentially explosive atmosphere. This means that even if a spark is generated, it does not cause an explosion. The attached images clearly show that we have chosen this method.

Voltage reduction

As explained above, the spark is generated while the two switching elements are separated from each other. The cause of the flying sparks is the ionisation of the air by the applied voltage. If the applied voltage is limited to a very low level (lower than the flashover voltage), this also reduces the risk of sparking. All sensors in the endangered area are therefore supplied with very low voltage. The problem here is that the sensors can no longer be evaluated. This necessitates the use of an additional component, the isolation amplifier.
This isolation amplifier is placed outside the Ex zone in the control cabinet and raises the signal to a level that makes readout possible again.

Sparks due to electrostatic charge

We are all familiar with electrostatic charges. When we walk over a carpet, for example, and then touch a fellow human being or conductive object, we receive a shock.
The friction caused a voltage potential to build up in our body, which is suddenly discharged. This sudden discharge can generate a spark. Basically, the same thing happens here as with electrical sensors. The air between us and the opposite side is ionised and a spark is generated. The cause of this spark is again an applied voltage (different voltage potential between us and our surroundings).

To avoid the danger of sparking in the potentially explosive area, the build-up of a voltage difference must therefore be prevented. We achieve this by ensuring that all components have the same voltage potential. For all components to have the same potential, it must be ensured that they are conductively connected to each other. For this reason, all the lift table components, from the main assemblies to the safety edge tubes, are earthed to each other. This prevents a voltage difference from being built up by the movement of the lift table and a dangerous spark from being generated.

Ex-protected motor

Electric motors also need to be specially protected in an Ex zone. However, it is not possible to reduce the voltage in this case. This necessitates elaborate and therefore cost-intensive encapsulation.

To save our customers these costs, we use one of the great advantages of hydraulic lift tables. We separate the drive unit spatially from the cylinders. In this case, a six-metre-long hydraulic line enabled us to reach an area outside the Ex zone. As this places the motor outside the hazard zone, a commercially available under-oil unit can be used in this case.

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