Protective earth (PE)

The housings of the ELM/EKM series are made of die-cast zinc and are thus metallic. This results in a need for clarification regarding the use of protective earthing against the risk of electric shock.

Attention: The relevant application standards refer to the surrounding control cabinet/control box as "housing", whereas this documentation refers to the Beckhoff terminal as "housing".

See also chapter "Notes regarding analog equipment - shielding and earth" in this documentation.

The housing offers the option of an M3 bolted connection for connecting a ring terminal to PE.

The procedure for this is as follows:

• Lever off the plastic cover from the ELM housing and retain if for later reuse, if required
• Secure the previously prepared ring terminal, which was crimped to the protective conductor, using an M3x4 screw; max. torque 0.5 Nm. Use a suitable tool.
  ATTENTION: The screw must not be longer than specified, in order to avoid it protruding into the interior, where it could cause damage. This would be evident if the unit is sent in for repair.
• Connect the PE cable to the protective conductor system.

Notes on whether a PE connection is necessary in the specific application

• A PE connection is required if the terminal could pose a risk of electric shock due to an inadmissible contact voltage. A distinction is made between two causes:
• if the terminal is subjected to high internal voltages (not SELV/PELV), this high voltage may reach the housing in the event of a fault. For such terminals, a PE connection is essential. See the corresponding mechanical options at the module. For background information please refer to product and device standards such as EN 61010.
  Note: The terminals of type ELM3004, ELM3002, ELM3104, ELM3102, ELM3504, ELM3502, ELM3604, ELM3602, ELM3704, ELM3702 operate with low voltage SELV/PELV, so that there is usually no potential risk.
• A connection to the protective earth conductor system must nevertheless be provided if the terminal operates with protective extra-low voltage (SELV/PELV), but there is a risk that a live conductor may come into contact with the housing in the event of a fault, resulting in unacceptable touch voltage. This is stipulated by application standards such as EN60204‑1 or EN61439‑1 relating to control cabinet design.
• It is therefore always necessary to check in which environment the application is used to ascertain whether a PE connection is required.

Note on protective earth (PE) with regard to analog measurements

The protective earth conductor system is specifically designed for discharging high currents. This may result in significant high-frequency interference, which could adversely affect an analog measuring device if it is/has to be connected to the protective conductor system. In such cases, a strictly star-shaped configuration of the FE and PE systems may be advisable, in order to have as few interference sources as possible on the PE system that are close to the analog measuring system. Ideally, no PE connection should be used at all. However, in this case the installation must comply with the two conditions referred to above, which may necessitate splitting the system into a high-voltage and a low-voltage control cabinet, so that no PE would be required for the latter.