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How Do I Ensure Proper Grounding for Rotem Equipment

Why do I need a “Good Ground”?

  • Safety:

     * Electrical equipment can be destroyed or slowly damaged by voltage spikes, lightning hits, etc.
     * Proper electrical grounding in combination with the controller’s internal protections is essential to protect the system

  • Noise Protection:

    * To reduce interference from power sources, switching power equipment, RF noise, cross-talks and other sources of interference.
    * Properly grounded metallic shields of the signal cables effectively prevent noise from entering into the system.  For example, loose or exposed wires become antennas for radio frequency signal pickup, and can form loops that radiate noise.

What is Proper Grounding?

  • Ground Rods: Ground rods are used to efficiently connect the system to earth where current dissipates in the soil.
  • Ground Wire: The ground wire is a large copper wire that connects the main circuit breaker panel to the ground rod.
  • Ground Clamps: Ground clamps are used to attach a ground wire to a ground rod. It is not enough to wrap the wire around a ground rod.

Measuring Ground Resistance Accurately

Ground connectivity must be measured at the controller’s ground wire!

  • Special Ground Testers

    * Enables measuring ground resistance without breaking the circuit
    * Available from various manufacturers (just Google)
    * Price range is ~1000$ at resellers, < 500$ at E-bay

  • Other methods are not reliable

    * Standard voltmeters do not show ground absence or high ground resistance
    * Visual inspection cannot be relied on!

Technical Details

The following information provides specific information about grounding Rotem equimpment.

Ground Rod

The ground rod's resistance must not exceed 5 Ohm.

Controllers

The power ground source from the electrical enclosure must be directly wired to the controller ground bar.

Power Terminal

The controller must be grounded through the dedicated ground terminal.

Sensors, Scales, and Signal Cables

Sensors, bird an silo scales, and other cable shields must be grounded at the controller .

Note: Use 22 AWG or lower, shielded cable only!

Communication Cable

Communication cable shields must be connected only at one end of every cable.

Silo

The silo's metal body should be grounded locally.

Roof

A metallic roof must be grounded properly.  Attach air terminals to the roof ridge and other high points and connect them to grounding electrodes on opposite corners of the building with a main connecting wire.

A ground connection should be provided at diagonal corners of the structure. Larger buildings (more than 250 feet in perimeter) should have additional grounding connections. A grounding connection to the earth every 100 feet along a building is recommended. A main wire should be run from the earth ground on one corner, over the building connecting each air terminal and terminating at the other earth ground.

 

Filtering Requirements

  • Required for noise protection
  • Some equipment (for example power inverters used with solar panels or frequency drivers used with variable speed fan drives) might inject noise into power line
  • There is mandatory filtering for such equipment by the state/country regulations
  • The filter specification is provided by equipment manufacturer