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4.1.8 Grounding the System (Not for U.S.)

Note on Possible Ground Loops

 
To avoid ground loops from remotely operated devices (V.24 [RS-232] system peripherals), the devices should be connected to the same low-voltage network (sub-distribution board) if possible.  
If the building floor plan does not permit this, you may need a line driver to isolate the external devices if any malfunctions occur.  

 
DANGER  
If one or two surface-mounted expansion cabinets are used in addition to the base cabinet, the metal connecting plates must be installed to properly ground the expansion cabinets. 
Failure to follow these instructions can result in electrical shock. 
The Hicom 150 E OfficePro system and the MDFU or MDFU-E must be grounded by a separate protective ground conductor (minimum cross-section: 2.5 mm2) as shown in Figure 4-12. Make sure that the ground conductor is securely installed and strain-relieved. 

Protective Grounding Options (Not for U.S.)

The illustrations starting with Figure 4-13 show different grounding options.
 
DANGER 
If your personnel are not qualified to work on the low-voltage network (230 Vac), you must hire a licensed electrician to install the ground using option 1b (Figure 4-14) or option 2 (Figure 4-15).  

Grounding the System and Main Distribution Frame (Not for U.S.)

Figure 4-12 Hicom 150 E OfficePro-Grounding the System and Main Distribution Frame (Not for U.S.)

Protective Grounding Option 1a (Not for U.S.)

Figure 4-13 Hicom 150 E OfficePro-Protective Grounding Option 1a (Not for U.S.)

Protective Grounding Option 1b (Not for U.S.)

Figure 4-14 Hicom 150 E OfficePro-Protective Grounding Option 1b (Not for U.S.)

Protective Grounding Option 2 (Not for U.S.)

Figure 4-15 Hicom 150 E OfficePro-Protective Grounding Option 2 (Not for U.S.)

4.1.9 Grounding the System (for U.S. Only)

Grounding the System Cabinets

The system cabinets are grounded by their power cord, but an earth ground is also required. Choose an earth ground with less than 2 ohms of resistance, such as:

Master ground busbar
Ground field
Copper ground rod

Run an earth ground conductor from the earth ground to the cabinet frame ground located in the center of the backplane. The minimum cross-section required is 14 AWG.

Figure 4-16 on page 4-32 shows the earth ground connections for the basic cabinet (BC). If expansion cabinets are added to surface-mounted systems, the metal connecting plates bond them to the basic cabinet. If two cabinets are mounted on the wall, the second cabinet requires an earth ground as well. Do not use the metal connecting plates on wall-mounted systems.

Earth Ground (for U.S. Only)

Figure 4-16 Basic Cabinet Earth Ground (for U.S. Only)

Grounding the Main Distribution Frame (for U.S. Only)

Follow the manufacturer's instructions for grounding the main distribution frame.

4.1.10 Checking the Protective Grounding

Procedure

Perform the tests in the table below to ensure that the system is properly grounded before startup.
Step 
Activity 
Target 
1.  
Measure the ohmic resistance of the ground connection between the ground bus and the system. 
< 1 ohm 
2.  
Measure the ohmic resistance of the ground connection between the protective ground conductor or PE of the ac power cable and the metal frames of the cabinets. 
< 1 ohm 
3.  
Measure the ohmic resistance to ground from the supplementary ground or PEN (protective earth neutral) conductor of the socket used.  
< 10 ohms 

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