Checking the Installation Site

Checking the Working Environment, Site Temperature, Humidity, and Altitude

The S12700 and S12700E series switches are for indoor use only. Ensure that the temperature, humidity, and altitude in the installation site meet the following requirements:

• The installation site must be clean, dry, well ventilated, and free from leaking or dripping water and dew.
• The installation site must be as free from dust as possible. A buildup of dust may cause electrostatic discharge on the chassis and impair electrical connections, which will reduce the service life and may cause failure of the switch.
• The switch must be installed in an environment where the temperature and humidity are within specifications. For the operating temperature and relative humidity ranges required for your switch, see the Hardware Description. In environments where the relative humidity exceeds 70%, using dehumidifiers or dehumidifying air conditioners is recommended.
• The installation site must be free from acidic, alkaline, or corrosive gases.
• Keep the switches away from direct sunlight.
• Do not block the air intake vents (left) or air exhaust vent (rear) of the switch. Do not face heat sources of other devices towards the air intake vents of the switch. Ensure that the distance between the air exhaust vents of the switch and other devices or cabinets is greater than 500 mm. Otherwise, heat dissipation of the switch will be affected.
• Before placing a switch on a workbench, ensure that the workbench is level, stable, and grounded, and is strong enough to support the weight of a fully configured switch.
• Ensure that the switch is installed correctly and securely. There should be no external power cables in contact with the switch, as such cables may damage the switch through leakage current.

Measuring the Ground Resistance

• Do not measure the ground resistance immediately after a rain.

• The ground resistance in the equipment room should be lower than 1 ohm. In special cases, the ground resistance should be no more than 5 ohms (no more than 10 ohms in an area with high soil resistivity).

• The current probe and voltage probe of the ground resistance tester must be vertical to a power line or an underground metal pipe.

Use a ground resistance tester to measure the ground resistance. Figure 5-1 shows how to place the current and voltage probes of the tester.

Figure 5-1 Positions of the current and voltage probes

Pay attention to the following points when measuring the ground resistance:

• The distance between the current probe and edge of the ground grid is d1, which is 4 to 5 times the maximum diagonal length (D) of the ground grid.

• The distance between the voltage probe and edge of the ground grid is d2, which is 50% to 60% of d1.

• Move the voltage probe along the line between the ground grid and current probe three times, over a certain distance (5% of d1) each time. If the resistance values obtained in the three movements are similar, the ground resistance is normal.

If the current probe cannot be placed over a distance of d1 away from the ground grid, change the distance in this way: In an area with equal soil resistivity, take 2D instead of d1 and take D instead of d2. In an area with unequal soil resistivity, take 3D instead of d1 and take 1.7D instead of d2.