Siemens SIMATIC PCS 7 OSx - Earth Ground; Isolating Ground and Neutral from Conduit

Hardware Overview
1-12
SIMATIC PCS 7 OSx 4.0.0 Hardware (PA RISC)
Power Requir ements (continued)
Ensure that the AC power receptacle is properly grounded to earth. In some
installations, a metal conduit that connects to the neutral phase at the
circuit-breaker box supplies the earth ground of the power receptacle.
Depending on site conditions, this metal conduit may conduct current from
other sources that can interfere with the operation of a computer or printer
plugged into the socket.
T o minimize this possibility , isolate earth ground and neutral from the
conduit (except at the service entrance housing); see Figure 1-2 . Use a
receptacle wired in accordance with National Electrical Manufacturers
Association specification, NEMA 5-15R. Also, follow these guidelines.
• Ensure that the protective ground wire resistance is less than 1 ohm.
• Ensure that the resistance to earth ground does not exceed 1 ohm;
ideally it should be 0.1 ohm or less.
Power
Company
Earth
Ground
Earth
Ground
Rod
Power
Company
Transformer
Service
Entrance
Conduit
Conduit
Hot
Neutral
Circuit
Breaker
Panel
Data T erminal or
Computer Equipment
Receptacle
Protective
Ground
Figure 1-2 Isolating Gr ound and Neutral from Conduit
Earth Gr ound