Supplement S1400

Guidelines for

System Grounding

- Contents -

IMPORTANCE OF GOOD GROUNDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

GENERAL RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

TRANSIENTS AND INTERFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

TYPES OF EARTH GROUNDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

SOIL CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

GROUNDING TECHNIQUES FOR 33XX SYSTEMS . . . . . . . . . . . . . . . . . . . 9 Several DPCs in Metal Cabinet w/ Power Supply . . . . . . . . . . . . . . . . . . . 10 Multiple DPC Cabinets w/ Local Supply in Each Cabinet . . . . . . . . . . . . 10 Multiple DPC Cabinets Powered by Single Supply . . . . . . . . . . . . . . . . . . 12 Multiple Clusters of DPC Cabinets Powered by Local Supplies . . . . . . . 14

IMPORTANCE OF GOOD GROUNDS

The equipment used with instrument systems must operate continuously within their stated accuracy over long periods of time with minimum attention. Since many system sites are unmanned and located in remote areas, failures resulting from an improperly grounded system can become costly in terms of lost time. A properly grounded system will help to: prevent electrical shock hazards resulting from contact with live metal surfaces; protect equipment from lightning strikes and power surges; minimize the effects of electrical noise and power transients; and reduce signal errors caused by ground wiring loops. Conversely, an improperly grounded system may exhibit a host of problems that appear to have no relationship to grounding. It is essential that the reader have a good understanding of this subject to prevent needless troubleshooting procedures.

Warning

This device must be installed in accordance with the National Electrical Code (NEC) ANSI/NFPA-70. Installation in hazardous locations must also comply with Article 500 of the code.

Supplement S1400 / 1

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Emerson Process Management 9110-00A, Series 9110, CI-9110 instruction manual Guidelines for System Grounding