MTEK6000 SERIES USER'S MANUAL
GROUNDING
The information presented here is merely a guideline to help customers avoid surge damage to the MTEK6000. None of these guidelines are to be construed as replacing or superseding rules and practices defined by the National Electrical Code (NEC), or the Classification of
Gas Utility Areas for Electrical Installations guidelines, as published by the American Gas Association (AGA) or other regulatory agency. A sound understanding of Federal, State and Local laws is fundamental to proper and legal installation work.
The MTEK6000 is configured so that the majority of the internal metal components within the device are connected (common) to the gas pipeline / meter to which the instrument is attached. Additionally, a large surge bypass MOV device has been provided inside the MTEK6000 that provides an alternate path (rather than through the correctors electronics!) for surge current to flow. One side of this device connects to the pipe through the index & meter. The other side is brought out through the enclosure to an external copper grounding lug. The separation of these two points allows for the existence of cathodic protection voltage levels on the pipe (typically about 1 volt below the surrounding soil) while still providing a path for surge current to safely bridge these points, find earth ground, and not damage the instrument.
If the MTEK6000 is to be connected to a telephone line (either
case it is of no benefit to earth ground the MTEK6000’s external lug.
When the external ground lug of the MTEK6000 is to be used, it should be connected to a common ground rod (or "bed" of grounding equipment) to which is securely tied all other equipment chassis, metal cabinets, and intrinsic ground brackets. Solid copper ground wire or ground strapping of an approved size and type must be used to tie this equipment to the rod. If possible, it is far preferable that all external equipment be tied to a single site ground, that the distance between the MTEK6000 and external equipment is kept at a minimum (less than 20 feet is best), and the ground rod be located no farther than halfway between the MTEK6000 and the other equipment.
If separate site grounds must be used, as when the MTEK6000 and UPS are separated by a distance greater than 20 feet, Metretek can provide an optional device, the SPM (Surge Protection Module). A pair of SPMs can properly protect both devices in this circumstance. Control drawings detailing proper wiring of SPMs (including hazardous areas) are included with the SPM.
REFERENCES
•National Electrical Code (NFPA): Article 250 – Grounding Articles 500 & 501- Hazardous (Classified) Locations
Article 504 - Intrinsically Safe Systems
•The IAEI Soares' Book on Grounding (Available through the NFPA)
•PolyPhaser Corp. Catalog of Lightning / EMP & Grounding Solutions Minden, Nevada (800)
January 2002 |