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EARTHING.doc (134 KB) Pobierz EARTHING Of EQUIPMENT Reasons for earthing equipment. Earthing is required to provide a low electrical resistance path from the fault to the supply. This is to ensure the operation of the fuses or circuit breakers, which are defined as safety critical items. The damage done to electrical equipment is proportional to the length of time the fault current is allowed to flow. The quicker a fuse or circuit breaker operates the less damage to the equipment occurs. The lower the electrical resistance, from the fault to the supply, the higher the current and the quicker the protection device will operate, limiting the damage to equipment This low resistance earth path also reduces the voltage at the fault point to as close as possible to earth potential. This reduces the voltage, which is present at the fault point to a level which minimises electrical shock, injury or death to personnel who may be in contact with the equipment at the time. The quicker the protection devices operate the less time there is for personnel to be in danger. API Recommendations API 14F sect 4.10.b API 14F sect 6.10.3.1 (1991) (1999) Equipment earth bonding / Grounding All exposed non-current carrying metal parts which may become live under fault conditions are too be earthed. Any equipment welded to the structure is classed as adequately connected. Skids and structures are to be connected to the main earthing system by cables of suitable size. The use of mounting bolts is not an acceptable method, and cannot adequately provide the low resistance path. Earth cables to the size given in the following tables are recommended Cables are to be bare or fully insulated and be coloured Green or Green with one or more yellow stripes. (Cable of other colours can be used as long as each end and the point of entry into enclosures, is clearly identified with permanent markings (Green & Yellow PVC tape)) These earth cables, green or green & yellow, are not to be used for any other purpose. EARTH CABLE SIZING AP1 Supply Cable Cross Sectional Size of Earth Cable Copper mm2 Area S mm2 S < 16 16 < S < 35 S > 35 S ( minimum 4mm2) 16 S/2 SUPPLY BONDING CABLES TAKING NEUTRAL CABLE SIZE. Cross section of neutral or main phase Minimum Cross sectional area of main conductor S mm2 equipotential bonding conductor mm2 S < 35 10 35 < S >50 16 50 < S > 95 25 95 < S > 150 35 150 < S 50 IEE offshore rules Table 2.2 Up to 3mm 3-125mm Over 125mm 1.5 stranded 3mm unstranded 50% but min3mm 64mm = 70mm ( standard size of cable) The neutral size is common to be smaller than the phase conductor on onshore distribution systems. It is common for rigs not to have neutral supplies. Caterpillar alternators have specific earthing requirements as indicated on the data plate, it gives the minimum size of earth conductors and is determined by the output of the alternator. Several rigs have DC generators for the DC motors. The earthing arrangements are to be the same with all exposed metal earthed to the skids and these skids connected by a cable with a size equal to the tables above for the largest cable supplying the skid. It would be envisaged 35mm2 would be the minimum. Flexible cables & Portable equipment Flexible cables with an internal earth core, of the same size as the conductor, used to supply equipment are classified as adequately earthed as the cable forms a direct path back to the supply point. This cable must be connected to earth at each end in addition to any junction boxes on the cable run. Land Rigs The use of flexible cables with internal earth cores needs to be carefully considered. On installations, which are disconnected for moves regularly, i.e. Land rigs, these must have a policy in place to test and record the earth connections on completion of any move. As this will add time and effort to the work the addition of external earth cables is recommended, as these will not be disturbed, and therefore will not be forgotten, during the moving of skid mounted equipment. ABS CABLE DATA ABS To 2.5 earth 2.5 2.5 to 8mm earth 4 8 and above earth A/2 120+ 70mm Earthing general requirements API 14F, IEE, AP1,Page 3 of 3 REV 1.0. 10-11-2001 Plik z chomika: martyrologia Inne pliki z tego folderu: Podstawy Elektroniki Tom.2.zip (4581 KB) Podstawy Elektroniki Tom.1.zip (3623 KB) elektrotechnika podstawy.doc (290 KB) Basic Switchboard Operation.pdf (9595 KB) DC Machine stuff.pdf (3348 KB) Inne foldery tego chomika: Zgłoś jeśli naruszono regulamin Strona główna Aktualności Kontakt Dla Mediów Dział Pomocy Opinie Program partnerski Regulamin serwisu Polityka prywatności Ochrona praw autorskich Caterpillar Chłodnictwo DP Nawigacja OIL RECORD BOOK Platforma wydawców Copyright © 2012 Chomikuj.pl