This article is about Material Selection Guide and Technical specification of Galvanized Rigid Steel (GRS) Conduit & Fittings (PVC Coated & HD Galvanized) for commercial buildings, plants and refinery projects as per international codes and standards.
| Direct buried conduit shall be PVC conduit Type DB-120 (minimum modulus of elasticity 500,000 psi) per NEMA TC 6 & 8 or Type EPC-40-PVC per NEMA TC 2. Exception: Direct buried conduit in class I division I shall be threaded, rigid steel, hot dip galvanized and PVC coated. |
| Concrete encased conduit shall be PVC conduit Type EB-35 or DB-120 (minimum modulus of elasticity 500,000 psi) per NEMA TC 6 & 8 or Type EPC-40-PVC per NEMA TC 2. |
| Conduit installed exposed (e.g., not embedded in walls) above ground in outdoor, industrial facilities shall be threaded, rigid steel per ANSI C80.1, and in addition it shall be hot-dip galvanized. |
| Conduit above ground in severe corrosive environments shall be as specified in SAES-P-104 Sec. 8.2 and, in addition, shall be factory PVC coated (minimum thickness of PVC: 40 mils ( 1 mm ) per NEMA RN 1. |
| GRS Conduit and Fittings Listing: All GRS conduit, factory GRS elbows, GRS couplings, and associated GRS fittings (i.e., uncoated and PVC-coated) shall be third-party listed as meeting the requirements of UL standards (UL 6, 514A, 514B, and 886 as applicable, or approved equal standards). [NFPA 70 NEC 344.6 and Annex A] |
Galvanized Rigid Steel (GRS) Conduit and Fittings Technical Specification & General Requirements
| GRS Conduit System Materials: Where practicable, dissimilar metals in contact anywhere in the system shall be avoided to eliminate the possibility of galvanic action. [NFPA 70 NEC 344.14] |
| Conduit fittings for outdoor rigid steel conduit and liquid-tight flexible metal conduit shall be cast or forged steel, cast iron or malleable iron, either hot-dip galvanized (preferably), or zinc electroplated as supplied by the manufacturer. No aluminum fittings or fitting accessories such as covers, sealing fitting plugs, etc., shall be used outdoor. Gray cast iron split type (EYSR) retrofit sealing fittings may be used if required for repair purposes. Exception: Rigid steel conduit and liquid-tight flexible metal conduit hubs manufactured from zinc, that are UL or CSA listed (e.g., Myers Scru-Tite hubs) are also acceptable. |
| GRS Conduit Fittings: GRS conduit sealing fittings shall be malleable iron. |
GRS Conduit Fittings: Conduit fittings for rigid steel conduit and liquid-tight flexible metal conduit used above ground in severe corrosive environments shall be as specified in B2 & B3 above (SAES-P-104 Sec. 8.9.1) and in addition, shall be protected by one of the following methods:
(a) Factory-coating with PVC (minimum thickness of PVC: 40 mils) per NEMA RN 1
(b) Field-coating prior to installation in accordance with SAES-H-101 APCS-22 (offshore), or APCS-26 (onshore), or
(c) By heat-shrinkable tubes or wrap-arounds, where the geometric configuration permits it.
| GRS Conduit Fittings: Conduit fittings for direct buried PVC coated rigid steel conduit shall be factory PVC coated. |
| New and Unused – Electrical materials shall be new and unused. |
| As Designed – Electrical materials shall be in accordance with the Saudi Aramco-approved project-specific design drawings, diagrams, schedules, lists, databases, and associated documents. |
| Free of Damage – Electrical materials shall be free of damage. |
| QC Before Installation – Electrical materials shall conform to all applicable requirements, standards, and specifications prior to release to be used as part of the work. |
| Identification – Electrical materials shall be identified by using tags, stamps, color coding, stencils or labels. The location and method of identification shall not affect the function or quality of the materials. |
| Traceability – Electrical materials shall be traceable from the manufacturer and supplier through delivery, storage, fabrication, erection, installation, repair, modification and use. |
Galvanized Rigid Steel (GRS) Conduit and Fittings – General Dimensional Requirements
| GRS Conduit Dimensions: Dimensions shall be in accordance with Attachment 1, Table 2. [ANSI/NEMA C80.1 Sec. 6.5] |
| GRS Conduit Minimum Size: The minimum conduit size shall be ¾ inch or equivalent in metric size, except for prefabricated skids. |
| GRS Conduit Maximum Size: Conduit larger than 155 mm (6 inch) trade size shall not be used. [NFPA 70 NEC 344.20(B)] |
| GRS Conduit Length: Standard GRS conduit shall be 3.05 m (10′-0″), including an attached coupling, and each end shall be threaded. Longer or shorter lengths with or without coupling and threaded or unthreaded shall be permitted. [NFPA 70 NEC 344.130] |
GRS Conduit Bending: Bends of GRS conduit shall be made so that the conduit is not damaged and the internal diameter of the conduit is not effectively reduced. The radius of the curve of any field bend to the centerline of the conduit shall not be less than indicated in Table 2, Chapter 9 (See Attachment 2). [NFPA 70 NEC 344.24]
| PVC-Coated GRS Conduit: Thickness of polyvinyl chloride (PVC) coating shall be a nominal 0.040 in. (1.02 mm). The tolerance on the coating thickness shall be +0.010 in. (0.25 mm) or -0.005 in. (0.13 mm). [NEMA RN 1 Sec. 3.1] |
| PVC-Coated GRS Conduit Coupling Sleeves: Length of PVC sleeve extensions shall be at least equivalent to the nominal conduit size for trade sizes up through 2 inches (53 mm). For trade sizes 2-1/2 inches (63 mm) through 6 inches (155 mm), the length of the sleeve extension(s) shall be at least 2 inches (50.8 mm). [NEMA RN 1 Sec. 3.5] |
| PVC-Coated GRS Conduit Coupling Sleeves: PVC sleeve nominal thickness shall be 0.040 in. (1.02 mm). The inside diameter (ID) of the overlapping sleeve shall be less than the outside diameter (OD) of the PVC-coated conduit. [NEMA RN 1 Sec. 3.5] |
Galvanized Rigid Steel (GRS) Conduit and Fittings – General Threading Requirements
| GRS Conduit Threading: Running threads shall not be used on conduit for connection at couplings. [NFPA 70 NEC Art. 344.42(B)] |
| GRS Conduit Thread Protection: Thread protectors shall be used on the exposed threads of the coated conduit. [NEMA RN 1 Sec 2.4] |
| GRS Conduit Threading: Conduit and threaded conduit fittings shall have tapered NPT threads in accordance with ANSI/ASME B1.20.1. |
| GRS Conduit Threading: The number of threads per inch (threads per 25.4 mm), and the length of the threaded portion at each end of each length of conduit, nipple and elbow shall be as indicated in Table 1, and shall conform to ANSI/ASME B1.20.1. The perfect thread shall be tapered for its entire length, and the taper shall be 1 in 16. [ANSI/NEMA C80.1 Sec. 6.6] |
| GRS Conduit Threading: Where conduit is threaded in the field, a standard cutting die with a 1 in 16 taper (3⁄4-in. taper per foot) shall be used. [NFPA 70 NEC 344.28] |
| GRS Conduit Threading: All cut ends shall be reamed or otherwise finished to remove rough edges. [NFPA 70 NEC 344.28] |
| GRS Conduit Threading: Field cut conduit threads shall be coated with a zinc rich protective coating. |
| GRS Conduit Fitting Threads: Threads of plugs, junction boxes and other fittings shall be lightly lubricated with a rust preventive grease such as Crouse Hinds thread lubricant (1000405418) or High Purity Goop (1000174895) before assembly. |
Galvanized Rigid Steel (GRS) Conduit and Fittings – Finishing and Identification Requirements
| GRS Conduit Marking: GRS Conduit Marking: Each length of conduit, elbow, and nipple shall be marked “Rigid Steel Conduit”, along with the manufacturer’s name, trade name, or trademark or other descriptive marking by which the organization responsible for the product can be identified. [ANSI/NEMA C80.1 Sec. 9.1.1] |
| GRS Conduit Marking: Nipples with unthreaded areas less than 2 inches (51 mm) long may be marked in accordance with the requirements of 9.1.1 on the smallest unit of shipping carton. [ANSI/NEMA C80.1 Sec. 9.1.2] |
| GRS Conduit Marking: Each coupling shall be die-stamped “EC” (electrical coupling) in letters not less than1/8-inch (3 mm) high. [ANSI/NEMA C80.1 Sec. 9.1.3] |
| GRS Conduit Marking: Conduit marking shall be at a minimum of once every 10 feet (3.05 m) and no less than once every piece. [ANSI/NEMA C80.1 Sec. 9.1.2] |
| GRS Interior Surface: The interior surface shall be free from injurious defects. [ANSI/NEMA C80.1 Sec. 5.3] |
| GRS Conduit Coating: The conduit shall be adequately cleaned before the application of the protective coating. The cleaning process shall leave the exterior and interior surfaces of the conduit in such a condition that the protective coating shall be smooth and adhere firmly. [ANSI/NEMA C80.1 Sec. 5.5] |
| GRS Conduit Exterior Coating: The exterior surface shall be either thoroughly and evenly coated with metallic zinc or protected with an alternate corrosion resistant coating (ACRC) (as specified in the 13th edition of UL 6 in Clauses 5.3.3, 6.2.4, 7.8 and 7.9). [ANSI/NEMA C80.1 Sec. 5.6.1] |
| GRS Conduit Interior Coating: The interior surface shall be protected by a zinc, or an organic coating. The interior coating shall have a smooth continuous surface. An occasional variation due to uneven flow of coating shall be acceptable. [ANSI/NEMA C80.1 Sec. 5.6.2] |
| GRS Conduit Finish: The exterior and interior surfaces shall be free from slivers, burrs, scale, or other similar injurious defects, and coverage of the coating shall be complete. [ANSI/NEMA C80.1 Sec. 8.2 and 5.3] |
| PVC-Coated GRS Conduit Exterior Coating: The PVC coating shall be free of blisters, bubbles, and pinholes. The PVC coating shall be continuous over the entire length of the conduit except at the threads, and shall be holiday-free at the time of manufacture. [NEMA RN 1 Sec. 3.6] |
| PVC-Coated GRS Conduit Coating – The inside of the PVC-coated conduit, couplings, and elbows shall be free of the PVC coating material. All sleeve extensions shall be square cut. [NEMA RN 1 Sec. 3.6] |
| PVC-Coated GRS Conduit Adhesion Test: The adhesion of the PVC coating to the conduit shall be greater than the strength of the coating itself. This shall be determined by making two circumferential cuts, above 1/2 in. (12.7 mm) apart, through the plastic to the substrate. A third cut shall be made perpendicular to and crossing the circumferential cuts. The edge of the plastic shall be carefully lifted with a knife to form a plastic tab. This tab shall be pulled perpendicular to the conduit with a pair of pliers. The plastic tab shall tear rather than any additional coating film separating from the substrate. [NEMA RN 1 Sec. 3.8] |
| PVC-Coated GRS Conduit: Any supplemental interior coating shall be smooth and continuous and shall be unaffected by heat of the exterior coating process. [NEMA RN 1 Sec. 2.3] |
| PVC-Coated GRS Conduit Couplings: Each coated coupling shall have a flexible PVC sleeve which extends from each end of the coupling and which will overlap the PVC coating on the conduit when the coupling has been installed on the conduit. [NEMA RN 1 Sec. 3.5] |
International Codes and Standards
| 1. NFPA 70 – National Electrical Code (NEC), 2008 Edition |
| 2. SAES-P-104 – Wiring Methods and Materials, January 2008 |
| 3. ANSI / ASME B1.20.1 – Pipe Threads, General Purpose (Inch), 1983 (R2006) |
| 4. ANSI / NEMA C80.1 – American National Standard for Electrical Rigid Steel Conduit, 2005 |
| 5. NEMA RN 1 – Polyvinyl-Chloride (PVC) Externally Coated Galvanized Rigid Steel Conduit, 2005 |
| 6. UL 6 – UL Standard for Safety Electrical Rigid Metal Conduit Steel, Thirteenth Edition |
| 7. UL 514A – Metallic Outlet Boxes, February 2004 |
| 8. UL 514B – Conduit, Tubing, and Cable Fittings, February 2004 |
| 9. UL 886 – Outlet Boxes and Fittings for Use in Hazardous (Classified) Locations – 2005 |
Table 2 – Dimensions and Weights for Rigid Steel ConduitA – ANSI/NEMA C80.1
Table 2, Chapter 9 – Radius of Conduit and Tubing Bends – NEC 2008
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