Conduit Installation Guidelines for Engineers
Conduit Installation Guidelines for Engineers
- All conduit shall be installed according to the contract drawings, the NEC, local codes, and this specification. If there is a difference in requirements, the most stringent shall apply. The conduit layout on the contract drawings, when shown, is diagrammatic and shall be verified by the contractor in the field. The contractor shall route conduit to avoid tripping hazards, blocking walkways, and access to valves and equipment. Conduit routing shall be coordinated with other trades and not interfere with dimensioned routings (for example, field piping including insulation, heating, ventilating and air conditioning (HVAC) ducting, or building cross bracing). Rigid or flexible conduit shall not use instrumentation or valves as a supporting method. This applies especially to solenoid valves, because the weight of the conduit destroys the casing and causes valve failure.
- All metal conduit shall be cut with a power hacksaw, band saw, or rotary pipe cutter. A (flute) reamer shall be used on the interior of the conduit until all burr is removed.
- All galvanized steel and aluminum conduit joints shall be coated with a metallic lubricant sealant (Lead Plate 250 as manufactured by Armite Laboratories or Crouse-Hinds STL).
- When conduit is run on pipe bridges or its own structure, the spans between structural members shall not exceed the requirements of the NEC.
- All metal conduit terminations shall have a nylon-insulating throat bushing, unless the termination is in a device having a threaded hub. Bushings and hubs shall be inspected for rough edges that can damage wire. All metal conduit terminating in nonmetallic enclosures shall have a nylon-insulating grounding bushing. All grounding bushings shall be jumpered together with a copper wire equivalent to the largest grounding conductor within the enclosure.
- All metal conduit stub-ups not directly connected to metallic enclosures by means of a locknut or equivalent connector (for example, conduit stub-ups into the bottom of motor control centers, switchgear, sub-station transformer terminal chambers) shall have a nylon-insulating grounding bushing. All grounding bushings shall be jumpered.
- RMC conduit connections to items such as, indoor sheet metal enclosures, panelboards, or pull boxes shall be made with two locknuts, one on the outside and on the inside along with an insulated throat grounding bushing. RMC conduit connections outdoors and in wet locations shall be made with Myers ‘Scru-tite’ hubs with grounding hubs or equal.
- All conduit runs to low-voltage motors (600 volts and below) in non-hazardous and Class 1, Division 2, hazardous areas shall have a section of liquid tight flexible conduit type LFMC at the motor terminal box to permit belt take-up and isolate vibration. Flexible conduit shall be routed and installed to avoid hot apparatus (for example, intercoolers or heaters).
- After all cables have been installed, all conduit runs terminating at cable trays shall be adequately sealed with an approved sealing compound, Polywater® FST or equal.
Conduit and Cable Entry into Equipment
- Conduit and cable shall enter field instruments, cabinets, terminal boxes, and switches at a bottom or side connection only. Drainage of water from the conduit system into instruments, cabinets, terminal boxes, or switches shall be prevented by the layout of the conduit and by installation of low point tees and conduit drains as required.
- Raceways passing through exterior walls of buildings or where subject to different temperatures shall be sealed per NEC using approved sealing compound, Polywater® FST or equal.
- Where raceway enters a building, structure or electrical equipment from an underground distribution system, it shall be sealed per NEC using approved sealing compound, Polywater® FST or equal.
- Spare conduits shall be installed as shown on the drawings. These conduits shall be cleaned and caps shall be installed at both ends.
- Above-ground Rigid Nonmetallic Conduit (RNC) installation requirements include:
- All bends shall be made only with bending equipment intended for the purpose.
- All joints shall be made using the PVC solvent cement according to the manufacturer’s recommendations. Solvent cement must be approved by the conduit manufacturer.
- Expansion couplings shall be installed in all conduit runs greater than 1.5 m (5 ft) per NEC and manufacturer’s recommendations. Expansion couplings shall be installed per manufacturer’s instructions based on maximum temperature change at location of installation.
- Conduit shall be supported with Carlon “Snap Strap” or equal wall hangers to allow for conduit expansion and contraction.
Cable Installation in Conduit
- A cable-pulling compound shall be used with all wire and cable pulls in conduit. The cable pulling compound shall be Polywater “J” (American Polywater Corporation). This compound meets the requirements of all currently approved MV cable suppliers. If substitutions are required, the compound shall be certified by the manufacturer of the cable as being harmless to the type cable used. No substitutions are permitted without written approval.
- Pulling of medium voltage cable in conduit shall be performed by using conductor for pulling, not only the insulation or cable jacket.
- The installation of low voltage cable shall be performed using industry accepted methods and tools manufactured for the pulling of wire and cable.
- A tension meter/recording device shall be used with all cable and wire pulls. Recorded data shall be made available for representative review.
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