Steel conduit

Figure 7.15 General thinning along the bottom of a steel conduit carrying carbonic acid-laden water.

Cathodic Protection of the Steel Conduits for Power Cables... 

In 110-kV high-voltage grids, gas pressure cables (external and internal gas pressure cables) are mainly laid in steel conduit. In service, the steel pipe is filled with nitrogen at a gas pressure of 15 to 16 bar. Figure 14-1 shows the cross-section of such an external gas pressure cable. 

Fig. 14-2 High-voltage cable grounded via dc decoupling devices (1) high-voltage installation, (2) insulating flange, (3) cable branching, (4) cable end sealing, (5) steel conduit, (6) dc decoupling devices.

This value is the basic standard that AWWA M-II specifies for steel conduit and pipe, as do the ASTM and ASME. As is obvious, there are a number of factors that contribute to pipe deflection. These are the external loads that will be imposed on the pipe, both the dead load of the overburden as well as the live loads of such things as wheel and rail traffic. The factors affecting RTR pipe deflection can be summarized as follows ... 

Wetted instrument parts and pockets generally in accordance with wetted plant items in applicable area. Transmitter housings generally coated as structural steelwork above or constructed from 304L stainless steel according to availability and life-cycle cost. Cable insulation to be PVC, and carbon steel conduit (coated in accordance with guidance above) to be employed throughout. 

Electric cables should be carried in steel conduits on the exterior of the walls. Incandescent lamps inside the building should be recessed into the walls and pro-... 

Steel conduits are made to a specification defined by BS 4568 and are either heavy gauge welded or solid drawn. Heavy gauge is made from a sheet of steel welded along the seam to form a tube and is used for most electrical installation work. Solid drawn conduit is a seamless tube which is much more expensive and only used for special gas-tight, explosion-proof or flameproof installations. 

The advantages of a PVC conduit system are that it may be installed much more quickly than steel conduit and is non-corrosive, but it does not have the mechanical strength of steel conduit. Since PVC conduit is an insulator it cannot be used as the CPC and a separate earth conductor must be run to every outlet. It is not suitable for installations subjected to temperatures below 25°C or above 60°C. Where luminaires are suspended from PVC conduit boxes, precautions must be taken to ensure that the lamp does not raise the box temperature or that the mass of the luminaire supported by each box does not exceed the maximum recommended by the manufacturer (lET Regulations 522.1 and 522.2). PVC conduit also expands much more than metal conduit and so long runs require an expansion coupling to allow for conduit movement and to help prevent distortion during temperature changes. 

PVC cabies encased in soiid drawn heavy-gauge screwed steel conduit terminated at approved enclosures having wide flanges and bolted covers. 

A steel conduit installation would be suitable for the following type of installation ... 

Where steel conduit or trunking forms the protective conductor, the standard test described above may be used, but additionally the enclosure must be visually checked along its length to verify the integrity of all the joints. 

Joints in steel conduit should be of the threaded type, tight fitting and painted to exclude moisture so as to avoid corrosion and an adverse effect on earth continuity. 

---