Cable entry

The terminal box must be suitable for being turned through 180°, for bottom or top cable entry. 

In the cubicle construction of a switchgear assembly the busbar chamber is normally located at the top of the assembly and runs through the length of it. It is usually suitable for extension, through fish joints at either end, if required at a later date. For installations having top cable entry, the busbar chamber may also be located at the bottom of the assembly or the depth of the panel increased, with an additional shroud between the top busbar chamber and cable chamber. From these main busbars are tapped the vertical buses for each vertical panel. Manufacturers may adopt different practices for horizontal and vertical busbar arrangements to economize on their cost of production. We illustrate the most common types of busbar arrangements. 

Except for conduit or cable entries into explosion-proof enclosures containing arcing or high-temperature devices (as described in Item I above), cables that will leak gas through the core at a rate of less than 0.007 ft /hr at 6 in. of water pressure need not be sealed if they are provided with a continuous gas/vapor-tight sheath. Cables with such a sheath that will transmit gas at or above this rate must be sealed if connected to process equipment that may cause a pressure of 6 in. of water at the cable end. 

U = this mark indicates that the certificate is a component certificate for electrical equipment which cannot operate on its own (e.g. cable entries for enclosures in increased safety - e -). 

The General requirements cover apparatus grouping and temperature classification, constructional requirements for enclosures and fasteners, connection facilities and terminal compartments, cable entries and supplementary requirements for rotating electrical machines, switchgear, plugs and sockets and luminaires. A third part of the standards cover type verifications and tests as well as marking requirements. 

Additional requirements for q-apparatus, e.g. for means of closing, cable entries and bushings, protective devices for temperature limitation, type and routine verifications and tests, are specified in the q-standards. 

In general, there are four methods for cable entries in pressurized apparatus ... 

Test of clamping of non-armoured cables in cable entries... 

In a similar way, the maximum temperature of cables in rated service is limited to values of +70°C for the entry point and of +80°C for the branching point of the conductors in cable entries (this is a general requirement for all types of protection, given in EN 50014 and IEC 60079-0). 

It is noteworthy that the general efforts towards increased current densities -A/mm2 - in cables for economic reasons contradict the high power design of such switchgear, due to the temperature limitations for cable entries. Figures 6.40(a)-(d) show the relationship overtemperatures of entry and branching... 

Figure 6.40(a)-(d) Overtemperatures at branching points and cable entries versus thermal losses. Low voltage switchgear EEx de I. The thermal losses indicate the heat dissipation of fuses, magnetic coils and transformers in the d main part. Two cables (I, II) with 3 AC, 50cps, conductor cross-section 6 mm2, one cable with 3 AC, 50 cps, conductor cross-section 70 mm2, at different current densities a. 

In a very general sense, terminal boxes, regardless of their type of protection (increased safety or flameproof), ensure an additional cooling surface and a greater distance between the thermic critical cable entries and the source of heat losses, compared with direct cable entries into the flameproof main compartment of the apparatus. 

Figure 6.41 Cable entry with thread mount.

Figure 6.42 Cable entry with flange mount.

Examples for cable entries suitable for high voltage cables are given in Figs 6.43 and 6.44 (for cast resin heads only). 

Figure 6.43 Cable entry for high voltage cables with sealing heads (cast resin). Type of protection EEx e I, EEx e II Certificates BVS 89.B.1098, BVS 89.C.2022 For cables with diameter 50... 80 mm.

In general, cable entries according to IEC 60079-1 and EN 50018 shall withstand the explosion pressure inside the enclosure and shall ensure the flameproofness by an adequate design and construction of all mechanical parts. In addition, the general requirements stated in IEC 60079-0 and EN 50014 shall be fulfilled. On the whole, to pass a flameproof enclosure with electrical power or electrical and optical signals four methods have been established (Figs 6.80 and 6.81) ... 

Figure 6.80 Techniques for cable entries into a flameproof enclosure (left to right) ...

The cable for power or signal transmission passes the flameproof enclosure on the direct way via a cable entry complying with the d -standards. This technique has its origins in the United Kingdom and France (including their historical spheres of economical influence), and in the countries of the former Eastern bloc. Examples for direct cable entries are given in Fig. 6.82. 

In some countries, e.g. the United Kingdom, terminal compartments in d have been installed in front of the d -enclosure. Notwithstanding this separate terminal compartment, the requirements for this cable entry technique are identical with those for direct cable entries. For these d -terminal compartments, the same thermal considerations are valid as for e -terminals, given in Section 6.7.2. The cable entry point is shifted away from the main enclosure with all its thermal losses inside, the terminal compartment inserted hereby acts as an additional cooling surface. ... 

In this example, the flameproof enclosure is fitted with a terminal compartment in increased safety - e As an alternative, flameproof cable entries or conduits may be fitted. 

Figure 6.117 Flameproof vessel light fitting (cable entry via conduit).

Bolts, cable entry devices (direct and indirect) and blanking elements are of the correct type and are complete and tight... 

These cable entries comply with the requirements given in General requirements and Flameproof enclosure - d e.g. EN 50014 and... 

Fitting of additional cable entries, exceeding the scope of the C certificate in number and/or size... 

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