To Use… or NOT to use.. Conduits or Cables

Conduit or Cable for Ex d or Ex de Enclosures

The term ‘Conduits’ refer to the use of Ex-certified metallic pipes to house the insulated electrical wires for transfer of electrical current.

To use conduits or cables in a certain hazardous location depends mainly on the specifications governing the whole situation and scenario. The rule of thumb is : If the specs being followed are NEC 500 then conduits .. if the specifications belong to the NEC 505 OR IEC 60079 family of documents then CABLES will be the choice.

In principle there are three methods of providing electrical connections:

Cables system with indirect cable entry, through separate Connection Boxes
Cables system with direct entry
Conduit Systems

Cables Systems with indirect and direct entries are specified in IEC complied systems and Conduit systems are only permitted in accordance with NEC 500.

Cable Systems:

Cable systems are mainly used in countries following IEC code. For this, high-quality cables, armored or unarmored, are laid uncovered. It is only in areas in which mechanical damage could be expected that they are laid in conduits that are open at both ends. (The ends of the conduits may require sealing for the purpose of VERMIN Proofing)

Method No.1

Cable is installed through Ex e / Exed Metallic or non-metallic, certified cable glands

Method No.2

Method No.3 (NEC Specified )

Merits & Demerits of the three systems of connecting an Ex d or Ex de enclosure to an electrical network.

Conduit System:

It is strong & robust
Fire-proof (all metal)
High cost of installation
Time consuming installation
Possibility of corrosion
High cost of changes/augmentations (Rigid design)
INSTALLER is responsible for Ex Integrity (Flameproof) because all installation is carried out on site.

Direct Cable Entry

Flexible & thus fast installation
Flexible design for changes
Low cost of maintenance
Cables require protection from damages
INSTALLER is responsible for Ex Integrity (Flameproof) because all installation is carried out on site.

Indirect Cable Entry

Flexible & thus fast installation
Flexible design for changes
Low cost for maintenance
Cables require protection from damages
Manufacturer is responsible for Ex Integrity (Flameproof) .Cables are just connected into the Ex e enclosure at site

Some Important Remarks from IEC 60079-14 (Edition 5)

No. 1

No.2

The OPEN CONDUIT SYSTEM

Conduits can be used for Mechanical Protection ONLY. Cables are drawn through the conduits and the ends of the conduits remain open . However some sort of sealing is definitely required to prevent the :-

Ingress of VERMIN inside the conduit
Prevent the flow of rain water though the conduits

This system is in contrast to the STANDARD SYSTEM of Conduit Installation (As per NEC 500)

(Example : The cables are connected through cable glands and protected by open conduits )

Another example of OPEN CONDUITS . (Control station is connected through non-metallic Cable Gland and connecting cable is protected through a open conduit. )