UL-60079-30-1:2017 pdf free download – STANDARD FOR SAFETY Explosive Atmospheres – Part 30-1: Electrical Resistance Trace Heating – General and Testing Requirements.
4.2 Mechanical strength
The mechanical strength of trace heaters shall be determined by the tests in 5.1.5, 5.1.6, 5.1.7 and 5.1.11.
Trace heaters which are identified for use only in areas with a low risk of mechanical damage are subjected to a reduced energy in the impact tests in 5.1.5 and a reduced force in the deformation test in 5.1.6, and shall be clearly marked as specified in 7.4 e).
Trace heaters may be supplied with additional mechanical protection to meet the requirements of this standard if they are supplied as an integral assembly (prefabricated), and contain the following statement in the instructions: “This mechanical covering shall not be removed and the trace heaters shall not be operated without the mechanical covering being in place”. In this case the tests in 5.1.5 and 5.1.6 shall be performed with the additional mechanical protection installed on the trace heater.
4.3 Terminations and connections
Terminations and connections may be identified as an integral part of a trace heater, or may be identified separately, as Ex equipment or as Ex components in accordance with IEC 60079-0. Integral terminations and connections are tested as part of a representative trace heater unit; see 5.1.1.
Electrical connectors supplied with integral components shall be certified for the current-carrying capacity of the trace heating conductors declared by the manufacturer and shall meet the other prescribed testing in this standard.
Electrical resistance trace heater terminations identified as separate components shall comply with the requirements of one or more of the types of protection listed in IEC 60079-0 suitable for the application, which may be supplemented and modified by the requirements of this standard. See also Table 1.
4.4 Circuit protection requirements for branch circuits
The minimum requirements for trace heating systems for use in explosive atmospheres are as follows:
a) a means of isolating all line conductors from the supply;
b) over-current protection provided for each branch circuit;
c) a means of protecting against earth faults by disconnecting all line conductors.
1) For TT and TN systems, each trace heater or trace heater branch circuit, the electrical
protection shall be capable of interrupting high impedance earth faults as well as shoricircuit
faults. This shall be accomplished by an earth-fault protective device, or a controller with earth- fault interruption capability for use in conjunction with suitable circuit protection. The preferred
trip level is nominal 30 mA or 30 mA above any inherent capacitive leakage characteristic of the heater as specified by the trace heater supplier.
2) For IT systems, an electrical insulation monitoring device shall be installed to disconnect the supply whenever the electrical resistance is not greater than 50 1IV of rated voltage.
Exception: Where conditions of maintenance and supervision ensure that only qualified persons service the installed systems, and continued circuit operation is necessary for the safe operation of the equipment or processes, earth-fault detection without interruption is acceptable if alarmed in a manner to assure an acknowledged response.