Seeking advice on the explosion protection rating for instrument explosion-proof boxes
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There is an instrument wiring box under the pipe gallery (far from the main equipment), with a designed explosion protection rating of ExdⅡBT4. The expert inspectors believe that there is a hydrogen pipeline in the pipe gallery, and the explosion protection rating for gases in this case does not match; therefore, it should be changed to Exd CT4. The design agency cannot be contacted. Please help answer: what criteria are used to determine the explosion protection rating at the pipe gallery? Is what the expert says reasonable?
If hydrogen is present, CT4 is required. Although the possibility of hydrogen spreading to this junction box is very low, it cannot be ruled out entirely. We generally apply CT4 to the entire area containing hydrogen-containing equipment and the surrounding pipelines, in order to avoid such awkward situations.
The ductwork has good ventilation and is generally classified as Zone 2; you can refer to the explosion-proof zone classification diagram prepared by the electrical engineering team for guidance. The junction boxes in Zone 1/2 can be of increased safety type or explosion-proof type, as specified in 8.1.11 of the \"HG/T 20512-2014 Code for Design of Instrument Piping and Wiring\". Since you are using an explosion-proof type, it is necessary to meet both the gas group and temperature group requirements; the expert is correct. If an increased safety type is used, only the temperature group is required, not the gas group; therefore, T4 can be used in hydrogen environments.
What are the main differences between the two?
It shall be in accordance with the explosion-proof area division diagram for electrical engineering, but the 2nd floor is acceptable
If hydrogen is present in the environment, an IIC level must be achieved.
The specifications are written very clearly; there’s no need to discuss them.
Just follow what the expert who conducted the inspection says; there’s no need to consider making any changes. That’s how things are in our factory. After this inspection, they say the changes have been made, but during the next inspection they say that more changes are needed