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Question: you perform a visual inspection on a temperature measuring loop...

Question details

You perform a ‘visual’ inspection on a temperature measuring loop where the hazard is Hydrogen. You observe that an intrinsically safe Zener Barrier is located in a safe area and marked [Ex ib] IIB. The barrier is earthed to the metalwork of the control panel using a thick green-yellow cable. Cabling goes from the barrier into a hazardous area through a first junction box marked Ex nA II T6, then through a second junction box marked Ex e II T6, to a temperature transmitter which is marked Ex ia IIC T4. These three pieces of equipment are located in a zone 1. From the second junction box, a cable goes to the non-isolated temperature transmitter. The transmitter is then connected via compensating cable to an earthed thermocouple that is located in a zone 0.

This installation as it stands is not acceptable. You, the inspector, must explain what you have found that is incorrect and how to put it right. There are four specific aspects of concern in this installation:

a) Earthing
b) Equipment grouping
c) Equipment Protection Level
d) Equipment selection

Note - The weighting of the installation issues above will indicate the scale of the problem. The explanations given need only be short if they are specific in nature.

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