Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning the protection requirements for the circuit feeding a socket in a hazardous area, is answered by SELECT:
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| Hazardous area - circuit protection requirements? |
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Question: When installing a 110V socket in a hazardous area from a distribution board having a common transformer that is centre tapped to earth, what are the protection requirements for the circuit feeding the socket? And also, what are the protection requirements for feeding the transformer? Please note that the transformer is 3kVA rated.
Answer: You have not mentioned what hazardous area you are talking about. If this is a hazardous area such as a construction site etc., then as the transformer is centre tapped, both live poles should be protected against fault current. This can be provided by using suitable double pole circuit breakers, or may - in some instances - be provided by using a suitable thermostat embedded in the primary winding of the transformer. This will cut off the supply to the primary winding and hence isolate the secondary side.
There are hazardous areas where there are risks of explosion because of the presence of flammable substances. In such cases, the above arrangement would be unsuitable.
Picture of a hazardous area courtesy of Emerson Process Management.
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