The circuit should have a fuse connect to the cathode of two zeners that are connected to ground. The opposite side of the zeners should be provided with a current limiting resistor. With regard to relays see UL913 13.3. It may be best to optically couple the output of the above barrier to the relay for control of the circuit. All of the above would need to be outside of the Class I Group D location unless it is in an explosion proof enclosure. If it is outside of the Haz. Loc. then it becomes Associated Appuratus with I.S. outputs. What ever is connected to the outputs and in the Haz. Loc. would then be the I.S. device. If it purely resistive then the zener voltage divided by the current limiting resistor sets up your spark ignition parameters, see UL913, Fig. 1. If it capacitive or inductive the other figures apply but it is more tricky. Good Luck.
Does the circuit have to be exosed to the real world? If not then an already approved EX enclosure will do the job. Christopher Caserta
Sr. Regulatory Engineer
ccaserta@enorthhampton.com
Ph:904-225-0360
Fax:904-225-0340
Looking for source of fuses that can be used in equip. intended for Class I, Div 2 installation. Protecting 24VDC, 5A with one and 120VAC, 2A with other fuse. They will be contained within a NEMA-4x SS enclosure, prefferably on DIN-rail.
