During the years I have worked at Pepperl+Fuchs, I have been asked a lot of questions regarding the implementation of intrinsic safety, or IS for short. As they say, “Knowing is half the battle,” so I decided to share a few of those questions and answers.
- Can I use any field instrument I want if I am using an IS barrier?
The simple answer is no. However, to accept the answer, you must know why this true. Yes, the galvanic isolated barrier or zener barrier does limit the current and voltage to the hazardous location. However, if the field device you are powering or sending a signal to is not IS rated, that device may still contain components that can store or generate energy which could ignite a hazardous material.
- What wire should I use for IS?
This is another great question. It seems simple, however, the more you know the better off you are when using IS. You can use any wire you want for IS, it doesn’t have to be shielded or a twisted pair. It can be any gauge wire that you want, solid or stranded. Yet with all these allowances, there are always good wiring practices that you should follow. Some are dictated by your plant’s standards and some are simply good wiring practices. The gauge of the wire shouldn’t be over 14 awg, and for most barrier manufacturers that’s the highest you can use when connecting to an IS barrier. Don’t go too small either, as you do tend to run into issues with capacitance and inductance, which can greatly reduce the distance that you can run your cable. Using a light blue color for the jacket is recommended practice for IS wiring. If you can’t use light blue, you must physically mark your wiring with visible labels. You don’t want someone confusing hazardous location wiring with general purpose wiring.
- Do I have to run my IS wiring in conduit?
The answer for that is no. When you use intrinsic safety as your method for running information to and from the hazardous location, the National Electrical Code in Article 504.20 indicates that any wiring method that is acceptable for unclassified locations is also allowed when installing IS equipment.
- Can I install my barrier in a Div. 2 location?
The answer to this question is almost always yes. You should always consult your barrier manufacturer’s control drawing to verify that it is certified to be mounted in a Div. 2 area. You should also review any notes that give rules and regulations as to how you can mount the unit in the hazardous location. Typically, it will refer you to ANSI/ISA and the NEC standard.