Class1 Division 1 location

[GeorgeW2]

What is the highest voltage that can be used as a intentionally safe circuit or signal? I’ve been researching this and I can not find anything addressing this.

 

[rbalex]

I believe you mean intrinsically safe.

Theoretically, there is no "highest voltage" since the real object is to restrict the system to the Minimum Ignition Energy (MIE) measured in milliJoules (mJ) of the ignitable material(s) involved and is a function of both Volts and Amps. Occasionally, ambient temperature and atmospheric pressure may come into play. Of course, there are practical maximums. The general standard for determining this is ANSI/ISA-12.06.01referenced in NEC Section 504.1 Informational Note.

 

[GeorgeW2]

Lol ,yes that’s what I was meaning it was a long day yesterday. I’ll review 504.1 I was under the impression that the voltage had to be around 8 volts AC or DC. And I was wondering if you could use 24 DC or AC or 12 VAC/DC?

 

[rbalex]

Before you start thinking about any voltage, read and understand Section 504.10(A) and understand you cannot make the control drawing necessary for a compliant installation.

 

[paulengr]

Before you start thinking about any voltage, read and understand Section 504.10(A) and understand you cannot make the control drawing necessary for a compliant installation.

It’s printed on the IS barrier as well as in the standard. There is nothing to 99% of these because it’s just PLC IO, it’s like loop sheets...a total waste of trees since we no longer typically have discrete field PIDs in most cases. I realize NEC makes a big deal out of this but it’s not.

Simple devices don’t need Listing. There are two categories. One is it doesn’t generate more than 1.5 V, 100 mA, and 25 mW. This is for thermocouples. The other is a passive device that doesn’t consume over 1.3 W. At 24 V you are limited to 50 mA. That’s enough to drive a lot of NAMUR devices like level and flow sensors. It handles switches, some lights, and RTDs, The IS barrier takes care of the current and voltage limiting. More advanced devices are available with more complicated rules.

 

[petersonra]

It’s printed on the IS barrier as well as in the standard. There is nothing to 99% of these because it’s just PLC IO, it’s like loop sheets...a total waste of trees since we no longer typically have discrete field PIDs in most cases. I realize NEC makes a big deal out of this but it’s not.

I used to think that the control drawings were a big deal too, but after a while I realized it's basically just the manufacturers instructions. Now it seems kind of curious that the NEC makes such a deal out of it when as a listed device you have to use it in accordance with the listing instructions anyway.

I'm inclined to agree that loop diagrams are complete waste of paper these days. It used to make sense when loops were a combination of electrical, pneumatic, mechanical, and often hydraulic components in unusual configurations. These days things are usually much much simpler.

If you want to talk about an absolute waste of paper look at ISA logic diagrams. These were often required by power plants. Who knows why. As often as not they were not followed anyway. I can remember arguing with people from Bechtel and Sargent and Lundy about the extent of such logic diagrams that would be required. I would point out to them that it was virtually impossible to describe a sequence of more than one or two steps in such a diagram in a way that was actually understandable, if it was actually possible. Usually we would get some dispensation that would require some minor work to describe the shutdown sequences of the equipment. I realize nobody really cared about these documents and probably never even looked at them and just stopped doing them and nobody really cared or seemed to notice.

 

[rbalex]

• The latest definition (description) of control drawing has been pulled out of Article 100 or Section 500.2, depending on the Code cycle, and settled (for the time being) in Section 504.10(A); a manufacturer's instructions may or may not be sufficient. See Section 504.10(A) IN No.1
• The OP said nothing about barriers; it only asked if there was a maximum voltage. See 504.10(A) IN No.2.
• Whether simple devices are required to be listed or not is irrelevant to the OP question.
• Logic diagrams are not P&IDs nor MFDs. Their purpose is to describe the interaction of system components.

 

[tom baker]

Logic drawings are the basis for the controls, where I worked as an instrument tech they were the first dwgs that were done.

 

[GeorgeW2]

It’s printed on the IS barrier as well as in the standard. There is nothing to 99% of these because it’s just PLC IO, it’s like loop sheets...a total waste of trees since we no longer typically have discrete field PIDs in most cases. I realize NEC makes a big deal out of this but it’s not.

Simple devices don’t need Listing. There are two categories. One is it doesn’t generate more than 1.5 V, 100 mA, and 25 mW. This is for thermocouples. The other is a passive device that doesn’t consume over 1.3 W. At 24 V you are limited to 50 mA. That’s enough to drive a lot of NAMUR devices like level and flow sensors. It handles switches, some lights, and RTDs, The IS barrier takes care of the current and voltage limiting. More advanced devices are available with more complicated rules.

Thanks for the info