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Thread: Separation of Different Intrinsically safe circuits

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    Separation of Different Intrinsically safe circuits

    I'm trying to get a panel UL Marked. My hang-up is on the separation between different IS circuits. According to NEC 504.30(B), the circuits can be shielded, or have an insulation of .25mm (.01") or better. However in UL 698A 9.2.1(b)(2), UL requires each IS circuit to have an insulation of 6mm (.25"). Can somebody tell me how they comply with the insulation requirement, or how they got around it?

    Any help would be appreciated.

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    Something seems off about the insulation requirements you listed for UL...is UL talking about cable insulation while NFPA 70 is talking about the individual conductor thickness? I have found that most TC-ER cables I have looked at meet the insulation requirements from NFPA 70 (2017) article 504. If you can keep the circuits seperated by at least 2 inches, that is your best bet. If you can't then you need a grounded metal partition to seperate the circuits. If you can't do that, then you can use an "approved" method to keep them seperated. You will need to ruminate the meaning of "approved" from article 100 to get moving with that exception.

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    > Can somebody tell me how they comply with the insulation requirement, or how they got around it?

    Who is "they", and what did they get around?

    I'm not sure what your argument is. I'm guessing the panel was wired per NEC (0.25mm insulation) rather than UL 698A (6mm insulation)?

    If so, you're probably in trouble. If you want to get (or claim) UL 698A certification, you have to meet UL 698A.

    I'm assuming this has come up because an inspector from UL (or another agency) has shown up to certify the panel and found it non-compliant.


    NEC requirements don't apply here. NEC is for installation - UL 698A is for equipment. You're making / certifying equipment (the panel), so only UL 698A applies. You can't use Art. 100 or anything else from the NEC to justify what you're doing.

    698A requires 6mm insulation, and has no option for using screened cables. So 0.25mm cables are not OK.


    You could try to pull separation requirements from another standard, but I wouldn't advise it. This will probably prompt your agency to apply >all< of the other standard, and it's unlikely the panel will comply.

    However, if you wanted to try, you could argue that the total insulation between conductors is 0.25mm/conductor, or 0.5mm total. This is sufficient to meet infallible separation requirements per UL 60079-11 Table 5, for circuits up to 60V peak. If accepted, this would mean that the circuits can be considered separated.

    Table 5 does not apply to the 6mm separation required for field wiring terminals of I.S. circuits, as detailed in §9.2.1(b)(1). But it could legitimately substitute for the insulation thickness required on I.S. cables per §9.2.1(b)(2).

    It would be completely up to the discretion of your UL inspector to decide if Table 5 can and should be applied in this context.

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