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Thread: Clearance/creepage in regard to PCBs for IEC 60079-7

  1. #1
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    Clearance/creepage in regard to PCBs for IEC 60079-7

    For IEC 60079-7 (Part 7: Equipment protected by increased safety rules) do PCBs need to follow the clearance/creepage requirements in regard to their layout? I know they have to in relation to nearby structures, for example other circuit boards or the enclosure. I thought they would except it says twice:

    "Unless otherwise required in this standard, the enhanced clearance distances for equipment of Level of Protection “ec” only apply to mains circuits and between isolated circuits. The enhanced clearance distances do not apply to printed wiring board mounted components."

  2. #2
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    I guess I will comment that IEC 60079-7 is meaningless in US domestic markets and the NEC doesn't recognize a Type "ec" protection technique.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #3
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    OSHA accepted the IEC 60079 series of standards several years ago (OSHA Approved Test Standards)

    There are currently 5 NRTL's that are accredited by OSHA to use the standard are:
    1. CSA Group Testing and Certification Inc. UL 60079-0, -1, -5, -6, -7, -11, -15, and -18
    2. Intertek Testing Services NA, Inc. ISA 60079-0, -2, -5, -6, -11, -15, -18, -25, -26, -28, and -31
    3. MET Laboratories, Inc. UL 60079-0, -2, -11, and -15
    4. SGS North America, Inc. ISA 60079-0, -1, -2, -5, -6, -7, -11, -15, -18, -26, -28, and -31
    5. Underwriters Laboratories Inc. UL 60079-0, -1, -5, -6, -7, -11, -15, and -18


    It's worth noting that there is no difference between the UL and ISA versions of the standards as they both collaborated on developing the US version of the standard.
    Regards,
    Dan Marr

    "Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

  4. #4
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    Quote Originally Posted by DM2-Inc View Post
    OSHA accepted the IEC 60079 series of standards several years ago (OSHA Approved Test Standards)

    There are currently 5 NRTL's that are accredited by OSHA to use the standard are:
    1. CSA Group Testing and Certification Inc. UL 60079-0, -1, -5, -6, -7, -11, -15, and -18
    2. Intertek Testing Services NA, Inc. ISA 60079-0, -2, -5, -6, -11, -15, -18, -25, -26, -28, and -31
    3. MET Laboratories, Inc. UL 60079-0, -2, -11, and -15
    4. SGS North America, Inc. ISA 60079-0, -1, -2, -5, -6, -7, -11, -15, -18, -26, -28, and -31
    5. Underwriters Laboratories Inc. UL 60079-0, -1, -5, -6, -7, -11, -15, and -18


    It's worth noting that there is no difference between the UL and ISA versions of the standards as they both collaborated on developing the US version of the standard.
    You might want to read UL's own evaluation of IEC equivalence. They "modified" plenty. I.e.,IEC 60079-7 and UL 60079-7 ain't the same thing.

    And the NEC still doesn't recognize a Type "ec" protection technique. See Section and Table 505.9(C)(2)(4).
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  5. #5
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    This question just refers to IECEx (basically ATEX), is that outside the scope of this forum?

    I found a clarification, third down at this link, but still can't figure out if they are saying if PCBs in general are exempt from clearance/creepage requirements or not. It states:

    The following provides clarification regarding what is meant by these terms:
    • The term "mains circuits" is intended to apply to any circuit directly connected to the premises supply.
    • The term "isolated circuits" is intended to apply between a mains circuit and earth and between a mains circuit and any secondary circuit that is isolated from it (such as by an isolating transformer or opto-coupler).
    • The term "printed wiring board mounted components" is intended to apply to both the body of the component and to the solder points. This term includes isolating components mentioned in the previous dashed item if mounted on a printed wiring board.

  6. #6
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    ATEX is definitely outside the scope of this forum. This is why UL/ISA had to seriously "modify" the IEC 60079 series (and several others) to make them conform to US domestic product standards.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  7. #7
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    Quote Originally Posted by rbalex View Post
    ...
    And the NEC still doesn't recognize a Type "ec" protection technique. See Section and Table 505.9(C)(2)(4).
    I reviewed the IECEx summary listed above. I note what is now called protection technique "ec" used to be "nA". Type "nA" is recognized in the NEC, however is must conform to UL/ISA 60079-15 at the moment.

    My "gut feel" only, since I don't have access to the latest IEC Standards, is the clearance/creepage restrictions do not apply to onboard components. This would be consistent with general IEC philosophies for Zone 2. In any case it would have to comply with an ANSI certified American National Safety Standard for US domestic use - NO "unconformed" IEC Standard does at the moment.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  8. #8
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    IEC 60079-0 / IEC 60079-18 Listed along with Conformance & Compliance

    Acceptable Provisions for Encapsulation:

    Marking "Ex m" II 2 G in accordance with IEC 60079-0 / IEC 60079-18 Marking "Ex mD" II 2 D in accordance with IEC 61241-0 Principle Parts that could ignite an explosive atmosphere by means of sparks or heat are potted so as to prevent ignition of the explosive atmosphere.

    The load on the components is limited or reduced - Increased clearance between live parts Applications - PCBs with electronic circuits.

    UL (in the U.S.) can perform CENELEC tests and their partner, DEMKO (in Denmark), can issue a test certificate for equipment use in the European community. Also, through its European subsidiaries, UL is able to provide technical support to declare products conform to CE Marking (Conformité Européenne) requirements. In addition, UL International DEMKO A/S can test and certificate for the Keymark and ENEC Mark, both of which are pan-European safety marks for a variety of electrical products.

  9. #9
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    I think the original quote gives the answer:

    "Unless otherwise required in this standard, the enhanced clearance distances for equipment of Level of Protection "ec" only apply to mains circuits and between isolated circuits. The enhanced clearance distances do not apply to printed wiring board mounted components."

    So you need to follow the creepage/clearance requirements from 60079-7 only for:
    - Distances between mains and other circuits, and
    - Distances where circuits need to be isolated from each other to achieve safety.

    The need for adequate distance to mains is obvious, and most type 'ec' circuits likely don't have any other circuits that have to be separated from each other to achieve safety.

    It also says PCB-mounted components are exempt. So you don't need to worry about following the creepage/clearance distances of 60079-7 for individual devices such as ICs, capacitors, etc.

    However, you do still need to meet the creepage/clearance requirements for whatever ordinary location industrial standards may apply. Type 'ec' basically says these normal industrial-spec distances are adequately safe for Div 2 / Zone 2 use, because faults and failures are not applied, but those "ordinary" distances do still have to exist.

    Hope this helps.

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