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Re: CQD answer published Monday, October 29, 2018 - Grounded conductor disconnect for fuel dispenser
1) Good morning, I'm not on CMP14 but you should look at FR7743 for the 2020 NEC. It answers the question. Thanks. J Grant Hammett
2) I do not serve on CMP-14, but I do recall that 514.11(A) was revised to align with the requirements in NFPA 30A (Code for Motor Fuel Dispensing Facilities and Repair Garages) and to clarify what is required for an emergency shutoff device at both an attend and an unattended self-service motor fuel dispensing facilities. Seems like I also recall CMP-14 discussing the fact that the requirement “to remove all external voltage sources, including power, communications, data, and video circuits” was (and is) already located at 514.13 (Provisions for Maintenance and Service of Dispensing Equipment) and that the requirement for switching the grounded conductor did not need to be repeated at 514.11(A). Some would argue that the emergency disconnect is not the same as the maintenance disconnect. Regards, L. Keith Lofland
3) The bigger question is, why was the requirement there in the first place? Dave
Hey all y'all thanks for your comments and follow-up question. The rule for also disconnecting the grounded conductor was restored by CMP14 by First Revision 7743 in the first draft. A sentence was added to not disconnect equipment grounding conductors. The following panel statement was provided: "The grounded conductor should be disconnected simultaneously with the all of the other conductors when the emergency disconnect is activated. It should also be clear that the equipment grounding conductors should not be disconnected. Added 2014 NEC wording at the end of 514.11(A) instead of the proposed new subsection (D)."
The "why" is not included in the panel statement and the original rule has been there since at least 1959 but the original proposal with a why does not seem to exist in the archives. A grounded conductor can carry current under normal conditions and it is possible the reason is to help ensure an arc will not occur because of the additional concern of the flammable fuel.
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