5-99 Log #2716 NEC-P05
(250-30(A)(4) Exception No. 2 (New) )
Final Action: Reject
Submitter: Donald A. Ganiere Ottawa, IL
Recommendation:
Renumber existing Exception as Exception No. 1 and add new Exception No. 2 as follows:
"Exception No. 2: Where a transformer is used as a separately derived system and where the transformer primary feeder circuit originates in the same building or structure, a grounding electrode shall not be required."
Substantiation:
There is no electrical or safety related reason to require a grounding electrode for a transformer used as a separately derived system when the primary power source for the transformer is located in the same building or structure. The requirements of 250.4(A)(1) are met without the use of a grounding electrode at the secondary side of the transformer. Lighting is not a problem within the building or structure. The only possible contact with a higher voltage system is a fault on the primary feeder and this fault will be cleared by the primary feeder equipment grounding conductor. The bonding required by 250.30(A)(1) will stabilize the voltage to earth under normal operating conditions. The same bonding in combination with the primary feeder equipment grounding conductor will limit the effect of line surges. The addition of a direct connection from the secondary side of a separately derived system to a grounding electrode provides no additional protection over that which is already provided by the primary feeder equipment grounding conductor.
Panel Meeting Action: Reject
Panel Statement:
The present requirements for separately derived systems to be grounded to a reference earth by a dedicated grounding electrode conductor apply to all systems without regard of installation inside or outside the building or structure served. The primary reason is to establish an earth ground reference and stabilize the system voltage around this reference. The equipment grounding conductor from the source to the separately derived system does not meet the requirements for size, not having a choke effect when installed in metal
raceways, multiple terminations, etc. The equipment grounding conductor's primary purpose is to provide a low impedance path for fault current in the event of a ground-fault on the system up to and including the primary of the transformer, not to act as the low impedance earth reference conductor.
Number Eligible to Vote: 16
Ballot Results: Affirmative: 15 Negative: 1
Explanation of Negative:
RAPPAPORT: The purpose of the grounding electrode conductor in the proposed Exception is to stabilize voltage. See my Comment on Affirmative on Proposal 5-91. An equipment grounding conductor, run with the feeder to the separately derived system and sized for the separately derived system, should be adequate.
