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Bulletin - E lectrical Code





443 Lafayette Road N.
St. Paul, Minnesota 55155
www.doli.state.mn.us
www.electricity.state.mn.us
(651) 284-5064
1-800-DIAL-DLI
Fax: (651) 284-5749

TTY: (651) 297-4198





Bulletin -
E
lectrical Code
National Electrical Code (NEC)
Article 547 - Agricultural Buildings

Following is a typical scenario and three electrical code questions
related to service configurations on an agricultural premises.
Scenario: Applicable electrical code; 2008 National Electrical Code (NEC) The premises is defined as agricultural by NEC Article 547 (Agricultural Buildings) The existing electrical infrastructure on the agricultural premises varies and was
installed at different times over many years All of the existing electrical infrastructure on the premises is presumed to have been
in compliance with the NEC that was in effect at the time of original installation Due to the changes in the NEC over many code cycles, specifically Article 547, some
of the existing electrical infrastructure on the premises does not comply with the 2008
NEC There is an existing 600 ampere non-fused, double-pole, double-throw transfer
switch mounted at grade level on the center yard pole (distribution point) A new 200 ampere underground feeder needs to be installed to a new storage shed
located 100 feet from the center yard pole (distribution point)
(Note All basic code requirements such as overcurrent protection, grounding,
bonding, terminations, physical protection, etc. are presumed to be in compliance)


Question - Is it permissible to install a new set of service conductors from the load side of the
non-fused grade-level transfer switch to the line side of an immediately adjacent, new,
service-rated disconnecting means that incorporates overcurrent protection?

Answer - Yes. NEC 547.9 states that a distribution point shall be permitted to supply any
building or structure located on the same premises. The NEC does not limit the number of
buildings on a multi-building premises.

Question - From the newly-installed service-rated disconnecting means at the center yard
pole (distribution point), is an equipment grounding conductor required to be installed with the
new 200 ampere underground feeder to the new storage shed?

Answer - Yes. NEC 547.9 states that an underground electrical supply shall comply with NEC
547.9(C). NEC 547.9(C) states that where the service disconnecting means and overcurrent
protection are located at the distribution point, the underground feeder to the building or
structure served shall meet the requirements of NEC 250.32 and Article 225, Parts I and II.
NEC 250.32(A) states that the building or structure supplied by the feeder shall have a
grounding electrode (or grounding electrode system). NEC 250.32(B) states that an
equipment grounding conductor shall be run with the supply conductors to the building or
structure disconnecting means and to the grounding electrode.

Question Is the existing 600 ampere non-fused, double-pole, double-throw transfer switch
mounted at grade level on the center yard pole required to be replaced with equipment that
provides overcurrent protection for the existing supply conductors that extend from the
distribution point?

Answer No. However, other code requirements must be considered and may require
upgrading of the equipment and compliance with the current electrical code. As an example,
additional load may result in the existing equipment to be undersized and require that it be
replaced with equipment of adequate rating.

AgriculturalBuildings_Bulletin_20081002.doc

Version Date October 2, 2008