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250.
32 Buildings or Structures Supplied By Feeder or Branch Circuit
What's Wrong
Here?
Code Q&A
Code Quiz
Rhode Island State
Electrical Code
Call for
Papers
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Top 2008 Code Changes
250.
32 Buildings or Structures Supplied By Feeder or Branch Circuit
By Mike Holt
The rule that permitted the re-grounding of the neutral
conductor at separate buildings and structures was deleted.
(B) Equipment Grounding Conductor. To quickly clear a fault
and remove dangerous voltage from metal parts, the building
disconnecting means shall be connected to the circuit
equipment grounding conductor of a type described in 250.118. Where the
supply circuit equipment grounding conductor is of the wire type, it
shall be sized to 250.122, based on the rating of the supply circuit
overcurrent device rating.
Exception: For existing premises, when an equipment grounding
conductor was not run to the building or structure disconnecting means,
the building or structure disconnecting means can remain connected to
the neutral conductor where there are no continuous metallic paths
between buildings or structures, ground-fault protection of equipment
isn't installed on the supply side of the circuit, and the neutral
conductor is sized no smaller than the larger of:
- The maximum unbalanced neutral load in accordance with 220.61.
- The rating of the circuit overcurrent device, in accordance with
250.122.
Caution: To prevent dangerous objectionable neutral current from
flowing onto metal parts [250.6(A)], the supply circuit neutral
conductor is not permitted to be connected to the remote building or
structure disconnecting means [250.142(b)].
In the 2005 NEC, 250.32(B)(2) permitted the neutral conductor to
serve as the effective ground-fault current path. This rule was
converted into an exception for existing premises. Using the neutral
conductor to connect metal objects to the effective ground-fault
current
path is a dangerous practice, especially if the neutral becomes open.
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Code Challenge
What's Wrong Here?
By Joe Tedesco
Think you know how this installation violates the
NEC? Visit EC&M's
Web site to see the answer.
Hint: D.C. exposure
Code Q&A
By Mike Holt
Q. We have motors that are interlocked,
preventing them from being on at the same time. Do we still have to add
them up for service and feeder calculations?
Visit EC&M's Web
site to see the answer.
Code Quiz
By Steven Owen
Q. When grounding the ferromagnetic envelope of
skin effect-heating systems, what are the grounding
requirements?
- Grounding is not required.
- Grounding one end only with an equipment-grounding conductor is
required.
- Grounding both ends with an equipment-grounding conductor is
required. Grounding any intermediate points in between the ends is also
permitted.
- GFCI protection (Class C, 30mA trip) is required.
Visit EC&M's
Web site for the answer and explanation.
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Code News Update
Rhode Island State Electrical
Code
On June 19, 2008 the Rhode Island Building Code
Standards Committee held a public hearing to hear testimony on the
adoption of the State Electrical Code (SBC-5). The SBC-5 technical
subcommittee recommended the adoption of the 2008 National Electrical
Code (NEC) without any technical amendments. It was recommended that
the
existing administrative amendments to SBC-5 be retained. The Rhode
Island Building Code Standards Committee accepted the technical
subcommittee recommendation and voted 14-1 to adopt the 2008 NEC. The
bill has been filed with the Secretary of State and became effective
Aug. 1, 2008, with a mandatory date of Nov. 1, 2008.
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