Much Needed Clarification of 250.4 (A) 5

Merry Christmas

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Proposing this change be made to 250.4 (A) 5, and that a new paragraph 250.4 (A) 6 be added after 250.4 (A) 5.


(5) Effective Ground-Fault Current Path. Electrical equipment
and wiring and other electrically conductive material
likely to become energized shall be installed in a manner that
creates a low-impedance circuit facilitating the operation of the
overcurrent device not exceeding the time specified in 250.4 (A) 6 or ground
detector for high-impedance grounded systems. It shall be capable
of safely carrying the maximum ground-fault current likely to be imposed on it from
any point on the wiring system where a ground fault may occur
to the electrical supply source. The earth shall not be considered
as an effective ground-fault current path.

(6) Maximum Permitted Overcurrent Device Disconnection Time. The maximum
total clearing time of an associated overcurrent device during a ground fault shall not
exceed any of the following:

(a) 1 second for final branch circuits protected at 30 amps or less, operating
over 50 volts to ground but not exceeding 150 volts to ground.

(b) 0.5 seconds for final branch circuits protected at 30 amps amps or less, operating
over 150 volts to ground but not exceeding 300 volts to ground.

(c) 0.25 seconds for final branch circuits protected at 30 amps or less, operating
over 300 volts to ground but not exceeding 600 volts to ground.

(d) 0.125 seconds for final branch circuits protected at 30 amps or less, operating
at over 600 volts to ground.

(e) 5 seconds for feeders and branch circuits protected at 35 amps or more but not
exceeding 350 amps, operating at over 50 volts to ground.

(f) 10 seconds for feeders and branch circuits protected at 400 amps or more, operating
over 50 volts to ground.

FPN: Disconnection time is typically derived via
the minimum fault current as determined by the total
combined circuit impedance present at the furthest
point of a circuit's fixed wiring compared to a device's
published time current curve. See Chapter 9, Table 9
for specific impedance values.

FPN: Faster disconnection times than maximum
limits above greatly reduce incident energy
at the point of a ground fault.

................................................................................................................................................................................................................................................................................................


Adding this would eliminate several exceptionally hazardous limitations of NFPA 70, allow for the deletion of two dozen NEC paragraphs, streamlining of the whole article 250, and prevent the ever expanding requriments of AFCI, GFCI, GFP and SPGFCIs.

CMP members refuse to define effective ground fault current path instead placing bets on costly, partially ineffective device requirements.
 
Last edited:

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Are you suggesting engineering design goals, or actual clearing-time testing of every circuit?
 

romex jockey

Senior Member
Location
Vermont
Occupation
electrician
Bravo MBrooke!
Seems this would define where the ~R~ubber hits ~Z~ ~R~oad ...
question, is this a standard anywhere else?

~RJ~
 
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