501.6(B) Fuses for Class I, Division 2 Locations
What is the importance of 501.6(B)(4)?
General Comment–These fuses are used to isolate a faulted fixture
ballast and maintain continuity of service. Listed or recognized
branch circuit or supplementary fuses may be used. Additionally,
the GLR fuse is used on ballasts that have a 200 ampere shortcircuit withstand rating such as Class P ballasts.
What is the meaning of 501.6(B)(3)?
The intent of this reference is to suggest the use of non-indicating,
filled, current-limiting fuses. The following is a partial list of filled,
non-indicating fuses which are current-limiting:
Data sheet 8003 on www.bussmann.com under application
information/publications provides a list of fuses meeting these
requirements. Some of these are:
20A
CIRCUIT
BREAKER
2,000 Amperes
20' 12 AWG WIRE Available
Class CC
Class J
Class L
LP-CC 1/2 - 30, KTK-R 1/2 - 30, FNQ-R 8/10 - 30
LPJ_SP 1 - 600, JKS 1 - 600
KRP-C_SP 601 - 6000, KTU 601 - 6000,
KLU 601 - 4000
Class RK1 KTN-R 1 - 600, KTS-R 35 - 600
Row of Fluorescent
Fixtures
Lighting
Panel
GLR Fuse
Opens
Fixture
Faulted Ballast
Ballasts
517.17 Requirements for Ground Fault Protection and Coordination in
Health Care Facilities
What does this section mean?
If ground fault protection is placed on the main service or feeder of
a health care facility, ground fault protection must also be placed
on the next level of feeders. The separation between ground fault
relay time bands for any feeder and main ground fault relay must
be at least 6 cycles in order to achieve coordination between these
two ground fault relays. In health care facilities where no ground
fault protection is placed on the main or feeder, no ground fault
protection is necessary at the next level down. Therefore, if the
requirements of Sections 230.95 and 215.10 do not require ground
fault protection, then no ground fault protection is required on the
downstream feeders either.
What is one of the most important design parameters of the power
distribution system of a health care facility?
Selective coordination. To minimize the disruption of power and
blackouts in a distribution system, it is absolutely mandatory that
the overcurrent protective devices be selectively coordinated.
What is selective coordination?
A selectively coordinated system is one in which the overcurrent
protective devices have been selected so that only the overcurrent
device protecting that circuit in which a fault occurs opens; other
circuits in the system are not disturbed. The danger of a major
power failure in a health care facility such as a hospital is self
evident. In any facility, a power failure is at least inconvenient, if
not quite costly; in a hospital, it can easily give rise to panic and
endanger lives. Continuity of electrical service by selective
coordination of the protection devices is a must. (See Section
240.12, System Coordination, of this bulletin for a more detailed
explanation of selective coordination. Also publication SPD,
Electrical Protection Handbook has a detailed explaination of
selective coordination.).
If the ground fault protection of the feeder coordinates with the main
ground fault protection, will complete coordination between the main and
feeder be assured for all ground faults?
No, not necessarily! Merely providing coordinated ground fault
relays does not prevent a main service blackout caused by feeder
ground faults. The overcurrent protective devices must also be
selectively coordinated. The intent of Section 517.17 is to achieve
“100 percent selectivity” for all magnitudes of ground fault current
and overcurrents. 100% selectivity requires that the overcurrent
protective devices be selectively coordinated for medium and high
magnitude ground fault currents because the conventional
overcurrent devices may operate at these levels. (See discussion
of Section 240.12, System Coordination, for a more detailed
explanation of selective coordination).
520.53(F)(2) Protection of Portable Switchboards on Stage
What does this section require?
Compliance with Sections 110.9 and 110.10 is mandatory. Shortcircuit ratings must be marked on the switchboard.
50,000A
available fault
current
CURRENTLIMITING
FUSE
Switchboard short-circuit
rating 50,000A when
protected by a currentlimiting fuse
55