Blocks and Holders
111
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Blocks and Holders
© 2005 Littelfuse
•
POWR-GARD
™
Products Catalog
Fuse Blocks
General Information
Fuse Block Selection
The following guidelines should help simplify the selection of proper
fuse blocks:
1. Determine the system voltage
Since fuses are selected on the basis of system voltage, fuse blocks are
selected to match the voltage rating of the fuse.
2. Determine the design short-circuit current
Available and/or design short-circuit current is an important
consideration when determining the class of fuse and fuse blocks to
use. If available short-circuit current cannot be determined, or if it will
vary with equipment location, select fuses with a 200,000 ampere
interrupting rating (A.I.R.) and mating fuse blocks with a withstand rating
of 200,000 amperes for maximum safety.
Class H fuse blocks will accept Class H or K5 fuses (which have an
interrupting rating of up to 50,000 amperes) and Class R fuses (which
have a 200,000 A.I.R.). To prevent the possibility of inserting a fuse
with the incorrect interrupting rating, the use of Class R fuse blocks is
recommended for use with Class R fuses. Use Class H fuse blocks with
Class H or K5 fuses. These fuse blocks are dimensionally the same, but
the Class R fuse blocks incorporate a rejection feature which allows only
Class R fuses to be inserted.
3. Determine the type and ampere rating of the fuse to be used
In addition to voltage and interrupting rating as discussed above, the
fuse ampere rating, opening characteristics (fast acting or time-delay)
and size are other important considerations in fuse selection. Once the
fuse type is selected, the mating fuse block can be chosen. Fuse blocks
are available in 30, 60, 100, 200, 400 and 600 amp ratings, and may be
used with a fuse rated at the corresponding amperage rating or below.
For example, a fuse block rated at 30 amperes may be used with a fuse
rated from 0 to 30 amperes.
4. Determine if NEC, CSA, UL, or other requirements
are applicable
If fuse blocks will be installed in equipment to be submitted for agency
approval, the requirements should be obtained from the approving
agency in advance of fuse and fuse block selection.
5. Select the type of wire termination
A choice of three types of wire termination is available:
a) Screw
*
— for use with spade lugs or ring terminals.
b) Screw with Pressure Plate
*
— for use with solid or stranded wire
without terminal. Recommended where vibration will be a factor.
c) Box Lug — the most durable. For use with all types of solid wire and
Class B and Class C stranded wire. Not for use with welding cable or
other rope-stranded conductors.
*
1
/
4
” Quick Connect terminals rated for up to 20A are
available on the Midget and Class CC fuse blocks.
6. Decide on the number of poles in each block
The number of poles for each set of fuses is determined by the
characteristics of the circuit. The option to gang individual fuse blocks
into long strips will be determined by the available space and by the
type of wire being used.
7. Determine if fuse clips need to be reinforced
Fuse clips may have a tendency to lose some of their tension over a
period of time. This may be prevented by specifying reinforced fuse
clips. Reinforced clips are standard on certain fuse blocks (see individual
product pages).
Ordering Information
The Littelfuse fuse block part number consists of 6 or 7 components, as
shown below and in the individual fuse block data tables.
For all Class R, H, J, T and 15, 20
& 60A Class G Fuse Blocks
For all Class CC, Midget and 30A
Class G Fuse Blocks
Screw
with
Pressure
Plate
(P)
Screw
(S)
Box
Lug
(C)
(1 pages)
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