SECTION 9-Fused Breakers
There are two types of fused breakers; AKRU 30, 800
ampere frame and AKRU 50, 1 600 ampere frame. Except
for the open fuse lockout device and the i ntegrally
mounted fuses on the upper studs, the AKR U-30 and -50
breakers are identical to the unfused AKR-30 and -50
models. Overcurrent trip devices are the same for both
types.
9.1 FUSE SIZES AND MOUNTING
Table 6 lists the range of fuse sizes available for these
breakers. The Class
L
fuses are mounted as shown in Fig .
51 . Other than the 800A size, which has a single mounting
hole per
tang ,
each Class L
fuse
tang has two holes
si
zed
fo
r
o
n
e
-
h
a
lf in
ch d iame
t
e
r
bol
ts.
Class
J
fuses rated 300 thru 600A have one mounting
hole per tang. The 300, 350 and 400A sizes require copper
adapter bars per Fig. 52.
All V2-1 3
fuse mounting bolts should be torqued to 200-
350
in.-lb. The
%-1 1
bolts which attach the C shaped fuse
adapters to the breaker studs should be torqued to 300-
525
in.-lb.
FIG. 51 - TYPICAL MOUNTING CLASS L
FUSES
9.2 SPECIAL 2500A FUSE FOR AKRU-50
This fuse provides a melting time-current characteristic
that coordinates with 1 600A trip devices. Compared physi
cally with a 2500A N EMA Class
L
fuse, the special fuse is
more compact (shorter) ; its tangs are specially configured
and offset to achieve the required pole-to-pole fuse spac
ing; a special primary disconnect assembly mounts directly
on the outboard tang of the fuse. Considering their unique
mounting provisions, when replacing these fuses the fol
lowing procedure should be adhered to (Refer to Fig. 53) :
a) Remove the primary d i sconnect assem bly from the
fuse tang, accomplished by first loosening the two keys
via their holding screw and pulling them u pward and out.
After the keys are removed , pull the d isconnect assem bly
off the end of the fuse tang.
NOT E :
This removal does not disturb the
disconnect's clamping force adjustment.
b) Remove the upper barrier.
c) Detach the inboard end of the fuse by removing the
two 1 /2 inch - 1 3 bolts. A ratchet and socket with a short
extension will be requied.
d) Remove the heat sink.
e) Remove the fuse.
f) I nstall the new fuse by reversing the disassembly
procedure. Ensure that the mating faces of the fuse and
heat sink are clean.
�DAPTER BARS (COPPER)
FIG. 52 - 300 THRU 600 AMP C LASS J
FUSE MOUNTING
41
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