PRODUCT BRIEF
NX® FAULT GUARD TOOL
Application Description: The NX Fault Guard Tool is a full range current-limiting fuse designed for energization of electrical
distribution transformers. The fuse can be applied anywhere it is desirable to provide temporary
fault current-limitation when energizing a load. This energizing tool will limit the available energy
to the load in case of a fault.
A typical application is to connect an overhead transformer and its expulsion fuse to the line
through the NX Fault Guard Tool. If a fault is present, the non-expulsion, current-limiting fuse in
the tool will operate quietly and harmlessly and limit the energy released into the protected equipment. This current-limiting action protects the lineman by limiting the blast from the expulsion fuse
and by preventing a possible catastrophic failure of the transformer.
Features:
•
•
•
•
•
•
•
•
Design Styles:
The NX Fault Guard Tool is available in two styles: Figure A - with metal stirrup or Figure B with electrical cable. The Fault Guard Tool equipped with the metal stirrup is for use with selfprotected transformers. The Fault Guard Tool with the self-retracting electrical cable is for use
with distribution transformers protected by open-type fuse cutouts (refer to pictures below).
Eliminate catastrophic transformer failure
Improve lineman safety from expulsion by-products
Protection during energization achieved without having to disrupt the service
Minimize the expulsion blast on any fuse cutout application
Reduce expulsion fuse noise substantially
Hot-line testing for a shorted surge arrester
Usable with any expulsion fuse cutout
Easy visual and audible verification of fuse operation
Figure A – Fault guard tool
with metal stirrup.
Figure B – Fault guard tool
with electrical cable.
Application Selection Chart:
TABLE 1: Fuse Cartridge Voltage and Current Selection for the NX Fault Guard Tool (in Amps)
Fuse
Voltage
System
Voltage *
15 kV or 23 kV
15 kV
4.8 kV
2.4 kV
6.9/7.2/7.62/7.9 kV
23 kV
19.9 kV
12/13.2/14.4 kV
Transformer Typical Expulsion Fault Guard Tool Typical Expulsion Fault Guard Tool Typical Expulsion Fault Guard Tool Typical Expulsion Fault Guard Tool Typical Expulsion Fault Guard Tool
Size KVA Fuse Link (K or T)À Cartridge SizeÁ Fuse Link (K or T)À Cartridge SizeÁ Fuse Link (K or T)À Cartridge SizeÁ Fuse Link (K or T)À Cartridge SizeÁ Fuse Link (K or T)À Cartridge SizeÁ
667
500
333
250
167
100
75
50
37.5
25
15
10
5
3
–
–
–
–
–
–
–
–
–
–
–
–
40
25
20
40
30
30
12
8
6
18
18
18
3
2
18
18
–
–
–
–
–
–
–
–
40
25
20
12
10
40
30
30
18
18
6
5
3
1
1
18
18
18
18
18
–
–
–
–
–
–
40
25-30
15-20
12
8-10
6-8
40
30
18
18
18
18
18
18
18
5
2-3
2
1
1
18
18
–
–
40
40
40
30
25-30
12-15
8-10
6-8
5-6
3-5
40
30
30
18
18
18
18
18
30
30
18
18
18
18
18
18
2-3
2
1
1
1
18
18
18
18
18
30
20
15
10
6
5
3
2
2
1
1
–
–
18
18
18
18
18
*Single-phase voltage on grounded-wye system.
ÀIf the expulsion fuse link used is different from the specified table, refer to Catalog Section 240-62 for more detailed information or contact the factory.
ÁThe specified fuse cartridge size is optimized for the specific transformer size and expulsion fuse link. In some cases, the applications can be consolidated in order
to reduce the number of cartridge sizes required. Refer to Catalog Section 240-62 for more detailed information or contact your Cooper Power Systems representative.
Determine the correct Fault Guard Tool fuse ratings from the application table above.
Then select the Fault Guard Tool and Fuse Cartridge from Table 2 and 3, respectively.
Fault Guard Tool
Catalog NumberÂ
With Metal Stirrup
FA21M1
With Electrical Cable
FA18M1
 Includes the upper and lower end fittings.
Fuse is sold separately.
Example: To order a 15 kV, 18 A Fault Guard Tool with
Electrical Cable, order: FA18M1 and FAG4A18R.
TABLE 3: Fault Guard Tool Fuse Cartridge Selection
(Fuse Only)Ã
Position:
1
2
3
4
5
6
7
F
A
G
_
A
_
R
Voltage Rating
Position 4
Description
"4"
"5"
15.5 kV
23.0 kV
è
TABLE 2: Fault Guard Tool Selection
è
Ordering Information:
Current Rating
15 or 23 kV, 6 thru 40 A
Position 6 Description
"18"
18 A
"30"
30 A
"40"
40 A
à Refer to Catalog Section 240-62 for more detailed information
on additional current ratings.
P.O. Box 1640
Waukesha, WI 53187
www.cooperpower.com
2000 Cooper Industries, Inc.
Bulletin 00039 June 2000 New Issue
Printed in U.S.A.
©
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