Primary and Secondary Fuse Recommendations for all Three Phase Transformers

 

Primary General Purpose Transformers
Secondary General Purpose Transformers
VA
208
240
480
600
208
240
380
480
3K
12 (20)
9 (17.5)
5 (9)
4 (7)
1.2
9
6
5
6K
25 (40)
20 (35)
9 (15)
8 (12)
2.5
20
12
9
9K
35 (60)
30 (50)
15 (25)
12 (20)
35
30
18
15
15K
60 (100)
50 (90)
25 (45)
20 (35)
60
50
30
25
30K
110 (200)
100 (176)
50 (90)
40 (70)
110
100
60
50
45K
175 (300)
150 (250)
70 (125)
60 (100)
175
150
90
70
75K
300 (500)
250 (450)
125 (225)
100 (175)
300
250
150
125
112.5K
400 (750)
350 (650)
175 (300)
150 (250)
400
350
225
175
150K
600 (1000)
500 (900)
250 (450)
200 (350)
600
500
390
250
225K
-
-
350 (650)
300 (500)
800
700
450
350
300K
-
-
500 (900)
400 (700)
1200
1000
600
500
500K
-
-
800 (1500)
650 (1200)
1800
1600
1000
800

 

Primary Drive Isolation Transformers
Secondary Drive Isolation Transformers
VA
230
460
575
230
460
7.5K
25 (45)
12 (20)
10 (17.5)
25
12
11K
35 (60)
17.5 (30)
15 (25)
35
17.5
14K
45 (85)
25 (40)
20 (35)
45
25
20K
70 (125)
35 (60)
30 (50)
70
35
27K
85 (150)
45 (80)
35 (60)
90
45
34K
110 (200)
60 (100)
45 (80)
110
60
40K
150 (250)
70 (1250
60 (100)
150
70
51K
175 (300)
80 (150)
70 (150)
175
80
63K
200 (350)
100 (175)
80 (150)
200
100
75K
250 (450)
125 (225)
100 (175)
250
125
93K
300 (500)
150 (250)
125 (225)
300
150
118K
400 (700)
200 (350)
150 (250)
400
200
145K
500 (800)
250 (450)
200 (350)
500
250
175K
-
300 (500)
225(400)
600
300
220K
-
350 (650)
300 (500)
700
350
275K
-
450 (850)
350 (600)
900
450
330K
-
600 (1000)
450 (800)
1200
600
440K
-
700 (1350)
600 (1000)
1400
700

 

Fuse = 1*125% next size higher if primary current is 9 Amp or higher. No secondary fusing required.
(Fuse) = (1*125%) next size smaller if primary current is 9 Amp or higher. Secondary fusing is required. See chart for size.

OUTPUT FUSE = 1*125% next size higher if secondary current is 9 Amps or higher. Recommend fuse size per NEC450.3[B] and commercially available fuse types.