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Industrial Control Transformers
Fuse Protection
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© 1999–2005 Schneider Electric All Rights Reserved 08/2005
Primary Fusing to Meet NEC
NOTES:
• Recommended fuse sizes per NEC Article 450-3.
• Transformers with primary only, select protection at 125%, if a standard size rating is not available, go to next higher rating.
• Transformers with primary only and current rating is less than 9 A, select protection at no more than 167%.
• Transformers with primary only and current rating is less than 2 A, select protection at no more than 300%.
• Transformers with primary and secondary, select primary protection at not more than 250% and secondary at 125%.
If a standard size rating is not available, go to next higher standard rating.
Recommended Fuse Sizes for the PRIMARY (use class CC time delay fuses) to Meet NEC
VA
120 Volts 240 Volts 480 Volts 600 Volts
Primary
Current
Amperes
Fuse
Rating with
Secondary
Protection
Fuse
Rating
without
Secondary
Protection
Primary
Current
Amperes
Fuse
Rating with
Secondary
Protection
Fuse
Rating
without
Secondary
Protection
Primary
Current
Amperes
Fuse
Rating with
Secondary
Protection
Fuse
Rating
without
Secondary
Protection
Primary
Current
Amperes
Fuse
Rating with
Secondary
Protection
Fuse
Rating
without
Secondary
Protection
25 0.21 1/2 1/2 0.10 1/4 1/4 0.05 1/8 1/8 0.04 1/10 1/10
50 0.41 1 1 0.21 1/2 1/2 0.10 2/10 2/10 0.08 2/10 2/10
75 0.63 1-1/2 1-1/2 0.31 6/10 6/10 0.16 3/10 3/10 0.13 3/10 3/10
100 0.83 2 2 0.42 1 1 0.21 1/2 1/2 0.17 4/10 4/10
150 1.25 3 3 0.63 1-1/2 1-1/2 0.31 6/10 6/10 0.25 6/10 6/10
200 1.67 4 4 0.83 2 2 0.42 1 1 0.33 8/10 8/10
250 2.08 5 3-2/10 1.04 2-1/2 2-1/2 0.52 1-1/2 1-1/4 0.42 1 1
300 2.50 6-1/4 4 1.25 3 3 0.63 2 1-1/2 0.50 1-1/8 1-1/8
350 2.92 7 4-1/2 1.46 3-1/2 3-1/2 0.73 2-1/2 1-8/10 0.58 1-4/10 1-4/10
500 4.17 10 6-1/4 2.08 5 3-2/10 1.04 3 2-1/2 0.83 2 2
750 6.25 15 10 3.13 7-1/2 5 1.56 3-1/2 3-1/2 1.25 3 3
1000 8.33 20 12 4.17 10 6-1/4 2.08 5 3-2/10 1.67 4 4
1500 12.50 N/A 15 6.25 15 10 3.13 7-1/2 5 2.50 6-1/4 4
2000 16.66 N/A 20 8.33 20 12 4.17 10 6 1/4 3.33 8 5