32 S&C Instruction Sheet 662-510
Appendix D
Recommended Voltage Ratings
In general, current-limiting fuses should have a maximum
voltage rating equal to, but not greater than 140% of, the
system line-to-line voltage because, for most applications,
the fuses can be exposed to full system line-to-line voltage
in clearing faults. Although there may be economic or
space-saving incentives for using current-limiting fuses
with voltage ratings “appropriate for system line-to-ground
voltage” (i.e., fuses with a voltage rating lower than line-to-
line voltage but greater than or equal to maxi mum system
line-to-ground voltage), S&C can only recom mend such use
in the following applications:
• Protection of single-phase transformers serving single-
phase loads
• Protection of three-phase lateral circuits fed by single-
conductor shielded cable (provided each transformer
on that lateral is individually fused so that the current-
limiting fuse serving the lateral will not be required to
clear secondary faults)
• Protection of single-phase lateral circuits fed by single-
conductor shielded cable where the load is line-to-ground
connected
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