TM 5-688
vendor be contacted to discuss the derating. It is
without rapid failure. Thus, no derating factors for volt-
always preferable to locate a vendor that will supply
age level are offered. Instead, it is recommended that
the equipment with the desired ratings before derating
transformers be used to step the higher voltage level
is attempted. The majority of vendors contacted are
down to a voltage level in the range of 100-127 VAC,
able to supply equipment rated at 50 Hz and a variety
which U.S. equipment can tolerate. It has been found,
of voltage levels, so derating should be necessary in
however, that most vendors of voltage-sensitive equip-
only a few cases.
ment are able to configure the equipment for 220-240
VAC and corresponding threephase voltage levels.
3-10. Summary.
3-9. Recommendations.
Appendix B can be used to rapidly identify the stan-
dard frequency and voltage levels in other countries. In
Derating factors were discussed and developed for the
cases where cities within a country differ in their elec-
six generic types of equipment. Appendix C, which
trical standards, the cities are listed separately. For
summarizes the discussion of derating factors present-
countries in which all cities have the same electrical
ed in this chapter, is useful in identifying derating fac-
standards, typically only the capital city is listed. In
tors quickly and easily. Although this chapter presents
these cases, assume that all cities in the country have
derating factors for equipment, it is recommended that,
the same electrical standards.
whenever a piece of equipment is to be derated, the
3-3
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