DIYbanter - View Single Post

wrote:
....

I dont know of anyone who makes a 300 amp service

A three hundred ampere service is a four hundred ampere enclosure with a
three hundred ampere breaker or fuses installed, two 150 ampere main
breaker panels installed in parallel from a single set of service entry
conductors, up to six main disconnecting means supplied from a single
set of service entry conductors that are sized to carry 300 amperes, and
the list goes on. The size of an electric service is based on the
calculated load with an allowance, if wanted, for future expansion. The
resultant amperage is the figure that governs the size of the service
entry conductors. The only time that the service Over Current
Protective Device (OCPD) has to match that ampacity is when it consist
of only one OCPD. If it is two or more OCPDs it can exceed the size of
the calculated load by a large amount as long as the calculated load is
within the ampacity of the service entry conductors that are installed.
This is just one of the things that is easy for untrained and
unqualified persons to get wrong when doing electrical installations.
If the eventual connected load exceeds the ampacity of the service entry
conductors the overload can cause a fault in the service entry
conductors that can lead to a burn down and may kindle a structure fire.
Service Entry Conductors do not have short circuit or ground fault
protection. In many cases the only protection they have against
overload is the conscientious work of the electrician in properly
executing the service calculations. This is why some localities do not
permit the use of multiple service disconnecting means that total to
more than the ampacity of the service in individual residential
properties.

240.6 Standard Ampere Ratings.
(A) Fuses and Fixed-Trip Circuit Breakers. The standard ampere ratings
for fuses and inverse time circuit breakers shall be considered 15, 20,
25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200,
225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600,
2000, 2500, 3000, 4000, 5000, and 6000 amperes. Additional standard
ampere ratings for fuses shall be 1, 3, 6, 10, and 601. The use of fuses
and inverse time circuit breakers with nonstandard ampere ratings shall
be permitted.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison