I have, in the past, purchased the paperback 2005 and 2008 versions of the NEC along with Mr. Miller's book. This year, I purchased the spiral bound version of the NEC 2011 and decided to not purchase Mr. Miller's book, though I may before its over with. The new NEC came with an offer to download a PDF copy of the entire NEC 2011, identical to the printed copy I had. It took a couple of phone calls and they had to send me an email with a link to the download and a password, but I did get the PDF. While copyright laws do not allow me to wholesale publish the code, they do allow for quoting or copying from copyrighted works for use in making a point in a discussion or a review of the material. Below is a paragraph from section 310 where the residential service or feeder amperage's are discussed, and this helps to explain why the table 310.15(B)(7) is not suitable for use in a garage feeder.
(7) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services
and Feeders.
For individual dwelling units of onefamily,
two-family, and multifamily dwellings, conductors,
as listed in Table 310.15(B)(7), shall be permitted as
120/240-volt, 3-wire, single-phase service-entrance conductors,
service-lateral conductors, and feeder conductors
that serve as the main power feeder to each dwelling unit
and are installed in raceway or cable with or without an
equipment grounding conductor. For application of this section,
the main power feeder shall be the feeder between the
main disconnect and the panelboard that supplies, either by
branch circuits or by feeders, or both, all loads that are part
or associated with the dwelling unit. The feeder conductors
to a dwelling unit shall not be required to have an allowable
ampacity rating greater than their service-entrance conductors.
The grounded conductor shall be permitted to be
smaller than the ungrounded conductors, provided the requirements
of 215.2, 220.61, and 230.42 are met
Note that this is specific to dwellings. Here is the table involved.
Table 310.15(B)(7) Conductor Types and Sizes for
120/240-Volt, 3-Wire, Single-Phase Dwelling Services and
Feeders. Conductor Types RHH, RHW, RHW-2, THHN,
THHW, THW, THW-2, THWN, THWN-2, XHHW,
XHHW-2, SE, USE, USE-2
Conductor (AWG or kcmil)
Service or Feeder
Rating (Amperes)
Copper
Aluminum or
Copper-Clad
Aluminum
100 4 2
110 3 1
125 2 1/0
150 1 2/0
175 1/0 3/0
200 2/0 4/0
225 3/0 250
250 4/0 300
300 250 350
350 350 500
400 400 600
Sorry, tables do not copy correctly, but the first column is amps, the second is copper wire size, and the third is aluminum or cu clad aluminum wire size. As you can see, #2 is fine for 100 amps........ FOR A DWELLING.
Now, table 310.15(B)(16) {formerly 310.16) gives you the info you need for OTHER THAN DWELLING (edit to add: "OTHER THAN DWELLING MAIN SERVICE OR FEEDER"). I cannot copy that table, it is a full page and will get scrambled, and is a secured, single user license......
Suffice to say, #2 AL using the 90°C column for USE-2 wire (which is what this quadplex wire is) is suitable for 100 amps, according to the table. HOWEVER, there is a problem, you cannot use the 90°C column because the code says you rate a circuit by the lowest temp rated device or equipment in the circuit. There are no 90°C rated circuit breakers or terminals manufactured for home or light commercial use, they are all rated 60°C/75°C and as such, you have to go to the 75°C column of the table to find the correct amperage for the circuit, which is 90 amps. The reason the table even has a 90°C column is for the purpose of derating the wire due to either high ambient temperatures or excessive numbers of current carrying wires in a conduit, then you get to use the higher temp column to begin the derating calculations, provided the wire is rated for the higher temp to begin with.
I hope this helps you understand the situation.
Charles
AFAIK,nobody in Cameroon,Denmark or Botswana would know or care about what anyone of us is trying to do in a ditch...
"Who is the ******* you talking to?" I said "Some ******** on the net!" I don't care if you have 10,000 posts that doesnt make you any smarter that's for sure.
