ECN Forum Forums General Topics of the Trade General Discussion Area Code question of the day

Thanks for the assistance. From time to time I like to provide an illustration of my posted question when I feel it can be of some help.

ah...sound and picture!!

I think this goes with it......

Question:
We installed a 200-ampere service in a home. The service panel is
rated 200 amperes and equipped with a 200-ampere main breaker. The
panel has sub-feed lugs at the bottom and we used these lugs to feed a
panel 20 feet away with 2 AWG AL conductors. These conductors
terminate in a 100-ampere main breaker in the second panel. The
inspector required us to put a 100-ampere breaker in the service panel
to feed these conductors citing 240-3 (1999 NEC). Is he correct?

Answer:
Section 240.4 (2002 NEC) reads the same as 240.3 (1999 NEC). This
section requires that conductors be protected against overcurrent in
accordance with their ampacities <b>unless</b> otherwise permitted in
240.4(A) through (G). Section 240.4(E) permits tap conductors to be
protected against overcurrent in accordance with 240.21.

Section 240.21(B)(2) permits tap conductors not over 25 feet long to
be run without overcurrent protection at the source if all of the
provisions of 240.21(B)(2) are complied with. Your installation
complied with (1) where the ampacity of the tap conductors is not less
than one-third of the rating of the overcurrent device protecting the
feeders (200A), and (3) where the tap conductors are suitably protected
from physical damage or are enclosed in a raceway. However, (2) that
requires tap conductors to terminate in a single overcurrent device
that limits the load to the ampacity of the tap conductors was not
complied with, since the ampacity of 2 AWG AL as shown in Table 310.16
is 90-amperes.

You may be using the 90ºC column where 2 AWG AL is rated at 100
amperes but this isn't permitted because the terminations in your
panels aren't rated 90ºC. You may be using Table 310.15(B)(6) where 2
AWG AL is rated at 100 amperes but this table only applies to
service-entrance conductors and feeder conductors that serve as the
main power feeder to a dwelling unit.

Since 240.6 shows a 90-ampere circuit breaker as being a standard
size, you must change the 100-ampere breaker to a 90-ampere breaker to
be in compliance with the NEC.


[This message has been edited by sparky (edited 06-24-2002).]

Thanks Bill for the diagram.

The Geo site does not work for me either.

Just remember, that is 25' Max. of 1/3 ampacity tap conductor and single OCPD.

[This message has been edited by Gwz (edited 06-24-2002).]

I saw that question and I believe the editor of the CQD missed the point of the question. He responded, correctly, with regard to ampacity. However, I think the question pertains to whether or not a CB is required at the supply end. Even if the questioner follows the inspectors directive by installing a CB at the supply end, the ampacity problem still exists. According to 310.15(6),the additional allowable ampacity for #2 al conductors is only where they are used as service entrance conductors, or where used as the main power feeder to a dwelling.

I totally overlooked the #2AL conductor ampacity issue. Sorry.... I was more focused on the Inspector's requirement of a 100 amp breaker in the service panel and not granting permission to use the take off lugs.
As I mentioned previously, I feel the use of the take off lugs is Code compliant.
Frank

From the same 200 amp service panel what is the largest size Sub-panel that can be fed from said panel ? Is it 200 Amps or 80% is there a rule of thumb for it.

-Mark-

[This message has been edited by motor-T (edited 06-24-2002).]

I think the installation is correct as posted as Redsy said, the respondant missed the point of the question.

-Mark-

Bear with me guys, I'm trying to learn, this is a test

[This message has been edited by MikeW (edited 06-24-2002).]

[This message has been edited by MikeW (edited 06-24-2002).]

Sorry, I thought I could show Frank's picture too by editing his URL (i think that is what they call it?) But it didn't work. I clicked on the following address and was able to view Frank's entire drawing. http://www.geocities.com/cinkerf/Sub-Panel.jpg

I apologize for cluttering up Frank’s topic. I thought I’d experiment and it didn’t work. I tried deleting messages and found only the moderator can do it. However when I typed the http world wide web address up in my address box I was able to view F.C.’s drawing. I’m trying to make some sense out of it but of course I can’t. Thanks.

[This message has been edited by MikeW (edited 06-24-2002).]

a good Q Mark, me..i say 1/2 the serving panel, general rule of 'thumb' only.

we could go see what is 'listed' for what...

there is also the 'demand load' avenue , where we could put eight 200A panels in a row......(now that's a bad design...)