All of the "Doit Yourself" books I have seen portray putting the
breaker protecting the subpanel in the mainpanel. My main panel
has places on the bus bars to connect wires directly. Does the
NEC allow me to just run wires from these lugs to a service
rated subpanel with a "main" breaker protecting ITs bus bars? I
have a 1978 NEC and 384-16 (I hope they maintain consistency in
numbers!) appears to say that the protection can go in either
place. But then I wonder why the books don't mention this.

I don't want to consume the two circuits in the main panel for
the feed.

The main panel is rated at 100A, and according the the label I
could put lots of doubles in it, but it is full of singles.

Thank you. webclark@rochester.rr.com

:All of the "Doit Yourself" books I have seen portray putting the
breaker protecting the subpanel in the mainpanel.

Reply I doubt that you will ever see an article in the NEC
stating that this rule will fit all wiring styles and situations
no matter what. In what you discribe concerning the lugs attached
to the buss in the main panel are protected by the main breaker
in that panel.

My main panel has places on the bus bars to connect wires
directly.

If I am reading what you have said accurately I am taking that
you have a couple of heavy lugs in your main service rated panel
that de-energize when that main service rated panel's main
breaker is shut off. This can very well be what you have. Many
panels on the market have what is called a feed through heater
lugs designed to serve non service rated panels [sub-panels].
These main service rated panels are usually listed and labeled by
a testing lab designed to do this type of sub- panel project.
Suppliying a sub-panel is approved by the NEC from these heater
lugs without limitation considering distance as long as those
feeders going to that sub-panel is rated in ampacity equal to the
ampacity of the main breaker in you main service rated panel
where those feeders are coming from. The main breaker in that
first panel protect those lugs in ampacity at the same rating
that it protects the entire main panel that breaker is in.
Remember to expect the main breaker in the panel serving power to
that feeder connected to those lugs is the overcurrent device
[breaker] protecting that feeder serving the sub-panel. That
overcurrent protection must be placed on the line side where that
feeder gets its power and not from the load side where that
feeder supplies power to.

Now there are rules that apply pertaining to panels fed from
panels called tap rules that allow the overcurrent device that
protects that feeder serving that subpanel its power to be
located on the load side in that panel if supplies power to.
However when these tap rules are applied you now would have two
main service rated panel but no sub panels. You would have two
main breakers one in each panel. The two tap rules most commonly
used are the 10' tap rule allowing a feeder to a second panel to
be installed without a breaker protecting its line side but the
breaker protecting that feeder located on the load side. This 10'
tap rule allows the feeder to be reduced in size compared to the
original feeder supplying its power no smaller than 1/10th the
size of the original feeder serving that tapped feeder. There is
also an unlimited tap rule applying to a one time tap located
outside but not entering a building beyond it nearest point of
entrance of that tapped conductor. Be careful using this
unlimited tap rule, Utility company's are tending to react
adversly to its use. These tap rules are found in Article 240-21-
B-1 and 5 in the 99 NEC.

Does the NEC allow me to just run wires from these lugs to a
service rated subpanel with a "main" breaker protecting ITs bus
bars?

What you meant to say is "to this non-service rated panel" If a
second panel is coming from a main service rated panel and is
served through the main overcurrent device [main breaker]  
located in the first main service rated panel, then that second
panel is a non-service rated panel no matter whether that second
panel has a main overcurrent device [main breaker] or not.

If that second panel is fed using the tap rules and that feeder
is not controlled by the main breaker in that first panel then
you have two main service rated panel and each panel must be
grouped together and both panels must have main breakers.


I have a 1978 NEC and 384-16 (I hope they maintain consistency
in numbers!) appears to say that the protection can go in either
place. But then I wonder why the books don't mention this.

I strongly advise you to put that 1978 NEC into your history
book. The NEC has been revised every three years since then.
Thousands of changed in the minimum safety standards have been
implemented since 1978 compared to the 1999 NEC. Also the 2002
NEC will be on the open market about November of this year with
even more changes in the rules.

However when I pulled my 1978 NEC out of my archives, I found the
main rule of 384-16 to say close to the same thing. Yet in the
content of that main rule little is left the same compared to the
99 NEC. By the way the 99 NEC is twice the size in width times
the length compared ot the 78 NEC also.

I don't want to consume the two circuits in the main panel for
the feed.


It is fine to not use the two circuits in that main panel serving
that second panel as long as that feeder serving that second
panel and that second panel is rated in ampacity as that main
breaker serving that first panel. Just make sure that those lugs
de-energize when you shut the breaker off those lugs shut off
too. You actually may use the two open circuit slots for a
smaller feeder or use the heater lugs you are talking of just
keep in mind those heater lugs are protected by the main breaker
in that main panel at its ampacity and the feeders must be the
same size as the feeder serving that main panel's power.

:
The main panel is rated at 100A, and according the the label I
could put lots of doubles in it, but it is full of singles.

If you panel is rated for 1/2 size breakers then it is allowed to
install 1/2 size breakers. These 1/2 size breaker come in most
ampacity ratings in 120 volt or even double double 220 volt
breakers with different amp rating of the 2 - 220 volt breakers
built as one breaker set.

Thank you. webclark@rochester.rr.com

Glad to hear from you and hope we were able to be of at least a
little help

Good Luck

Wg

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