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#94875 08/16/05 07:42 PM
Joined: Mar 2003
Posts: 92
G
gserve Offline OP
Member
Can someone explain to me the NEC rules on sub panels? What I want to know is the maximum amount of panels if any and maximum size(amps) of each. Example: 200A service and client wants 2 100A subs off of this. Can this be done this way and meet code? Please clarify Thanks

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#94876 08/16/05 07:49 PM
Joined: Jan 2003
Posts: 4,391
I
Moderator
There are no NEC rules regarding the number of 'sub panels' or overcurrent devices that can be supplied by a certain size service or feeder.

The only thing that matters is the calculated load.

Wire a house that has 100 outlets, put 10 on a circuit and you end up with 10 breakers.

Now wire the same house but the owner wants each outlet on a home run. You would have 100 outlets with 100 breakers but the calculated load would not have changed.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#94877 08/16/05 07:50 PM
Joined: Feb 2005
Posts: 693
L
Member
Some panels are listed with the maximum current that may be taken from one lug, so you may have to make sure you do not place any breakers opposite the 100-amp breakers.


Larry Fine
Fine Electric Co.
fineelectricco.com
#94878 08/16/05 08:53 PM
Joined: May 2002
Posts: 1,716
R
Member
Let's make it three for three. [Linked Image]

Put as many sub fed panels as you want downstream of the main, their cumulative loads are governed by the main itself.

If the main starts tripping on over current, you need to back up.

Roger

#94879 08/26/05 12:07 AM
Joined: Mar 2005
Posts: 240
Member
i thought there was a six switch rule.

h20

#94880 08/26/05 05:50 AM
Joined: Jan 2003
Posts: 4,391
I
Moderator
H2O, there is a "six switch rule" but that does not have any effect on the number of sub-panels allowed.

With a few exceptions the six switch rule means you must be able to kill the entire building by opening no more than six switches.

As an example if you had a building with a single 200 amp breaker as the service disconnect you would only have to open that one switch in order to kill the entire building regardless of how many sub panels where connected to it.

Think about a very large building, there may be hundreds of sub-panels located throughout the building. But at the service entrance there will be no more than six switches to kill the entire building.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#94881 08/26/05 07:14 AM
Joined: Dec 2004
Posts: 1,064
D
Member
Great explanation Bob.......

Dnk....

#94882 08/26/05 06:12 PM
Joined: Jan 2003
Posts: 4,391
I
Moderator
Thank you. [Linked Image]

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#94883 08/27/05 12:33 PM
Joined: Mar 2005
Posts: 240
Member
iwire that makes sense.
now that it was explained in english(vs nec-ism) yuk yuk.

h20


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