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#94875 - 08/16/05 04:42 PM sub panel rules
gserve Offline
Member

Registered: 03/11/03
Posts: 92
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 04:49 PM Re: sub panel rules
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
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

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#94877 - 08/16/05 04:50 PM Re: sub panel rules
Larry Fine Offline
Member

Registered: 02/18/05
Posts: 684
Loc: Richmond, VA
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

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#94878 - 08/16/05 05:53 PM Re: sub panel rules
Roger Offline
Member

Registered: 05/18/02
Posts: 1779
Loc: N.C.
Let's make it three for three.

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

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#94879 - 08/25/05 09:07 PM Re: sub panel rules
watersparkfalls Offline
Member

Registered: 03/08/05
Posts: 210
Loc: Washington...Not DC
i thought there was a six switch rule.

h20

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#94880 - 08/26/05 02:50 AM Re: sub panel rules
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
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

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#94881 - 08/26/05 04:14 AM Re: sub panel rules
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
Great explanation Bob.......

Dnk....

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#94882 - 08/26/05 03:12 PM Re: sub panel rules
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Thank you.

Bob
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#94883 - 08/27/05 09:33 AM Re: sub panel rules
watersparkfalls Offline
Member

Registered: 03/08/05
Posts: 210
Loc: Washington...Not DC
iwire that makes sense.
now that it was explained in english(vs nec-ism) yuk yuk.

h20

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