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#35233 - 03/06/04 07:37 AM The archaic 42-circuit limit
Sir Arcsalot Offline
Member

Registered: 11/17/03
Posts: 117
Loc: Lynden, Washington
As I do highway and land surveying work as opposed to electrical work for a living, maybe there's something I do not understand about the 42-circuit limitation spelled out in NEC 408.15 for lighting and appliance panelboards. It just seems like a totally arbitrary limit when the panelboard's load cannot exceed the ampacity of the main disconnect anyway (or at least it shouldn't be able to).

I've read other posts in this forum mentioning the limitation based on a fire investigation done many years ago, my memory ain't like it was when I was younger but I think it was a 1928 Chicago fire or something like that. Yet, our neighbors to the north apparently can obtain lighting/appliance panelboards up to 84 circuit capacity- I seriously doubt there has been an increase in fires for reasons mentioned in the first paragraph.

With all of the dedicated circuits now required by the NEC, I believe this limitation should be either substantially increased or eliminated as long as the main OCP device protecting such a panelboard is in keeping with its rated capacity.

Since I do live within a few miles from the Canadian border, maybe I could smuggle one across- then again, it may not be able to handle non-metric loads :-)

This forum is a great place indeed to learn and communicate; kudos to the hosts!!!
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#35234 - 03/06/04 07:55 AM Re: The archaic 42-circuit limit
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Yeah you got be careful mixing non metric and metric electricity.

I spend a lot of time in buildings with many dedicated ciruits.

We run into the 42 circuit limit all the time before we run out of electrical capacity

What we do is use double or triple tub panels 84, or 126 circuits respectively on one feeder.

I agree that 42 seems to be just an arbitrary number but I like the limit.

42 circuits worth of branch circuit wiring in one tub is enough for me, 126 circuits spread out in three tubs is nice to work with.

Just my opinion, Bob
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#35235 - 03/06/04 10:57 AM Re: The archaic 42-circuit limit
CRW Offline
Member

Registered: 02/11/01
Posts: 160
Loc: Bethlehem, PA USA
Some panels are manufactured now with more than 42 circuit spaces. Square D makes one with a low voltage control feature for lighting, and there are around 46 or 48 spaces, I can't remember.

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#35236 - 03/06/04 11:03 AM Re: The archaic 42-circuit limit
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
As far as residential goes, a dozen circuits would be a lot here. There are still plenty of homes wired in the 1950s/60s with only 4 circuits!

 Quote:
Sir Arcsalot


Love that name!



[This message has been edited by pauluk (edited 03-06-2004).]

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#35237 - 03/06/04 11:05 AM Re: The archaic 42-circuit limit
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
The spaces may be there but I doubt you can put breakers in the spaces.

 Quote:
408.15 Number of Overcurrent Devices on One Panelboard.
Not more than 42 overcurrent devices (other than those provided for in the mains) of a lighting and appliance branch-circuit panelboard shall be installed in any one cabinet or cutout box.
A lighting and appliance branch-circuit panelboard shall be provided with physical means to prevent the installation of more overcurrent devices than that number for which the panelboard was designed, rated, and approved.

For the purposes of this article, a 2-pole circuit breaker shall be considered two overcurrent devices; a 3-pole circuit breaker shall be considered three overcurrent devices.


The spaces are probably for elements of the control system.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#35238 - 03/06/04 11:12 AM Re: The archaic 42-circuit limit
CRW Offline
Member

Registered: 02/11/01
Posts: 160
Loc: Bethlehem, PA USA
Bob, I realize that the code says 42, but these panels were loaded to over 42, with guts from the factory, all spaces occupied. I didn't notice at first till we were finishing numbering the circuits. When I asked the foreman, he just said that's what they gave us, that's what we're using. The prints were all engineered like that, and I never saw the inspector's response, if any.

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#35239 - 03/06/04 11:31 AM Re: The archaic 42-circuit limit
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Well that is interesting. hmmmmmm?

I do not think I would have installed it without checking further on this.

The panels we have assembled for us are put together many times at panel shops of large distributors, I would not assume that just because they built it that it complies.

Don I know you have said there are times we can exceed 42 OCPDs would this be one of those time?
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Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#35240 - 03/06/04 12:48 PM Re: The archaic 42-circuit limit
u2slow Offline
Member

Registered: 09/18/03
Posts: 198
Loc: Salt Spring, BC, Canada
 Quote:
Not more than 42 overcurrent devices (other than those provided for in the mains) of a lighting and appliance branch-circuit panelboard shall be installed in any one cabinet or cutout box.


The use of the word 'and' is suspicious. Sounds to me like a panel supplying a combination of lighting and appliance loads has a 42-circuit limit. Whereas a dedicated lighting panel could be larger. Otherwise 'or' should be used in the ruling.

What do you guys think?

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#35241 - 03/06/04 04:48 PM Re: The archaic 42-circuit limit
CRW Offline
Member

Registered: 02/11/01
Posts: 160
Loc: Bethlehem, PA USA
 Quote:
The use of the word 'and' is suspicious. Sounds to me like a panel supplying a combination of lighting and appliance loads has a 42-circuit limit. Whereas a dedicated lighting panel could be larger. Otherwise 'or' should be used in the ruling.


I never looked at it that way, and it's possible that you have something there, bu the only definitions I see for the different types of panelboards is in 408.14(A)and (B). Looks like it's either "lighting and appliance" or "power".

After the paragraph Bob quoted from 408.15, it says "a lighting and appliance branch-circuit panelboard shall be provided with physical means to prevent the installation of more than overcurrent devices than that number for which the panelboard was designed, rated, and approved." These panelboards had nothing to prevent more than 42 breakers from being installed; they looked like they were designed to hold all of them (hoever many that was, I forgot--44-46-48, whatever.)

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#35242 - 03/06/04 06:37 PM Re: The archaic 42-circuit limit
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
Power panels do not have the 42 circuit limit like "lighting and appliance branch circuit panels" do. The types of loads served do not determine the type of panel.
 Quote:
408.14 Classification of Panelboards.
Panelboards shall be classified for the purposes of this article as either lighting and appliance branch-circuit panelboards or power panelboards, based on their content. A lighting and appliance branch circuit is a branch circuit that has a connection to the neutral of the panelboard and that has overcurrent protection of 30 amperes or less in one or more conductors.
(A) Lighting and Appliance Branch-Circuit Panelboard. A lighting and appliance branch-circuit panelboard is one having more than 10 percent of its overcurrent devices protecting lighting and appliance branch circuits.
(B) Power Panelboard. A power panelboard is one having 10 percent or fewer of its overcurrent devices protecting lighting and appliance branch circuits.

The panelboard in question may have been intended as a power panelboard and it is being illegally used as a lighting and appliance branch circuit panelboard.
Don
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