Limit to number of circuit breakers in panel

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jksmith82 said:
I remember the Square D panel. 80 or so circuits. What impressed me about that panel was it actually had enough room on the bus bars for all the neutrals and grounds that the panel can hold.

Jim
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Maybe it's just me but I don't like putting all my eggs in one basket, so to speak!
 
When I worked for Siemens and went through what was essentially the original ITE training program (meaning it was very old by then), the 42 pole limit (not CIRCUITS by the way, POLES) was based upon the following:

1. It only applied to "lighting and appliance panelboards", defined as having 10% or more pole spaces that were 30A or less, so basically residential and commercial panels. This rule didn't apply to "industrial panelboards".

2. Add that with the fact that the boxes were designed to fit in between standard wall studs.

3. Now add that the topmost breaker handle can't be higher than 6'7" off the floor, using more than 42 poles in a panel resulted in the bottom most breaker being down closer to "toddler height" off of the floor. There is no actual lower height restriction in the NEC, but the panel mfrs were concerned about Resi panels allowing little ones to get too close, so they wanted to stick to a self-imposed limit of 24" up off of the floor (which interestingly made it into the Mobile Home paragraph).

So within those conditions and limitations, the shear number of possible conductors was not going to fit from a box fill perspective, because 42 poles could POTENTIALLY be 42 single pole breakers that would need neutrals, resulting in 84 branch conductors crammed into that annular space around the bus and breaker frame.

So why has it changed? No idea.
 
Jraef
"went through what was essentially the original ITE training program "
That was a giant workbook for that program, I did one when it was GouldITE over here on the right side of the map.
Small world.
 
Jraef said:
When I worked for Siemens and went through what was essentially the original ITE training program (meaning it was very old by then), the 42 pole limit (not CIRCUITS by the way, POLES) was based upon the following:

1. It only applied to "lighting and appliance panelboards", defined as having 10% or more pole spaces that were 30A or less, so basically residential and commercial panels. This rule didn't apply to "industrial panelboards".

2. Add that with the fact that the boxes were designed to fit in between standard wall studs.

3. Now add that the topmost breaker handle can't be higher than 6'7" off the floor, using more than 42 poles in a panel resulted in the bottom most breaker being down closer to "toddler height" off of the floor. There is no actual lower height restriction in the NEC, but the panel mfrs were concerned about Resi panels allowing little ones to get too close, so they wanted to stick to a self-imposed limit of 24" up off of the floor (which interestingly made it into the Mobile Home paragraph).

So within those conditions and limitations, the shear number of possible conductors was not going to fit from a box fill perspective, because 42 poles could POTENTIALLY be 42 single pole breakers that would need neutrals, resulting in 84 branch conductors crammed into that annular space around the bus and breaker frame.

So why has it changed? No idea.
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I agree that a 14-1/4" wide loadcenter can get really crowded if everything must exit from either top or bottom. Even with a 40 space box the knockouts start running out and access to connector setscrews is dicey.

But the math simply doesn't work in regard to the concern over the height of the lower breakers. A 40 space main breaker Siemens loadcenter has all breakers within a 24" space. If the main breaker is at 78", the bottom breakers are at 54". Bump it up to 80 spaces and you have the bottom breaker at 34", and the bottom of the cabinet at 28".... still above the mobile home 24" requirement. And the door latch is well off of reach of a child, and can easily be locked.
 
Adamjamma said:
Maybe because of the half breakers? Breakers were thicker in old days
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half size and tandems have been around for a very long time.

I have a plant I do work in that has some tandem QO breakers in a couple places that I can almost promise you were original in the mid to late 1960's. They were non CTL type, but I believe the CTL requirement came later, like maybe 15-20 years later. If you used CTL rated ones you couldn't install anymore than the panel was designed to accept as they had a rejection feature for slots that weren't intended for them.

Today a lot of the panels are designed to accept a tandem in every slot.

With the AFCI requirements we now have for dwellings you don't see tandems being used, they haven't made any tandem AFCI's (so far) so that 40/80 panel is mostly still a 40 circuit panel in a dwelling. I suppose the mobile and manufactured homes are still using "quad breakers" for some 240 volt loads and there is a very small number of 120 volt circuits that don't require AFCI protection in a dwelling.
 
kwired said:
half size and tandems have been around for a very long time.

I have a plant I do work in that has some tandem QO breakers in a couple places that I can almost promise you were original in the mid to late 1960's. They were non CTL type, but I believe the CTL requirement came later, like maybe 15-20 years later. If you used CTL rated ones you couldn't install anymore than the panel was designed to accept as they had a rejection feature for slots that weren't intended for them.

Today a lot of the panels are designed to accept a tandem in every slot.

With the AFCI requirements we now have for dwellings you don't see tandems being used, they haven't made any tandem AFCI's (so far) so that 40/80 panel is mostly still a 40 circuit panel in a dwelling. I suppose the mobile and manufactured homes are still using "quad breakers" for some 240 volt loads and there is a very small number of 120 volt circuits that don't require AFCI protection in a dwelling.
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CTL was added as Article 384.15 in the 1965 code.
 
Craigv said:
CTL was added as Article 384.15 in the 1965 code.
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OK.

Pretty sure nobody was enforcing code around here back then either, so who knows how long it took for something like that to start being voluntarily complied with. Probably depends on when price of non CTL breakers went up enough to matter to the installer.
 
kwired said:
OK.

Pretty sure nobody was enforcing code around here back then either, so who knows how long it took for something like that to start being voluntarily complied with. Probably depends on when price of non CTL breakers went up enough to matter to the installer.
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This took a long time to implement. Non-CTL loadcenters weren't produced after 1965, but given available stock, availability of non-CTL breakers, and how long it takes to replace an existing fuse/breaker panel, this took decades. I service a campground that has cabins, restrooms, pumphouses, etc. that still have non-CTL loadecenters.
 
Square D has 60 and 80 space homeline loadcenters.

I think the NQ panelboards and QO loadcenter max is 72 spaces.

I’ve used a few of the 60-space loadcenters on larger homes that only need a 200A service.


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brantmacga said:
Square D has 60 and 80 space homeline loadcenters.

I think the NQ panelboards and QO loadcenter max is 72 spaces.

I’ve used a few of the 60-space loadcenters on larger homes that only need a 200A service.


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Not certain about loadcenters, but I have used 84 space NQ before.
 
kwired said:
Not certain about loadcenters, but I have used 84 space NQ before.
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I was completely wrong on both ...

NQ goes to 84

QO goes to 54 with plug on neutrals in MLO on single phase, 60 in MCB, and the old style QO only goes to 42.

Seems odd they only show 54 circuits in the MLO; I thought all of their QO loadcenters had field convertible mains and used the same bus.


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