Tandem Breakers / Box Fill

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Rock86

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new york
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Electrical Engineer / Electrician
Not sure if this falls in this category, but i'll give it a shot....

Recently (and i'm sure this happens a often) my boss went on a site survey and sent a picture of a 30 pole panel packed with 16 tandem breaker (32 circuits). Tandem breakers are legal... but I'm looking at the picture and the conductor count is quite high. Now a Square D 42 Pole panel allows 84 circuits, but does that allowance of 84 circuits allow for the number of conductors within the panel?
 
Unless the panel is designed for more breakers than the size is based on the manufacturer design. AFAIK the 42 circuit SQ. D panel is rated for 42 breakers full size and no twins are allowed. I have never seen a 42 cir panel capable of twins
 
That panel is 39" tall.... Forgive me but that would be a total nightmare in my opinion. I knew Sq.D had an 80 cir panel but I thought they were all full size breakers.
 
Most breaker panels are shown as "xx spaces / xx circuits" and you can extrapolate how many spaces accept tandems from that.
 
I believe Siemens, Ge and some others have a 40 cir. panel and it is called 40 cir-- all full size. They also have a 20/40(20 full size or 20 twins as Larry stated thus my confusion when you said 42 cir. panel.
 
Try and max out circuit capacity on a 40/80 panel with all the afci requirements now, haven't seen any tandem afci unless someone else has.
 
Fred B said:
Try and max out circuit capacity on a 40/80 panel with all the afci requirements now, haven't seen any tandem afci unless someone else has.
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IMO it is a terrible design to have 80 circuits in one panel. If a house is big enough for 80 circuits I am going to have many sub panels thru out the house.

I can see a straight 80 being used in a commercial setting but not in a residence.
 
Alright so although we can agree it is a terrible design... how does everyone feel about the box fill calculation should someone load a panel full of tandem breakers?
 
We frequently use 84 circuit PANELBOARDS in homes, especially when using HomeWorks Lighting controls. Most homeowners and designers limit where they will let us install our equipment. We usually get the garage, laundry room or mudroom (if they have one). Sometimes there are decent size mechanical rooms but the plumbers and HVAC guys are really good at wasting as much space as they can so limit what we get.

I wish they would offer wider loadcenters. I get the design to fit standard stud spacing but most of the time its not that big a deal to shift a stud a few inches. With Square D and Eaton CH you only get about 1" of gutter space since their AFCI's are so long. Wider boxes would also make getting a large number of cables into the box.
 
Rock86 said:
Alright so although we can agree it is a terrible design... how does everyone feel about the box fill calculation should someone load a panel full of tandem breakers?
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Bottom line what is the load demand, if it doesn't violate mfg design spec and it's circuits are not "overloaded" you are limited to whining if you got to try to trace and change a circuit. Wouldn't want to be that guy. Even then I think you'd be hard pressed to justify a panel full of 50/20 double pole tandems for box fill space.
 
The main thing you need with the larger 84 circuit panels is about 84 neutral terminations. But the gutters are packed when that many conductors are in there. I think you could do it, as even a 1" x 1" space can take a lot of conductors. If you keep them straight and tightly cable tie them, they will fit. You may then need to remove the cable ties when you're done so you don't have a bundle derating issue. The way residential panels get wires twisted and inter-twined, it will probably be a mess after a period of time. Even worse if breakers are moved and there are now splices in the gutters.
 
curt swartz said:
We frequently use 84 circuit PANELBOARDS in homes, especially when using HomeWorks Lighting controls. Most homeowners and designers limit where they will let us install our equipment. We usually get the garage, laundry room or mudroom (if they have one). Sometimes there are decent size mechanical rooms but the plumbers and HVAC guys are really good at wasting as much space as they can so limit what we get.

I wish they would offer wider loadcenters. I get the design to fit standard stud spacing but most of the time its not that big a deal to shift a stud a few inches. With Square D and Eaton CH you only get about 1" of gutter space since their AFCI's are so long. Wider boxes would also make getting a large number of cables into the box.
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Want wider use the commercial NQ series, you get 20 inch wide x 5.5~6 inches deep. Don't have to use bolt on breakers as it accepts those or plug on. Will need to be QO series though, they don't make one of these for Homeline.
 
suemarkp said:
The main thing you need with the larger 84 circuit panels is about 84 neutral terminations. But the gutters are packed when that many conductors are in there. I think you could do it, as even a 1" x 1" space can take a lot of conductors. If you keep them straight and tightly cable tie them, they will fit. You may then need to remove the cable ties when you're done so you don't have a bundle derating issue. The way residential panels get wires twisted and inter-twined, it will probably be a mess after a period of time. Even worse if breakers are moved and there are now splices in the gutters.
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Correct the "gutter" has a lot of space for 60 amp and less conductors. GFCI/AFCI's can take up some that space, but those don't come in twin/tandems either so that offsets things some, especially if you have quite a few AFCI's to begin with. Then unless you use the "quads" for some of your 2 pole circuits you are also at one wire per "space" with those as well.
 
suemarkp said:
The main thing you need with the larger 84 circuit panels is about 84 neutral terminations. But the gutters are packed when that many conductors are in there. I think you could do it, as even a 1" x 1" space can take a lot of conductors. If you keep them straight and tightly cable tie them, they will fit. You may then need to remove the cable ties when you're done so you don't have a bundle derating issue. The way residential panels get wires twisted and inter-twined, it will probably be a mess after a period of time. Even worse if breakers are moved and there are now splices in the gutters.
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Granted, this is not an 84-circuit panel, but a full panel need not be cluttered, and I have never used a cable-tie in a panel.

DSC00852.JPG
 
LarryFine said:
Granted, this is not an 84-circuit panel, but a full panel need not be cluttered, and I have never used a cable-tie in a panel.
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Very much as we do it but how do you find enough ko's in an 80 cir panel. Also they re not much larger than a 40 circuit panel
 
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