Twin Breakers in Panels
- Thread starter jdeuce
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mdshunk
Senior Member
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- Right here.
Re: Twin Breakers in Panels
You cannot under any circumstance have more than 42 circuits in any single lighting and small appliance panelboard. Many panelboard manufacturers limit how many and in what slot 'twin' or 'tandem' breakers may be installed for each model of panel. This may be listed on the stickers in the panel (for instance 30 space, 40 ckt, which would mean you could only use 10 twins).
You cannot under any circumstance have more than 42 circuits in any single lighting and small appliance panelboard. Many panelboard manufacturers limit how many and in what slot 'twin' or 'tandem' breakers may be installed for each model of panel. This may be listed on the stickers in the panel (for instance 30 space, 40 ckt, which would mean you could only use 10 twins).
bphgravity
Senior Member
- Location
- Florida
Re: Twin Breakers in Panels
This factor is controlled by the manufacturer of the panelboard and not the NEC. The only limit imposed by the NEC is the "not more than 42 overcurrent devices" as specified in Section 408.15.
This factor is controlled by the manufacturer of the panelboard and not the NEC. The only limit imposed by the NEC is the "not more than 42 overcurrent devices" as specified in Section 408.15.
pierre
Senior Member
- Location
- Westchester County, New York
Re: Twin Breakers in Panels
From the UL White Book
CLASS CTL PANELBOARDS
Class CTL panelboards incorporate physical features which, in conjunction with the physical size, configuration, or other means provided in Class CTL circuit breakers, fuse holders, or fusible switches, are designed to prevent the installation of more overcurrent protective poles than that number for wihch the device is designed and rated.
CIRCUIT BREAKERS, MOLDED-CASE AND CIRCUIT BREAKER ENCLOSURES (DIVQ)
CLASS CTL
Some curcuit breakers are not provided with a means to prevent their installation in Class CTL assemblies. These circuit breakers are for use in old style, non-Class CTL equipment and are marked "For Replacement Use Only, Not CTL Assemblies."
When I first broke into this industry, I was taught those kind of breakers were for use anywhere we needed them...
I know a little better now.
From the UL White Book
CLASS CTL PANELBOARDS
Class CTL panelboards incorporate physical features which, in conjunction with the physical size, configuration, or other means provided in Class CTL circuit breakers, fuse holders, or fusible switches, are designed to prevent the installation of more overcurrent protective poles than that number for wihch the device is designed and rated.
CIRCUIT BREAKERS, MOLDED-CASE AND CIRCUIT BREAKER ENCLOSURES (DIVQ)
CLASS CTL
Some curcuit breakers are not provided with a means to prevent their installation in Class CTL assemblies. These circuit breakers are for use in old style, non-Class CTL equipment and are marked "For Replacement Use Only, Not CTL Assemblies."
When I first broke into this industry, I was taught those kind of breakers were for use anywhere we needed them...
I know a little better now.
mdshunk
Senior Member
- Location
- Right here.
Re: Twin Breakers in Panels
Teach me, Pierre...
For instance, the Square D tandems... some have a "hook" on them that goes into a slot on the mounting rail for certain slots. I assume these are CTL style. Some plug on like a regular breaker. I assume that these are non CTL or "replacement only" style. Am I right? or no?
Also, there used to be a tool that you used to punch out the "slot" on the mounting rail of Square 'D' panels to get the "hook" style tandem to install. Was this a "bootleg" tool to get around that UL requirement?
Teach me, Pierre...
For instance, the Square D tandems... some have a "hook" on them that goes into a slot on the mounting rail for certain slots. I assume these are CTL style. Some plug on like a regular breaker. I assume that these are non CTL or "replacement only" style. Am I right? or no?
Also, there used to be a tool that you used to punch out the "slot" on the mounting rail of Square 'D' panels to get the "hook" style tandem to install. Was this a "bootleg" tool to get around that UL requirement?
james wuebker
Senior Member
- Location
- Iowa
Re: Twin Breakers in Panels
mdshunk, I know were your coming from but the code states no more than 42 overcurrent (devices).So if your have a SQ. D 200 amp panel with 42 slots in it are you saying have I only can put 42 single pole breakers in it? Can I put 6 tandoms breakers in it if the panel is listed to do so? That would give me 36 single pole breakers and 6 tandom breakers with a total of 48 circuits. Is this OK? I believe it is. What is your take on this?
Jim
mdshunk, I know were your coming from but the code states no more than 42 overcurrent (devices).So if your have a SQ. D 200 amp panel with 42 slots in it are you saying have I only can put 42 single pole breakers in it? Can I put 6 tandoms breakers in it if the panel is listed to do so? That would give me 36 single pole breakers and 6 tandom breakers with a total of 48 circuits. Is this OK? I believe it is. What is your take on this?
Jim
mdshunk
Senior Member
- Location
- Right here.
Re: Twin Breakers in Panels
There is a couple of instances where you could have a "full" 42 space panel and still be able to use tandems. In the case of a QO panel, if you had some QO2 style 2 pole breakers that take up four slots, or if you were using some QO21125SL plug-on subfeed lug adaptors, then you'd have spaces taken up that don't count toward the 42 space circuit count. In this event, you could use tandems in a "full" 42 space panel. This may be some of the reasons why some "full size" panels are listed as being able to accept a few tandems. If memory serves, though, Square D only makes 40 space residential panel as the biggest model for some reason.
[ May 22, 2005, 10:18 PM: Message edited by: mdshunk ]
You are not permitted under any circumstance to install any amount of single pole pole or double pole or tandems in a lighting and small appliance panel that would result in a total circuit count greater than 42. Period. That's been in the NEC since the 1933 revision. A tandem breaker is two overcurrent devices in a single package.
There is a couple of instances where you could have a "full" 42 space panel and still be able to use tandems. In the case of a QO panel, if you had some QO2 style 2 pole breakers that take up four slots, or if you were using some QO21125SL plug-on subfeed lug adaptors, then you'd have spaces taken up that don't count toward the 42 space circuit count. In this event, you could use tandems in a "full" 42 space panel. This may be some of the reasons why some "full size" panels are listed as being able to accept a few tandems. If memory serves, though, Square D only makes 40 space residential panel as the biggest model for some reason.
[ May 22, 2005, 10:18 PM: Message edited by: mdshunk ]
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Twin Breakers in Panels
mdshunk,
You are correct the breakers with the hook are CTL. The non-hook style are often called cheaters. The installation tool was for old loadcenters (60s-70s)to remove the factory CTL knockouts.
Jim,
You can only install the number of tandem breakers "listed" by the manufacturer. In no situation should more than 42 circuits be installed in a single enclosure (408.15). Most panelboards are not designed to accept any tandem breakers
mdshunk,
You are correct the breakers with the hook are CTL. The non-hook style are often called cheaters. The installation tool was for old loadcenters (60s-70s)to remove the factory CTL knockouts.
Jim,
You can only install the number of tandem breakers "listed" by the manufacturer. In no situation should more than 42 circuits be installed in a single enclosure (408.15). Most panelboards are not designed to accept any tandem breakers
james wuebker
Senior Member
- Location
- Iowa
Re: Twin Breakers in Panels
Mdshunk, Your correct on the SQ.D residential panels. Only 40 spaces not 42. I put in a tons of these and must have type it in wrong when writing. Now on the 42 space rule, does it apply to commercial & industrial? I just put in a 240 volt 3 phase that had 54 slots in it. Of course I didn't put in 54 breakers. Installed some 125 amp breakers that took up 6 spaces each and a few 30 amp 3 pole breaker but still wondering if the 42 space rule applies to this?
Thanks!
Jim
Mdshunk, Your correct on the SQ.D residential panels. Only 40 spaces not 42. I put in a tons of these and must have type it in wrong when writing. Now on the 42 space rule, does it apply to commercial & industrial? I just put in a 240 volt 3 phase that had 54 slots in it. Of course I didn't put in 54 breakers. Installed some 125 amp breakers that took up 6 spaces each and a few 30 amp 3 pole breaker but still wondering if the 42 space rule applies to this?
Thanks!
Jim
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Twin Breakers in Panels
Not exactly.
See NEC-2002 408.14 and 408.15. If it's a power panelboard, the 42 handle rule doesn't apply.
Not exactly.
See NEC-2002 408.14 and 408.15. If it's a power panelboard, the 42 handle rule doesn't apply.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Twin Breakers in Panels
As to the 2005 edition, there are no changes in 408.34, the section that distinguishes power panels from lighting and appliance panels, and that establishes the 42 circuit limit.
I think we can safely infer from the original description that this is a dwelling unit, and that the panel in question would meet the definition of "lighting and appliance branch-circuit panelboard." So the 42 breaker limit would apply.
As to the 2005 edition, there are no changes in 408.34, the section that distinguishes power panels from lighting and appliance panels, and that establishes the 42 circuit limit.
Re: Twin Breakers in Panels
Take a standard QO panel..... I can fill the thing with qo-twins with no physical restrictions.
Say on a 200 amp rated panel. You're gonna fuse as such, 200 amps. The bus is rated for 200 amps.
If the total load of the panel exceeds 200 amps the main will trip or fuse will blow. So how is this a danger to the panel? How many 2 section panels have you install with a "feed thru" lug at the bottom of the bus to the second panel. What's the difference?
Lets see thats 84 circuits on a main. Is the first panel bussing rated for 400 amps.... I think not.
Another example it what we call "trailor panels"
200 amp main with feed thru lugs (UL approved) with 6 spaces for normal breakes.
Bottom line here is rule I follow for safety reasons
100 amp.... 20 spaces
125 amp.....24 spaces
150 amp.....30 spaces
200 amp.....40/42 spaces
200 amps is 200 amps, you exceed it, the main trips
end of subject.
Take a standard QO panel..... I can fill the thing with qo-twins with no physical restrictions.
Say on a 200 amp rated panel. You're gonna fuse as such, 200 amps. The bus is rated for 200 amps.
If the total load of the panel exceeds 200 amps the main will trip or fuse will blow. So how is this a danger to the panel? How many 2 section panels have you install with a "feed thru" lug at the bottom of the bus to the second panel. What's the difference?
Lets see thats 84 circuits on a main. Is the first panel bussing rated for 400 amps.... I think not.
Another example it what we call "trailor panels"
200 amp main with feed thru lugs (UL approved) with 6 spaces for normal breakes.
Bottom line here is rule I follow for safety reasons
100 amp.... 20 spaces
125 amp.....24 spaces
150 amp.....30 spaces
200 amp.....40/42 spaces
200 amps is 200 amps, you exceed it, the main trips
end of subject.
izak
Senior Member
- Location
- Springfield, MO
Re: Twin Breakers in Panels
more circuits add to the inside ambient operating temperature of the panel
a half-size breaker decreases the exposed surface area by 50%. that would decrease the breaker's ability to dissipate heat by probably 50%
more circuits add to the inside ambient operating temperature of the panel
a half-size breaker decreases the exposed surface area by 50%. that would decrease the breaker's ability to dissipate heat by probably 50%
james wuebker
Senior Member
- Location
- Iowa
Re: Twin Breakers in Panels
bigjohn67
You have some good ideas and I can agree with some of them but 408.15 states no more than 42 overcurrent devices of a lighting & appliance branch-circuit panelboard shall be installed in any(one cabinet or cutout box). So if you were to add sub panels from the main panel your total circuits could end up with more than 42 circuits total. I don't see a problem with this. I believe why they want to limit this per panel is due to the heat factor that can be added.
Bye now,
Jim
bigjohn67
You have some good ideas and I can agree with some of them but 408.15 states no more than 42 overcurrent devices of a lighting & appliance branch-circuit panelboard shall be installed in any(one cabinet or cutout box). So if you were to add sub panels from the main panel your total circuits could end up with more than 42 circuits total. I don't see a problem with this. I believe why they want to limit this per panel is due to the heat factor that can be added.
Bye now,
Jim
charlie
Senior Member
- Location
- Indianapolis
Re: Twin Breakers in Panels
Big John, it is OK to voluntarily limit the number of circuits to less than the Code or the listing permits but I question the safety aspects of your reason. The panelbords are tested with the maximum number of circuits and load so they are indeed safe in that respect if they are installed correctly. In other words a 200 ampere 20/40 panelboard is tested at 200 amperes and with all ?" circuit breakers.
Izak, as long as the panelboard is listed for it, the ?" circuit breakers are fine and the heat load is OK.
Big John, it is OK to voluntarily limit the number of circuits to less than the Code or the listing permits but I question the safety aspects of your reason. The panelbords are tested with the maximum number of circuits and load so they are indeed safe in that respect if they are installed correctly. In other words a 200 ampere 20/40 panelboard is tested at 200 amperes and with all ?" circuit breakers.
Izak, as long as the panelboard is listed for it, the ?" circuit breakers are fine and the heat load is OK.
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