Reason for the CTL Panel Rule

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CERA 2254

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Electrician
This is something that recently has really piqued my curiosity. Can anyone shed light on why the CTL rule even exists? It seems odd to me to have a panel that only fits tandem style CTL breakers in certain spots and not all. I say this because let’s say for example you have two open spaces that will not fit tandem 20A breakers, but you could install a 2 pole 100A breaker. Seems odd to be able to install a potential 100A load on the bus tab but somehow a potential 40A of load is not acceptable on the same bus bar tab? Why would it matter how many circuits they are as long as everything within the limits of the bus bar and main overcurrent device?

Christian
 
CERA 2254 said:
This is something that recently has really piqued my curiosity. Can anyone shed light on why the CTL rule even exists? It seems odd to me to have a panel that only fits tandem style CTL breakers in certain spots and not all. I say this because let’s say for example you have two open spaces that will not fit tandem 20A breakers, but you could install a 2 pole 100A breaker. Seems odd to be able to install a potential 100A load on the bus tab but somehow a potential 40A of load is not acceptable on the same bus bar tab? Why would it matter how many circuits they are as long as everything within the limits of the bus bar and main overcurrent device?

Christian
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On the smaller residential load centers I always assumed it was to limit the conductors in the panel. Neutral bar spaces were limited as well. Larger load centers were limited to 42 spaces.
 
ptonsparky said:
On the smaller residential load centers I always assumed it was to limit the conductors in the panel. Neutral bar spaces were limited as well. Larger load centers were limited to 42 spaces.
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I have always been curious about it too. I wonder if it was neutral bar spaces.

Doesn't the 42 space limit no longer exist and that was from the "lighting panelboard" vs "appliance panelboard" thing?
 
At least as far back as the 50's panels needed to have restrictions on where breaker 30A and smaller could be installed. This apparently was a carry over from fusible panels.

At the same time breaker panels were sold with wiring diagrams showing where tandem breakers were allowed (pre-CTL)

In the 60s the 30A restriction was removed and CTL was instituted.
 
Hmm, I had never heard the 30A part of that, interesting.

CTL (Circuit Total Limitation) was not implemented until the 1965 Code. Prior to that, there were no restrictions to the number of devices you could plug into a panel, other than the physical room. So because a lot of early breaker panes were 60 or even 30A, the advent of “tandems” allowed people to seriously overload panels when we began using more and more electricity in homes in the 50s. So they implemented CTL to force panel manufacturers to have another physical limit to the maximum number of pole spaces, as well as limiting it to 42 poles regardless of the rating. In 2008 they repealed that 42 pole rule, so in EFFECT the CTL rule is pointless, but it takes a long time for mfrs to change panel designs, so most smaller panels still have the CTL designs in place.

You can still but “Non-CTL” versions of tandem breakers in some brands that have been around long enough, ostensibly to install into pre-1965 panels. Technically it’s a Code violation to install them in CTL panels, and the manufacturers make them purposefully more expensive to help discourage DIYers from buying them. That is only partly successful…
 
Jraef said:
You can still but “Non-CTL” versions of tandem breakers in some brands that have been around long enough, ostensibly to install into pre-1965 panels. Technically it’s a Code violation to install them in CTL panels, and the manufacturers make them purposefully more expensive to help discourage DIYers from buying them. That is only partly successful…
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Eaton has stated that NON-CTL breakers can be installed legally in their new panels as long as there are not more circuit breakers than it is listed for. I have an new Eaton 40/80 panel that has no feature to reject NON-CTL breakers. The NEC needs to clear up this confusion and get rid of the CTL nonsense.
 
Jraef said:
Hmm, I had never heard the 30A part of that, interesting.

CTL (Circuit Total Limitation) was not implemented until the 1965 Code. Prior to that, there were no restrictions to the number of devices you could plug into a panel, other than the physical room. So because a lot of early breaker panes were 60 or even 30A, the advent of “tandems” allowed people to seriously overload panels when we began using more and more electricity in homes in the 50s. So they implemented CTL to force panel manufacturers to have another physical limit to the maximum number of pole spaces, as well as limiting it to 42 poles regardless of the rating. In 2008 they repealed that 42 pole rule, so in EFFECT the CTL rule is pointless, but it takes a long time for mfrs to change panel designs, so most smaller panels still have the CTL designs in place.

You can still but “Non-CTL” versions of tandem breakers in some brands that have been around long enough, ostensibly to install into pre-1965 panels. Technically it’s a Code violation to install them in CTL panels, and the manufacturers make them purposefully more expensive to help discourage DIYers from buying them. That is only partly successful…
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Prior to 1965 you were supposed to follow the manufacturer's instructions, like the panel schedule. Contractors were not doing this so CTL came into existence.

I have documentation from 1958 describing the 30A location issue and showing loadcenters rated for a limited number of tandems, like a QO2030xxxx.
 
Now that the 42 circuit limit is gone for panels as long as the number of breakers doesn't exceed the number listed by the manufacturer the breaker (be it CTL or NON- CTL) should not matter.
 
Maybe they can drop the price on the cheater tandems then.

Nowadays QO panels where the old round plastic rail has turned into a metal neutral bus for PON and they no longer have the tandem hook slots. You can still put the cheater tandem in, but it costs a lot more.
 
Birken Vogt said:
Maybe they can drop the price on the cheater tandems then.

Nowadays QO panels where the old round plastic rail has turned into a metal neutral bus for PON and they no longer have the tandem hook slots. You can still put the cheater tandem in, but it costs a lot more.
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I doubt they'll ever "give" on the price but it does force people to buy an already more expensive product that costs the same to manufacturer
 
The old rating was a UL listing as type N1 which allowed 15 & 20A breakers everywhere, but 39A and larger only in restricted locations.
 
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