Jerramundi
Senior Member
- Location
- Chicago
- Occupation
- Licensed Residential Electrician
Greetings once again brethren!
Somehow I've managed to stay busy through December 2020 and have been absent from the forum for a few months, but now that I need something from you all, I'm back! *Slightly hesitant, guilty chuckle* Slight difference this time though - I've actually done a good chunk of homework before coming here!
In the something like 11-12 years I've been in the field, this is the first time I've encountered a Class NI Panel...
Essentially, I figured I'd just share what I've learned thus far, possibly get some feedback, and maybe get a discussion going.
..........................................................................................................................
Here's my understanding thus far... The rub is that Class NI was replaced by Class CTL?
It feels like an accurate, but yet severely lacking summary.
My understanding is that Class NI stands for "Non-Interchangeable" and that, in the 1959 NEC, there is an explicit reference to "Non-Interchangeable Circuit Breakers" in § 240.25 (G) Non-Interchangeable Circuit Breakers.
The article is generally about making it difficult to increase the amperage on a branch circuit breaker... or implicitly providing a "...physical means to prevent the installation of more overcurrent devices than that number for which the panelboard was designed, rated, and approved" ...post installation.
In § 240.25 (G) (3) (Note) set the effective date of this article is set for July 1, 1960, confirming the reference date to the terminology as 1959 without having to go back any further in the history of the NEC.
§ 240.25 (G) (3) (Note) was deleted in the 1962 NEC, presumably because the effective date had now passed, the article was active code, and the effective date was no longer relevant. Confirming the existence of § 240.25 (G) Non-Interchangeable Circuit Breakers in 1962 via a deletion of one of its' components and not the whole.
There is zero mention of § 240.25 (G) Non-Interchangeable Circuit Breakers in the 1965 NEC... and there are only a few mentioned of the word "Interchangeable," all of which refer to something else entirely... inferring deletion.
This is where Mike's Newsletter on Circuit Breakers: CTL Assemblies kicks in where he says, "...CTL means 'Circuit Total Limiting. Circuit Total Limiting' (CTL) was introduced when the words '...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' was added to Section 384-15 in the 1965 NEC..."
At this point, a relationship of "replacement" between the 1965 NEC § 240.25 (G) Non-Interchangeable Circuit Breakers and the addition of the text above to § 384.15 Number of Overcurrent Devices on One Panel Board, which is about limiting the number of circuit breakers in a panel to 42. § 384.15 Number of Overcurrent Devices on One Panel Board existed prior to 1965, but the language that Mike claims introduced Class CTL (Circuit Total Limiting) did not.
The above code references infer a timely replacement of Class NI with Class CTL.
Additionally, there is the practical understanding of what Class NI and Class CTL accomplish, which are both some sort of physical means, typically a "rejection feature" on the breaker, the busbar, or both, to prevent you from installing more breakers (e.g. tandems) "...than the panelboard was designed, rated, and approved" for.
Mike's Newsletter on Circuit Breakers: CTL Assemblies also states that "...Panelboards made since 1967 have been marked 'Class CTL Panelboard."
(Just an FYI, as of 2008, this language was moved to § 408.54 Maximum Number of Overcurrent Devices.)
..........................................................................................................................
Somehow I've managed to stay busy through December 2020 and have been absent from the forum for a few months, but now that I need something from you all, I'm back! *Slightly hesitant, guilty chuckle* Slight difference this time though - I've actually done a good chunk of homework before coming here!
In the something like 11-12 years I've been in the field, this is the first time I've encountered a Class NI Panel...
Essentially, I figured I'd just share what I've learned thus far, possibly get some feedback, and maybe get a discussion going.
..........................................................................................................................
Here's my understanding thus far... The rub is that Class NI was replaced by Class CTL?
It feels like an accurate, but yet severely lacking summary.
My understanding is that Class NI stands for "Non-Interchangeable" and that, in the 1959 NEC, there is an explicit reference to "Non-Interchangeable Circuit Breakers" in § 240.25 (G) Non-Interchangeable Circuit Breakers.
The article is generally about making it difficult to increase the amperage on a branch circuit breaker... or implicitly providing a "...physical means to prevent the installation of more overcurrent devices than that number for which the panelboard was designed, rated, and approved" ...post installation.
In § 240.25 (G) (3) (Note) set the effective date of this article is set for July 1, 1960, confirming the reference date to the terminology as 1959 without having to go back any further in the history of the NEC.
§ 240.25 (G) (3) (Note) was deleted in the 1962 NEC, presumably because the effective date had now passed, the article was active code, and the effective date was no longer relevant. Confirming the existence of § 240.25 (G) Non-Interchangeable Circuit Breakers in 1962 via a deletion of one of its' components and not the whole.
There is zero mention of § 240.25 (G) Non-Interchangeable Circuit Breakers in the 1965 NEC... and there are only a few mentioned of the word "Interchangeable," all of which refer to something else entirely... inferring deletion.
This is where Mike's Newsletter on Circuit Breakers: CTL Assemblies kicks in where he says, "...CTL means 'Circuit Total Limiting. Circuit Total Limiting' (CTL) was introduced when the words '...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' was added to Section 384-15 in the 1965 NEC..."
At this point, a relationship of "replacement" between the 1965 NEC § 240.25 (G) Non-Interchangeable Circuit Breakers and the addition of the text above to § 384.15 Number of Overcurrent Devices on One Panel Board, which is about limiting the number of circuit breakers in a panel to 42. § 384.15 Number of Overcurrent Devices on One Panel Board existed prior to 1965, but the language that Mike claims introduced Class CTL (Circuit Total Limiting) did not.
The above code references infer a timely replacement of Class NI with Class CTL.
Additionally, there is the practical understanding of what Class NI and Class CTL accomplish, which are both some sort of physical means, typically a "rejection feature" on the breaker, the busbar, or both, to prevent you from installing more breakers (e.g. tandems) "...than the panelboard was designed, rated, and approved" for.
Mike's Newsletter on Circuit Breakers: CTL Assemblies also states that "...Panelboards made since 1967 have been marked 'Class CTL Panelboard."
(Just an FYI, as of 2008, this language was moved to § 408.54 Maximum Number of Overcurrent Devices.)
..........................................................................................................................
- Class NI = Non Interchangeable
- Class CTL = Circuit Total Limiting
- There exists a historical record of the NEC, which implies a direct replacement of Class NI (Non Interchangeable) Circuit Breakers and Class CTL (Circuit Total Limting) Circuit Breakers.
- CTL Panels require CTL Breakers.
- Manufacturers make breakers marked "Replacement Use Only - Not CTL Assemblies" for Non-CTL Assemblies to accommodate earlier panelboards.
- A Non-CTL Breaker in a CTL Panel is Red Tag territory.
