Thread: ? for electrical experts-Class NI

Before the Class CTL panels came along in 1968? there was a UL designation for Class NI panels. I seem to recall reading something about 3/4" versus 1" wide breakers and something about rejection features, but I have not been able to find out much about this class of circuit breakers. I would especially like to know when Class NI was introduced or required.

Originally Posted by Mark Reinmiller

Before the Class CTL panels came along in 1968? there was a UL designation for Class NI panels. I seem to recall reading something about 3/4" versus 1" wide breakers and something about rejection features, but I have not been able to find out much about this class of circuit breakers. I would especially like to know when Class NI was introduced or required.

That's N as in North follwed by a one (1) as in a number, not an "i" (I) as in India.

Class N1-N6 for example Class N1, N2S, N2P, etc.

The obsolete Square D convertible split Bus panel we were discussing/pictured part of label later shared) was a class M (as in Mother, not N as in North) 1 (one, not i ) panel.

Class CTL (CircuiT Limiting) were introduced circa 1964/65, required labeling & find information in Standards for panelboards and molded case circuit breakers. Your vintage editions of the UL White Book and the UL Marking Guides for both Standard products as well as the vintage editions of the Standards for the equipment, and NEMA Classification system, I suspect, will prove helpful in your endeavors.

Originally Posted by H.G. Watson, Sr.

That's N as in North follwed by a one (1) as in a number, not an "i" (I) as in India.

Class N1-N6 for example Class N1, N2S, N2P, etc.

The obsolete Square D convertible split Bus panel we were discussing/pictured part of label later shared) was a class M (as in Mother, not N as in North) 1 (one, not i ) panel.

Class CTL (CircuiT Limiting) were introduced circa 1964/65, required labeling & find information in Standards for panelboards and molded case circuit breakers. Your vintage editions of the UL White Book and the UL Marking Guides for both Standard products as well as the vintage editions of the Standards for the equipment, and NEMA Classification system, I suspect, will prove helpful in your endeavors.

Thank you H.G.

I went back into my files to add some notes regarding this subject and I found a file I saved showing sales literature for a Class NI panel (I believe this is the letter i, but could be wrong). The first paragraph below is from that literature. Below that is the NEC reference. I think this may answer a question I had regarding the age range of panels marked Class NI. However, this does raise other questions. I guess I am not familiar enough with panels of that vintage. It appears to indicate that once you install a 15 or 20 ampere breaker then it would be difficult to remove the breaker and install a breaker higher than 20 amperes. I assume this is different than the N1, etc. classes you are referring to. I did see some references to those classes on the web, but did not followup any further.

Originally Posted by Mark Reinmiller

Thank you H.G.

I went back into my files to add some notes regarding this subject and I found a file I saved showing sales literature for a Class NI panel (I believe this is the letter i, but could be wrong). The first paragraph below is from that literature. Below that is the NEC reference. I think this may answer a question I had regarding the age range of panels marked Class NI. However, this does raise other questions. I guess I am not familiar enough with panels of that vintage. It appears to indicate that once you install a 15 or 20 ampere breaker then it would be difficult to remove the breaker and install a breaker higher than 20 amperes. I assume this is different than the N1, etc. classes you are referring to. I did see some references to those classes on the web, but did not followup any further.

What "paragraph below"??? What "the NEC reference" ??? ???

You cannot install a breaker for a circuit requiring or uilizing a neutral to the B phase...

Not sure what you're referring to since you didn't identify a panel, nor did you provide the promised quotation nor the citations.

The NEC required limitations in the 1965 edition for poles/circuit limiting in chapter 4 for L&ABPs. Class CTL referenced in the standards and mfg by 1964.

Originally Posted by H.G. Watson, Sr.

What "paragraph below"??? What "the NEC reference" ??? ???

You cannot install a breaker for a circuit requiring or uilizing a neutral to the B phase...

Not sure what you're referring to since you didn't identify a panel, nor did you provide the promised quotation nor the citations.

The NEC required limitations in the 1965 edition for poles/circuit limiting in chapter 4 for L&ABPs. Class CTL referenced in the standards and mfg by 1964.

Forgot to attach.

CLASS NI-All 250 volt, 100 ampere maximum panelboard breakers are Underwriters' Laboratories approved Class NI. All use the same simple non-interchangeable system to meet the requirements of Article 240-25 (g) of the 1959 National Electrical Code. Completely visible, this system is not only foolproof but also the easiest to work with of any method yet devised. There is no extra work with 15 and 20 ampere branches (80% of the circuits), no loose parts, and no restrictions on changing breakers in the same class. All of these features are provided as standard at no extra cost.

240-25. Circuit-Breakers. Circuit-breakers shall conform
to the following:

(g) Non.lnterchangeable Circuit Breakers. Non-inter-changeable circuit breakers used for lighting and appliance branch circuits in residential, and other occupancies except where the conditions of maintenance and supervision assure that overcurrent protective devices and branch circuit wiring will be maintained at proper rating, shall be non-inter-changeable in accordance with the following provisions:
(1) Circuit breakers rated within the range of 0-250 volts, alternating current and not more than 100 amperes shall be classified as regards current as follows:
Amperes
0-20
21-50
51-100
(2) Such circuit breakers or their multiple mounting and bussing means shall be so arranged that it will be difficult, after a circuit breaker has been installed, to replace it with a breaker of a higher ampere classification.
(3) Such circuit breakers of higher than 0-20 ampere classification shall be difficult to install in the spare spaces which are left for future additions.

Note: The provisions of Paragraph 240-25(g) shall become effective
on July 1, 1960.