- Circuit total limitation
Circuit total limitation (CTL) is one of the present-day standards for electrical panels sold in the United States according to the National Electrical Code. The 1965 edition of the NEC, article 384-15 was the first reference to the circuit total limitation of panelboards. As of 2008[update], the location of this language is at Article 408.54.
Reputable manufacturers have not made non-CTL panels since 1965.
'Non-CTL replacement only' circuit breakers being installed in CTL panels
External images In this example, the panel has space for 24 CTL breakers, 12 on the left, 12 on the right. Using non-CTL breakers, especially at the bottom, it has 26 poles in use, with 8 & 2 halves still available to be used. This is both an overloaded back-panel and one that has potential to be overloaded even more. Another example, though less potential for overloading than the first.
Circuitboards/panelboards built prior to 1965 do not have circuit total limiting devices or features built into them. Even so, pre-CTL circuit breakers "for replacement use only" continue to be sold to the general public, even to this day.
People are able to go to their local hardware or "big box" home improvement store, and purchase "cheater" breakers that are actually for "replacement use only" in pre-1965 panelboards.
As a result, numerous unsafe situations have resulted where panels were dangerously overloaded because these non-CTL breakers continue to be sold. With overuse of non-CTL breakers, current is being placed on the panel's bus-bars in excess of the designed capacity of that panel.
The 2008 code did away with the previous 42 circuit limitation on panelboards. One can now order panelboards with as many as 84 circuit places, and a corresponding ampacity rating.
If a panelboard with a sufficient number of breaker positions is installed in the first place, the need for non-CTL breakers should be eliminated.
NEC and UL white book (quotations)
NEC (NFPA-70) 408.54: Maximum Number of Overcurrent Devices
A 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 listed.
For purposes of this section, a 2-pole circuit breaker or fusible switch shall be considered two overcurrent devices; a 3-pole circuit breaker or fusible switch shall be considered three overcurrent devices.—Quote from the 2008 NEC Article (NFPA-70)
CLASS CTL PANELBOARDS
Circuit-limiting panelboards (known as "Class CTL" panelboards) are identified by the words "Class CTL" on the UL Listing Mark.
Class CTL panelboards incorporate physical features which, in conjunction with the physical size, configuration, or other means provided in Class CTL circuit breakers, fuseholders or fusible switches, are designed to prevent the installation of more overcurrent protective poles than that number for which the device is designed and rated.—2008 UL "White Book"
CIRCUIT BREAKERS, MOLDED-CASE AND CIRCUIT BREAKER ENCLOSURES (DIVQ)
USE, 4th paragraph
Some circuit 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."—2008 UL "White Book"
43. For replacement not CTL — The marking "For replacement use only not CTL assemblies" appears on breakers that do not have means to prevent their installation in class CTL assemblies. These breakers are intended for replacement in older assemblies still in service, which pre-dates the Class CTL requirements for circuit breakers and panelboards.— Marking guide molded case circuit breakers March 2008", pg. 13 (included 2/3 way into the same pdf file as "the white book")
- ^ Terrell Croft, Wilford I. Summers, Frederic Hartwell. "American Electricians' Handbook". 15th Edition. p. 4.52. http://books.google.com/books?id=y-vq2G1lHUMC&pg=PT2144&lpg=PT2144&dq=(NFPA+OR+NEC)+408.54&source=bl&ots=fJbfDAdBdl&sig=1fgfhsEulN8PH8XkqnqV3z1yI8g&hl=en&ei=Jb6sSe_lGozKMvny_O0E&sa=X&oi=book_result&resnum=1&ct=result#PPT2144,M1.
- ^ "UL's Guide Information for Electrical Equipment: The White Book 2008". p. 90. http://www.ul.com/regulators/2008_WhiteBook.pdf.
- ^ 'White Book", pages 90 & 262
- ^ See "bullet" in 2008 NEC between Articles 408.30 and 408.36, where 2005's Article 408.35 appeared.
- ^ UL's Guide Information for Electrical Equipment: The White Book 2008, page 262 (http://www.ul.com/regulators/2008_WhiteBook.pdf)
- ^ UL's "GUIDE INFORMATION FOR ELECTRICAL EQUIPMENT THE WHITE BOOK 2008", page 90 (http://www.ul.com/regulators/2008_WhiteBook.pdf)
- ^ http://www.ul.com/regulators/2008_WhiteBook.pdf
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