Circuit total limitation

Circuit total limitation (CTL) is a legacy standard for electrical panels sold in the United States according to the National Electrical Code. This standard requires an electrical panel to provide a physical mechanism to prevent installing more circuit breakers than it was designed for. This has generally been implemented by restricting the use of tandem (duplex) breakers to replace standard single pole breakers.

Code Requirement

The 1965 edition of the NEC, article 384-15 was the first reference to the circuit total limitation of panelboards.^[1] As of 2008^[update], the ___location of this language is at Article 408.54 now titled "Maximum Number of Overcurrent Devices.". However, this rule never prevented panel overloads, as any ampacity breaker can be used in any slot. The rule was repealed in 2008.

Non-CTL for replacement only

Circuitboards and panelboards built prior to 1965 did not have circuit total limiting devices or features built-in. To support these old panels, non-CTL circuit breakers that bypass the rejection feature are still sold "for replacement use only."^[2] As a result, numerous unsafe situations have resulted where panels were dangerously overloaded because these non-CTL breakers continue to be used.^{[citation needed]} With the use of non-CTL breakers, panels can be configured with the total number of circuits in excess of the designed capacity of that panel.

The 2008 code did away with the previous 42 circuit limitation on panelboards.^[3] 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.

Eaton Bryant Cutler-Hammer

Eaton CTL breakers add a small metal clip on the back of the breaker, which prevents insertion in non-notched bus stabs. From 2019 or so new Eaton panels have only un-notched bus stabs, rendering the CTL breaker types obsolete ^[4]. Eaton has long made both types, but attached a price premium to the more flexible Non-CTL breakers:

BD	CTL	Single width, two independent breakers
BQ	CTL	Double width, three independent breakers
BQC	CTL	Double width, two common trip circuits
BR	Non-CTL	Various types
BRD	Non-CTL	Various types, all BR compatible
BRDC	Non-CTL	Double width, two common trip circuits

While it is physically possible to remove the Eaton clip, this violates the listing, and could result in fragments of plastic or metal entering the breaker and preventing proper operation.

In their 2019 catalog Eaton specifies that their non-CTL breakers are "Suitable for use in plug-on neutral style loadcenters ^[5] which negates the replacement only rule.

Siemens

Siemens uses a similar rejection clip to Eaton, but adds an additional plastic extension to back up the clip. Non-CTL clip free breakers have the "NC" suffix. As with Eaton the selling price is higher to discourage use.

Square D Fuses

A non-removable rejection clip, model RFK06, can be fitted to reject non-R fuses.

Gallery

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  Cutler-Hammer ONE pole CTL circuit breaker
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  Cutler-Hammer ONE pole CTL Circuit Breaker close-up
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  Cutler-Hammer CHEATER or Non-CTL Circuit Breaker
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  Cutler-Hammer CHEATER or Non-CTL Circuit Breaker
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  Cutler-Hammer TWO pole CTL Circuit Breaker
•  
  Cutler-Hammer TWO pole CTL Circuit Breaker

See also

• National Electrical Code

References

1. Terrell Croft; Wilford I. Summers; Frederic Hartwell (17 August 2008). American Electricians' Handbook. McGraw Hill Professional. p. 4.52. ISBN 9780071642583. {{cite book}}: |work= ignored (help)
2. "UL's Guide Information for Electrical Equipment: The White Book 2008" (PDF). p. 90. Archived from the original (PDF) on 2008-09-13.
3. See "bullet" in 2008 NEC between Articles 408.30 and 408.36, where 2005's Article 408.35 appeared.
4. https://knowledgehub.eaton.com/s/article/What-is-the-difference-between-the-BD-BQ-and-BQC-breakers ^{[bare URL PDF]}
5. https://www.eaton.com/ecm/groups/public/@pub/@electrical/documents/content/vol01_tab01.pdf ^{[bare URL PDF]}

External links

• "Removal of 42 Circuit Limitation for Lighting and Appliance Panelboards"". National Electrical Code 2008.^{[permanent dead link]}