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(2) Relays and circuit breakers providing ground-fault protection of equipment * (3) Ground-fault circuit interrupter devices 240.8 Fuses or Circuit Breakers in Parallel. Fuses and circuit breakers shall be permitted to be connected in parallel where they are factory assembled in parallel and listed...

(2) Relays and circuit breakers providing ground-fault protection of equipment * (3) Ground-fault circuit interrupter devices 240.8 Fuses or Circuit Breakers in Parallel. Fuses and circuit breakers shall be permitted to be connected in parallel where they are factory assembled in parallel and listed as a unit. Individual fuses, circuit breakers, or combinations thereof shall not otherwise be connected in parallel. 240.9 Thermal Devices. Thermal relays and other devices not designed to open short circuits or ground faults shall not be used for the protection of conductors against overcurrent due to short circuits or ground faults, but the use of such devices shall be permitted to protect motor branch-circuit conductors from overload if protected in accordance with 430.40. 240.10 Supplementary Overcurrent Protection. Where supplementary overcurrent protection is used for luminaires, appliances, and other equipment or for internal circuits and components of equipment, it shall not be used as a substitute for required branch-circuit overcurrent devices or in place of the required branch-circuit protection. Supplementary overcurrent devices shall not be required to be readily accessible. 240.11 Selective Coordination. If one or more feeder overcurrent protective devices are required to be selectively coordinated with a service overcurrent protective device by other requirements in this Code, all feeder overcurrent protective devices supplied directly by the service overcurrent protective device shall be selectively coordinated with the service overcurrent protective device. 240.12 Orderly Shutdown. Where an orderly shutdown is required to minimize the hazard(s) to personnel or equipment, a system of coordination based on the following two conditions shall be permitted: * (1) Coordinated short-circuit protection * (2) Overload indication based on monitoring systems or devices Informational Note: The monitoring system may cause the condition to go to alarm, allowing corrective action or an orderly shutdown, thereby minimizing personnel hazard and equipment damage. ENHANCED CONTENT Collapse With coordinated overcurrent protection, the faulted or overloaded circuit is isolated by the selective operation of only the OCPD closest to the overcurrent condition. This selective operation prevents power loss to unaffected loads. Coordinated short-circuit protection automatically opens the circuit by localizing and de-energizing the faulted portion of the circuit, but an overload condition is not required to result in automatic opening of a protective device. Instead, an alarm can be used to warn of the overload condition, and remedial action can be taken. In some circumstances, an orderly shutdown of a system or process is more critical to personnel and equipment safety than is the automatic operation of the OCPD in response to an overload. Examples of overcurrent protection with and without coordinated protection are illustrated in the following exhibit. For selective coordination requirements for specific systems or equipment, see 620.62, 645.27, 695.3(C)(3), 700.32, 701.32, and 708.54. 240.13 Ground-Fault Protection of Equipment. Ground-fault protection of equipment shall be provided in accordance with 230.95 for solidly grounded wye electrical systems of more than 150 volts to ground but not exceeding 1000 volts phase-to-phase for each individual device used as a building or structure main disconnecting means rated 1000 amperes or more. This section shall not apply to the disconnecting means for the following: * (1) Continuous industrial processes where a nonorderly shutdown will introduce additional or increased hazards * (2) Installations where ground-fault protection is provided by other requirements for services or feeders * (3) Fire pumps ENHANCED CONTENT Collapse Section 240.13 extends the requirement of 230.95 to building disconnects, regardless of whether they are classified as service disconnects, building disconnects for feeders, or even branch circuits. Where ground-fault protection for equipment is installed at the service equipment, and feeders or branch circuits are installed from that service to supply other buildings or structures, the disconnecting means at any subsequent building is not required to be provided with ground-fault protection if the service device provides the required protection. Installations performed prior to the 2008 edition of the NEC permitted “re- grounding” of the grounded conductor at the separate building if an equipment grounding conductor was not included with the supply circuit. Where re-grounding of the neutral occurs downstream from the service, the re- grounding could nullify the ground-fault protection (or result in unwanted operation of the protection) because the neutral current has parallel paths on which to return to the source. Feeders or branch circuits supplying other buildings or structures might have to be isolated to allow for proper operation of the service ground-fault protection, and separate ground-fault protection installed at the building disconnecting means is then necessary to meet the requirements of 240.13. See also 210.13, 215.10, and Article 225, Part II, for the requirements for building disconnects not on the utility service. 240.15 Ungrounded Conductors. (A) Overcurrent Device Required. A fuse or an overcurrent trip unit of a circuit breaker shall be connected in series with each ungrounded conductor. A combination of a current transformer and overcurrent relay shall be considered equivalent to an overcurrent trip unit. Informational Note: See Parts III, IV, V, and XI of Article 430 for motor circuits. (B) Circuit Breaker as Overcurrent Device. Circuit breakers shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 240.15(B)(1), (B)(2), (B)(3), and (B)(4). (1) Multiwire Branch Circuits. Individual single-pole circuit breakers, with identified handle ties, shall be permitted as the protection for each ungrounded conductor of multiwire branch circuits that serve only single-phase line-to-neutral loads. (2) Grounded Single-Phase Alternating-Current Circuits. In grounded systems, individual single-pole circuit breakers rated 120/240 volts ac, with identified handle ties, shall be permitted as the protection for each ungrounded conductor for line-to-line connected loads for single-phase circuits. (3) 3-Phase and 2-Phase Systems. For line-to-line loads in 4-wire, 3-phase systems or 5-wire, 2-phase systems, individual single-pole circuit breakers rated 120/240 volts ac with identified handle ties shall be permitted as the protection for each ungrounded conductor, if the systems have a grounded neutral point and the voltage to ground does not exceed 120 volts. (4) 3-Wire Direct-Current Circuits. Individual single-pole circuit breakers rated 125/250 volts dc with identified handle ties shall be permitted as the protection for each ungrounded conductor for line-to-line connected loads for 3-wire, direct-current circuits supplied from a system with a grounded neutral where the voltage to ground does not exceed 125 volts. ENHANCED CONTENT Collapse The basic rule is that circuit breakers open all ungrounded conductors of the circuit when they trip (automatic operation in response to overcurrent) or are manually operated as a disconnecting means. For 2-wire circuits with one conductor grounded, this rule is simple and needs no further explanation. For branch circuits comprised of multipole ungrounded conductors that do not meet the conditions of B(1) through B(4), multipole common trip circuit breakers are required. The following exhibit shows where multiple common trip circuit breakers are required. Handle ties are not permitted because the circuits are supplied from ungrounded systems. Multiwire branch circuits are permitted to supply line-to-line connected loads where the loads are associated with a single piece of utilization equipment or where all the ungrounded conductors are opened simultaneously by the branch-circuit overcurrent device (automatic opening in response to overcurrent). The most widely used method is to install a multipole circuit breaker with an internal common trip mechanism. The use of such multipole devices provides overcurrent protection and the required disconnecting means. The breaker is operated by an external single lever internally attached to the two or three poles of the circuit breaker, or the external lever can be attached to multiple handles operated as one. The second method permitted for multiwire branch circuits is to use two or three single- pole circuit breakers and add an identified handle tie to function as a common operating handle. This multipole circuit breaker is field assembled by externally attaching an identified common lever (handle tie) onto the two or three individual circuit breakers. The circuit breakers can be used as the protection of line-to-line connected loads in grounded single-phase and grounded 3-phase alternating current systems, but this requirement is limited to circuit breakers rated 120/240 volts. Handle ties do not cause the circuit breaker to function as a common trip device; rather, they only allow common operation as a disconnecting means. The term identified requires the use of hardware designed specifically to perform this common disconnecting means function. The use of homemade hardware such as nails or pieces of wire to perform this function is not an identified means. The next exhibit shows where handle ties are required for single-pole circuit breakers on multiwire branch circuits serving line-to-neutral loads. The exhibit below shows where handle ties are required for single-pole circuit breakers on multiwire branch circuits serving line-to-line loads. The multiwire branch circuits shown in the top and middle diagrams supply a single piece of utilization equipment in accordance with 210.4(C), Exception No. 1. For those branch circuits, common trip operation is permitted but is not required. Section 240.15(B)(4) covers protection of direct-current circuits and permits the use of two single-pole circuit breakers (rated for dc application) with identified handle ties to be used for the overcurrent protection of line-to-line connected loads. The 3-wire circuits covered by this requirement are multiwire branch circuits per the definition in Article 100 and as such are subject to all of the requirements specified in 210.4. 240.16 Interrupting Ratings. Branch-circuit overcurrent protective devices shall have an interrupting rating no less than 5000 amperes. Part II. Location 240.21 Location in Circuit. Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply except as specified in 240.21(A) through (H). Conductors supplied under 240.21(A) through (H) shall not supply another conductor except through an overcurrent protective device meeting the requirements of 240.4. (A) Branch-Circuit Conductors. Branch-circuit tap conductors meeting the requirements specified in 210.19 shall be permitted to have overcurrent protection as specified in 210.20. (B) Feeder Taps. Conductors shall be permitted to be tapped, without overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1) through (B)(5). The tap shall be permitted at any point on the load side of the feeder overcurrent protective device. Section 240.4(B) shall not be permitted for tap conductors. ENHANCED CONTENT Collapse An OCPD is not permitted to be supplied by a tap conductor having an ampacity less than its rating. For example, the use of a 500-kcmil THWN copper conductor (380 amperes, per Table 310.16) as a tap conductor to supply a 400-ampere rated device is not permitted. Note that the lengths specified in 240.21(B) and (C) apply to the conductors, not to a raceway enclosing the conductors or to the distance between the enclosures in which the tap conductors originate and terminate. (1) Taps Not over 3 m (10 ft) Long. If the length of the tap conductors does not exceed 3 m (10 ft) and the tap conductors comply with all of the following: * (1) The ampacity of the tap conductors is as follows: o a. Not less than the combined calculated loads on the circuits supplied by the tap conductors o b. Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors Exception to b: Where listed equipment, such as a surge-protective device(s) [SPD(s)], is provided with specific instructions on minimum conductor sizing, the ampacity of the tap conductors supplying that equipment shall be permitted to be determined based on the manufacturer’s instructions. * (2) The tap conductors do not extend beyond the switchboard, switchgear, panelboard, disconnecting means, or control devices they supply. * (3) Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which extends from the tap to the enclosure of an enclosed switchboard, switchgear, a panelboard, or control devices, or to the back of an open switchboard. * (4) For field installations, if the tap conductors leave the enclosure or vault in which the tap is made, the ampacity of the tap conductors is not less than one-tenth of the rating of the overcurrent device protecting the feeder conductors. Informational Note: See 408.36 for overcurrent protection requirements for panelboards. (2) Taps Not over 7.5 m (25 ft) Long. Where the length of the tap conductors does not exceed 7.5 m (25 ft) and the tap conductors comply with all the following: * (1) The ampacity of the tap conductors is not less than one-third of the rating of the overcurrent device protecting the feeder conductors. * (2) The tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This device shall be permitted to supply any number of additional overcurrent devices on its load side. * (3) The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means. ENHANCED CONTENT Collapse The following exhibit illustrates an installation that meets the feeder tap requirements of 240.21(B)(2). The ampacity of the 3/0 AWG, Type THW copper conductor (200 amperes) is more than one-third the rating of the overcurrent device (400 amperes) protecting the feeder circuit. See also Table 310.16 for the ampacity of copper conductors in a raceway. (3) Taps Supplying a Transformer [Primary Plus Secondary Not over 7.5 m (25 ft) Long]. Where the tap conductors supply a transformer and comply with all the following conditions: * (1) The conductors supplying the primary of a transformer have an ampacity at least one-third the rating of the overcurrent device protecting the feeder conductors. * (2) The conductors supplied by the secondary of the transformer shall have an ampacity that is not less than the value of the primary-to-secondary voltage ratio multiplied by one-third of the rating of the overcurrent device protecting the feeder conductors. * (3) The total length of one primary plus one secondary conductor, excluding any portion of the primary conductor that is protected at its ampacity, is not over 7.5 m (25 ft). * (4) The primary and secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means. * (5) The secondary conductors terminate in a single circuit breaker or set of fuses that limit the load current to not more than the conductor ampacity that is permitted by 310.14. ENHANCED CONTENT Collapse This section covers applications where the conductor length of 25 feet is applied using the length of one primary conductor plus the length of one secondary conductor for the measurement. The transformer primary conductors are tapped from a feeder, and the secondary conductors are required to terminate in a single OCPD. The exhibit below illustrates the conditions of 240.21(B)(3)(1) through (5). The overcurrent protection requirements of 408.36 for panelboards and 450.3(B) for transformers also apply. See also 240.21(C)(6) if the primary conductors are protected in accordance with their ampacity. (4) Taps over 7.5 m (25 ft) Long. Where the feeder is in a high bay manufacturing building over 11 m (35 ft) high at walls and the installation complies with all the following conditions: * (1) Conditions of maintenance and supervision ensure that only qualified persons service the systems. * (2) The tap conductors are not over 7.5 m (25 ft) long horizontally and not over 30 m (100 ft) total length. * (3) The ampacity of the tap conductors is not less than one-third the rating of the overcurrent device protecting the feeder conductors. * (4) The tap conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This single overcurrent device shall be permitted to supply any number of additional overcurrent devices on its load side. * (5) The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means. * (6) The tap conductors are continuous from end-to-end and contain no splices. * (7) The tap conductors are sized 6 AWG copper or 4 AWG aluminum or larger. * (8) The tap conductors do not penetrate walls, floors, or ceilings. * (9) The tap is made no less than 9 m (30 ft) from the floor. ENHANCED CONTENT Collapse The exhibit below shows a feeder tap in a high bay building as an example of an installation complying with 240.21(B)(4). Outside Taps of Unlimited Length. Where the conductors are located outside of a building or structure, except at the point of load termination, and comply with all of the following conditions: The tap conductors are protected from physical damage in an approved manner. The tap conductors terminate at a single circuit breaker or a single set of fuses that limits the load to the ampacity of the tap conductors. This single overcurrent device shall be permitted to supply any number of additional overcurrent devices on its load side. The overcurrent device for the tap conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto. The disconnecting means for the tap conductors is instal?led at a readily accessible location complying with one of the following: o a. Outside of a building or structure o b. Inside, nearest the point of entrance of the tap conductors o c. Where installed in accordance with 230.6, nearest the point of entrance of the tap conductors ENHANCED CONTENT Collapse This tap conductor requirement is similar in some respects to an installation of service conductors. The conductors are supplied from a feeder at an outdoor location and run to a building or structure without limitations on the tap conductor length. The OCPD provides overload protection for the tap conductors. The fused switch or circuit breaker is installed at a readily accessible location either inside or outside a building or structure at a point nearest to where the tap conductors enter the building or structure. This disconnect is subject to the applicable requirements covering feeder disconnecting means in Part II of Article 225. Transformer Secondary Conductors. A set of conductors feeding a single load, or each set of conductors feeding separate loads, shall be permitted to be connected to a transformer secondary, without overcurrent protection at the secondary, as specified in 240.21(C)(1) through (C)(6). Section 240.4(B) shall not be permitted for transformer secondary conductors. Informational Note: See 450.3 for overcurrent protection requirements for transformers. ENHANCED CONTENT Collapse Section 240.21(C) prohibits using the next higher standard size OCPD to protect transformer secondary conductors. The secondary terminals of a transformer are permitted to supply one or more than one set of secondary conductors. For example, the secondary terminals could supply two separate sets of secondary conductors that feed two panelboards. One set of conductors could be installed using the 25-foot secondary conductor rule of 240.21(C)(6), while the other set of conductors could be installed using the 10-foot secondary conductor rule of 240.21(C)(2). Each set is treated individually in applying the applicable secondary conductor requirement. The NEC requires the protection of both conductors and transformers. Article 240 contains requirements for protection of conductors, and Article 450 contains requirements for the protection of transformers. It is possible to protect both conductors and transformers with the same device, if the device meets the requirements of both articles. Protection by Primary Overcurrent Device. Conductors supplied by the secondary side of a single-phase transformer having a 2- wire (single-voltage) secondary, or a three-phase, delta-delta connected transformer having a 3-wire (single-voltage) secondary, shall be permitted to be protected by overcurrent protection provided on the primary (supply) side of the transformer, provided this protection is in accordance with 450.3 and does not exceed the value determined by multiplying the secondary conductor ampacity by the secondary-to- primary transformer voltage ratio. Single-phase (other than 2-wire) and multiphase (other than delta-delta, 3-wire) transformer secondary conductors are not considered to be protected by the primary overcurrent protective device. Transformer Secondary Conductors Not over 3 m (10 ft) Long. If the length of secondary conductor does not exceed 3 m (10 ft) and complies with all of the following: The ampacity of the secondary conductors is as follows: o a. Not less than the combined calculated loads on the circuits supplied by the secondary conductors o b. Not less than the rating of the equipment containing an overcurrent device(s) supplied by the secondary conductors or not less than the rating of the overcurrent protective device at the termination of the secondary conductors Exception: Where listed equipment, such as a surge protective device(s) [SPD(s)], is provided with specific instructions on minimum conductor sizing, the ampacity of the tap conductors supplying that equipment shall be permitted to be determined based on the manufacturer’s instructions. The secondary conductors do not extend beyond the switchboard, switchgear, panelboard, disconnecting means, or control devices they supply. The secondary conductors are enclosed in a raceway, which shall extend from the transformer to the enclosure of an enclosed switchboard, switchgear, a panelboard, or control devices or to the back of an open switchboard. For field installations where the secondary conductors leave the enclosure or vault in which the supply connection is made, the secondary conductors shall have an ampacity that is not less than the value of the primary-to-secondary voltage ratio multiplied by one-tenth of the rating of the overcurrent device protecting the primary of the transformer. Informational Note: See 408.36 for overcurrent protection requirements for panelboards. ENHANCED CONTENT Collapse The size-rating relationship between the primary OCPD and the secondary conductors is necessary because the transformer primary device provides short-circuit ground-fault protection for the transformer secondary conductors. The ampacity of the conductors must be adequate for the calculated load and not less than the rating of the device or OCPD in which the conductors terminate. The following example illustrates application of this requirement. Industrial Installation Secondary Conductors Not over 7.5 m (25 ft) Long. For the supply of switchgear or switchboards in industrial installations only, where the length of the secondary conductors does not exceed 7.5 m (25 ft) and complies with all of the following: Conditions of maintenance and supervision ensure that only qualified persons service the systems. The ampacity of the secondary cond