230.90 Overcurrent Protection of Ungrounded Service Conductors.
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Each ungrounded service conductor must have overcurrent protection, based on the calculated load of the building.
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Each ungrounded service conductor must have overcurrent protection, based on the calculated load of the building.

An overcurrent device must be placed in series with each ungrounded service conductor.  An overcurrent device may be placed in series with a grounded conductor only if the circuit breaker simultaneously opens all conductors of the circuit.

Five exceptions modify the general statement in 230.90 that the rating of the service overcurrent device cannot be greater than the ampacity of the service conductors.

Exception No. 1 refers to motor loads and says that part of the service load which consists of motor loads should be calculated according to Article 430.

Exception No. 2 says service overcurrent protection may follow 240.4(B) or (C), which allows the next higher standard setting of overcurrent devices, if the service is rated up to 800 amps.

Exception No. 3 says two to six sets of circuit breakers or fuses may be used to provide overload protection.  The sum of the ratings of the circuit breakers or fuses can be larger than the ampacity of the service conductors, as long as the service conductors are large enough to carry the load.

Exception No. 4 refers to overcurrent protection for fire pumps.

Exception No. 5 allows service overcurrent protection for 120/240-volt, 3-wire, single-phase dwelling services to be selected from Table 310.15(B)(6).

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Electrical Continuing Education for License Renewal: 230.90 Overcurrent Protection of Ungrounded Service Conductors. Question
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