NEC requirements for motor circuits and transformer installations tested on journeyman and master electrician exams.
30 cards · basic cards · AI-written, checked twice. Edit anything.
- Where must the motor disconnecting means be located?
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In sight of the motor and driven machinery, or if not, the disconnecting means must be capable of being locked in the open position.- How many motor disconnecting means are required for a single motor?
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One disconnecting means, which may serve one or more motors if they are on the same circuit.- What is the minimum horsepower rating of a motor disconnecting means?
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Not less than 115% of the motor full load current, or the horsepower rating must equal or exceed the motor horsepower.- What type of device provides motor overload protection?
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An overload relay (thermal or magnetic) that is responsive to motor current.- Where must motor overload protection be located in the circuit?
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In the motor circuit, protecting the motor conductors from the point where they receive power up to the motor terminals.- What NEC article covers motor circuit requirements?
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Article 430.- What NEC article covers transformer installation?
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Article 450.- How far must a transformer be kept from combustible materials?
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At least 3 feet horizontally and 5 feet vertically, unless the transformer is rated for less clearance.- When is transformer secondary disconnect protection required?
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A secondary disconnect is not always required; a transformer rated 1000 volts or less with a secondary circuit of 150 volts or less may not need one.- What is transformer ventilation required for?
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To dissipate heat and prevent the transformer from overheating.- What are the two main winding temperature classes for transformers?
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Class A (140 degrees Celsius rise) and Class H (180 degrees Celsius rise), though others exist (B, F).- How must a transformer tank be grounded?
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The transformer tank must be grounded with a copper conductor or by connection to the grounded equipment.- When determining motor branch circuit overcurrent protection size, what is the basic calculation?
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125% of the motor full load current, rounded up to the next standard breaker or fuse size.- How are motor full load currents determined?
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From NEC Tables 430.247, 430.248, or 430.249 based on motor type and horsepower, or from the motor nameplate.- What must motor conductor sizing be based on?
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125% of the motor full load current (or the value from the nameplate if higher).
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