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?
- 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?
- 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?
- 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?
- An overload relay (thermal or magnetic) that is responsive to motor current.
- Where must motor overload protection be located in the circuit?
- 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?
- Article 430.
- What NEC article covers transformer installation?
- Article 450.
- How far must a transformer be kept from combustible materials?
- At least 3 feet horizontally and 5 feet vertically, unless the transformer is rated for less clearance.
- When is transformer secondary disconnect protection required?
- 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?
- To dissipate heat and prevent the transformer from overheating.
- What are the two main winding temperature classes for transformers?
- 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?
- 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?
- 125% of the motor full load current, rounded up to the next standard breaker or fuse size.
- How are motor full load currents determined?
- 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?
- 125% of the motor full load current (or the value from the nameplate if higher).
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