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Questions and Answers
A circuit breaker trips automatically when there is an ______.
overcurrent
Silver and copper are examples of good electrical ______.
conductors
One major advantage of a fuse is its reliability and ______.
stability
Materials like rubber and glass are classified as ______.
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Single-throw knife switches must be installed so that gravity does not tend to ______ them.
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Wires are electrical conductors which are 8 mm2 (AWG no. 8) or ______.
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Stranded wire consists of a group of wires twisted together to form a metallic ______.
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Double-throw knife switches can be mounted with the throw oriented either ______ or horizontal.
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Service entrance conductors subjected to physical damage shall be protected by ______.
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The service disconnecting means shall consist of no more than ______ switches or circuit breakers.
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For a one family dwelling, the service disconnecting means should have a rating of ______ where the initial computed load is 10 kVA or more.
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Electrical Metallic Tubing (EMT) is a type of ______ used for service entrance conductors.
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The type of wiring method used for service entrance conductors must comply with the applicable ______.
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In a two circuit installation, the service disconnecting means shall have a rating of not less than ______ amperes.
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Type MC cables are used as an approved means of ______ for service conductors.
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Service entrance conductors can be installed in methods such as Open-wiring on insulators or ______ tubing.
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A circuit breaker serves as both an ______ protective device and a switch.
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A ______ is an overcurrent protective device that uses a fusible element to open the circuit.
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Ampacity refers to the ______-carrying capacity of an electric conductor.
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The panelboard should be installed near the ______ center for optimal wiring efficiency.
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A branch circuit consists of circuit conductors between the final overcurrent device and the ______.
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An overcurrent can be caused by equipment ______, short circuits, or ground faults.
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Conductors must be protected against overcurrent according to their ______.
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The panelboard is designed to be accessible only from the ______ side.
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Study Notes
Circuit Breakers vs. Fuses
- Circuit breakers trip automatically during overcurrent situations and can be reset after correcting the fault, while fuses must be replaced once blown.
- Fuses are known for their reliability and stability, requiring minimal maintenance compared to circuit breakers, which need periodic testing.
- Cost-wise, fuses are typically less expensive than circuit breakers.
Standard Ampere Ratings
- Standard Ampere ratings for fuses and inverse time circuit breakers range from 15 to 6000 Amperes in various increments.
Installation Guide for Knife Switches
- Single-throw Knife Switches: Must be positioned to prevent gravity from closing them. Inverted models require a locking device.
- Double-throw Knife Switches: Allowed to be mounted vertically or horizontally, with locking devices needed for vertical configurations.
Electrical Conductors and Insulators
- Conductors: Materials with low resistance to current. Examples include silver, copper, aluminum, and iron.
- Insulators: Materials with high resistance to current. Notable examples are rubber, porcelain, glass, and dry air.
Wires and Cables
- Wires are defined as conductors smaller than 8 mm² (AWG no. 8), while cables are larger, available in solid or stranded forms.
- For limited loads on single branch circuits, recommended sizes are 3.5 mm² for copper and 5.5 mm² for aluminum or copper-clad aluminum.
Service Entrance Conductors Installation
- Must comply with applicable codes using methods such as Rigid Metal Conduit (RMC), Electrical Metallic Tubing (EMT), or Service-Entrance Cables.
Protection for Service Entrance Conductors
- Protection methods include RMC, IMC, EMT, or approved cable types to safeguard against physical damage.
Service Disconnecting Means
- A service disconnecting mechanism is mandatory to isolate all conductors in a building from service-entrance conductors.
- Up to six switches or circuit breakers can be mounted in a single enclosure for ease of access.
- Must have adequate ratings based on load requirements, with specifics like 15 A for single circuit installations.
Panelboards
- Constructed to house buses, protective devices, and control switches, panelboards must be conveniently located, typically near heavy load areas like kitchens and laundry rooms.
Branch Circuit Protection
- Overcurrent is defined as any current exceeding the rated capacity, caused by overloads or short circuits.
- Conductors must be protected against overcurrent as per their ampacities.
Functions of Circuit Breakers and Fuses
- Circuit breakers serve dual purposes: acting as switches and overcurrent protection devices equipped with auto-tripping features.
- Fuses function by employing a fusible element that opens the circuit during overcurrent, making them one of the most common protective devices.
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Description
This quiz explores the fundamental differences between circuit breakers and fuses. Understand the advantages and disadvantages of each system, with a focus on reliability, maintenance, and operational safety.
