Chapter 3.9, 3.10, 3.11, 3.12, 3.13 Flashcards
From Branch Circuit Requirements to Design Example
3.9 Title
Branch Circuit Requirements
A building electrical systems consists of several ________ that extend out from the __________ or _______.
circuits, switchboard or panelboard
A ______________ is that portion of the building wiring system that extends beyond the final over current protection device that is protecting the circuit.
Branch Circuit
It provides power from a circuit breaker or fuse in the panelboard to single or multiple points of use called __________.
Branch circuiting, outlets
An __________ is a point in a wiring system where current is taken to supply an appliance, piece of equipment, or lighting installation.
Branch circuiting, outlet
A ______________ is compose of an overcurrent protection device (fuse or circuit breaker), wiring, and one ore more outlets
branch circuit
This of branch circuit serves one receptacle or piece of equipment such as for a range, clothes dryer, large copy machine, or other piece of machinery.
Individual Branch Circuit
The _____________ is sometimes known in the trade as a dedicated or special purpose circuit.
Individual Branch Circuit
A branch circuit supplies two or more outlets for lighting and appliances. This type of circuit may be referred to as a lighting circuit; this is a carryover from the days when electricity was first used in buildings and its predominant purpose was lighting. There are usually a number of general purpose branch circuits supplying lights and outlets in different rooms around a residence, commercial or industrial building.
General Purpose Branch Circuit
These circuits usually lead directly from the distribution panel to the appliance and do not serve any other electrical devices.
Individual Branch Circuit
A branch circuit supplies two or more outlets for lighting and appliances.
General Purpose Branch Circuit
This type of circuit may be referred to as a lighting circuit; this is a carryover from the days when electricity was first used in buildings and its predominant purpose was lighting.
General Purpose Branch Circuit
There are usually a number of general purpose branch circuits supplying lights and outlets in different rooms around a residence, commercial or industrial building.
General Purpose Branch Circuit
This is the type of branch circuit that supplies energy to one or more outlets to which appliances are to be connected. They supply fixed electric equipment, such as refrigerators, washers, and other large appliances and electrical devices.
Appliance Branch Circuit
__________ do not supply lighting fixtures.
Appliance branch
_____________ cannot exceed 20A.
Appliance branch circuits
A branch circuit consisting of two or more underground (hot) conductor having a voltage bet ween them and a common neutral (grounded) conductor that is shared between the ungrounded conductors such as in a 120/240 V three wire circuit.
Multiwire Branch Circuit
Other branch circuits specific to a particular occupancy may also be required. For example, the following branches are required in health care facilities such as hospitals, nursing homes, and dental facilities.
Multiwire Branch Circuit
An emergency system of feeders and branch circuit that provides adequate power to patients and personnel. It must automatically connect to an alternate power source such as generator when the normal power source is interrupted.
Life Safety Branch Circuit
An emergency system of feeders and branch circuits intended to provide power to task illumination, special power circuits, and selected receptacles serving areas and functions related to patient care.
Critical Branch Circuit
It must automatically connect to an alternate power source such as a generator when the normal power source is interrupted.
Critical Branch Circuit
______________ duplex receptacles are fed with a 120/ 240V circuit having two ungrounded (hot) conductors, a grounded neutral conductor, and a grounding conductor.
Split wired
One ____________ feeds power to upper outlet and the other _____________ conductor feeds the lower outlet
grounded (hot), ungrounded (hot)
The _____________ conductor is shared between both circuits.
grounded (neutral) conductor
____________ allows power to be drawn from two separate circuits on one duplex receptacle.
Split wiring
The ________________ is determined by the rating of the overcurrent protection device (fuse or circuit breaker) used to protect the wiring in the circuit from excessive current flow.
branch circuit rating
The wiring in the circuit must safely deliver current to the connected load and the overcurrent protection device protects this wiring, so the circuit rating matches the rating of the overcurrent protection device.
T
The connected load on a branch circuit is the sum of all loads connected in a circuit. It is found by totaling the connected volt amp (VA) load at each outlet connected to the circuit.
T
Design of a building electrical installations computations with power, expressed in Watts, voltage, in volts, amperage in amps, and volt-amps in volts and amperes.
T
All electric -resistant appliance ir pieces of equipment such as an oven, water-heater and space heater(no blower) and lights generally have power (wattage) ratings equal to their connected loading (VA rating).
T
In contrast, all electromechanical (having a motor) appliances or pieces of equipment generally will have a VA rating larger than the power (P) rating.
T
Design of a branch circuit involves sizing conductors and over current protection (fuse or circuit breaker) that match the circuit rating.
T
General purpose circuits feed _____________ for lighting or other purpose.
more than one outlet
When a general purpose circuit feeds fixed appliances and luminaries or portable appliances, the total of the fixed appliances should be no more than 50% of the branch circuit rating.
T
When a portable appliances will be used on a general purpose circuit, the limit for any one portable appliance is 80% of the branch circuit rating.
T
In commercial applications, convenience receptacles are computed at a load of 1.5 A(180VA) per receptacle and are limited to 80% of the rating. This limits a branch circuit serving only receptacles to its rating divided by 11/ 2A.
T
A 20 A, 120 V branch circuit would have a theoretical maximum of 2400 VA (20A, 120V, 2400 VA), but it is common practice to limit the connected load to 80% of the circuit rating.
T
When the load on the circuit will be continuous operating load, the total load should not exceed 80% of the circuit eating.
t
These circuits provide power to a single outlet such as a receptacle serving a range, clothes dryer, or copy machine.
Individual Circuits
These circuits serve TWO OR MORE OUTLETS to which only appliances are connected.
Appliance Circuits
A ___________ is a connected load that operates for 3hr or more at any time.
continuous load
When determining a circuit rating, most loads deemed continuous must have a circuit rating calculated at ______ of the circuit’s connected load.
125%
On a branch circuit, _________ is tied to circuit rating.
conductor size
Ungrounded and grounded conductors must be sized so that conductor ampacity is at least the branch circuit rating.
T
The ampacity of a conductor can be smaller than the circuit rating but not larger.
F
- is the most widely used wiring method in residential dwellings.
Type NMB cable
______ cable must have 194 degrees F (90degrees C) conductor insulation rating, which is designated by a “B” on the cable sheath.
NM
used for receptacle and lighting circuits
AWG No. 12 and AWG No. 14
is commonly used for electric water heaters
AWG No. 10/2
with ground for electrical dryers and cooktops
AWG No. 10/3
with ground for ranges and wall mounted ovens
AWG No. 8/3 or AWG No. 6/3
used for electrical ranges, cooktops, wall ovens, and clothes dryers.
Type SER or other four wire cable
______ must be selected to match the load they control.
Switches
A panelboard - like enclosure called _____________ is used in large lighting installations that require many switches.
lighting control panel
_____________ must be selected to match the appliance or equipment they serve.
Receptacles
Ordinary convenience receptacles and switches are generally wall mounted and there are no specific height requirements for switches and receptacles.
T
Normally, ________ are mounted approximately 48 in. (1.2m) above finished floor (AFF), convenience receptacles at 16in. (400mm) AFF and convenience receptacles in bathrooms and restrooms at 44in. (1.1m) AFF, unless otherwise specified.
switches
___________ are customarily installed with the grounding slot oriented downward.
Receptacles
Unless the receptacle is controlled by a ______, the receptacle is frequently aligned with the grounding slot upward.
switch
Ordinary convenience receptacles and switches are general wall mounted and there are no specific height requirements for switches and receptacles.
T
In contrast to historical practice, it is recommended that receptacles be installed with the grounding slot oriented upward to improve safety.
T
By orienting the grounding slot upward, the grounding pin would be the first blade to contact the object, which would not create a short-circuit.
T
An _________________, a fuse or circuit breaker serves to limit current levels in a conductor by interrupting power when current limitations are exceeded. It prevents excessive heat from damaging conductors and related equipment.
overcurrent protection (OCP) device
The _________ of a fuse or circuit breaker must be equal to or greater than the voltage of the circuit in which the fuse is applied.
voltage rating
The _____ carried by the electrical circuit or system protected by an OCP device must not exceed the maximum current rating of the circuit breaker.
current
the _________________ for circuit breakers should be at least 5000 A and 10 000 A for fuses.
amperes interruption current (AIC) rating
The _____ or ______________ must be installed at a location in the circuit where the conductors receive power (generally at the panelboard).
fuse, circuit breaker
The __________ must protect the ungrounded conductors in a circuit to ensure that power to the circuit is interrupted by the ______.
OCP device
The ___________ and _____________ are not protected by overcurrent protection.
neutral (grounded), grounding conductors
A ___________ is a set of conductors that carry a comparatively large amount of power from the service equipment to a second panelboard, called a ___________, where branch circuits further distribute the power.
feeder, subpanelboard
____________ must designed to provide sufficient power to the branch circuits they supply so the feeder conductor size is based on the __________ to be supplies by the ________.
Feeders, maximum load, feeder
_________ should be capable of carrying the amount of current required by the load, plus any current that may be required in the future.
Feeders
It is not likely that all connected loads on a feeder will in operation at a specific time. Thus, feeder conductors do not need to be sized to carry the total connected load served by the feeder. Additional capacity may be warranted for future expansion.
T
___________ and ________ can be used as distribution equipment, at a point downstream from the service entrance equipment.
Switchboards, panelboards
_____________ and _____________ and having at least 10% of the circuits rated at 30 A or less are identified as lighting and appliance panelboards.
Panelboards feeding lighting and convenience receptacles
________________ feed other panelboards (called subpanelboards), motors, and transformers, but not circuits powering lights and convenience receptacles.
Power distribution panelboards
In a single panelboard, not more than ______ overcurrent protection devices may be used for protecting lighting and appliance branch circuits.
42
When locating overcurrent protection in a panelboard, it is important to balance the anticipated load so that both bus bars are carrying a similar load.
T
In service equipment panelboards, the _____ and ____________ are bonded together. In ____________, the neutral is isolated from the ground.
neutral, equipment grounding conductors, subpanelboards
In general, a ____ or _________ must be installed at a location in the circuit where the conductors receive power.
fuse, circuit breaker
Generally, this location is in the __________ or _________ before the conductors leave to convey current to the outlets in the circuit.
panelboard, load center
Large enough to supply the compute load of the building or area of the building being served.
Service Equipment
The most common sizes of residential service equipment are 100, 125, 150, and 200.
Residential service equipment
All __________ and ____________ shall have a clear area 30 in(0.75m) wide and 36 in (0.9m) deep in front.
service equipment, electrical panels
The required clearance can be found in the ______. Typically, minimum vertical clearances of 18ft (5.5m) above roadways, 12ft above driveways, and 10 ft above sidewalks are the required minimum.
Code
Commonly used aluminum conductors
RHW, THWN, THIN, XHHW, AND USE
An _____ (2.4m) clearance is required above low sloped (less than 4in 12 slope) rooflines. A ___ (0.9m) clearance is required for steep sloped roofs.
8ft, 3ft
It is also necessary to bury _____________ sufficiently below grade to reduce the hazard of unintentional contact
underground conductors
The required depth of burial can be found in the _________
Code
Minimum earth cover varies from 6 to 24 in (150 to 600mm).
T
Transformer combinations, such as wye- wye, delta-delta, delta-wye, wye-delta- are available for use in buildings.
T
The first symbol indicates the configuration of the primary windings and the second the configuration of the secondary windings.
T
- popular unit used in large commercial buildings and industrial facilities.
A480 V primary, 208 VY/120V secondary, three phase transformer
_________ and __________ conductors are sized to carry 100% of the ampere rating of the overcurrent protection.
Primary and secondary
The _______ has required tamper- resistant receptacles to be installed in all 125 V, 15 and 20 A electrical receptacles in hospital pediatric areas for nearly three decades. Recently, the ___ introduced requirements for all 125v, 15- and 20A electrical receptacles in new residential construction to be a ___________________.
NEC, tamper resistant receptacles
Product such as plastic plug-in inserts and wall plates witch contact shutters are available for tamper resistance, but do not meet these requirements.
T
There are many other settings where children may be at risk , including day care centres, children’s play areas, elementary and nursery schools, doctor’s offices and lobbies, and retail establishments featuring children’s attire or toys.
T
All ______________ must have either the words “___________” or the letters “___“(minimum 3/16 in or 5mm high) on the device as a clear indication that this is a ___________________.
tamper- resistant receptacles, tamper resistant, tamper- resistant receptacle
The NEC introduced requirements for use of GFCI protection of outdoor convenience receptacles within ______ of grade level. In residential installations, GFCI protection is required at all____, single phase 15 A and 20A outlets in the locations listed below.
6& 1/2 ft or 2m, 125V
The requirements ______ apply to equipment rated at 240 V.
do not
Outdoor convenience outlets within ____________ of grade level (1973 edition) and revised to include all exterior convenience outlets (1993 edition).
6& 1/2 ft or 2m
Bathroom convenience outlets (1975) edition
T
Readily accessible convenience outlets in garages (1978 edition), except where not readily accessible such as outlets dedicated to an overhead door opener or freezer.
T
_________ circuit breakers may be added in panel boards of older buildings to replace ordinary circuit breakers. For homes protected by fuses, the __________ or ___________ GFCI protection is ______________.
GFCI circuit breakers, convenience receptacle, portable type, highly recommended
Ideally, the ______________ should be involved in the project from the very beginning.
electrical engineer
The ___________ is the person who could best discuss the electrical component of project planning with the power company.
electrical designer
___________ guides the designer to a solution that best suits the need of the building occupant. The _________ achieves the solution by:
- observing and evaluating existing installations and adapting them to meet the project requirements
- applying electrical systems theory
-applying code requirements
Experience, designer
_________ of an electrical system begins with the layout of all outlets or outlet connections.
Design
The number and type of lighting outlets should be fitted to the various seeing tasks
T
All convenience receptacles on 15A and 20 A general purpose circuits should be of the ___________, minimizing the hazard of shock from short circuits.
grounding type
_________ protection should be PROVIDED on receptacles where required by local code.
GFCI
______ protection should be USED on convenience receptacles where required by local code
AFCI
All rooms that have more than one entrance should be equipped with ______________ at each principal entrance.
MULTIPLE SWITCH CONTROLS
_____________ should be located at the lockset or latch side of doors or at the traffic side of arches, and within the room or area where the lighting outlets are located.
WALL SWITCHES
One or more lighting outlets should be located at or near all ________ entrances. _______ should be switched or automatically controlled,
exterior, Outlets
For each single family dwelling, at least one duplex __________ shall be installed outdoors to be readily available from ground level.
receptacleO
One or more outlets may be required for exterior equipment.
T
Outlets for ambient and task lighting should be provided. General illumination outlets should be ________ controlled
wall switch
Convenience receptacles in living areas should be placed so that no point along the floor line in any usable wall space is more than ______ from a receptacle outlet in that space.
6 ft
One or more receptacles for entertainment equipment should be provided at bookcases, shelves, or other suitable locations.
T
When general illumination is to be provided from portable lamps, then at least two separate wall switched plug in positions should be provided.
T
An _______ for a fireplace may be required.
outlet
A __________ on a 120 V circuit should be considered.
smoke detector/ alarm
______________ involve computing the demand load for a building system or a distribution system extending from a ____________.
Load computations, panelboard
This load includes the total of all general lighting, appliance, and equipment loads in the building.
Load computations
The ___________ allowed by the code takes into account that all of the electrical connection will not be in use at one time.
demand load
