Electrical Systems Design-Branch Circuits and Feeders

What are 3 types of conductors?

service conductors, feeder conductors, branch-circuit conductors

What are 4 types of branch circuits?

Appliance branch circuits, general-purpose branch circuits, individual branch circuits, multiwire branch circuits

What is a nonlinear load?

A load where the waveform of the steady-state current doesn’t follow the waveform of the applied voltage

What article specifies how we shall identify the grounded conductors of different systems?

200.6(D)

How shall we identify each ungrounded branch circuit?

by phase and system

How many types of loads can branch circuits with voltages not over 120V between conductors supply?

3

Branch circuits with which voltages can supply listed electric discharge luminaires?

Branch circuits with voltages over 120V and not more than 277V to ground

How many kinds of loads can branch circuits with voltages over 277V but less than 600V between conductors supply?

3

Which article of the NEC contains definitions?

Article 100

What is a service conductor per the NEC?

A service conductor is a conductor from the service point to the service disconnecting means. They supply power to the service equipment.

Where can service conductors be located?

overhead or underground per article 230

What is service equipment?

the necessary equipment, usually consisting of a circuit breaker or switch and fuses and their accessories, connected to the load end of service conductors to a building or other structure, or an otherwise designated area, and intended to constitute the main control and cut-off of the supply.

What are feeder conductors?

The wires leaving the service equipment

What is a feeder per the NEC?

all the circuit conductors between the service equipment, the source of a separately derived system, or other supply source, and the final branch-circuit overcurrent device

What’s an appliance branch circuit?

a branch circuit which supplies energy to one or more outlets to which appliances are connected

Can appliance branch circuits have permanently connected luminaires that aren’t part of an appliance?

No

What’s a multiwire branch circuit?

A branch circuit consisting of 2+ ungrounded conductors with a voltage between them, and a neutral conductor with equal voltage between it and each ungrounded conductor and that’s connected to the neutral conductor of the system.

What’s a general purpose branch circuit?

A general purpose branch circuit is a branch circuit supplying 2+ receptacles or outlets for lighting and appliances.

What’s a branch circuit?

A branch circuit is the circuit conductors between the final overcurrent device protecting the circuit and the outlets.

What’s an individual branch circuit?

A branch circuit supplying only one utilization equipment.

Can we consider multiwire branch circuits as multiple circuits?

Per 210.4, yes. Nothing fancy, no apparent exceptions, just “A multiwire circuit shall be permitted to be considered as multiple circuits.”

Where do the conductors in a multiwire branch circuit have to originate from?

All conductors in a multiwire branch circuit must originate from the same panelboard or similar distribution equipment.

What does the Informational Note 1 for 210.4(A) say?

The neutral conductor in multiwire branch circuits supplying power to nonlinear loads can carry more current than the ungrounded conductors. This is due to nonlinear loads producing harmonic currents.

Give examples of nonlinear loads.

Electronic equipment, electronic/electric-discharge lighting, adjustable speed drive systems, and other equipment powered by solid-state rectified power supplies.

Where do we post the method we use to establish the identification of the system grounded conductors?

We post this method permanently at each branch-circuit panelboard.

What does 210.5(C)(1) require?

210.5(C)(1) requires that each ungrounded branch-circuit conductor be identified by phase or line and system where a building has more than 1 voltage system. Identification must take place at all termination, connection, and splice points. We can ID conductors by a separate color code, mark them with tape, tag them, or ID them with another means acceptable to the AHJ. We have to document the method used and make it readily available or post it in each branch-circuit panelboard. The label cannot be handwritten and must be suitably durable for its environment. When a place has different systems but each system has the same voltage class, we can use the same identification means.

What kinds of loads can branch circuits with voltages not over 120V between conductors supply?

1. Terminals of lampholders applied within their voltage rating

2. auxiliary equipment of electric discharge lamps

3. Cord-and-plug-connected or permanently connected utilization equipment

What can branch circuits with voltages over 120V but not more than 277V to ground supply?

They can supply cord-and-plug-connected or permanently connected utilization equipment or 8 types of listed luminaires.

1. Electric-discharge luminaires with integral ballasts

2. LED luminaires with LED drivers located between the branch circuit and the lampholders

3. Incandescent or LED luminaires with medium-base or smaller screw shell lampholders. The lampholders must be supplied with 120V or less from the output of a stepdown autotransformer, LED driver, or other power supply that’s an integral part of the luminaire

4. Luminaires with mogul-base screw shell lampholders

5. Luminaires without lampholders

6. Luminaires with lampholders, other than the screw-shell type, when used within the voltage rating of their lampholders

7. Auxiliary equipment of electric-discharge or LED-type lamps

8. Luminaires converted with listed retrofit kits incorporating integral LED light sources or accepting LED lamps in accordance with 210.6(C)(1) to (5)

What kinds of loads can branch circuits rated over 277V to ground and not over 600V between conductors supply?

1. Electric-discharge auxiliary equipment.

2. Cord-and-plug-connected or permanently connected utilization equipment other than luminaires

3. Luminaires for special DC applications.

What conditions apply to electric-discharge auxiliary equipment supplied by branch circuits with voltages over 277V but less than 600V between conductors?

Installation’s limited to outdoor ares, like roads, bridges, sports fields, and parking lots. The lamps must be mounted in permanently installed fixtures mounted no less than 22’ in height on poles and similar structures or no less than 18’ in height on other structures such as tunnels.

What conditions apply for luminaires for special DC applications supplied by branch circuits with voltages over 277V but less than 600V between conductors?

The luminaires must provide a listed, DC-rated ballast with either isolation provisions to protect against electric shock during relamping or no provisions for changing the lamps.

When were the first requirements for GFCI protection added to the NEC?

1971

In the first requirements for GFCI protection, where was GFCI protection required?

Dwelling unit bathrooms and outdoor receptacles of dwelling units

How does the NEC define a bathroom?

An area including a sink (basin) with one or more of:

1. toilet

2. tub

3. urinal

4. shower

5. bidet

6. similar plumbing fixture

Again, a sink (basin) must be present for a room to qualify as a bathroom.

True/false: All bathroom receptacles shall be GFCI protected.

True, per 210.8(A)(1)

Per 210.11(C)(3), what are the branch circuit requirements for a bathroom?

There must be one or more 120V 20A branch circuit supplying the bathroom receptacles. An exception allows a 20A branch circuit to feed the receptacle and other equipment in a single bathroom. This circuit should have no other outlets.

What are the requirements for installing receptacles near bathroom sinks?

210.52(D) requires that we install at least one receptacle adjacent and within 3’ of the outside edge of each sink (basin).

What are the GFCI requirements for garages?

We need to install GFCI-protected receptacles in garages.

What kinds of accessory buildings need GFCI protection?

Accessory buildings with a floor located at or below grade level not intended as habitable rooms and limited to storage areas, work areas, and areas of similar use need GFCIs.

What kinds of outlets in garages and accessory buildings needing GFCI protection need GFCI protection?

120V, 1⏀, 15A and 20A receptacles in such buildings need GFCI protection.

True/false: All outdoor receptacles need GFCI protection.

True, with one exception.

What is the one exception to the rule about outdoor receptacles needing GFCI protection?

Outdoor receptacles that aren’t readily accessible but supplied from a dedicated branch circuit to serve electric snow-melting, deicing, or pipeline and vessel heating equipment in accordance with 426.28 or 427.22 are exempt from the GFCI requirement.

What are the GFCI requirements for crawl spaces?

All receptacles in crawl spaces where the crawl space is at or below grade level shall be GFCI protected. Such crawl spaces may also wet or damp locations, so equipment used there should be listed for such locations.

What are the GFCI requirements for dwelling unit basements?

All 125V-250V receptacles in dwelling-unit basements shall be readily accessible unless they supply permanently installed fire alarm or burglar alarm systems.

What receptacles in dwelling unit kitchens need GFCI protection?

All receptacles installed in dwelling unit kitchens and intended to serve countertop surfaces need GFCI protection.

Why do receptacles in kitchens intended to serve countertop surfaces need GFCI protection?

Most devices meant for countertop use don’t have an EGC. Because water and grounded surfaces are both common in kitchens, a shock hazard exists.

Which receptacles near a sink need GFCI protection?

All receptacles within 6’ of the top inside edge of the sink bowl need GFCI protection.

What does 406.5(G)(1) specify?

Receptacles should not be installed in the face-up position in countertop or work surfaces unless listed for such applications.

What does 406.5(F) specify?

Receptacle assemblies for installations in countertop or work surfaces must be listed for those applications.

What does 406.5(G)(2) specify?

Receptacles can’t be installed in the face-up position if located in the area under a sink or basin.

What are the rules for GFCI protections that aren’t in dwelling units?

All 125V through 250V 1⏀ receptacles in bathrooms and on rooftops in other than swelling units shall be GFCI protected. All 50A or less, 1⏀ receptacles rated 150V to ground or less and all 100A or less, 3⏀ receptacles rated 150V to ground or less in any of the 12 locations listed in 210.8(B) must offer GFCI protection for personnel.

What do combination-type AFCIs do?

They provide protection from series arcs, parallel arcs, and line-to-ground arcs.

What are three means specified in 210.12(A)(1) to (6) that can be used to provide required AFCI protection for all 120V, 1⏀, 15A and 20A branch circuits supplying outlets or devices installed in dwelling unit kitchens, family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, rec rooms, closets, hallways, laundry areas, or similar rooms or areas?

1. A listed combination-type AFCI installed to protect the entire branch circuit

2. a listed branch/feeder-type AFCI installed at the origin of the branch circuit in combination with a listed outlet branch-circuit AFCI installed at the first outlet box on the branch circuit marked to indicate that it’s the first outlet

3. a listed supplemental AFCI CB installed at the origin of the branch circuit in combination with the AFCI that’s installed at the first outlet box on the branch circuit

What’s the minimum branch circuit conductor size?

Minimum branch circuit conductor size shall be equal to or greater than the noncontinuous load plus 125% of the continuous load.

What is the minimum ampacity of branch-circuit conductors?

They must have a minimum ampacity that is not less than the larger of either (a) the noncontinuous load plus 125% of the continuous load, per 310.14, where the circuit supplies continuous and noncontinuous loads, or (b) the maximum load that will be served after any adjustment or correction factors have been applied, per 310.15.

Why do we have the requirement to increase continuous loads by 25%?

Equipment, in general, isn’t built to handle continuous loads without imposing an increase in generated heat. If equipment’s listed for continuous loads at 100%, the 25% isn’t needed.

What happens, in general, when the branch circuit supplies more than 1 receptacle for cord-and-plug-connected loads?

The conductors shall have an ampacity no less than the rating of the branch circuit.

What is the ampacity requirement for conductors of multioutlet branch circuits supplying receptacles for cord-and-plug-connected portable loads?

They shall have an ampacity of no less than the rating of the branch circuit. this is the rating of the overcurrent device.

What is the ampacity fo the conductors in multioutlet branch circuits for cord-and-plug connected loads?

Their ampacity should be equal to the rating of the branch-circuit overcurrent protective device because they have random, unpredictable loads.

What is the minimum ampacity of tap conductors supplying electric ranges and other cooking units from a branch circuit not exceeding 50A?

no less than 20A

How long should the taps in tap conductors supplying electric ranges and cooking units from a branch circuit not exceeding 50A be?

They should not be longer than needed to service the appliance. They should include any leads that are part of the appliance and smaller than the branch-circuit conductor.

What is the minimum ampere rating for a single receptacle on an individual branch circuit?

It shall have an ampere rating no less than the branch circuit. this ONLY applies to single receptacles.

True or false: we consider connectors that are supplied by permanent pendant cords as receptacle outlets.

True

What does 210.50(C) specify?

Appliance receptacle outlets installed in dwelling units for specific applications must be located a maximum of 6’ from the intended appliance location. Other sections of the Code may provide more restrictive requirements.

How long can a cord for in-sink waste disposers be?

Between 18 and 36 inches

How long shall the cords of trash compactors and dishwashers be?

Between 3’ and 4’

How long should the cords on cord-and-plug-connected range hoods be?

18” to 36”

What is the max distance from any point on the floor line in any wall space to a receptacle outlet?

6’. We include wall space provided by freestanding bar-type counters or railings in this measurement. We include the space occupied by fixed panels in exterior walls, excluding sliding panels, in this measurement.

What is the minimum length of wall space requiring a receptacle outlet?

2’

What determines the location of receptacle outlets for countertops and work surfaces in kitchen and dining rooms of dwelling units?

the wall counter space, island counter space, peninsular counter space, separate spaces in these rooms

How far apart do we install receptacle outlets for countertop and work surfaces?

12” or wider. Multioutlet assemblies 12” or wider with 2+ receptacles are considered as 1 receptacle outlet.

What’s the max distance a receptacle outlet can be from any point along a wall line, measured horizontally?

24”

Where don’t we need to install receptacle outlets in kitchens and dining rooms?

directly behind ranges, counter-mounted cooking units, or sinks

How many receptacles are required based on the area of countertop or work surface?

We need at least 1 receptacle for the first 9 square feet. After that, we need one receptacle per additional 18 square feet.

How far shall receptacle outlets be from the outer ends of peninsular countertops and work surfaces?

We need at least 1 receptacle outlet within 2’ of the outer ends of peninsular countertops or work surfaces. The installer, designer, or building owner can determine the locations of additional required receptacle outlets.

How far can receptacle outlets be above the countertop or work surface?

They can be no more than 20”.

How far below the countertop or work surface be?

They can be located neither more than 12” below the countertop or work surface nor where the countertop or work surface extends more than 6” beyond its support base.

What happens if the width of the counter behind the appliance is less than 12” for the purposes of receptacle placement?

The range, counter-mounted cooking unit, or sink is considered to divide the countertop space into two separate spaces as defined in 210.32(C)(4). Each separate space must comply with the applicable requirements of 210.52(C)

How shall we position wall receptacle outlets relative to the outside edges of basins?

We must install at least one wall receptacle outlet within 36” of the outside edge of each basin and on a wall adjacent to the basin location.

Where must we install exterior receptacles?

At least one receptacle shall be installed outdoors at grade level at the front and back of each one-family dwelling and each unit of a two-family dwelling. At least one receptacle outlet shall be readily accessible at grade level and no more than 6’6” above grade level.

What does Section 310.12 do?

It’s used to size service and feeder conductors supplying dwellings with 120/240V, 1⏀, 3-wire systems.

What should the ampacity of feeder conductors rated no more than 1000V be?

In general, they should have an ampacity no less than is needed to supply the load.

How should we size feeders?

Feeders shall be sized to carry not less than 215.2(A)(1)(a) or (b) and comply with 110.14©. Feeders supplying continuous loads or continuous and noncontinuous loads in any combination must have a minimum allowable ampacity of no less than the noncontinuous loads plus 125% of the continuous load.

When are delta 4-wire systems popular?

They’re popular where there’s a large 3⏀ load, a large 1⏀ line-to-line load, and a small 1⏀ line-to-neutral load.

What is an open delta?

It’s a configuration used by utilities where there’s a large 3⏀ load, a large 1⏀ line-to-line load, and a small 1⏀ line-to-neutral load. This allowed utilities to provide 3-phase power using 2 transformers with the possibility of increasing capacity in the future by installing one transformer for a closed delta configuration. This transformer configuration is one that is listed in the definition of neutral point. The neutral point is located at the midpoint of one of the phases. The neutral conductor is connected to the neutral point and grounded. It provides 120 V, line to neutral, for 120 V, 1ϕ loads. This configuration also provides 240 V, 1ϕ, line to line, and 240 V, 3ϕ. Care must be used when these systems are used. The voltage measured between the Bϕ conductor and the neutral conductor is 208 V (120 V × 1.73 = 208 V). This Bϕ conductor is called the high-leg. And I do not get any of that.