Section 2: Definitions

2.1 Accessible
2.2 Accessible (Readily Accessible)
2.3 Branch Circuit
2.4 Continuous Load
2.5 Feeder
2.6 Grounded – Grounding
2.7 Ground-Fault Protection of Equipment
2.8 In Sight From (Within Sight From, Within Sight)
2.9 Qualified Person
2.10 Separately Derived System

2.1 Accessible
The disconnect adjacent to HVAC equipment above a dropped ceiling is considered “accessible” even though access to it requires use of a ladder.

The term accessible when describing the requirements for access to equipment is defined in Article 100 as follows: Admitting close approach; not guarded by locked doors, elevation, or other effective means.

For equipment to be accessible it must not be guarded by locked doors or by elevation above the floor or platform.  However, if a key is made available to the personnel requiring access, then equipment behind a locked door is considered accessible.

The term accessible when describing the requirements for access to wiring methods is defined in Article 100 as follows:  Capable of being removed or exposed without damaging the building structure or finish or not permanently closed in by the structure or finish of the building.

For wiring methods to be accessible they must be capable of being removed without damaging the building finish and cannot be closed in by the building structure.  For example, a junction box covered with sheet rock is not considered accessible.  However, a junction box located above a lay-in (or drop) ceiling is considered to be accessible.  Another example is a busway switch installed on a busway located in the ceiling of an industrial facility.  The switch is considered accessible even if it is located more than 6-ft. 7-in. above the floor.

Review Question Section 2.1

5. Accessible (as applied to equipment) means admitting ________ approach.

2.2 Accessible (Readily Accessible)

Readily accessible equipment must not be blocked by obstacles and must be capable of being reached quickly without the use of tools or ladders.

Overcurrent devices must be readily accessible so they can be reached in case of an emergency.  Equipment that is mounted higher than 6-ft. 7-in. is not considered readily accessible because it cannot be reached while standing on the floor or platform.

Service equipment is required to be located in a readily accessible location.  The service disconnecting means must be capable of being operated quickly to disconnect utility power from a building or structure.  Equipment is still considered readily accessible if it is located in an electrical equipment room that is locked, as long as qualified persons have the key.

GFCI receptacle outlets must always be readily accessible.

Review Question Section 2.2

6. What does readily accessible mean?

Switchgear in a locked room is considered “readily accessible” provided those requiring ready access have a key.

2.3 Branch Circuit
Branch circuit conductors are installed between the final overcurrent device and the load supplied by the circuit.

A branch circuit consists of the circuit conductors between the final overcurrent device and the outlet the circuit supplies. The overcurrent device protecting a branch circuit is either a circuit breaker, as shown in the illustration, or a fuse. The outlet is equipment that utilizes electricity such as, luminaries, motors, or heaters. Whether this equipment is hard wired or cord and plug connected to a receptacle it is still considered a branch circuit.

A branch circuit can be dedicated to a single outlet or it may be a general purpose branch circuit supplying two or more lighting outlets or receptacles for appliances.

A common practice in industrial locations is to use 50 amp receptacles on branch circuits for certain types of equipment. This allows equipment to be quickly moved from one place to another.

Multiwire branch circuits are commonly used in commercial, institutional, and industrial locations. A multiwire branch circuit consists of a shared grounded (neutral) conductor and two or three ungrounded conductors, each protected by a fuse or circuit breaker. When single pole circuit breakers are used on a multiwire branch circuit, handle ties must be used to connect the handles together.

A multiwire branch circuit supplying two separate groups of fluorescent luminaries is considered to be two branch circuits.

Review Question Section 2.3

7. Which of the following installations is a branch circuit?

2.4 Continuous Load

A continuous load is a load that is on for 3 hours or more. Lighting in a commercial or industrial location is always considered a continuous load.

The wire size and overcurrent protection for continuous loads is calculated at 125% of the load. For example, the wire to feed a 100 amp lighting load in an office building must be selected to carry 125 amps. The overcurrent protection for the load must be set at 125 amps also.

The increased size of the wire and overcurrent protection for continuous loads is to allow for the heat buildup at the terminals of equipment. The amount of current in a circuit does not actually increase after 3 hours. But the heat at the equipment terminals does increase over time and a larger wire will be less likely to overheat, and a larger fuse or circuit breaker will not nuisance trip because of higher temperatures.

Review Question Section 2.4

8. A continuous load is a load where the maximum current is expected to continue for ___ hours or more.

Lighting is considered a continuous load if it operates for 3 or more hours.

2.5 Feeder
Feeders are the circuit conductors between service equipment and the final branch-circuit overcurrent device.

The definition of a feeder in Article 100 is “All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.” For example, the conductors that run from the load side of a 200-amp fusible disconnect to a 200-amp subpanel are considered to be feeder wires.

In the photo, the switchboard is being supplied by a feeder from the main distribution panel. It also would be possible to have a feeder from this switchboard feeding a panelboard located elsewhere in the building.

The difference between a feeder and a branch circuit is that a feeder usually runs from one overcurrent device to another overcurrent device and a branch circuit is installed from the final overcurrent device to the outlet(s).

Review Question Section 2.5

9. Which of the following circuits is a feeder?

2.6 Grounded/Grounding

The term grounded is defined in Article 100 as “Connected (connecting) to ground or to a conductive body that extends the ground connection.

For conductors or equipment to be grounded they must be connected to earth. Equipment connected to building steel is grounded only if the building steel is itself connected to earth. The building steel does not take the place of earth, and the equipment would not be grounded if the building steel didn’t extend the ground connection, by being physically in contact with earth.

Grounding requires non-current carrying metal parts to be connected to an equipment grounding conductor that is connected to earth. The connection put all the metal parts of electrical equipment and raceways at basically the same electrical potential as earth, which is zero volts. So, even under fault conditions, there is practically no voltage difference between equipment that is properly grounded and the earth or anything that is in contact with the earth such as structural steel, concrete floors, metal water pipes or you!

In the photo the grounding electrode conductor is connected to a grounding electrode. The grounding electrode is a driven ground rod.

Review Question Section 2.6

10. According to the definition, which of the following connections is grounded?

Electrical systems are grounded by being connected to the earth through the grounding electrode system.

2.7 Ground-Fault Protection of Equipment
Ground-fault protection of equipment is required for solidly grounded wye connected electric service disconnects rated 1000 amperes or more if the voltage exceeds 150 volts to ground but does not exceed 600 volts phase-to-phase.

Ground fault protection of equipment is designed to protect equipment from damaging line-to-ground fault currents by causing the service disconnecting means to open all ungrounded conductors.

Systems designed to provide Ground Fault Protection of Equipment typically have a 30-mA trip level. These 30-mA protective systems are designed to protect equipment from damage due to overheating or fire and should not be confused with 5-mA ground-fault circuit interrupters (GFCI’s), which are designed to provide personnel protection from electrical shock.

Solidly grounded Wye electric services of 1000-amps or more rated at more than 150 volts to ground but not exceeding 600 volts phase-to-phase are required to have ground fault protection for equipment. For example, a 1000-amp, 277/480-volt service disconnect is required to have ground fault protection of equipment.

A ground fault on a large service can quickly develop into a phase-to-phase fault and cause massive damage to equipment and extreme danger to personnel. Ground fault protection for equipment will de-energize the service when the ground fault current reaches the trip point.

Review Question Section 2.7

11. Which of the following statements about ground fault protection of equipment is true?

2.8 In Sight From (Within Sight From, Within Sight)

The NEC uses the terms in sight from, within sight from, or within sight of to mean the same thing. These terms mean that the equipment must be visible and within fifty feet.

An equipment disconnect that is in sight from the equipment means the person working on the equipment can control the disconnect. A disconnect that is within sight of a machine means the electrician or operator of the equipment can see the machine before energizing it.

Within sight from means two things: (1) Not further than 50-ft.; (2) There must be a clear line of sight between the two pieces of equipment.

If a disconnect is located 25-ft. away from a piece of equipment, but the disconnect is located around a corner, then the disconnect is not with sight of the equipment. If the equipment is clearly visible while standing at the disconnect, but the distance is greater than 50-ft. then they are not within sight from each other.

The disconnect in the photo is located next to the HVAC unit it supplies. The disconnect is clearly visible and within 50-ft. of the HVAC unit, so the Code considers them to be within sight of each other.

Review Question Section 2.8

12. In which installation would the two types of equipment be considered within sight of each other?

The in sight from or within sight of requirement means a disconnect has to be visible and not more than 50-ft. from equipment it supplies.

2.9 Qualified Person
A “qualified person” has the knowledge and skill related to the installation, construction, and operation of electrical equipment and the safety training necessary to identify and avoid the hazards it prevents.

A qualified person has the skills and knowledge required to perform the installation, construction and operation of electrical equipment and has received safety training in recognizing and avoiding possible hazards.

Inspectors that sub-contract an electrician should recognize that an individual may be a qualified person in one area and not qualified in another area.  For example, a person could be qualified to work on equipment 600 volts and less, but not over 600 volts.

State licensing in the electrical trade does not make someone a qualified individual, and the number of years of practical experience is not part of the definition of a qualified person.  A qualified person does have the skills and knowledge to install electrical equipment and no one can be considered qualified unless they have demonstrated a thorough knowledge of electrical construction practices.

Qualified persons are required to have safety training appropriate for the work they perform.  The standard for safety training in the electrical trade is NFPA 70E, Standard for Electrical Safety in the Workplace.

Review Question Section 2.9

13. One who has skills and knowledge related to electrical installations and has received safety training on the hazards involved is known as a _________ person.

2.10 Separately Derived System

A separately derived system is defined in Article 100 as “An electrical source, other than a service, having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections.

Most transformers and some generators are considered separately derived systems.  A generator that has a grounded (neutral) conductor bonded to the frame of the generator is a separately derived system.  When used as standby power for a grounded electrical service, the generator transfer switch is required to switch the neutral.

Another example of a separately derived system is the typical transformer with a 480 volt primary and a 120/208 volt secondary.  The neutral secondary conductor is derived from the transformer and there is no direct connection to the transformer primary conductors.

With each of these separately derived systems, bonding and grounding is required on the secondary side of the transformer.  Grounding at a transformer is similar to grounding at the service; the grounded conductor is connected to a grounding electrode conductor.

Grounding and bonding conductors of a separately derived system are permitted to be connected to grounding and bonding conductors of other sources such as the service grounding electrode system.

Review Question Section 2.10

14. Which of the following statements about separately derived systems is correct?

Most Transformers are separately derived systems.