UNDERGROUND SERVICES AND UNDERGROUND WIRING

ADVANTAGES OF UNDERGROUND WIRING
The advantages of underground electric service are attractiveness (lack of physical and visual clutter overhead), service reliability, and long life. The principal disadvantage is high cost. To overcome this, utilities frequently use direct burial techniques that, by eliminating a raceway, reduce costs considerably.

Because direct buried cable cannot be pulled out if it faults, as is the case with raceway-installed cable, restoration of service after a cable fault is time-consuming. It is recommended that the decision on which technique will be used be based upon the consideration of these factors:

• The cost premium for underground raceway installation, including handholes if required.
• The history of outages for direct burial installation by this installer, in the immediate area
• Cost and availability of repair service (utilities frequently will repair customer-owned underground service laterals for a fee)
• Impact of electric service outage in terms of time delays, inconvenience, necessity of digging up lawns and paved areas, and cost impact in the case of a commercial facility.

UNDERGROUND WIRING METHODS
The methods available for underground wiring are:
• Direct burial
• Installation in Type I, concrete-encased duct
• Installation in Type II, direct burial duct

The first alternative offers low cost and ease of installation, with the disadvantage regarding repairs stated previously. The second offers high strength and permanence, but at the highest price of the three. The last offers median cost but little strength. It is applicable only for installations on undisturbed earth and/or under light paving.

Nonmetallic duct (conduit) intended for underground electrical use is commercially available in two wall thicknesses. NEMA (National Electrical Manufacturers Association) Type II with a heavy wall provides the physical protection required for direct burial installation with no concrete encasement.

Type I is manufactured with a thinner wall and is intended for encasement in a minimum of 2 in. (50 mm) of concrete. Common trade names for asbestos-cement and fiber ducts are Transite and Orangeburg. Plastic conduit is referred to as PVC or simply as plastic.

Nonmetallic conduit is most frequently used without concrete encasement for low-voltage and signal wiring and with encasement for high-voltage wiring. It offers several advantages over steel conduit for underground work, such as lower cost and freedom from corrosion.

When underground electric wiring is ductinstalled and the run extends over several hundred feet (meters) (the exact distance depending upon the pulling tension), a pulling handhole or manhole is necessary. Handholes are used for low-voltage power and signal cables and for runs with a small number of cables. Manholes are used for high-voltage cables and where large duct banks must be accommodated.

Precast handholes and manholes are readily available in many standard sizes and are usually cheaper than field-formed and poured units.

Cable used in underground wiring must be specially manufactured and approved for that purpose. Type SE is the basic service entrance cable, constructed with a moisture- and flameresistant covering. When it is provided with moistureproofing for underground use, the designation is SE type U, or simply USE.

Underground cable for other than service runs is classified as type UF (underground feeder).

PARTS OF ELECTRIC SERVICE ENTRANCE BASICS

How to install service entrance? You will only know it if you know its parts. The details of how the service lateral or triplex cable provided by the electrical utility is fastened and spliced to the customer’s service point are illustrated in Fig. 5-3.

The bare neutral/grounding cable that supports the triplex is fastened at one end to the utility pole and the other end is fastened at the service point with a combination insulator and anchor bolt crimped onto the cable. This attachment method leaves the end of the neutral/grounding cable and the bare ends of the two insulated “hot” conductors available for splicing.

Electrical utility employees splice these three ends to corresponding ends of the customer’s service entrance (SE) cable, which is installed by the electrical contractor. The three ends of the customer’s SE cable are pulled through the bushings in a protective metal hood called the weatherhead or service head with enough slack to permit an adequate drip loop to be formed when the three conductors are spliced.

The drip loop, which must be at least 36 in. long, prevents water from entering the weatherhead. Without a drip loop, water could drain down the conduit to the cable connections inside the meter base to the bus bars that power the watthour meter, corroding them and causing a short circuit.

The details of two different aerial feed service entrances are illustrated in Fig. 5-4. A 200-A service entrance made with three-wire service entrance (SE) cable is shown in Fig. 5-4a. The cable from the weatherhead is brought down to the meter base, where the busbar connections to the meter are made. Another length of SE cable goes from the meter bus bars to the loadcenter.

A second version of a 200-A service entrance has the SE cable protected by metal or nonmetallic conduit between the weatherhead and the meter base, as shown in Fig. 5-4b. The service entrances for 175- and 100-A service are identical except that the SE cable has either a 175- or a 100-A rating. The limits of the meter height dimensions above grade level are approved by NEC 2002.

A 200-A service with the triplex cable terminating on a metal conduit mast is shown in Fig. 5-5. The mast projects high enough to comply with NEC 2002 for the minimum distances of the triplex termination above the ground. The hollow pipe functions as both a mast and a conduit for SE cable from the weatherhead to the meter base. As in Fig. 5-4, the service entrances for 100- to 175-A service are identical except for the lower SE cable ratings. All of the dimensional limits shown are those approved by NEC 2002.

GUIDE FOR INVESTIGATION OF CUSTOMERS’ HIGH-BILL ELECTRICITY INQUIRIES ON THE CUSTOMERS’ PREMISES

As a representative of the company, an employee who is assigned to investigate a customer’s inquiry concerning his billing has a dual responsibility. First, make absolutely certain that all service used by the customer is being accurately registered on the meter. Attempt to explain some of the metering factors to a customer who does not understand them to assure the customer of the accuracy of the meter.

The following is a plan suggested for conducting metering investigations. Steps 1 and 2 are frequently performed by a representative of the commercial department of the company. In many companies, only Steps 3 and 4 are performed by meter department personnel.

Step 1
A. Upon arriving at the customer’s home or place of business, the company representative should introduce himself, show his identification card or badge when requested, and explain the purpose of his visit. He should also advise the customer that, in the process of checking, the electric service might be momentarily interrupted.

B. The meter readings should be compared with those on the last bill. If an error is apparent, it should be explained to the customer and reported to the billing section.

C. If the customer’s question concerning his bill cannot be explained from the aforementioned, the company representative should ask the customer if any appliances have been added recently. Inquiry about appliances that affect seasonal loads is particularly important.

These may include air conditioners, dehumidifiers, space heaters, and heating cables. It should also be determined whether the customer has replaced any major appliances recently. The replacement of a refrigerator with a newer, frost-free model may result in an increase in operating cost, and this should be explained to the customer.

D. Ask the customer if there has been an increase in the number of persons living in the household.

E. Ask the customer if situations have occurred that were out of the ordinary routine of the household. These would include such things as more entertaining than usual, guests visiting in the home, an illness in the family, and other factors that would increase the customer’s bill.

F. If the customer’s inquiry can not be explained after carrying out the parts of Step 1, proceed to Step 2.

Step 2
A. Check for causes of abnormally high consumption.
1. Dirt- or lint-clogged filters on furnace or air conditioning units.
2. Leaky hot-water faucets where electric water heaters are used.
3. Defective water pump.
4. Use of electric range units for space heating.
5. Heating water on range.

B. If the preceding investigation is sufficient, discuss these factors with the customer briefly, pointing out any reasons you have found for the increase in the customer’s electric bill.

C. If further investigation is necessary, proceed to Step 3.

Step 3
A. If there is a load on the meter, ask the customer to shut off all appliances and lighting at the appliance or light switch. Recheck if the meter continues to indicate a load and determine absolutely whether rotation is due to a missed load or loss to ground. If there is a loss to ground, this should be checked with a stop watch and the rate of loss established.

B. If possible, it should then be determined which circuit is grounded and, if convenient to the customer, the circuit should be disconnected by removing the fuse or opening the circuit breaker. The condition should be explained to the customer and he should be advised to have the condition corrected by a wireman before using the circuit again. If the loss to ground is found to be a defective appliance, it should be disconnected and the customer advised to have repairs made before reconnecting the appliance.

Step 4
If no explanation for the bill has been reached, the meter should then be checked for accuracy, creep, proper constant, and correct register ratio. The results of each check should be noted on the investigation order.

GOOD PRACTICES FOR METERING PERSONNEL

Efficient metering personnel will make good installations. In doing so, they will observe certain practices that will be helpful to both their company and the customers. These good practices have many benefits. They insure good service by preventing unnecessary outages.

They insure good customer relations by preventing damage to the customer’s equipment. Also, the meter employee will not have to return to the customer’s premises for things forgotten or left undone and thereby undermine the customer’s confidence in electric metering.

All these benefits, in turn, help the company and the employee. Following are some of the good metering practices, not necessarily in order of importance. Competent metering employees will:

Recognize their responsibilities while on the customer’s premises.
• Take the nearest and safest route to accomplish the work.
• Take care not to damage any of the customer’s property.
• Leave the area clean upon completion of the job.
• Report any hazards to the meter department supervisor.

Work in the safest possible manner.
• Keep in mind that no job is so important that it cannot be done safely.
• Inspect all meter wiring connections for correctness
• Check connections to prevent outages, damage to meter installation, damage to customer’s property, and personal injury.

Inspect for loose connections.
• A loose connection can cause intermittent service or it can cause a complete outage. Loose connections generally arc, causing a fire hazard. Even if there is no fire damage, heating around the connection occurs.
Inspect for good grounding.
• Check for equipment ground at the installation. Realize that no ground at the installation is a potential hazard and report it to the supervisor.

Pay attention to details.
• Check meter voltage links. Inspect connections between two dissimilar metals.
• Connection between two dissimilar metals often causes corrosion.
• Corrosion can be prevented by using the proper connector and by protecting the connector and conductors against oxidation.
• Wires corroded at a joint have the same effect as a loose connection since corrosion has a high resistance and causes heating, which, in turn, assists the corrosive action.

Check for proper voltages.
• Voltage should be checked before installing the meter.
• A reversal of the power and lighting leg on a four-wire delta system causes excess voltage on customer’s equipment. Also, a reversal of the hot leg and ground has serious consequences.
• Grounded conductors and the power leg of four-wire delta services should be permanently identified.

Check phase rotation.
• Phase rotation on installations which have been disconnected temporarily for service work should be checked. If a reverse phase rotation is connected to the customer’s motors, they will reverse, possibly causing extensive damage. This could also mean personal injury.

Check for single phasing.
• It is possible to prevent damage to the customer’s property by disconnecting or warning the customer to disconnect the load on a three-phase service when one phase is out. A running three-phase motor may continue to run on single phase but will overheat. A stopped motor may attempt to start but cannot, which causes overheating.

Observe direction of disk rotation.
• Whenever possible, try to get a load applied to the meter in order to check for correct disk rotation.

Check for diversion.
• Always check for circuits tapped ahead of the meter or current transformers.

Check for correct installation information.
• Check for correct phase, amperes, volts, and frequency.
• Check for such details as multipliers, full scales, readings, and similar data.
• Check all written records against actual nameplate data.

Check to see if meter is level.
• An out-of-plumb meter may be inaccurate. Besides being inaccurate, it presents an unsightly appearance to the customer and may undermine his confidence in the electric metering.

Give the entire job a good once over before leaving it.
• Check the job in general for good workmanship and safety before leaving. Be sure the area surrounding the meter is left clean and neat.

Meter employees are the company in the eyes of many customers. They can make a good impression on the customer by being neat in dress, accurate in work, and courteous at all times.

Having equipment and tools in good, clean condition will build the customer’s confidence in the company and assure the customer of the employee’s skill. Sloppy dress, actions, and equipment leave a poor impression.

There are probably many other practices which are followed on local levels throughout the country, but if employees observe those listed, they will turn out a good job.

Failure to follow any one of these practices may result in extensive property damage, personal injury, outage of service, or a loss of revenue. And, last but by no means least, it may impair that valuable asset to a public utility—good customer relations.

RESIDENTIAL WIRING GROUNDING SYSTEM BASIC INFORMATION

Responsibility for adequate grounding on the customer’s premises lies with the customer and not with the utility company.

Grounding is one of the most important subjects covered by the National Electrical Code and this code is very clear in regard to the purposes of grounding. It reads:

Circuits are grounded to limit excessive voltages from lightning, line surges, or unintentional contact with higher voltage lines and to limit the voltage to ground during normal operation.

The National Electrical Code requires the grounding of one conductor of electrical systems in which the voltage to ground does not exceed 150 volts. One of the wires in a single-phase, three-wire system, and also in a four-wire wye system is called the neutral conductor and is grounded within the company distribution system.

This same conductor, whenever brought onto the customer’s premises, must again be connected to a ground at a point as close to the entrance to the structure as possible, but at no other point. Since a two-wire system comprises the neutral conductor and one line conductor, the grounding of the neutral in the two-wire system follows the same rules as those applied in the three-wire system.

Grounding at one point only on the customer’s premises guards against the possible hazards due to difference in ground resistance. Also, with only one ground, it is easy to check the presence and adequacy of the grounding circuit.

In residential wiring systems, not only must the neutral conductor be grounded, but exposed metal such as cabinets and conduits which might come in contact with ungrounded current-carrying wires must also be grounded.

Most commonly, the ground connection to the neutral wire is made in the first switch, distribution panel, or meter mounting device installed as a part of the service equipment. The ground connection must be made on the supply side of the customer’s switch.

At this point, the neutral wire is connected to the metal enclosure, meter socket, or switch box and grounding of both neutral wire and “non-current-carrying parts” of the system is effected by one grounding conductor. There is, however, an important distinction. On the supply side of the service-disconnecting device, the grounded conductor may be used for grounding the meter socket or trough and service equipment.

On the load side, this grounded conductor shall not be used to ground equipment or conductor enclosures. Exceptions to this rule are made only for the frames of 120/240 volt electric ranges and electric clothes dryers which may be grounded to the neutral conductor of a three-wire circuit.

In city areas where there is a public water system, the grounding wire is connected to the water pipe near the point it enters the building.

To avoid corrosion, connectors for use on copper pipe should be made of copper; those for use on galvanized pipe should be made of galvanized iron. In areas not served by an extensive public water system or where plastic pipe is used, there can be difficulty getting a dependable ground connection.

A satisfactory ground connection is one which presents a low resistance to the flow of electric current. Such a ground connection usually consists of a rod, at least eight feet in length, driven into the ground adjacent to the building served.

MAGNETIC CONTACTORS - BASIC INFORMATION

WHAT ARE MAGNETIC CONTACTORS?

A contactor is a switch. Instead of a handleoperated, movable blade, a contactor uses contact blocks of silver-coated copper, which are forced together to make (close) or are separated to break (open) a circuit. 

The common wall-mounted light switch is a small, mechanically operated contactor.

A relay is an electrically operated contactor. Most contactors are operated by means of an electromagnet that causes the contacts to close. They open either by spring action or by gravity.

Contactor terminology is somewhat different from that of switches. Its condition when deenergized is its normal state. Thus, a contactor whose contacts are open when the coil is not energized is referred to as normally open (NO), whereas a contactor whose contacts are closed when deenergized is referred to as normally closed (NC). 

Units intended for motor connection are called motor starters. Current, voltage, and number of poles have the same nomenclature for contactors and relays as for switches.

The great advantage of contactors over switches is their facility for remote control. Switches must be manually thrown—or, in very special cases, thrown by a motor. 

The magnetic contactor, by contrast, is inherently a remotely controlled device, making it ideal for myriad control functions. It can be controlled by a manual or remote push button or by automatic devices such as timers, float switches, thermostats, pressure switches, and so on. 

Because control can be both remote and automatic, contactors are universally used in the control of lighting,

heating, air conditioning, motors, and the like.

COST OF USING ELECTRICAL ENERGY BASIC INFORMATION

POWER CONSUMPTION COMPUTATION TUTORIALS

A watt-hour meter is always connected into some part of the service-entrance equipment to record the amount of energy used. Billing by the utility is generally done on a monthly basis.

The meter might be mounted on the side of the house or on a pedestal somewhere on the premise on the lot line. The utility makes this decision.

The residence discussed in this text has one meter, mounted on the back of the house near the sliding doors of the Master Bedroom. The kilowatt (kW) is a convenient unit of electrical power.

One thousand watts (w) is equal to one kilowatt. The watt-hour meter measures and records both wattage and time.

For residential metering, most utilities have rate schedules based on “cents per kilowatt-hour.” Stated another way: How much wattage is being used and for how long?

Burning a 100-watt light bulb for 10 hours is the same as using a 1000-watt electric heater for 1 hour. Both equal 1 kilowatt-hour.

kWh = WATTS X HOURS/1000 = 100X10/1000 = 1 kWh

In these examples, if the electric rate is $0.08 cents per kilowatt-hour, the cost to operate the 100-watt light bulb for 10 hours and the cost to operate the electric heater for 1 hour are the same—$0.08. Both loads use 1 kilowatt-hour of electricity.

EXAMPLE
Find the cost of operating a color television set for 8 hours. The label on the back of the television set indicates 175 watts. The electric rate is $0.10494 per kilowatt-hour.

Cost = 175 x 8 x $0.10494/ 1000
        =  $ 0. 146 9 (approx. 15¢)

SERVICE ENTRANCE CABLE INSTALLATION BASIC INFORMATION AND TUTORIALS

The installation of service-entrance cable is covered in NEC Article 338. Service-entrance cable for above ground use is supplied in one of two varieties. A “U” style consists of two insulated conductors with a bare neutral wrapped around the insulated conductors in a spiral configuration.

At terminations, the spiral neutral conductor is unwound and twisted together to form the third or neutral conductor. A 4-wire variety of Type SE cable is manufactured and is suitable for installation where a separate neutral and equipment grounding conductor are required, such as for wiring ranges, dryers, and some panels.

As shown in figure below, fittings are specifically designed to facilitate installation of service-entrance cable outside the building. These fittings include a weatherhead and raintight and non-raintight cable clamps.

Typical hardware used for installation of service entrance cable for services.

Sill plates are available to protect the cable and weatherproof the installation where the cable is routed inside the building. The cable must be protected against physical damage in accordance with NEC 230.50.

Be sure to check with the local electrical inspector, as some jurisdictions limit the length of serviceentrance
cables inside a building. It is considered more fragile than a metal raceway such as EMT, IMC, or rigid steel conduit and requires protection against physical damage in accordance with NEC 300.4.

Verify Which Overhead Clearances Apply
Electricians must abide by the NEC. Utilities must go along with the National Electrical Safety Code. These codes may have different clearance requirements for service-drop conductors and drip loops.

When involved with installing an overhead service, check with your electrical inspector to determine which code is enforced in your area. The installation requirements of the serving electric utility must always be complied with so long as they do not reduce the requirements of the NEC.

CALCULATING THE MELTING POINT OF A COPPER CONDUCTOR TUTORIALS

The melting point of a copper conductor can be calculated by using these values:

• 1 ampere (RMS current)
• for 5 seconds
• for every 16.19 circular mils of cross-sectional area of the conductor.

NEC 250.122(B) states that if the ungrounded conductors are sized larger for any reason, the equipment grounding conductor shall be increased proportionately, based on the cross-sectional area of the ungrounded conductors for that particular branch circuit or feeder.

The need to increase the size of the ungrounded conductor might be for voltage drop reasons, or because high values of fault current are possible. In NEC 250.2 we find a definition of an effective ground-fault current path:

An intentionally constructed, permanent, lowimpedance electrically conductive path designed and intended to carry current under ground-fault conditions from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protective device or ground fault detectors on highimpedance grounded systems.

* Under fault-current conditions, the possible burning off of an equipment grounding conductor, a bonding jumper, or any conductor that is dependent on safely carrying fault current until the over current protective device can clear the fault results in a hazard to life, safety, and equipmen

SINGLE PHASING OF MOTORS BASIC INFORMATION

A 3-phase motor can be subjected to a situation referred to as “single phasing.” Single phasing means one phase is open—somewhere. See Figure 1 and Figure 2.

FIGURE 1

Example of secondary single phasing. The windings in the motor are wye-connected. When a secondary single phasing occurs, the current in one phase drops to zero amperes and the current in the other two phases increases to approximately 1.73 X 10 5 17.3 amperes. Two sets of phase windings are burned out because the motor did not have proper overload protection. 

FIGURE 2

Example of secondary single phasing. The windings in the motor are delta connected. When a secondary single phasing occurs, the current in one phase conductor drops to zero amperes and the current in the other two phase conductors increases to approximately 1.73 X 10 = 17.3 amperes.

Note that the current in one phase winding in the motor increases to 11.6 amperes and the current in the other two phase windings now in series have a current flow of 5.8 amperes. The phase winding with the 11.6 amperes burns out. Proper motor overload protection would have overload devices in all three phases sized at 125% of the motor’s full-load current rating. 

When an “open” occurs somewhere in the branch circuit supplying the motor while the motor is running, properly sized overload devices will sense the 17.3-ampere current flow and cause the relay to open the circuit, taking the motor off line and protecting the motor from burnout.

Proper motor overload protection would have overload devices in all three phases sized at 125% of the motor’s full-load current rating. When an “open” occurs somewhere in the branch circuit supplying the motor while the motor is running, the overload devices will sense the 17.3-ampere current flow and cause the relay to open the circuit, protecting the motor from burnout.

The current values shown in the figures are for a “pure” single phasing condition with one motor only in the circuit. Nothing can prevent single phasing. Single phasing can be caused by such things as a downed power
line, the utility company’s primary transformer fuse or cutout being open, an open connection, a bad termination, an open splice, a broken conductor, burned open contacts in a motor controller, bad contacts in a switch or circuit breaker, an open winding in the supply transformer, or misalignment.

Figure 3 shows a primary single-phase condition in a wye-delta connected transformation. Similar conditions occur in a delta-wye or delta delta transformation. Prior to 1971, the NEC Table 430-37 permitted 3-phase motors to have overload protection in only two phases. At that time, when a primary and or secondary single phasing occurred, there were numerous motor burnouts.

FIGURE 3

Example of primary single phasing on a wye-delta system. An “open” occurs in the primary while the motor is running. All three conductors are still supplying current to the motor. The motor has overload protection in only two phases as permitted prior to the 1972 NEC. One phase has no overload protection.

The current in two phases increases to approximately 1.15 X 10 = 11.5 amperes. The current on one phase increases to approximately 2.3 X 10 = 23 amperes. The winding subjected to the 23 amperes burns out. Depending on which phase of the primary opened, there is a one-out-of-three chance of motor burnout. Had there been motor overload protection in all three phases, the overload devices would have sensed the increase in current and taken the motor off line.

Why so many motor burnouts? Because the motor winding for the phase subjected to the damaging increase in current just might be the phase that did not have overload protection—a one-outof- three chance of motor burnout! The 1971 NEC began to require overload protection in all three phases, NEC Table 430-37.

The current values in these diagrams are theoretical. In the real world, unexpected things can happen. A 3-phase motor will probably not start if one phase supplying the motor is open. However, if a large, lightly loaded 3-phase motor is running at the time of single phasing, and other smaller motors connected to the system are running, the large motor acts as a generator and will actually feed back into the system on the open phase.

This does not create a true symmetrical 3-phase system (120° phase displacement), but it creates a distorted, asymmetrical 3-phase system. This generated phase might be called a “phantom phase.” Smaller motors not fully loaded on the system might start or continue to run, leading to motor burnout unless the problem is corrected, Figure 4.

FIGURE 4

A 3-phase motor running at the time a single phasing occurs. If lightly loaded, this motor could continue to run. As it rotates, it will generate and feed back into the system a distorted third phase. Other motors on the line will “see” this distorted 3-phase supply and might start or continue to run. Motor failure can be expected—not a good situation. Properly sized motor overload protection is the key to keeping motor burnouts to a minimum.

SERVICE ENTRANCE AND NEUTRAL CONDUCTOR SIZING BASIC INFORMATION

Service-Entrance Conductor Size
A set of service-entrance conductors is installed from the termination box to each service disconnecting means. The minimum size of the service entrance conductors is determined by performing a load calculation in accordance with NEC Article 220.

On reviewing the load calculation form for any of the occupancies, you will find the service disconnecting
means and overcurrent protection is sized not smaller than 125% of the continuous load and 100% of the noncontinuous loads. In addition, the minimum size of the neutral or grounded conductor is determined.

Finally, the minimum size is determined for the raceway that encloses the service-entrance conductors
and feeders.

The following table shows the switch rating, the rating of the fuse in the switch, and the sizes of the ungrounded (hot) and grounded (neutral) as well as the size of the EMT to be installed to enclose the conductors.

Sizing the Neutral Conductors
Several factors come into play when sizing the neutral conductors for the service as well as for the feeders. Requirements include these:

• NEC 215.2(A)(1) requires that the grounded conductor be not smaller than an equipment grounding conductor determined from NEC Table 250.122. We made adjustments in the size of some neutral conductors as shown in the load calculation forms.

• NEC 220.61 provides procedures for calculating the feeder or service neutral load. We used these
requirements in calculating the neutral load for each feeder and service disconnecting means.

• NEC 250.24(C)(1) requires that the grounded conductor, that is, the neutral conductor, in a service
shall not be smaller than the required grounding electrode conductor. Grounding electrode conductor sizes are given in NEC Table 250.66.

• In NEC 250.24(C)(2) the grounded conductor is not permitted to be smaller than 1/0 AWG
when part of a parallel set if the conductors are installed in separate raceways.

This rule applies to the underground service conductors as they are installed in parallel but does not apply to
any of the service disconnecting means as none of these have parallel service conductors.

EXHAUST FAN INSTALLATION CONSIDERATIONS BASIC INFORMATION AND TUTORIALS

To turn the exhaust fan on and off, an ac general use, single-pole snap (toggle) switch is installed on the wall below the fan. The electrician will install an outlet box approximately 1 ft from the ceiling (see the electrical plan), from which he will run a short length of flexible metal conduit to the junction box
on the fan.

The fan exhausts the air from the Bakery. The fan is installed through the wall, approximately 18 in. below the ceiling.

Some occupancies will have a roof-mounted exhaust fan that is ducted to a supply grill on the ceiling of the facility or to hoods located above cooking equipment. NEC 430.111 permits this switch to serve as both
the controller and the required disconnecting means.

Important: As you study the following motor branch circuit information, be sure to clearly understand that 430.6(A)(1) tells us to select motor branch-circuit conductors, disconnecting means, controllers, and the branchcircuit short-circuit and ground-fault protection based on the current values found in Tables 430.247, 430.248, 430.249, and 430.250 rather than on the motor nameplate. NEC 430.6(A)(2) instructs us to use the actual motor nameplate current rating to determine the motor’s overload protection.