View source for 901.16 Construction Inspection Guidelines for Sec 901

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'''Description (for Sec 901.1)'''

'''Definitions.'''  Refer to [[901.15 Glossary|EPG 901.15 Glossary]] for definitions of terms and equipment used in highway lighting work.

'''List Of Equipment And Materials.'''  Each proposal containing highway lighting has a list of equipment and material, which the contractor is required to submit to MoDOT before work commences. On this list the contractor indicates trade names and catalog numbers of the items he proposes to install. Since Project Operations-Materials does not have personnel or test facilities to perform electrical tests on this apparatus the list provides MoDOT the information needed for a check against the specifications. 

Specifications for electrical equipment are actually performance, or end result specifications, rather than detailed material specifications. They were written around performance specifications of many manufacturers of superior quality electrical equipment. Thus, by checking the type of equipment and its catalog number as submitted, MoDOT can usually determine whether or not proposed equipment will meet specifications. As electrical equipment is continually being improved, modified, and sometimes completely redesigned, it is a problem to keep catalog information and specifications up-to-date. The performance specification minimizes this difficulty. 

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When the contractor starts to assemble equipment and materials at the job site, it is the inspector’s responsibility to confirm that the type and model number of items agree with those previously approved.  Permission to substitute equipment and material in lieu of that previously approved shall not be granted without approval from the Project Operations-Construction.  Subsequent changes in the approved equipment and material list do not require documentation by change order. 

'''General.''' The sequence of operations for installing a lighting system varies somewhat from project to project. On some projects lighting is let in conjunction with roadway work, while other projects involve only lighting that is to be installed after certain portions of roadway work are completed. Still other lighting projects are let after all roadway work has been completed. 

The ''Engineering Policy Guidelines'' cannot cover every case that might arise. These instructions are intended to help the inspector cope with most installation problems. They are not necessarily given in the sequence a contractor may use in installation of such facilities. 
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Before the contractor commences any work, it is good practice to check with the supplying electric utility to determine whether location of the substation or control station and plan configuration of equipment thereon is satisfactory with them. This is done by [http://wwwi/design/default.htm Design] while the project is in the design stage, but the utility sometimes has a policy change between time of design and actual construction which will affect the substation or control station. There have also been cases where supply voltage was changed or the supply line was moved to a different location in the interval between design and construction. Time and expense can be saved if the utility is again contacted for approval of contract plans before construction commences.  Any change from the design agreement will require documentation by a letter from the utility company. 

Check for overhead power lines that may not have proper clearance.  Proper clearance is determined by the line to ground voltage of the transmission line.  The power company will inform MoDOT of clearance needed.  Vertical clearance shall be in accordance with [[643.3 Policy, Standards and Regulations#643.3.3 Definitions and General Information|Vertical Clearance for Overhead Crossings]].  

On projects where 45 ft. mounting height poles are specified, clearance from overhead primary lines is especially important since the higher poles will place them nearer high voltage conductors (above 2.3 kilovolts).  When high voltage comes in contact with a steel or aluminum pole most of the current will go directly to ground.  However, there is generally enough over-current to damage the luminaire, the pole and bracket cable and occasionally the control cabinet and its contents.  

In cases where our pole is located near the midspan of a high voltage line, extra lateral clearance is needed due to wind-induced, side sway of the high voltage conductors.  Here again, the power company will be contacted to determine the maximum sideways displacement of the power line under the most extreme conditions that would be a combination of high winds and high temperatures. 

'''Power Supply Asssembly (for Sec 901.8)'''

'''Substation And Control Station Erection.'''  After the substation location has been approved by the supplying utility, the contractor may proceed with arming and erecting the substation pole. Since most substations are designed for step-down of a high voltage system to a 240/480 volt secondary supply, the main portion of this article covers inspection procedures on this type of substation. Erection of a pole mounted, secondary service control station and its inspection, however, will differ only to the extent that less equipment will be involved. 

The inspector will note that a minimum of dimensions is given on the standard drawing. None are given for spacing equipment on cross arms. Location of equipment on cross arms is not critical from the standpoint of actual weight or electrical safety. It is good practice, however, to have the contractor install the control transformer far out on the cross arms. Location of the distribution transformer on the opposite end of arms is to varied according to its weight. This will give a balanced condition for the equipment. If equipment is not balanced, the pole will, in a short time, start to bend toward the greatest load. If a cluster type mounting unit is specified in lieu of cross-mounting for the transformer and oil switch, only the height of cluster need be checked. 

Since arms of the substation pole must be in position to accommodate the incoming primary line, the pole must be turned as shown on the plans. This presents no difficulty except for position of the photoelectric control. The photoelectric control must be placed so that its cell or “eye” is north oriented.  Before the substation pole is erected, the inspector is to discuss this problem with the contractor so the pole will face in the proper direction and still be able to orient the “eye” of the photoelectric control in the general direction of north. 

Some photoelectric controls are so constructed that the “eye” may be rotated with ease.  Other acceptable types are rigidly mounted and must be oriented by proper mounting.  

Before the substation is accepted, the supplying utility should make its hookup and install its metering equipment, if required.  The utility will then either accept the substation as complying with its rules and safety codes, or will suggest minor changes with which MoDOT must comply.  The contractor will be made aware that the utility’s requirements as well as those of MoDOT must be met.  

In several areas in the state, MoDOT is not permitted to place a pole mounted control station.  In these areas, a concrete base must be poured and the control cabinet mounted on top of the base.  It is secured with four anchor bolts placed in the concrete base.  The inspector will note that the neutral conductor is grounded by a ¾ in. x 10 ft. copper clad rod driven into the soil before the concrete base is poured.  If rock is encountered and the ground rod cannot be driven to the proper depth, it is permissible to drive the ground rod in a location where there is no rock and run a No. 6 bare copper conductor from the rod through the base and attach it to the power company’s ground.  If conditions are such that the rod cannot be driven within a reasonable distance of the base, then it is permissible to lay the rod horizontally on top of the rock and backfill.  Driving or drilling a ground rod into solid rock does not provide an adequate grounding condition. 

'''Trenching, Cable Conduit Installation And Backfilling (for Sec 901.10)'''  This operation consists of excavating for the type of trench called for on the plans, placing one or more cable conduits unreeled from a cable trailer and backfilling the excavation in the specified manner. The above operation would seem to be one of few problems, however, Traffic informs us that repairing underground faults, shorts and grounds is one of the major expenses they have when maintaining highway lighting.  Sharp rocks, broken glass and other sharp objects work their way through the plastic duct and the insulation and, in time, cause problems.  In view of this potential problem, the inspectors are to inspect the excavation and the backfilling operation carefully.  Even when the backfilling operation requires sand, it is always possible that objectionable material can be incorporated with the sand due to carelessness or inattention. Cable conduit is to be bent or kinked during installation to the point where the conductors cannot be easily pulled from the duct. 

'''For Sec 901.10.2.'''  On projects where Type I (24 in.) trenching is specified, the contractor is permitted to install cable conduit by plowing rather than by trenching method.  This operation is usually performed by a crawler type vehicle or a large tractor that is specially equipped with a modified plow shear and a large cable payout reel.  A narrow trench of the specified depth is cut, the cable conduit fed directly to the bottom of the trench and the displaced earth falls back into its original position.  The ideal use of plowing is on long runs where little maneuvering of the plow is required.  Under ideal conditions there is very little work to be done in restoring the earth to its original condition. 

'''Pullboxes (for Sec 901.11)'''  Excavating, forming, and pouring of pullboxes are to be inspected in accord with instructions concerning similar structures contained in Division 600 of the ''Missouri Standard Specifications for Highway Construction''.  The inspector should remind the contractor that the standard shows minimum dimensions.  The contractor may make the pullbox as large and as deep as the working area will permit. Remind the contractor that any extra work or materials involved in such enlargement will be at the contractor's expense. 

'''Pole, Bracket Arm, And Luminaire Installation (for Sec 901.12)'''  Current design provides for 30 ft. and 45 ft. mounting height luminaries.  Provisions are made for mounting each type of pole on either a concrete foundation, a steel pile foundation or a screw anchor foundation. The contractor generally has the option of selecting the type of foundation. 

'''For Sec 901.12.1.''' The concrete base is excavated, formed, and poured in accordance with the plans. Inspection of this operation is similar to procedures set out in Division 700 of the ''Missouri Standard Specifications for Highway Construction'' for inspection of structures. In addition to these instructions, the inspector is to make certain that the incoming conduit is capped to prevent concrete from entering and that the anchor bolts are firmly held in place to accept the bolt circle of the pole base or transformer base. Also, orientation of the anchor bolts is important so that the pole base or transformer base is not skewed in relation to the centerline of roadway. 

'''For Sec 901.12.2.'''  Inspection procedures for installation of I-Beam and circular pile foundations are the same. Some contractors elect to assemble the pole, bracket arm, transformer base, pole and bracket cable, and foundation as a complete unit before erection; other contractors set the pole foundation first and bolt the pole base or transformer base on at a later time.  If the contractor assembles the complete unit on the ground prior to erection, the inspector shall make sure the unit is rigidly held in the proper position during backfilling and tamping.  If the contractor uses quick-setting polyurethane foam, the inspector must check to see that the foam has properly set up before the contractor releases the pole boom clamps.  In the event that the contractor sets the pole foundations before bolting on the pole or transformer base, the inspector should be sure that proper grade and vertical alignment are held during the backfilling process. Out-of-plumb foundations necessitate the use of several shims to attain proper pole position. 

'''For Sec 901.12.3.'''  If screw anchor foundations are used, they must be installed prior to bolting on the pole base or transformer base because a special fitting is required to attach the screw anchor plate to the power take-off of a specially equipped vehicle. The installation of the screw anchor foundation, done by an experienced work crew, is a high-speed operation. Inspection of this operation is essentially the same as for any foundation; proper vertical alignment and grade as well as the proper position of the cable-duct entrance are the essential items. 

'''For Sec 901.12.4.''' All bolt-down poles can be easily adjusted by use of shims for plumb when viewed from the centerline of the roadway. The top of the pole is to be raked (leaned) away from the luminaire a minimum of 3 in. A plumb bob is considered a satisfactory instrument for checking pole erection.  The adjustment of a butt base pole must be accomplished at the start of backfilling operations. 

Occasionally, because of a conflict with a roadway item, it is sometimes necessary to shift a pole from plan location. A shift of 5 to 10 ft. along the shoulder line will not materially affect the design of the lighting pattern.  If it becomes necessary to shift a pole over 10 ft., district Design is to be consulted.  It may be necessary to re-space several poles to maintain design uniformity and intensity. 

If it becomes necessary to shift a pole farther from the edge of the pavement than the plan location, the shift shall be made in increments equal to the change in bracket arm lengths.  Standard bracket arms are fabricated in 4, 6, 8, 10, 12 and 15 ft. lengths.  It is desirable that the luminaire’s plan position be maintained as nearly as possible in relation to pavement edge. 

It may be appropriate to allow for extra time to the contract for fabrication and placement of poles if the site conditions have changed such to require changes to the pole design or dimensions. 

'''For Sec 901.12.5.'''  The butt base lighting pole (pole and pole foundation are an integral unit) is set in the same manner as a Type AT pole.  Again, the inspector should be assured that the pole is held in proper position during the backfilling process. 

While the contractor is assembling the pole, in the case of the 2-piece 45 ft. mounting height pole, attaching the bracket arm and luminaire, the inspector should check the entire operation. The luminaire should be inspected for shipment damage and that it has the proper voltage rating.  A very often overlooked but an important item is the bushing that is inserted into the wire entrance of the pole prior to bolting on the mast arm.  This bushing prevents wire abrasion, bracket arm movement from wind loads and normal vibration.  Pole and bracket cable should be securely fastened to ballast terminals in accordance with the wiring diagram furnished with each luminaire.  For the 30 ft. mounting height, luminaire positioning is done after the pole has been erected. The pole and bracket cable is terminated in the base of each pole to a fused, slip connector assembly.  The underground cable-conduit is terminated to the line side of the fused, slip connector assembly.  The inspector should make certain that all connections are tight and that the bare neutral conductor is secured to the grounding lug of each pole. 

'''Circuit Testing (for Sec 901.14).'''  After a multiple lighting project has been completed, resistance tests shall be made on each circuit and the secondary voltage shall be checked at the control panel.  It is worthwhile to perform tests immediately so as to establish responsibility for later damage.  Immediately before acceptance the final test will be required.  

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|'''DANGER!''' The inspector is to use extreme caution in making these tests to avoid serious electrical shocks.  A lethal voltage of 480 volts, line-to-line, and 240 volts, line-to-ground, exists in the control panel during voltage tests. 
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The resistance measuring instrument the contractor may use for making conductor cable insulation tests is a simple DC generator.  This utilizes a hand operated crank to generate 500 volts.  The contractor may choose to use a motor driven generator.  The generator induces a potential of 500 volts between conductor and ground.  Any weakness, nicks or cuts in insulation or any leaks in splices will create a current path through the insulation to ground.  The generator scale is graduated in ohms to give a direct reading in resistance units.  Other permitted resistance measuring devices may be battery powered. 

'''Resistance Measuring Device (for Sec 901.14.1) '''  Before making insulation tests, the resistance measuring device, commonly called a “megger”, should be given 3 simple tests to ensure reliable readings.  These tests are performed as follows: 

:1. With no test leads connected to megger terminal, crank the instrument at a rate of at least 3 revolutions per second or until slip clutch starts to function. Since there is no current path across the terminals, indicator needle should read infinity. 

:2. Connect test leads to megger, submerge line lead in water and connect ground lead to any convenient grounding point. Make certain that line test lead is not submerged in water or touching the ground. Megger crank is again turned at a fairly uniform rate of 3 or more revolutions per second for several seconds. Indicator needle should again read infinity. 

:3. Connect test leads to megger and short the tips of test leads together. Turn the megger crank slowly. Needle should read zero. 

:4. Failure of megger and its test leads to pass any of above tests indicates (1) an internal current leak in megger if it fails the first test, (2) defective leads if it fails the second test, or (3) a defective megger, or an open circuit test lead, if it fails the third test. The megger should be operated on as solid a platform as is available. Take care that megger terminals are kept dry. Normally, unless the megger’s operation seems inconsistent, the above tests are made only once. 

If the megger appears to be in proper operating condition, resistance tests of conductor cable should be performed at the control panel. Magnetic trips of all breakers should be turned to “OFF” position and the manual switch should be turned to “OFF” position. This procedure de-energizes all circuits in the control cabinet. This is extremely important as a safety precaution. 

The ground lead of megger is to be connected to the ground wire or ground terminal strip in the control cabinet. The megger lead should be connected to either of the 2 cables at the bottom, or load, side of breaker. The megger should be cranked as steadily as possible at 3 RPS for at least one minute. During this time, if indicator needle stays constantly above minimum resistance requirements listed in contract, the circuit is acceptable. If needle drops below minimum requirements at any time during test, the contractor is to be required to take whatever action is necessary to upgrade the circuit to meet minimum requirements.  Such action may consist of burning lamps of the system for several hours to dry out any moisture that may have collected on ballast terminals.  The contractor may have to rewrap one or more handhole cable splices.  Defective or damaged cable causes low resistance readings.  There are many factors combinations of factors that cause low resistance readings.  It is the contractor’s responsibility to determine the cause of trouble and to correct it.  The inspector is to carefully observe the contractor’s methods of troubleshooting circuit defects to gain helpful experience for future work. 

Open circuit voltage and full load voltage should be measured with an AC volt meter of suitable range, 0 to 600 volts.  The secondary no-load voltage is checked from line-to-line and from line-to-ground at the top of each magnetic circuit breaker located in control cabinet.  For this test the magnetic circuit breakers should be tripped to “OFF” position and the manual switch turned to “ON” position.  Full load voltage is checked at the bottom of each magnetic circuit breaker.  For this test the magnetic circuit breakers are tripped to “ON” position and the manual switch is also turned to “ON” position.  The readings obtained should be within 5% of no-load voltage for which system was designed.  Failure of secondary voltage to be within the above limits will require adjustment of connections to secondary taps of the distribution transformer. 

'''Cable Splicing (for Sec 901.15)''' During new cable installation, splicing is permitted only in junction boxes and handholes.  Splicing of conductors is to be done with a mechanical device that will hold the conductors tightly together to provide a current path not less than the original conductor cross-sectional area.  These mechanical devices are listed in the specifications.  Provisions are included for use of any new type of conductor splice that may prove to be better than those specified. 

After the conductor splice has been made, it is covered with insulating material. The step-by-step procedure is outlined in the contract.  Cable splicing should not be done in extremely damp or rainy weather as moisture will reduce the quality of the completed splice. In a pole base splice, where incoming line cables are spliced to pole and bracket cable by a fuse-disconnect device, the completed splice is to be placed in the pole center with the splice pointing upward. This will form a drip loop and keep any moisture that may run down the pole and bracket cable from entering the splice. 

'''Conduit Systems.''' When cable is pulled through any conduit, the inspector checks the cable for abrasion and slashes as it emerges from conduit.  Normally interior surfaces of a conduit are smooth but damaged ends can result in a rough or jagged surface that will slash the cable jacket as it is pulled.  Specifications require that bushings be placed on conduit ends when cables are pulled into place.  This will usually prevent any burrs or rough edges on conduit ends from damaging the cable.  However, this will be carefully checked.  Sometimes a rough edge has not been completely covered by the bushing, or a bushing may become loosened or displaced during the cable pulling operation.  

Drains are required at low points of conduit systems located within a structure.  Refer to  [http://www.modot.org/business/standards_and_specs/SpecbookEPG.pdf#page=11 Sec 707.3.1].  Installation of drains or drain holes in junction boxes or conduits are to be given careful attention by the inspector.  Failure to install or provide drains in conduit junction boxes and conduits can result in damaged cable and cracked structures due to water collecting in the conduits and freezing.  

After the contractor has completed cable splicing, continuity checks, and resistance tests on circuits located in structures, the inspector confirms that all pull box covers are firmly fastened in place and sealed.  Sealing is particularly important when the pull box is located in the sidewalk.  Proper sealing eliminates the opportunity for surface water and deicing salts to enter the conduit system.  A conduit system will always be subject to condensation; however, every attempt should be made to eliminate any possibility of surface moisture entering the system. 

'''Pushed Conduit.'''  This item usually presents difficulty unless the contractor is well prepared for the work.  Specifications allow the contractor to use several methods.  The inspector will determine that the conduit is reasonably close to plan grade and location where it emerges on the opposite side of the road.  Experience shows it would be unreasonable to expect the contractor to push a conduit some 30 to 40 ft. and maintain exact grade and stationing.  In soil that contains no rock, a blunt tip on the conduit end will usually yield best results.  In rocky soil the contractor must normally use a drill to arrive at the other side of the roadway within a foot or two of plan location.  After conduit has been pushed into place, galvanizing on the outside of the conduit will have suffered considerably.  Under severe conditions there may be little galvanizing remaining.  There is no practical means of repair so this undesirable condition must be accepted. 

'''For Sec. 901.18.11.'''  If modifications of circuit wiring become necessary, the following design data is to be used for cable or cable-conduit quantity computations: 

:On Regulator Pole - 20 ft. per circuit. 

:Regulator pole to lighting pole, lighting pole to lighting pole or pullbox – center-to-center distance +5%. 

:In lighting pole - 5 ft. for each connection. 

:In concrete pullbox - 3 ft. per run. 

When lighting is included in a contract containing other items of roadway and bridge work, special attention is to be given to conflicts that may arise between cable conduit trench and other roadway items. If careful attention is not given this matter, later operations by other workmen are apt to damage the cable. Ideally, the time to install a lighting project is after all other roadway work has been completed. Then any cable damage that occurs is due to operations of the electrical contractor. This is not always practicable since cable conduit is sometimes located beneath treated or paved shoulders and must be installed before placing shoulder base material. In these cases it is necessary to excavate the cable trench to plan depth and lay the cable conduits. Take care to protect them at future pole locations by having boards or plywood placed over cables before backfilling the trench. 

'''Sample Calculations (for Sec 901.18.11.1)''' Re-routing of buried cable circuits is usually a relatively simple procedure insofar as actual construction is concerned. However, if the circuit or circuits are lengthened, it becomes necessary to calculate voltage drop between adjacent luminaires and voltage drop of the entire circuit involved. 

To calculate voltage drop of a circuit, line current and line resistance must be known. Then, by using Ohm’s Law, E = IR; where E = impressed secondary voltage, I = line current, and R = resistance of conductor cable, the voltage drop of any particular circuit may be calculated.   

For a sample problem that frequently occurs on a lighting project, assume the following data and circuit diagram. The circuit shown below is a typical multiple or parallel arrangement of LED-C luminaires using line-to-line voltage of 480.

[[image:901.16 Schematic Wiring Diagram.jpg|center|700 px|thumb|<center>'''Fig. 901.16 Schematic Wiring Diagram'''</center>]]

Luminaire current draw varies from manufacturer to manufacturer. For the sample calculation, one ampere shall be used.  The conductor cable from pole to pole is No. 8 gauge.   Resistance of pole and bracket cable will be ignored as the resistance in these short runs can be considered negligible.  Resistance of No. 8 gauge cable is 0.66 ohms per 1000 ft.  With this information proceed with the sample calculation: 

====<center>''Table 901.16.1''</center>====
{| border="1" class="wikitable" style="margin: 1em auto 1em auto"
|+ '''''Property of Conductors'''''
! style="background:#BEBEBE"|AWG Wire Size !!style="background:#BEBEBE"|Resistance Ohms per 1000 ft.
|-
|align="center"|14||align="center"|2.68
|-
|align="center"|12||align="center"|1.69
|-
|align="center"|10||align="center"|1.06
|-
|align="center"|8||align="center"|0.66
|-
|align="center"|6||align="center"|0.426
|-
|align="center"|4||align="center"|0.269
|-
|align="center"|2||align="center"|0.169
|-
|align="center"|1||align="center"|0.134
|-
|align="center"|0||align="center"|0.106
|-
|align="center"|00||align="center"|	0.084
|}			


Table 901.16.1 shows various conductor cable resistances and the current draw by luminaires varies from manufacturer to manufacturer.  

Using Ohm’s Law: E = IR, 

:Voltage drop to the 1st luminaire will be; 8 A. x 2 x 1200 ft. x 0.66/1000 = 12.672 

:Voltage drop to the 2nd luminaire will be; 7 A. x 2 x 200 ft. x 0.66/1000 = 1.848 

:Voltage drop to the 3rd luminaire will be; 6 A. x 2 x 200 ft. x 0.66/1000 = 1.584 

:Voltage drop to the 4th luminaire will be; 5 A. x 2 x 200 ft. x 0.66/1000 = 1.320 

:Voltage drop to the 5th luminaire will be; 4 A. x 2 x 500 ft. x 0.66/1000 = 2.640 

:Voltage drop to the 6th luminaire will be; 3 A. x 2 x 200 ft. x 0.66/1000 = 0.792 

:Voltage drop to the 7th luminaire will be; 2 A. x 2 x 200 ft. x 0.66/1000 = 0.528 

:Voltage drop to the 8th luminaire will be; 1 A. x 2 x 200 ft. x 0.66/1000 = 0.264 

::Total Voltage Drop = 21.648 

::Percentage Voltage Drop = 21.648/480 x 100 = 4.51% 

The above example demonstrates that the permissible voltage drop of 5% has not been exceeded. Assume that because of conflict with other roadway items the cable run between luminaires No. 4 and No. 5 must be increased by 1000 ft. To determine if the design voltage drop of 5% is exceeded, the voltage drop for the entire circuit must be recomputed. 

Sample computations are:

:Voltage drop to the 1st luminaire will be; 8 A. x 2 x 1200 ft. x 0.66/1000 = 12.672 

:Voltage drop to the 2nd luminaire will be; 7 A. x 2 x 200 ft. x 0.66/1000 = 1.848 

:Voltage drop to the 3rd luminaire will be; 6 A. x 2 x 200 ft. x 0.66/1000 = 1.584 

:Voltage drop to the 4th luminaire will be; 5 A. x 2 x 200 ft. x 0.66/1000 = 1.320 

:Voltage drop to the 5th luminaire will be; 4 A. x 2 x 1500 ft. x 0.66/1000 = 7.920 

:Voltage drop to the 6th luminaire will be; 3 A. x 2 x 200 ft. x 0.66/1000 = 0.792 

:Voltage drop to the 7th luminaire will be; 2 A. x 2 x 200 ft. x 0.66/1000 = 0.528 

:Voltage drop to the 8th luminaire will be; 1 A. x 2 x 200 ft. x 0.66/1000 = 0.264 

::Total Voltage Drop = 26.928 

::Percentage Voltage Drop = 26.928/480 x 100 = 5.61% 

Voltage drop now exceeds the 5% allowable. To bring the relocated circuit’s voltage loss down to an acceptable value, the conductor gauge must be increased for some distance to correct this low voltage condition. Since the load from the control cabinet to the first luminaire is 8 amperes and shows the largest voltage drop, it seems logical to increase conductor cable size along this particular run. It should be stressed here that any increase in cable size necessary to lessen voltage drop shall always begin at the substation and continue as far as necessary even if the run from control cabinet to the first luminaire does not originally have the largest voltage drop on the circuit. The cable shall be placed, without splicing, from pole base to pole base. 

From the conductor resistance table choose the next larger conductor, which would be No. 6 gauge, with a resistance of 0.426 ohms per 1000 ft.  The calculations using two No. 6 gauge conductors from the substation to luminaire No. 1 are shown below:

:Voltage drop to the 1st luminaire will be; 8 A. x 2 x 1200 ft. x 0.426/1000 = 8.179 

:Voltage drop to the 2nd luminaire will be; 7 A. x 2 x 200 ft. x 0.66/1000 = 1.848 

:Voltage drop to the 3rd luminaire will be; 6 A. x 2 x 200 ft. x 0.66/1000 = 1.584 

:Voltage drop to the 4th luminaire will be; 5 A. x 2 x 200 ft. x 0.66/1000 = 1.320 

:Voltage drop to the 5th luminaire will be; 4 A. x 2 x 1500 ft. x 0.66/1000 = 7.920 

:Voltage drop to the 6th luminaire will be; 3 A. x 2 x 200 ft. x 0.66/1000 = 0.792 

:Voltage drop to the 7th luminaire will be; 2 A. x 2 x 200 ft. x 0.66/1000 = 0.528 

:Voltage drop to the 8th luminaire will be; 1 A. x 2 x 200 ft. x 0.66/1000 = 0.264 

::Total Voltage Drop = 22.435 

::Percentage Voltage Drop = 22.435/480 x 100 = 4.67% 

Since the redesigned circuit’s voltage drop is now below the 5% tolerance the necessary change order may be prepared for approval and subsequent authorization to the contractor. 

Capacitive or inductive reactance was not considered in the computations, and a power factor of 1.0 was assumed.  This is due to the fact that with the power factor correction specified in ballast characteristics, the lighting load can be considered resistive for all redesign purposes.


[[Category:901 Lighting]]