5. Since the distance from the generators to the laundry is only 50 feet, the

voltage drop in this distance will be negligible, and the load-carrying capacity of

the wires becomes the deciding factor. Referring to table 1, for a 34W 127/220V

system, a No. 4 wire will carry 57- KVA which is well in excess of the required 41.

A No. 6 wire, however, can carry only 38 KVA which is below the required capacity.

Hence, a No. 4 wire is required.

7. In military practice the percent voltage drop is taken as a percentage of the

voltage at the generator, or

.

If

we

let

X

=

the voltage at the generator, then X -208 is the voltage drop, and the above

relationship yields the following:

8. Refer to figure 8, attached memorandum. Enter 250 feet at the bottom right

horizontal scale; proceed vertically to the No. 8 curve; proceed horizontally from

this point to the vertical line representing a load of 6 KVA (on the bottom left

horizontal scale). At this point the voltage drop is read as 3.2 percent using the

lower voltage drop figures.

11. From table 5, attached memorandum, the sag for 150 foot spans at 60F is 26

inches or 2'2".

From figure 10, attached memorandum, the required clearance for

primary feeder lines is 20 feet if they must cross public streets and driveways to

resident garages. The wires must therefore be attached 20' + 2'2" or 22'2" above

the ground.

12. From figure 10, attached memorandum, the required clearance for primary

feeder lines is 28 feet over railroad tracks.

This, plus the 2'2" sag found in

problem 11, gives a required mounting height of 28' + 22" or 30'2" for the wires.

13. Using figure 12, attached memorandum, enter 450 feet on the right vertical

scale, and proceed horizontally to the curve for 4/0 (0000) wire size.

At this

point proceed vertically downward to the bottom horizontal scale and read the

minimum allowable sag to be 8 feet.

14. Your assistant has allowed an excessive voltage drop for this particular

section of feeder,

.

This leaves only 6.0 - 5.5 = 0.5% allowable drop

for sections

AC, IL, and LN.

In effect, he has used up most of his allowable

voltage drop

on section CI and thus left very little for the subsequent sections of

the feeder.

Remember the 6 percent is the total drop allowed from the generator to

the farthest

load.

15. Demand load on section AC is computed as follows:

Group

I

6.50 KVA

II

2.00 KVA

III

2.50 KVA

IV

4.00 KVA

V

2.00 KVA

Building 5

3.00 KVA

Total demand

20.00 KVA

Integrated Publishing, Inc.
6230 Stone Rd, Unit Q
Port Richey, FL 34668
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