MIL-HDBK-1004/10

EQUATION:

V

=

MK

(19)

m

where

0.0876 I2R

M

=

K

=

LP/E

m

and

V

=

annual cost of power losses ($)

I

=

current flow (A)

R

=

resistance of 100 feet of cable

P

=

power cost (cents/kWh)

E

=

power source (rectifier) efficiency (%)

L

=

length of cable (feet)

Values for M for commonly used wire sizes and various currents from 10 to 100

A are given in Table 11.

The formula for determining the annual cost of fixed charges is:

EQUATION:

F=ESL

(20)

where

F

=

annual fixed charges ($/yr)

E

=

estimated annual charges (see a) below)

S

=

initial cable cost ($/ft)

L

=

cable length (ft)

a) The estimated annual charges used will vary. They are the sum

of depreciation, interest, taxes, insurance, operation, and maintenance. As

shown below, a value of 0.11 is typical for government installations where

taxes and insurance are not considered:

Depreciation

=

0.02

Interest

=

0.06

Taxes

=

0

Insurance

=

0

Operation &

Maintenance

=

0.03

Total (E)

=

0.11

Wire Splices and Connections. Wire splices and connections are a

6.7.2

source of undesirable circuit resistance and are a weak point in the

reliability of the system since they often fail due to corrosion or mechanical

damage. The number of connections should be kept to an absolute minimum and

the type of connection used should have low resistance, high reliability, and

good resistance to corrosion. As described in para. 10.6, both mechanical

94

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