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ETL 1110-9-10(FR)
5 Jan 91
RMFT =
0.254 ohm (Resistance per 1000
lin ft of No. 4 AWG HMWPE
insulated cable [table A-6])
RNEG =
25 x 0.254
1000
RNEG =
0.006 ohm
Total wire resistance therefore is:
RW
=
RT/B
+
RPOS
+
RNEG
=
0.009
+
0.005
+
0.006
RW
=
0.020 ohm
c)
The piping is essentially bare, so structure-to-
d)
Calculate total circuit resistance
(RC)
from
equation 1-3:
RT
= RA + RW + RC (Because the cathodic
protection system uses a single deep
anode groundbed RA = RN)
RT
= 0.65 + 0.020 + 0.0
RT
= 0.670 ohm
7)
Calculate rectifier voltage (VREC) from equation 1-17:
VREC
= (I) (RT) (120%)
Where:
I
=
40 amp (Current requirement from step
2, paragraph 2-5b)
RT
=
0.670 ohm (Total circuit
resistance
from previous calculation)
120%
=
Rectifier
voltage
capacity
design
safety factor
66
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