4
SAN Annunciator Manual
A power consumption/wire sizing calculation must be performed to
determine the wire size for a given load and wire length. Refer to the
worksheet section, the SAN-CPU Current Worksheet, to determine
SAN-CPU loading.
R max
+
2.4 V
20.4 V
SAN-CPU Circuit
The value of R
MAX
is determined using Ohm’s Law for current values
from 0.25 to 3.5 amps:
2.4
R
MAX
= ------------
I
MAX
Where:
R
MAX
= Maximum allowable wire resistance
I
MAX
= Wire resistance per 1000’ pair.
2.4 = Maximum allowable voltage drop.
Using wire resistance Table 1, the maximum SAN-CPU distance from
the power supply using any listed wire gauge may be determined as
follows below. Table 2 was derived using this method.
R
MAX
D = ------------ X 1000
R
/1000”PAIR
Where:
D= Distance in feet.
R
MAX
= Maximum allowable wire resistance.
R
/1000’ PAIR
= Wire resistance per 1000’ pair.
Wire Resistance
Wire Size
Resistance Per 1000’ Pair R
/1000’ PAIR
#18
13.0
Ω
#16
8.0
Ω
#14
5.2
Ω
#12
3.2
Ω
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