GAI-Tronics 7335-002 Multi-Party 24 V DC Amplifier Enclosures - Manual (Page 3)

Pub. 42004-141G
Model 703-002, 7325-102, and 7335-002 Multi-Party 24 V DC Amplifier Enclosures Page 3 of 12
f:\standard ioms - current release\42004 instr. manuals\42004-141g.doc
08/13
Maximum Cable Distance in Feet*
Number of
Units
No. 14 AWG
Total / Between
No. 12 AWG
Total / Between
No. 10 AWG
Total / Between
No. 8 AWG
Total / Between
1 977 / 977 1,554 / 1,554 2,471 / 2,471 3,931 / 3,931
2 651 / 325 1,037 / 518 1,648 / 824 2,620 / 1,310
3 489 / 163 777 / 259 1,236 / 412 1,966 / 655
4 391 / 98 622 / 155 988 / 247 1,572 / 393
5 325 / 65 518 / 103 823 / 165 1,310 / 262
6 279 / 46 444 / 74 706 / 117 1,123 / 187
9 196 / 21 311 /34 494 / 55 786 / 87
*Based on the following assumptions:
 Continuous tone (alarm) signals driving each station’s speaker amp to a maximum of 12 watts.
N OTE : If the station is used for speech (audio) signals only, the distances stated above can be
multiplied by a factor of 2 because speech signals do not have the energy content that a
continuous tone has; therefore, they do not require as much average current and thus less cable IR
drop will result.
 GAI-Tronics-supplied cable is used.
 Wire resistance (ohms) is the nominal value for the applicable AWG at 1,000 feet of bare copper,
stranded wire @ 20º C (68º F). Wire resistance values used are as follows:
No. 14 AWG = ~2.525 ohms; No. 12 AWG = ~1.588 ohms; No. 10 AWG = ~0.999 ohm; No. 8 AWG = ~0.628 ohm
 DC V at cable run’s feed point (Float charge of connected batteries) = ~26.6 V dc
 DC V at the last unit in cable run = 21 V dc minimum
 Station unit current draw (I) is the same regardless of the unit’s placement along the cable run for
ease of calculation. (1.1 amperes when unit is producing a 12-watt sine wave output.)
 Distances reflect a 3% reduction for margin of error.
For conditions other than above, the following formula may be helpful in calculating the approximate
maximum distance for a SINGLE station.
For CONTINUOUS tone applications with minimum distortion:
For SPEECH operation only, multiply the above result by a factor of 2.
Example: What is the approximate maximum distance for a single dc station if the voltage feed is 27.5
V dc and a No. 14 AWG wire is used @ 20º C?
Info:
 No. 14 AWG @ 20º C = ~0.002525 ohm per foot  2 for LOOP R
 V
FEEDPOINT
= 27.5 V dc
Solution:
(27.5 V – 21 V) / ((2
 0.002525 ohm per foot)  1.1 amps)
= 6.5 / 0.005555
= 1,170 feet (for CONTINUOUS TONE signal), or up to ~2,340 feet (factor of 2) for SPEECH signals