Maximum cable distance in feet – GAI-Tronics 7335-002 Multi-Party 24 V DC Amplifier Enclosures User Manual

Page 3

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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

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