EST EST3X - 25 or 70 VRMS NAC wire length; Address formats; Card address

Appendix A: System calculations
248 EST3X Technical Reference Manual
25 or 70 VRMS NAC wire length
The maximum allowable wire length is the farthest distance that a pair of wires
can extend from the amplifier to the last speaker on the notification appliance
circuit without losing more than 0.5 dB of signal. Calculating the maximum
allowable wire length using this method ensures that each speaker operates at
its full potential.
Several factors influence the maximum allowable wire length:
• Wire size
• Output signal level of the amplifier driving the circuit
• Number of speakers installed on the circuit
To calculate the maximum allowable wire length for a 0.5 dB loss, use the
following formula:
Maximum length = (59.25 × Amplifier output²) / (Wire resistance × circuit load)
Where,
• Amplifier output is the signal level in VRMS supplied by the amplifier driving
the circuit
• Circuit load is the total watts required by the audio circuit
• Wire resistance is the resistance rating of the wire per 1000 ft pair, see
Table 78.
For example, the maximum allowable wire length for an audio circuit consisting of
a 30 W, 25 VRMS amplifier driving thirty 1 watt speakers, using 18-gauge wire
would be 95 ft.
94.95 = (59.25 × 25²) / (13 × 30)
Table 78: Wire resistance ratings
Wire Size
Resistance per 1,000 ft pair (ohms)
18 AWG (0.75 mm
²) 13.0
16 AWG (1.0 mm
²) 8.0
14 AWG (1.50 mm
²) 5.2
12 AWG (2.5 mm
²) 3.2
Table 79 and Table 80 on page 249 give the maximum allowable wire lengths for
various wire sizes and loads. Use Table 79 when designing circuits for amplifiers
set for 25 VRMS output. Use Table 80 when designing circuits for amplifiers set
for a 70 VRMS output.