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DMX 101: A DMX 512 Handbook
16 Elation Professional ®
4.2 Cabling
Standard DMX 512 requires twisted-pair, shielded, low-capacitance data cable (Figure 7) designed for RS-485
(such as ACCU-Cable from Elation). The twisted-pair configuration ensures that any interference affects both
signals equally. This practice is common to good data cable, helping the signal driver eliminate any interference.
The cable shield also protects against interference. A shield ‘drain’ wire makes connector installation easier.
Figure 7
There are many cabling characteristics to consider when designing a system. The following list contains a few
such characteristics for consideration:
•
Impedance (110-120 Ohm recommended)
•
Capacitance (< 25 pF cond.-to-cond., < 40 pF cond.-to-shield recommended)
•
Attenuation
•
Number of conductors/pairs (minimum 1 pair)
•
Number of twists per foot
•
Conductor material/diameter
•
Wire gauge (AWG)
•
Maximum current and temperature
•
Inner and outer jacket material
•
Minimum bend radius
•
Maximum pull tension
NOTE: Many people often substitute cheaper balanced audio cable (regular microphone cable) with tragic
results. Audio cable cannot support the signal rate required by the high speed DMX protocol. While
the signal may pass over short distances, it is highly susceptible to interference and degradation,
causing unpredictable results (such as blinking lights, confused intelligent fixtures, etc.).
OUTER
JACKET
SHIELD
PAIR 1
PAIR 2
DRAIN
INNER
JACKET
4