Parts of a DMX cable

[browna]

Hi,

 

I have wired a 5pin DMX cable. I understand what all the wires are for. What are the sheets of foil, and cotton strands for, in the cable? Do do need to have 5 pins fully wired a 5-pin connector, because I have 2 spare, is this correct? If not, what do I need to do?

 

Thanks!

[Frag_Me]

Don't worry about the 2 pins with nothing on, in most applications you can just leave them alone.

 

The foil is a shield for the cable to protect it from EM problems (to put it very simply, and AFAIK). Cotton I believe is just a filler which also helps to maintain the shape of the cable. I could be wrong though!

[Tomo]

Anatomy of a DMX cable:

 

Outer Jacket - Protects the goodness inside.

Cotton - Helps you split the jacket when terminating the cable - make a nick in the jacket and then pull the cotton into the split.

Foil - Shield. This should be connected to Pin 1 via one or more drain wires. The shield protects the cores from RF interference, improving the signal quality.

Inner Insulation - Prevents data cables from shorting against the foil or each other.

Inner Cores - The actual coppery goodness that conducts the electrical signal.

 

Foil is only found in installation cable, as it's not very flexible.

For flexible cable, the shield is usually a braided or wrapped set of thin copper filaments - braid is better, but a pain to terminate!

 

DMX cable should contain one or two shields, plus two pairs of cores twisted together.

Depending on the installation, the second pair may be tied back and ignored, for use as a spare in the event of failure (or as a 'return' path if somebody doesn't pull enough cable), or may be wired to pins 4 and 5 of the XLR-5 connector.