twisted conductors for noise reduction?

Status
Not open for further replies.
Off the top of my head, I can't think of any code requirement that prevents you from doing so... but typically, twisted conductors are for reduction of signal loss at high frequencies or data rates, and usually installed as a cable rather than individual conductors. Shielded cable is used to help prevent rfi from being impressed upon the conductors and/or radiated into the atmosphere.
 
Qes,
Twisting cancels magnetic fields in multi-conductor wiring but may not reduce line noise coupling from external sources without overall cable shielding. There are a lot of variables in circuit characteristics that enter into signal noise susceptability that twisting will not compensate. If you are seeking comments to a specific case, describing the electrical function and physical condition might help for a resolution.
 
The reason wire pairs are twisted in data and audio use (aka 'balanced' lines) are to assure that any interference picked up by the pair is of equal value in both conductors. This way, the input they feed can cancel the interference by a method called "common-mode noise rejection."

Any signal common to both conductors is ignored, and only the difference signal is amplified and used. The greater the number of twists per foot, the higher the frequency (i.e., the shorter the wavelength) of the noise that can be rejected this way.

With power wiring, the only real advantage of twisting might be to reduce the emmission of electromagnetic waves leaving the conductors, as suggested by Gndrd.
 
Its called Transposed, or Tri-plexed...

In large feeders you can actually order them this way.

With large amounts of current, say starting large motors, the cable will flex due to the elevated magnetic field. I have actually seen that! Is also is supposed to reduce the impedance values in short circuit conditions. Not so sure about that.... But makes sense.

You get them pre-twisted by stripping or just running some MC.... Within code, yeah.... It's done all the time in cables, and have once had it required as a spec'. If you do it yourself, make sure it is clock-wise. (Like all pre-made cables.) Clock-wise on a clock-wise system draws the conductors together, counter-clock-wise repells....
 
e57 said:
If you do it yourself, make sure it is clock-wise. (Like all pre-made cables.)
Click to expand...

Never say always.

We get MC that is twisted both ways, a few feet clockwise a few feet counter clockwise and repeat.
 
e57 said:
If you do it yourself, make sure it is clock-wise. (Like all pre-made cables.) Clock-wise on a clock-wise system draws the conductors together, counter-clock-wise repells....
Click to expand...

I've thought about this a couple of times, and I can't see any possible way the direction of twisting makes a difference in the way the wires attract or repel each other. When current flows to a load in one conductor, and back to the source in another conductor, the magnetic fields add together in the space between the conductors, and cancel each other in the spaces away from the conductors. If I remember right, I think this draws the conductors together. I just don't see how clockwise, counterclockwise, or no twisting would affect the forces seen by the wires :confused: Do you have any references on this?

Steve
 
e57 said:
Its called Transposed, or Tri-plexed...

If you do it yourself, make sure it is clock-wise. (Like all pre-made cables.) Clock-wise on a clock-wise system draws the conductors together, counter-clock-wise repells....
Click to expand...

:confused:

If I look at a twisted pair of wires (running North and South) from the North end and they are twisted in a clockwise rotation, then when I view them from the South end, aren't they twisted in a counterclockwise rotation?

Taking two cables and twisting them (either clockwise or counterclockwise) would draw them together.
 
Gent's t avoid confusion, if in Australia, it goes the other way. :)

Bob, I have never seen and go in, or change to the other direction. You get that cheap cable? ;)
 
Status
Not open for further replies.
Top