In Episode 4 of No Dumb Questions, we explain electrical skew, defined as the difference in arrival time between two signals traveling to the same destination. Even if signals start together, they can arrive at different times depending on how the transmission path behaves, which becomes critical at very high data rates.
A simple analogy: if two cars travel the same distance but one takes a more direct route than the other, the faster arrival creates a measurable timing difference—this is skew. Minimizing skew is crucial in high-speed communications, where even tiny timing mismatches can degrade signal quality and data integrity.
We break down the three main causes of electrical skew in wiring systems:
- Velocity of Propagation (VOP) Mismatch: Differences in dielectric insulation materials (e.g., FEP vs. PVC) cause signals to transmit at different speeds, leading to earlier signal arrival on the higher-VOP material.
- Unbalanced Mechanical Tension (“Barber Poling”): Uneven tension during wire twisting causes one wire to take a straight, parallel path while the other follows a longer, orbital path.
- Mismatched Wire Diameters: Twisting wires of unequal diameters causes the smaller wire to travel a longer effective orbital path around the larger conductor.
To minimize skew, we ensure identical dielectric materials with equal VOP, maintain balanced mechanical tension during twisting, and use conductors with matching diameters.
Key Technical Takeaways
- Definition: Electrical skew is the time delay difference between two signals arriving at their destination.
- VOP Impact: Mixing insulation materials (such as FEP and PVC) creates timing differences due to varying propagation speeds.
- Barber Poling: Unbalanced tension during twisting causes one wire to take a longer orbital path than the other.
- Diameter Consistency: Twisting unequal wire diameters forces the smaller conductor into a longer path, increasing skew.
- Mitigation Strategy: Match dielectric materials, control twisting tension, and maintain equal conductor diameters.
Next up! Episode 5: What is Litz wire?
Episode 4 Transcript – What is Skew and How is It Minimized?
Welcome to No Dumb Questions
Welcome to another segment of No Dumb Questions, where the only dumb question is the question you don’t ask.
Today’s question is what is skew and how is it minimized?
So what is skew and how do we define it? Skew is the difference in time it takes for two signals to arrive to the destination. A good analogy of this would be if we had a ten foot table, and we had car A and car B. Car A driving straight down the table and car B swerving.
What would the difference in time be of their arrival? If car A beat car B by 10 seconds, the skew would be 10 seconds per ten feet or one second per foot.
Why is minimizing skew important? When communicating at fast data rates, expressed in gigabytes per second, minimized skew is crucial to getting a quality signal.
I’m going to go over the three reasons that are most commonly causing skew in electrical wires.
Reason 1: Differences in Velocity of Propagation (VOP)
Reason number one. There’s a difference in velocity of propagation or VOP.
So, for example, differences in the dielectric material that may cause that are: we could use two different materials. We could use a FEP and a PVC. The FEP is with a higher velocity of propagation where the PVC has a lower velocity of propagation. Therefore the electrical wire insulated with FEP dielectric will transmit faster than the electrical wire insulated with the PVC dielectric. Therefore, the FEP signal will arrive sooner than the PVC signal.
Reason 2: Unbalanced Tension and “Barber Poling”
Reason number two. You may have unbalanced tension when twisting two wires together leading to an effect called “barber poling” where one wire takes a straight parallel path and the other wire takes a long orbital path.
Here is an example of that. This is two wires twisted together. However, when we untwist them and compare the total length, we can see that one wire is much longer than the other. Therefore, it’s taking a longer path to the destination.
Reason 3: Mismatched Conductor Diameters
Reason number three why you might have electrical skew. You may have mismatched diameters that you are twisting together.
This is an exaggerated example, but if we had cable A and cable B with a much larger diameter, and we twisted them together, the circumference that the larger cable would have to twist around is much smaller than the circumference that the smaller wire has to twist around. Therefore, it’s going to take a more orbital path, the smaller wire, versus the larger wire, which is going to be in more of a parallel path.
Summary: How to Minimize Electrical Skew
So in summary, how do we minimize electrical skew?
First, we ensure that the dielectric materials are equal. They have equal velocity of propagations and that we’re not diluting them with colorants, for instance, to unbalance those.
Second, we ensure that we use equal tension so that we can mechanically balance a twisted pair and ensure that the mechanical length of two legs of a twisted pair are equal in length.
And finally, we ensure that both legs of a twisted pair are equal in diameter. Therefore, we can eliminate the “barber poling”.
So I hope I helped answer that question today of what is skew and how do we minimize it? For any additional questions, reach out to New England Wire. And don’t let skew “skew up” your signals.
And that concludes today’s segment of No Dumb Questions.