Cable Design Equations
Balanced Pair
| Cable Type |
CAPACITANCE (pF/ft) |
IMPEDANCE (Ω) |
Unshielded
Twisted Pair |
 |
 |
Shielded
Twisted Pair |
 |
 |
Overall
Shielded &
Cabled |
 |
 |
where:
C = Mutual capacitance (pF/ft.)
d = Diameter of the conductor (in.)
D = Diameter over the insulation (in.)
ε = Insulation dielectric constant (see Table II)
f = Stranding factor (see Table I)
ZO = Characteristic impediance
No. of
Strands |
Stranding
Factor
f |
| 1 |
1.000 |
| 7 |
0.939 |
| 19 |
0.970 |
| 37 |
0.980 |
| 61 |
0.985 |
| 91 |
0.988 | TABLE I |
| Material |
Dielectric
Constant ε (pF/ft) |
Velocity of
Propagation
VP (%) |
| ECTFE (Halar®) |
2.60 |
63 |
| PFA (Teflon®) |
2.15 |
68 |
| PVC |
5.00 |
45 |
| PVC (Semi-rigid) |
3.60 |
53 |
| PVDF (Kynar®, SOLEF®) |
7.70 |
36 |
| Polyethylene |
2.29 |
66 |
| Polypropylene |
2.25 |
67 |
| Polyurethane |
6.50 |
39 |
| Rubber - butyl |
4.0 |
50 |
| Rubber - natural |
5.0 |
45 |
| Rubber - SBR |
4.0 |
50 |
| Rubber - silicone |
3.1 |
57 |
| TFE Teflon® |
2.1 |
69 |
| TPE |
5.0 |
45 |
| Teflon® |
2.10 |
69 |
| Tefzel® |
2.6 |
62 | TABLE II |
Coaxial Cable
where:
C = Capacitance (pF/ft.)
d = Diameter of the center conductor (in.)
D = Diameter under the shield (in.)
ε = Insulation dielectric constant (see Table III)
f = Stranding factor (see Table I on previous page)
L = Inductance |
| Material |
Dielectric
Constant
ε (pF/ft) |
Power
Factor
(PF) |
| FEP (Cellular) Teflon® |
1.40 |
0.0002 |
| FEP (Solid) Teflon® |
2.10 |
0.0003 |
| PE (Cellular) |
1.56 |
0.0003 |
| PE (Solid) |
2.26 |
0.0003 |
| PE (Semi-Solid) |
1.29 |
0.0003 | TABLE III | |
| |
Standard Wire & Cable Company can supply you with the right sizes, types, and quantities of product you need to keep you on schedule and your management happy. We have been doing this for companies since 1947.
If you need a non-stock item, don't worry. We will make it for you. Custom cable and custom heat shrink shapes are another of our specialties. We will design, engineer, and manufacture to meet your exact requirements.
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Compliant |
