2.6

Question:

 

When is an ÖLFLEX® or UNITRONIC® cable deemed "low-capacitance" and what advantages does this offer over other cables?

 

 

Answer:

 

The capacitance (C) of a component – in this case a cable – represents its ability to store electrical energy. A cable with low capacitance can be used over longer distances and offers lower transmission losses than a standard cable of the same length.
Whether or not a cable qualifies as "low-capacitance" depends on the insulation material that is used. In the field of data network cables, pure air would be one of the best and thus also one of the lowest capacity insulation materials. However, since it is technically impossible to use air as core insulation and to strand the bare copper conductors without contact, a range of different plastics are used for insulation purposes. Air has a dielectric constant of 1. Similarly, all insulation plastics used in cable technology also have a specific dielectric constant, which is measured at a specified frequency and ambient temperature.

 

The dielectric constant indicates the factor by which the capacitance increases when air is replaced with a different insulation material such as polyvinyl chloride (PVC) or polyethylene (PE). The higher the dielectric constant, the greater the capacity. The lower the constant, the better suited the material is to electrical core insulation. Compared to other insulation materials, PE for instance has a very low dielectric constant of approx. 2.2, which is why it is used for higher quality products such as LAN, BUS or coaxial cables. In some cases, small air bubbles or foam are encapsulated in the PE insulation to further improve the transfer quality. Depending on its composition, PVC takes up a mid-table position with values between 3.5 and 7. With dielectric constants of up to 9.0, elastomers such as chloroprene rubber are at the bottom of the pile when it comes to insulation materials for data network cables; even when used for connecting or control cables, relatively thick insulation wall thicknesses of such materials are required to achieve satisfactory insulation performance. Symmetrical core stranding can also have a positive effect on the capacitance (e.g. ÖLFLEX® SERVO 9YSLCY-JB with its three-part, green/yellow protective earth conductor).
A cable can be described as "low-capacitance" if the mutual capacitance specified in the catalogue for a PE-insulated cable, for example, is approx. half that of a cable which merely has PVC insulation, for instance.

 

Example:
UNITRONIC® FD (PVC-insulated)    =    mutual capacitance 140 nF/km
UNITRONIC® FD P plus (PP-insulated)    =    mutual capacitance 60 nF/km (thus qualifying as low-capacitance)

The electrical capacitance is measured in Farad (F).