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Non-shielded drive cables are thinner and lighter

17 October, 2008

Two Japanese companies – OKI Electric Cable and Fanuc – claim to have developed a non-shielded motor drive cable that reduces significantly the impact of conducted noise caused by inverter switching. The SYM (symmetrical) cable is said to be up to 15% thinner, 20% lighter as well as being more flexible than shielded cables with a similar performance.

OKI says that the cables can double the recovery efficiency of conducted noise current, compared to conventional servomotor drive cables.

“We have succeeded in achieving an industry-first, high recovery rate of conducted noise current by making the inductance of the earth cable small,” explains OKI Electric Cable’s president, Takashi Hattori. 

As inverter switching speeds become faster, conducted noise levels are increasing. Conventional cables with large earth cable impedances have low noise current recovery efficiencies, increasing the likelihood that peripheral equipment will malfunction because of conducted noise.

The usual methods for reducing this risk are to use thick earth cables, to connect several earth cables in parallel, or to use braided wired and shielded cables. However, such cables are stiff and have large diameters. Moreover, the shield coatings can be expensive and can degrade the installation characteristics, according to OKI.

The new cables achieve a noise current recovery efficiency that is equivalent to a shielded cable by reducing the earth cable inductance to the same level as a shielded cable. Although the cables are thinner and lighter than shielded cables, they have similar noise current recovery efficiencies.

OKI says its has achieved the improved performance by balancing the three centres of the earth cable and motive power line, without using a shield. And, by bringing the cables closer and reducing the earth cable`s impedance, the noise effect becomes small.

By eliminating the need for shielding, which adds another step when fabricating cable terminals, the new cables are said to be more flexible and much easier to terminate and install.

According to Hattori, the new cables do not contain any of the six substances specified in the European RoHS Directive. 

OKI and Fanuc have patents pending for the new cable in Japan and elsewhere. The cable is available immediately in rated temperatures and voltages up to 105°C and 600V. 


 




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