Correctly sizing a VFD Cable for your drive and motor is really not difficult if you know where to look. By knowing what sections of the National Electrical Code (NEC) to ref- erence, you can correctly size cable conductor size for your system. Just follow these five simple steps to size cables for low voltage drive systems with operating voltages not greater than 575 volts. STEP ONE: Determine the minimum temperature rating of your equipment. Temperature ratings are important to know when derating the cable for the application as higher temperature ratings allow cables to handle more current. The NEC tables for ca- ble ampacity for low voltage cables have columns for 60°C, 75°C and 90°C. The column you use will be based on the minimum temperature rating of your drive terminals, your motor terminals, and your VFD Cable. Most drive terminals are rated for 75°C. All Southwire VFD Cables carry a 90°C conduc- tor temperature rating but this is not true of all VFD Cables from other manufactures. Motor terminal temperature ratings can vary from 60°C to 90°C. Each of these temperature ratings needs to be verified with the manufacturer’s datasheets or user manuals. If other equipment is being used that is in the cable’s path, like a quick disconnect, collect that devices temperature raring too. Once you have all the temperature ratings, record the minimum value.
Southwire® Industrial Power Cable products do not have a defined shelf life. These products are composed of hard goods (metal, polymer, etc., ...) that are designed for many years of service once installed. As long as the products are not damaged during storage/handling and they are stored in a facility that protects against exposure to weather (sunlight and precipitation), there should be no degradation to the electrical and mechanical performance of the products and no reduction in service life. When storing cable the following precautions should be considered
DC Hi-Pot Testing is used for proof testing shielded cables (5kV to 46kV) in the field. The test can be done at various times such as acceptance of new cable installation, maintenance testing to track insulation degradation and as a pre and post test for splicing existing cables to new ones. The test will expose gross imperfections that are caused by improper handling, installation techniques or termination workmanship. A DC Hi-Pot test is not capable of locating the point of failure, rather it gives you an assessment of the whole system.
Strand-fll sometimes called moisture-block is a tar like substance that is applied between each lay-er of a concentric stranded copper or aluminum phase conductor. During the stranding process and at slightly elevated temperatures this tar like substance becomes fuid enough to be forced through a pump and applied geometrically in such a manner that the interstitial space between every strand is flled with the tar. The tar is then allowed to cool whereas it becomes stable and remains in place.
A dual rated cable is a cable that lists two different voltage ratings on its jacket. For instance, a cable with 115 mils insulation thickness may have a jacket with a print legend that lists both 5kV and 8kV voltages at 133% and 100% insulation levels respectively on it. Therefore, this cable may be used on both 5kV and 8kV systems.
Southwire is a company with a keen environmental awareness. We seek to leave the lightest footprint possible on the environment in the course of manufacturing and delivering our products to market. To that end Southwire Company has innovated a product that accomplishes one of our environmental objectives – A medium and 600 volt Ethylene Propylene Rubber (EPR) insulation that contains no lead.
A variable-frequency drive (VFD) cable is a special cable construction for the inverter-to-motor cable that has some or all of the following attributes:
• An overall shield that keeps bad stuff such as electrical magnetic interference (EMI) from escaping.
• A robust insulation system that keeps good stuff such as voltage and current from escaping.
• A symmetrical design that reduces the amount of bad stuff in the cable, such as common mode current and EMI.