TERMINATING 5KV NON-SHIELDED CABLE? NO STRESS RELIEF USED BUT BE CAREFUL
Termination kits for 5kV non-shielded cable are not mandatory, but they're a good idea.
- Published in Southwire's T&D Update newsletter in November 1997
- Reprint permission granted
If you're installing 5kV non-shielded cable, watch out for tracking. According to Section 310-6 of the National Electrical Code (NEC), you can use non-shielded conductors up to 8kV, providing they have "Insulation resistant to electric discharge and surface tracking, or the insulated conductors) shall be covered with a material resistant to ozone, electric discharge, and surface tracking." At conductor ends, added protection can be provided with a termination kit.
Termination Kits Protect Conductor Ends
"The NEC allows non-shielded cable up to 8kV," says Dave Mercier, Southwire applications engineering manager, "but you have to be very careful. Non-shielded systems above 2,400V can be a challenge, especially when you terminate the conductors."
At the higher voltages, contamination on non-shielded conductors can be the starting point for discharge currents on the surface of the insulation. The current flow erodes the insulation surface. That can lead to cable failure.
"The ends of non-shielded conductors are the most exposed to contamination, and the most prone to tracking," Mercier says. "That's why it's a good idea to use a termination kit with non-shielded cable." Non-shielded cable terminations are made of material that reduces damage caused by tracking.
Kits Don't Provide Stress Relief
A termination kit for a non-shielded cable contains the same basic components as a kit for shielded cable, with one exception: the stress relief material.
Mercier explains, "With shielded cable, when you strip back the insulation shield, it sets up concentrations of electrical stress ill the insulation. To protect the insulation, you need some way to relieve those stress concentrations. With non-shielded cable, you can just cut back the insulation and terminate the cable, like 600V building wire. You don't need stress relief."
Southwire manufactures non-shielded cable for use at voltages up to 5,000V. Accessory manufacturers supply termination kits that work at up to 8,000V. Mercier says, "Follow the NEC requirements in any non-shielded application. And with any termination kit, it's important that you follow the manufacturer's instructions." |
