The effect of soft films on the D. C. breakdown of polyethylene cable insulation

Experimental samples of polyethylene insulated wire failed at 100 KV DC when there was a film of Vistac #4 on the conductor, whereas similar wire without the Vistac stood about 275 KV DC. There were two possibilities: 1) Simple mechanical damage. Vistac might accumulate in the tip during extrusion and penetrate the wall of hot polyethylene. 2) A real electrical effect of Vistac. It was postulated that any adjacent film of material of considerably lower dielectric strength than the insulation proper might lower the overall breakdown.