New production technology. External shielding layer is injected production with stable resistivity and reliable performance. To produce external shielding layer, then inject the insulating layer, this way, can make the interface between the insulating layer and external shielding layer integrity, certainly no air gap; The insulating layer does not have the sewing thread, so it does not have the safe hidden danger. Since the electric conduction tube is lengthened, there is a big tolerance scope for the installing size, then it can reduce the installment fault. It eliminate from water entering, so it is more reliable and safer. And it can be used in the adverse circumstances, such as, mine, high-humidity region.