Test 14: Continuity Of Insulation – Enamelled Round And Tape Wrapped Round Wire

1 Test 2: Continuity of insulation (applicable to enamelled round wire and tape wrapped round wire)
1.1 General
Continuity of insulation is expressed by the number of faults per length of wire detected by means of an electrical test circuit.
1.2 Low-voltage continuity (nominal conductor diameter up to and including 0,050 mm) A wire specimen of (30 ± 1) m shall be pulled with a speed of (275 ± 25) mm/s between two felt pads, which shall be immersed in an electrolytic solution of sodium sulphate in water (30 g/l) with the conductor of the wire and the solution connected to an electrical circuit with an open-circuit d.c. test voltage of (50 ± 3) V (see Figure 5). The force applied to the wire shall not exceed 0,03 N. Faults shall be detected by means of a suitable relay along with a counter. The counter shall operate when the wire coating has a resistance of less than 10 kΩ for a period of at least 0,04 s. The counter shall not operate when the resistance is 15 kΩ or  more. The fault detection circuit shall operate with a speed response of (5 ± 1) m/s and with a  fault counter repeating at a rate of (500 ± 25) counts per minute when a bare wire is tested.
One test shall be made. The number of faults per 30 m of wire length shall be reported.

1.3 High-voltage continuity (nominal conductor diameter over 0,050 mm up to and including 1,600 mm)
1.3.1 Principle
A wire specimen with the conductor earthed is pulled over a “V” grooved electrode (pulley) or through a graphite brush electrode at a constant speed. A d.c. test voltage is applied between the electrode and earth. Any faults in the insulation of the wire are detected and recorded on a counter. The result is listed in faults per 30 m.

1.3.2 Equipment
The following equipment shall be used:
– high-voltage power supply providing a smooth filtered d.c. voltage with a ripple content less than 5 %, with an open-circuit test voltage adjustable from 350 V to 2 000 V with a short-circuit current limited by internal series resistance to (25 ± 5) μA at any test voltage and with not more than 75 % drop in voltage in case of a 50 MΩ fault resistance;
– fault detection circuit, which operates at a fault current as shown in Table 4 with a speed of response of (5 ± 1) ms and with a fault counter repeating at a rate of (500 ± 25) counts per minute when a bare wire is tested;
– dual high-voltage electrode pulleys according to Figure 6 made of stainless steel and providing a wire contact length of approximately 25 mm on each pulley;
– high-voltage electrode pulley according to Figure 7 made of stainless steel and providing a wire contact length of 25 mm to 30 mm;
– graphite fibre brush electrode assembly according to Figure 8, constructed so that the conductive brushes completely surround and contact the wire surface for a length of (25 ±2,5) mm (see Figure 6).

The graphite fibre brush electrode shall be inspected, cleaned, or
replaced if excessive wear or accumulation of foreign material is present. The graphite brush electrode assembly shall be electrically isolated for the duration of the test to prevent false readings at the specified voltages;
– earthed guide pulleys having an outside diameter of (50 ± 0,25) mm and root diameter of (40 ± 0,25) mm and spaced (140 ± 2) mm apart;
– surge damping resistor of 4,7 MΩ ± 10 % installed in the high-voltage line.
NOTE: The earth insulation for the high-voltage electrode should be a high-resistivity material, non-hygroscopic, non-tracking and easily cleaned, having a clearance for maintaining a continuous voltage of 3 000 V. No shielding should be used on the high-voltage lead since a minimum capacitance to ground is required during switching and
counting events. The drive motor should be the brushless type and should have sufficient power to maintain the required speed to pull 1,600 mm wire.





1.3.3 Procedure
A wire specimen of 30 m ± 1 m shall be pulled with a speed of (275 ± 25) mm/s over the highvoltage electrode pulley or through the graphite brush electrode mounted between the earthed guide pulleys with the conductor of the wire and the electrode connected to the electrical circuit, with the open-circuit d.c. test voltage adjusted according to Table 5 with a tolerance of ±5 % and with a positive polarity with respect to the earthed conductor of the wire.

1.3.4 Result
One test shall be made. The number of faults per 30 m of wire length shall be reported.