NT 6: Trails on Cables
Cable quality assurance
The quality of the products we manufacture and/or use is frequently a much discussed issue. Quality must be verified and measured by means of a reliable method, one that can be repeated over in time. There are national as well as international cable manufacturing standards which establish the testing methods that will assist in defining the quality of the product produced.
Trials distinctly fall into two different categories: electrical and mechanical. In all cases, the aim of the tests is to assess cable quality to guarantee the electrical safety that a cable must deliver.
Marlew's quality control laboratory is furnished with all the necessary equipment and qualified technical staff to conduct the tests according to the different manufacturing standards. Additionally, the quality assurance system used represents an important complementary tool to deliver high quality products.
In 2005, our AR MILIAR® and AI MILIAR® instrumentation cables as well as MP ARTEMP® and MT ARTEMP® fire-retardant products achieved Underwriters Laboratories Inc. certification to UL 13. Power cables and control cables in our COPERINT®, COPERCOM®, CONPREX® and CORCOM® lines are compliant with the Electrical Safety specifications defined under IEC 60502-1, as established by Argentina's Secretariat of Commerce, Industry and Mining under Resolution 92/98.
Classification of tests
Standards determine several assessment levels since the cable is composed of more than one raw material. For this reason, there are different tests for the finished product and its components. These include:
1. Raw material testing
2. Manufacturing processes testing
3. Production testing
a. Routine testing
b. Sample testing
c. Type testing
Raw material testing
Raw materials are tested to verify and ensure that the elements composing the cable meet the relevant associated specifications.
The materials tested are mainly the raw materials used for conductors (copper, alloys), insulation (PVC, XLPE, polyethylene, LSZH), shielding (copper, aluminium/polyester tapes), armouring (steel, aluminium) and sheathing (PVC, LSZH, polyethylene, thermoplastic rubber).
In general, metals are tested for their electrical and elongation resistance while insulation and sheathing materials are tested for their mechanical performance, for example breakdown charge and elongation in natural state and after ageing, cold bending, etcetera.
Testing of manufacturing processes
Critical manufacturing processes are a 100% controlled and systematically verified. The main tests measure the electrical resistance of the threads and the application of voltage (with spark testers) during insulation extrusion, to ensure that the dielectric is not punched along 100% of the insulated conductor.
a. Routine tests:
These tests are conducted on 100% of the finished cables and their main purpose is to verify the electrical integrity of the cable in terms of service and human safety during installation and use.
In accordance with Marlew's standards and quality parameters, each spool or reel produced is tested to:
- Measure the electrical resistance of all the conductors in the cable
- Verify insulation resistance between conductors
- Verify dielectric strength between conductors
- Verify dielectric strength between conductors and screen and armour (if applicable)
- Measure the electrical resistance of the shield (if applicable)
- Measure mutual capacitance between conductors (for databus cables)
The results are reported through a so-called test protocol, which is electronically filed, and, if so requested by the customer, a copy of this document can be submitted together with the finished product.
Sampling is carried out on a regular basis (in compliance with the associated standard or the company's in-house quality system plan) and is aimed at verifying that the product meets the relevant design specifications.
Depending on the different standards, sampling is conducted to verify:
- Dimensions (insulation, sheath).
- Pulling strength and elongation before and after ageing of plastic materials.
- Heat deformation.
- Cold bending.
c. Type tests
Type tests are performed to check that the cable works satisfactorily and serves the application that it has been designed for.
These tests do not need to be repeated except when changes are introduced in cable construction or materials.