A comprehensive review of six major standards for light-duty cables used in ships, including the National military Standard, the US military standard, and classification society standards

I. Provisions of foreign military standards

1. American military standards

The current valid military standards for ship cables in the United States mainly include three general specifications, namely MIL-DTL-24643C: 2011, MIL-DTL-24640C: 211 and MIL-DTL-915G: 2002, as well as related single specifications. Among them, the one involving light-duty cables is MIL-DTL-24640C: In 2011, including 300V and 600V cables. In addition, there is the military manual MIL-HDBK-299, which compares and summarizes the data of all Marine cables, including light cables, to guide cable selection.

The standard name of the US military standard MIL-DTL-24640C: 2011 is "General Specification for Marine Light Low Smoke Cables", which means that the objects specified are low smoke cables rather than halogen-free cables. The standard does not have halogen content requirements for insulation. The core wire adopts SAE AS 81044/12 or SAE AS 81044/9 aviation insulated core wire. The insulation is cross-linked polyolefin and polyvinylidene fluoride (PVDF), and the sheath is made of cross-linked polyolefin. Its main features are thin insulation layer, small outer diameter and light weight.

At present, the main supplier of wire cores is Raykham of the United States, also known as Teco Company. In the past, China mostly purchased wire cores of SPEC 44 specification from this company and then processed and produced them. However, this type of wire core cannot meet the halogen-free requirements proposed in GJB 774A-2020.

In addition, MIL-DTL-24643C: 2011 has referred to cables as low smoke zero halogen cables and also put forward zero halogen requirements for insulation. It clearly stipulates that the halogen content of insulation, sheath and filling should be less than 0.2%. As the ship environment is roughly the same, when MIL-DTL-24640C is updated in the future, halogen-free requirements for cable insulation may also be put forward.

2. German military standards

The main German standard for ship cables is VG 95218. This standard includes a series of detailed specifications, covering general requirements, test methods, materials, cores, structures, inspections and other detailed contents of cables. The relevant standards for light cables mainly include four standards: VG 95218-61, VG 95218-64, VG 95218-65 and VG 95218-66, which respectively correspond to power cables and communication cables with different shielding forms.

This standard sets out performance requirements such as low smoke, halogen-free, low toxicity and flame retardancy in light of the ship environment. The development concept of "lightweight" cables is not only to optimize process parameters such as structure and thickness, but also to improve the performance parameters such as temperature resistance grade and current carrying capacity of the product. Under the determined power, the thickness of the insulation layer of the product is reduced to decrease the outer diameter and mass of the cable.

3. British military standards

In the early days, British ship cables mainly followed the naval standard, namely the NES standard. Later, it was uniformly incorporated into the standards of the British Ministry of Defence, namely the DEF STAN standards.

The relevant standards for ship cables mainly include: Def Stan 02-512 (NES-512) "Guidelines for the Use of Cables, Electrical and Related Items", which stipulates the classification, characteristics and applications of ship cables; Def Stan 02-517 (NES-517) "Cable Requirements", mainly used to clarify the technical specifications of various types of cables; Def Stan 02-525 (NES-525) "Requirements for Thin-walled Insulated Cables with Limited Fire Hazard", mainly used for small-sized thin-walled cables; Def Stan 02-526 (NES-526) "Requirements for Rubber Insulated Sheathed Cables for General Purposes with Limited Fire Hazards" is currently the core specification for cable selection for British Navy ships; Def Stan 02-527 (NES-527) "Requirements for Fire-resistant, High-temperature Area and Flame-retardant Sheathed Cables", mainly applicable to flame-retardant and fire-resistant cables; DEF STAN 61-12 "Metric Wires, flexible cords and Cables" is the current general requirement for all types of cables by the Ministry of Defence of the United Kingdom.

Among them, the relevant standards and specifications concerning light thin-walled cables for ships are mainly Def Stan 02-512 Part 8, Def Stan 02-525 and Def Stan 61-12 Part 25, etc. Def Stan 02-512 Part 8 is used to guide the selection and application of light cables; Def Stan 02-525, as a supplement to Def Stan 61-12 Part 25, mainly stipulates small-sized cables with a cross-sectional area not exceeding 2.5mm² that are not included in the standard of Def Stan 61-12 Part 25. The maximum cross-section stipulated in Def Stan 61-12 Part 25 is 10mm². Both Def Stan 02-525 and Def Stan 61-12 Part 25 are product standards, requiring the insulated wire core to comply with Def Stan 61-12 Part 18 and the sheath to comply with Def Stan 61-12 Part 31.

Based on this, these two standards put forward the following requirements: The nominal thickness of the insulating layer is 0.20 to 0.25 mm; From the perspective of the actual environment and service life, mechanical properties such as insulation shrinkage, dynamic cutting through, wear resistance, notch expansion, and non-stickiness at high temperatures are specified. It is stipulated that the wire core must pass the heat resistance test (120℃, 40,000 hours), and the thermal life cycle performance such as withstand voltage without breakdown after 168 hours of accelerated thermal aging. The requirements for low smoke, halogen-free and low toxicity indicators have been put forward.

Ii. Provisions of domestic military standards

1. National military standard

At present, the effective general specifications for ship cables in China include GJB 1916-1994 "General Specification for Low Smoke Cables and Flexible Cords for Ships" and GJB 774A-2020 "General Specification for Wires and Cables for Ships".

Among them, GJB 1916-1994 basically adopted the contents of MIL-C-24643A-1994 except for the conductor cross-sectional area and structure, without providing specific material properties and structural parameters. The industry independently referred to the US military standards for material properties. GJB 774A-2020 replaces GJB 774-1989, providing specific material performance requirements and adding specific indicators for low smoke and halogen-free cables. The main content of GJB 774-1989 adopts MIL-C-915F: 1985 (mainly for common halogen-containing cables).

However, it is regrettable that neither GJB 1916-1994 nor GJB 774A-2020 covers the relevant content of light-duty cables, including the naming, structure, special performance requirements for insulation layer materials and insulation thickness regulations of light-duty cables. The operational guidance significance is limited and needs to be supplemented and explained in a subsequent single standard.

2. Naval military standards

In view of the lack of technical indicators stipulated in GJB 1916-1994 and its poor operability, the revised GJB 1916A was not released. GJB 774A-2020 does not have a single standard and supporting document. There are no structural parameters for specific products, and its guiding role is limited. The Surface Vessel Equipment Bureau of the Navy Equipment Department has proposed the formulation of the Navy military standard "General Specification for Ship Power Cables" and the corresponding detailed single specifications, which have been submitted for approval.

During the formulation of the "General Specification for Ship Power Cables", on the one hand, it drew on the relevant technical contents of GJB 774A-2020, and on the other hand, based on the actual needs of ships and the application conditions of cables, it improved the missing contents of GJB 774A-2020.

The "General Specification for Power Cables for Ships" has added the naming and structural description of light-duty power cables, clearly stating that their series code is JQ. They adopt thin-walled insulation and single-layer sheath structure, but do not reduce the performance of the finished cables. This has pointed out the direction for the design, manufacture and application of light-duty power cables for ships, and also laid the foundation for the subsequent compilation of individual specifications.

3. Classification society regulations

At present, the major classification society standards all have relevant descriptions of cables, except for the ABS classification society standards of the United States and the DNV-GL standards of Norway. Basically, there are no clear regulations on the adoption of standards.

The ABS Classification Society of the United States stipulates in its "International Guidelines for Ship Construction and Classification (2021)" that light-duty cables must meet the requirements of MIL-DTL-24640C: 2011.

The DNV-GL specification specifically issued the relevant technical specification for light cables, DNVGL-CP-0400: 2019 Lightweight Electric Cables specifies the relevant requirements for the product structure, materials, performance and tests of lightweight Cables. Considering that thin-walled insulation may affect the physical and mechanical properties of the wire core, and thereby may affect the overall performance and usage safety of the product, This specification has raised the requirements for insulation and the physical and mechanical properties of the wire core. The tensile strength requirement for insulation has been increased to 20MPa, and the wire core has added performance requirements such as dynamic cutting through, cut expansion and wear resistance. In terms of thermal performance, the thermal life cycle should pass the test at 105 ° C for 20,000 hours in accordance with the BS 3G 230 method. The 168h accelerated thermal aging temperature is raised to 150℃, and it is required that no withstand voltage breakdown occurs. At the same time, the requirements for overload performance and high-temperature insulation without sticking have been added.

Iii. Analysis of the Current Industry Situation

At present, light-duty cables for ships are mainly used for military vessel matching. Due to the lack of relevant content descriptions and structural parameter regulations in the national military standard general specifications, and the fact that the Navy's military standard general specifications and detailed specifications have not been issued, there is still a gap in this cable standard.

On the one hand, each industry manufacturer formulates its own enterprise standards to guide production. For instance, referring to MIL-DTL-246433C: 2011, in order to reduce weight, they directly and artificially lower the thickness without changing the material, adopt a structure similar to that of Raykmann wire cores, and do not consider halogen-free performance, etc. On the other hand, there are also cases where user demand units do not have detailed requirements for the technical indicators of light-duty cables for ships. They take the cable parameters of individual manufacturers in the early stage as the overall requirements and continue to use the technical parameters from many years ago without any changes.

Both of these aspects are adverse consequences caused by the lack of a connection bridge between cable producers and users due to the failure of the industry to formulate national military standards or industry military standards related to light cables. There is a deviation between the standardized products and the performance requirements. The same model of products may have different structures and performance deviations, or even fail to meet the requirements, resulting in a low degree of standardization and inconsistent product performance, with various drawbacks emerging.

Therefore, it is extremely urgent to formulate unified standards that are in line with the actual situation of our country to guide and regulate the production and use of light cables for ships. At the same time, the formulation of standards for light-duty cables used in ships must take into account design, manufacturing, selection and application requirements.