Differences of PVC Vs. Silicon Test Lead Cables

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Complete Guide: PVC Vs. Silicone Test Lead Cables

There are many different variations of electrical cable for different electrical requirements. Whether it's the cable size/gauge, voltage rating or insulation material, these variables influence cable quality and performance for a specific electrical application. This guide aims to explain the differences between these popular insulating materials. Discover what test lead cable is best for your intended purpose with this cable insulation guide. 

1 - What is PVC Cable Insulation?

2 - What is Silicone Cable Insulation?

3 - What Are The Advantages and Disadvantages of PVC Test Lead Cable?

4 - What Are The Advantages and Disadvantages of Silicone Test Lead Cable?

5 - Differences Between PVC and Silicone Cable Insulation

6 - Summary

7 - Warwick Test Supplies Recommended Cable

1 - What is PVC Cable Insulation?

The full name of PVC is Polyvinylchloride, and the main ingredient is Polyvinyl chloride. PVC is an amorphous white powder that can be manufactured to be a hard or flexible end product. Stabilizers and additives are added during manufacture in practical applications to improve the end materials stability to heat, light, elasticity and flexibility. PVC used to be the world&#;s largest production of universal plastic and was first used as a cable insulation material during the second world war to replace rubber.  PVC is hard wearing, long lasting, uses less energy to process compared to other plastics flexible and is recyclable. PVC cable insulation does not harden and crack over time.

2 - What is Silicone Cable Insulation?

Silicone Cable Insulation is a type of Silicone Rubber that contains; Silicone together with carbon, hydrogen and oxygen. Silicone Rubbers were first used as a cable insulation in the 's but at the time struggled to become popular as it had limited thermal and strength properties as well as difficulties in the manufacturing process. These limitations have long since been overcome. With the use of additives and fillers silicone rubber has become a popular insulation material as it is generally non-reactive, stable and resistant to extreme environments. Due to these properties and its current ease of manufacturing and shaping, silicone rubber can be found in many electrical related components.

3 - PVC Test Leads

Advantages Of PVC Test Lead Cables

PVC cables are traditionally the most popular cable type for electrical applications as they provide durable performance and longevity (25-30 years working life) at a low cost. PVC insulation is highly resistant to foreign materials, and static electricity. The hard nature of the insulation material can reduce cable manoeuvrability and flexibility.

• PVC is relatively low cost and available in a wide range of colours
• PVC is durable and offers longevity
• PVC is resistant to; chemicals, corrosion, impact, abrasion and weathering
• PVC is Static Electricity proof. Leads easily kept clean.
• PVC test leads typically feature a white internal insulation and coloured external insulation. Easy to spot cable damage.

Disadvantages Of PVC Test Lead Cables

Despite PVC insulated cables traditionally being the most popular cable type, they do have some drawbacks. PVC cable is not as flexible as silicone cable. This can be an important factor when cabling is in enclosed and poorly accessible locations. Cable routing and testing can be easier to perform with the highly flexible silicone cable type. PVC's second noticeable disadvantage is a lower resistant to heat (-40 to 105°C) than Silicone. Accidental scorch damage from soldering in manufacture or excess current and resistance on live PVC cables can result in heat marking of the PVC or in its worst case fire risk.

• PVC is not as 'flexible' as Silicone cables.
• PVC has a lower heat resistance compared to Silicone cables. 

4 - Silicone Test Lead Cables

Advantages of Silicone cables

Silicone insulated cables have an outstanding thermal range of -90°C to 200°C+. This temperature range demonstrates it's greater resistance to heat than PVC insulated cables. Silicone test leads offer superior manoeuvrability and flexibility than the PVC alternative.

• Silicone insulated cables offer the highest manoeuvrability and cable flexibility
• Silicone insulation offers very high heat resistance 
• Silicone is resistant against oils and solvents

Disadvantages of Silicone Cables

Silicone insulated test lead cables are generally more expensive than there PVC test lead cable alternative. In recent years the price difference has increased due to a world shortage of silicone. The properties of silicone cable are less hard-wearing and more susceptible to damage from piercing or cuts than its PVC alternative. Silicone properties generate static-electricity, so they have a tendency to pick up dirt and grit making them harder to keep clean and spot imperfections or cable damage

• Silicone leads are more expensive than PVC leads
• Susceptible to cable damage and less hard wearing than PVC Leads
• Silicone leads generate static-electricity
• Silicone Test leads typically have a single insulation colour. Difficult to identify cable damage. 

5 - Difference Between PVC and Silicone Cables

For more information, please visit PVC Insulated Power Cable.

• PVC Cables are considerably cheaper than Silicone Cables
• Silicone Cables offer greater flexibility than PVC Cables
• Silicone Cables have a superior thermal range (greater fire resistance) than PVC Cables
• PVC Cables do not create static and are easier to keep clean than Silicone Cables

6 - Summary

It&#;s clear from the outset that both cable insulation types offer good performance for test lead cable. However, like any electrical component each cable insulator has its advantages and disadvantages. Cable performance heavily depends on what cable type is used in a specific electrical application. The characteristics of the cables are different and so are the scenarios they&#;re best suited to. Unfortunately, it's not as simple as a &#;one type fits all&#; approach. Warwick Test Supplies would advise matching cable characteristics with the intended electrical application. Contact Us if you&#;re unsure and we&#;ll advise where possible.

7 - Warwick Test Supplies Recommended Cables

Here at Warwick Test Supplies we manufacture a wide range of test cables for various applications. Over the years we have trialled and tested many leads. We highly rate and recommend the three test leads below, all of which offer; durability, longevity and good value for money. 

By: Leon Markwell

The thousands of kilometres of PVC insulated and sheathed cables in current use are not without installation and operational problems and this article looks at some that are found in domestic installations.

There are more than twenty million dwellings in the UK and most would be wired in PVC insulated or PVC insulated and sheathed cables, which have generally provided an economic installation and good service. PVC insulation and sheathing on electrical cables was introduced in the late &#;s and early &#;s to replace rubber insulation and sheathing as it was more practical, and not being a naturally occurring compound could be produced in quantity as required.

Unfortunately, now that we know much more about pollution and environmental concerns PVC is often referred to as the &#;poison plastic&#; due to the toxins it can release during manufacture, when exposed to fire, or decomposed in landfills. These toxins have been linked to health problems, along with the possible release of dioxin and phthalate that are possible contributing factors to the hazards it might pose to human health and the environment. There is mounting environmental pressure to ban PVC, but currently, this is not seen as practical due to its excellent properties as an electrical insulator and the need to provide practical alternatives.

However, the thousands of kilometres of PVC insulated and sheathed cables in current use are not without installation and operational problems and this article looks at some that are found in domestic installations.

The &#;green goo&#;

This problem will be well known to the more mature electrician, but many apprentices and younger operatives may not have had experience of this and the IET Helpline still receives calls on it, as do other organisations.

When PVC insulation was first produced the &#;plasticiser&#; chemical added to the PVC mix to allow flexibility (modern waste pipes etc. are unplasticised PVC &#; uPVC) in some PVC compounds the plasticiser was not chemically bonded into the mix, and thermal cycling of the conductors due to changing load current drew the plasticiser to the surface of the copper conductor, where it dissolved minute traces of copper (hence the green colour) and on vertical cable runs to switches and socket-outlets the force of gravity over the years has drawn it to the lowest point, the switch or outlet. Higher ambient temperatures will accelerate the process and movement down vertical cables.

The main instances arose during the s and s, before reformulation of the PVC fixed this problem, although some cases are still seen today.  

The goo is only ever-present in small quantities, it is messy and of low toxicity but should not be touched with bare hands. The goo is conductive due to the copper in it and when found should be cleaned away to prevent possible tracking. It can be cleaned away with methylated spirits, wearing gloves and paying proper attention to hygiene, and after use the cleaning materials must be properly disposed of.

Figure 1: An example of the 'green goo' (picture reproduced with permission from Goodwin Electrical)

Rewiring the affected final circuits may be considered, but if it is of limited extent regular periodic inspection and insulation resistance testing should be carried out to monitor the problem. It is also suggested by some that the resistance of conductors should be monitored to ascertain that conductors are not being over dissolved with their resistance thereby increasing. There is no specific guidance on the frequency of periodic inspection and testing and this can only be judged by experience of the particular installation. 

Expanded polystyrene and PVC sheathed cables

This is a more significant, although less common, problem than the goo, especially in loft spaces of dwellings. Expanded polystyrene is a light, inexpensive and easily handled material with great thermal insulation properties, making it useful for thermal insulation properties. However, if expanded polystyrene is in intimate contact with PVC sheathed cables, over time a chemical reaction can draw out the sheath plasticiser to form a sticky layer on the outside of the cable. In many cases as the plasticiser in the cable soaks into the expanded polystyrene it shrinks back and in the majority of cases no longer remains in contact with the PVC and deplastisation ceases. But in some cases, it has been reported that the plasticiser migrates out of the PVC, absorbing into and softening the polystyrene, which, in one instance, adhered to the PVC sheath, leaving a brittle cable that cracked and split, exposing live conductors, which was reported to have caused a fire in the local timbers within a dwelling. The plasticiser may also be readily flammable and without any fire breaks or seals a fire could spread to other parts of a building space.

It is reported that expanded polystyrene is most affected, but it can also occur with ABS or polycarbonate. It is stated by some manufacturers that modern PVC sheath compounds no longer react with expanded polystyrene, but if PVC sheathed cables are expected to be in contact with expanded polystyrene or other similar materials the advice of the cable manufacturer should be sought for the design.

Bitumen products and PVC sheathed cables

Bitumen and bitumen-based products are widely used in construction for roofing and waterproofing, and not so long ago a bitumen filled cable seal was used as a part of the incoming electricity supply cut-out to terminate a Paper Insulated Lead Covered (PILC) supply cable into a dwelling. Again, the PVC plasticiser can leach out of the cable and soften the bitumen, and in some severe cases, it can leak out of the cut-out chamber or make any waterproofing application useless.

Summary 

Over the many years of use of PVC, cable manufacturers have identified most compatibility problems and resolved them, however, there are always new building products coming onto the market. It is wise to check with a cable manufacturer when installing PVC insulated and sheathed cables in any new or unusual situation, or when it is proposed to use chemicals such as wood preservative on timber they are fixed to or perhaps paint over the cables. 

This article has considered some of the possible physical installation risks to PVC insulated and sheathed cables, but of course, the general thermal risks of cable operation due to current carrying, installation in thermal insulation and operating temperature and environment will also always be present.

Contact us to discuss your requirements of AC90 Cable. Our experienced sales team can help you identify the options that best suit your needs.