Cable Insulation Types Explained for Engineers
Engineering decisions don’t come much more critical than the ones that need to be made on cable insulation. When a professional engineer selects the right insulated cables for a particular application, they can be sure of these crucial products providing the necessary dielectric strength to prevent unwanted current flow.
Making the most suitable selection of cable insulation, then, is vital for shielding conductors from environmental risks and mechanical damage. It also goes a long way to ensuring the highest standards of safety in accordance with regulations such as BS 7671 in the UK (otherwise known as “the IET Wiring Regulations”).
If you are an engineer attempting to decide between the various insulated cables on the market, you will need to consider such factors as operating temperature, installation method, environmental conditions, voltage rating, and adherence to British and harmonised standards.
Introducing The Key Cable Insulation Types Used in UK Electrical Installations
As you might have guessed given our mention of BS 7671, we are chiefly aiming this guide at UK readers. However, much of what we state here will be broadly applicable to projects carried out in other parts of the world, too.
Keeping our focus on Britain, though, the insulation materials used in cables in this country are broadly categorised into two groups: thermoplastics (such as PVC) and thermosets (for example, XLPE).
Below, then, we’ll take a closer look at these core material categories. Along the way, we’ll document the properties of these forms of cable insulation, together with their typical applications, advantages, disadvantages, and other things you ought to know.
- Thermoplastics
Thermoplastic materials soften when subjected to heat, while cooling results in them hardening. This makes such materials easy to process, but it limits their high-temperature performance.
- Polyvinyl Chloride (PVC)
PVC is relatively affordable, easy to install, and can be counted on to resist moisture and abrasion. Such qualities help make PVC insulated cables a suitable choice for general-purpose, low-voltage fixed wiring.
Standard PVC cables, such as BS 6004 twin and earth (T&E) options, are typically rated for a maximum continuous conductor temperature of 70°C. They soften if exposed to temperatures of more than this, and become brittle in the cold.
A further significant downside of PVC cables is the fact that they release toxic hydrochloric acid (HCl) fumes when burning.
- Low Smoke Zero Halogen (LSZH)
These often (but not always) thermoplastic-based cables are mandatory in many public buildings, hospitals, and tunnels around the UK. Even if exposed to fire, they emit minimal smoke and no toxic acid gases.
- Thermosets
The manufacturing process for thermoset materials sees them undergo a chemical “cross-linking” process. As a result, these forms of cable insulation don’t melt or drip even when temperatures escalate.
- Cross-Linked Polyethylene (XLPE)
This material sees extensive use in BS 5467 Steel Wire Armoured (SWA) cables. Compared to PVC, a fundamental benefit of this type of cable insulation is its higher thermal rating of 90°C. This allows for heightened current-carrying capacity or smaller conductor sizes.
On the other hand, XLPE is a pricier cable insulation material than PVC, as well as less flexible (though still workable). Careful termination is also necessary to avoid damage.
Nonetheless, XLPE’s distinctive combination of strengths lends itself well to such typical applications as power distribution cables, underground supplies, renewable energy connections, and SWA for industrial or commercial use.
- Ethylene Propylene Rubber (EPR)
Another thermoset option offering a typical maximum operating temperature of 90°C, EPR can sometimes perform well up to 105°C if a specialist grade is chosen.
Are you on the lookout for a form of cable insulation that is highly flexible, with good electrical properties and excellent resistance to heat and chemicals? In that case, this could be the one to choose. This material’s track record of performing well in wet or harsh environments helps explain its widespread use in marine, mining, and offshore applications.
Do bear in mind, though, the higher cost of EPR, as well as its slightly lower dielectric strength than XLPE in some high-voltage applications.
Knowledge Is Power When Choosing Between Cable Insulation Types
Naturally, as you seek to whittle down your options for your intended application, you will need to take into account a variety of technical factors. These will encompass such aspects as thermal rating, current capacity, and the specific environment in which the insulated cables will be used.
Regardless of your project, when you take the time to better understand the range of cable insulation types that exist, you will be better placed to specify cables that satisfy the highest standards of performance, safety, and compliance.
