RELICON gel filled cable joints for connecting cables above and below ground

Date: 20/06/2017


What should I choose – gel or cast resin cable joints?

Connecting cables is a basic skill for electricians, and over the years most develop their own preferences for creating, insulating and protecting cable joints. Naturally, these may vary according to the current and environmental factors involved, but in many cases when sealing and protecting a cable joint it is possible to choose between several options, of which gel and cast resin jointing kits are among the most popular.

So, what factors should installers be taking into account when choosing between gel and resin joints, and what are the pros and cons of each?

Gel and resin joints have the same purpose, but they look very different, are installed in different ways and can serve different purposes. For example, gel joints are intended for use with low voltages. Resin joints are also most often used with low voltages, but different formulations of resin are available and some can be used with medium voltages. This is important because, of course, one of the most important determinants of joint selection is the voltage level; the joint must be able to cope with the voltage involved, and joints designed for low voltages may fail if subjected to too high a current.

Gel joints
Gel and resin joints look very different. Gel joints have a rigid shell, made of polypropylene that resists UV light, extremes of temperature and impact – obviously, this is to protect the electrical connection within the joint when it is installed, in day-to-day use. The shell comes pre-filled with a specialist gel, which is non-toxic and highly insulating (˃20kV/mm). Fitting a gel joint is very simple and does not require any special training. When the cable ends have been connected using an appropriate terminal, the installer simply pushes the connection into the gel and snaps the casing closed. The gel encloses the point at which the cables join, this insulates the new connection and keeps out water, dust and anything else that may contaminate or corrode the joint. Typical gel joints have an ingress protection rating of IP68.

Gel cable joints are very quick and easy to install and unlike resin joints there is no curing time, so they can be buried, boxed or otherwise hidden as required, straight away. Gel jointing kits have an indefinite shelf life, so they can be stored in a van or depot for long periods, and can be used as straight through or branch joints because they come in a range of dimensions. Perhaps most importantly, gel joints can easily be re-opened after installation, for testing and/or inspection purposes. Consequently, they are ideal for general domestic and light industrial uses.

Cast resin joints
In contrast, cast resin joints require a little more skill to install and time for the resin to cure (usually about 50 minutes) before the cable can be buried or concealed. However, they are probably a little more versatile than gel joints. Resin joints can be used with both armoured and non-armoured cables, with a wider range of voltages, and provide a very robust join once the resin has cured. They are more appropriate for cables with larger cross sections, and better able to cope with heavy-duty conditions and harsh environments, than gel joints. 

While installing cast resin joints does take some skill, the process has recently been made much easier by some companies, such as HellermannTyton, whose patented mixing system gives installers a clear view throughout. All the installer has to do is place the joint within the moulding shell, then mix the two-part resin in the transparent pouch supplied. When the resin changes colour, the installer knows it is ready to use, and they just attach the supplied leak-proof nozzle to the pouch and pour the resin into the shell. It is easy for the installer to see when the shell has been completely filled. The resin takes around 50 minutes to cure, at which point the joint is fully encapsulated. Cast resin provides a permanent, highly durable and maintenance-free solution and can be used for various cable and jointing configurations, including straight through, parallel and ‘Y’ branch joints.

Why choose one over the other?
Manufacturers supply both gel and cast resin jointing kits – these contain everything the electrician needs to connect the cables and insulate the joint, so both are user-friendly, ‘out of the box’ solutions. There is a great deal of overlap in their applications; both are ideal for low-voltage settings, for example, and both are easy to use – although cast resin takes a little more skill, innovative packaging has simplified the process considerably.

A further similarity is that both solutions can be used inside and outdoors, and underground. However, where conditions are likely to be hostile, for example under water or in installation ducts, the more robust and durable cast resin may be the best choice. Indeed, it could be argued that cast resin is generally a little more versatile, in that it can be used in a wider range of settings, but this has to be weighed against the sheer speed and convenience of gel joint installation, and the gel kits’ indefinite shelf life. Wherever it is known that access to the joint will be needed in the future, for example for testing purposes, in settings such as homes and offices the gel option is a clear winner.

Of course, there are other factors, beyond the scope of this article, that installers must consider when joining cables. These include environmental matters – is the joint sealed with a non-toxic substance that complies with local regulations and will not harm human, animal or plant life? Is the chosen solution manufactured to comply with applicable standards, and certified as doing so? However, none of these issues need be a problem if electricians take care to choose gel and/or cast resin jointing kits produced by reputable manufacturers and certified to the highest standards. For the really good news is that today, there is an ‘out of the box’ joint sealing solution out there for just about every installer, and every setting.


RELICON gel joints used for connecting cables

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