Should you choose gel or cast resin cable joints? Steve Slater, HellermannTyton’s UK Product Manager – Electrical Installation, offers some pointers.
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’s possible to choose between several options, of which gel and cast resin jointing kits are among the most popular.
So, what factors should installers take 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 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 doesn’t 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’s 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’re 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’re 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’re 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’s ready to use, and they just attach the supplied leak-proof nozzle to the pouch and pour the resin into the shell. It’s 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.
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 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.
Whatever the requirement, the really good news is that nowadays there’s an ‘out of the box’ joint sealing solution for just about every installer, and every setting.