Spring clamp or screw terminal in wiring accessories: which to choose

Two ways to secure a conductor

Behind every switch, dimmer and socket outlet sits the same task: a copper conductor has to press against a live part with sufficient contact pressure for years. With a screw terminal you tighten a screw that clamps the conductor directly or via a pressure plate. With a spring clamp (also called a push-in terminal) you push the stripped conductor into an opening, after which a steel spring presses it against the busbar.

Both systems are standardised and safe, provided you use them for what they are designed for. The difference lies in installation time, the type of conductor, releasing the wire and how the connection behaves over the years.

Installation speed: where the gain is

With a spring clamp the connection takes two actions: strip to the indicated length and push in. No screwdriver, no tightening, no doubt about whether the screw is really tight. With a screw terminal you add loosening, inserting and tightening for each conductor, plus a brief pull test.

That saves a few seconds per connection, but it adds up. A worked example: a house with 60 switch and socket points and an average of three conductors per point comes to 180 connections. At 10 seconds saved per conductor that is half an hour per house, and 20 hours across a project of 40 houses.

The second gain is in checking. A spring clamp is either right or wrong: the conductor is pushed in to the stop or it is not. With a screw terminal the quality depends on the tightening torque, and that is not always consistent at the end of a working day.

Reliability: contact pressure over the years

Copper deforms slowly under pressure. A screw terminal that was tight on installation can gain a little play after years of heating and cooling: the contact pressure drops, the contact resistance rises and the joint runs warmer. That is why retightening screw terminals in distribution boards is a well-known maintenance item. Behind a switch in a flush box that hardly ever happens, so there the installation has to be right first time.

A spring clamp maintains its own contact pressure: the spring follows the conductor as it settles. Spring clamps are therefore not very sensitive to vibration and temperature changes and do not need retightening. A properly tightened screw terminal on solid conductor also lasts for decades (apply the tightening torque specified by the manufacturer, usually below 1 Nm for wiring accessories), but a spring clamp leaves less room for an installation error.

Solid or flexible conductor

This is the most important practical difference. A push-in terminal is designed for solid conductor: the single-core 1.5 or 2.5 mm² wire that is drawn into conduit in Dutch housing. A solid conductor is stiff enough to push the spring open and then stays straight in the clamp.

Flexible conductor (fine-stranded, as in flex cords) cannot simply be pushed into a push-in terminal: the fine strands splay out and the spring grips them poorly. Flexible conductor only works with a ferrule, and only if the terminal datasheet permits it. A screw terminal accepts solid and flexible conductor without further ado, although a ferrule on fine-stranded copper is the neat solution there too.

Rule of thumb: housing and renovation with solid single-core wire, choose spring clamps with confidence. If you work a lot with flexible conductor, for example surface-mounted installations with flex, a screw terminal or a spring clamp with ferrules is more convenient.

Releasing and reuse

A screw terminal can be loosened and retightened as often as you like; the conductor goes back in unchanged. With a spring clamp you release the conductor through the release opening: press the spring in with a small screwdriver and pull the conductor out.

The clamped part of the conductor usually shows a slight impression of the spring afterwards. Cut off the end and strip it again before reinserting. That costs a few centimetres of wire, so allow enough length in the flush box. In a refurbishment where switches are moved several times, a screw terminal is slightly more forgiving.

Which range has what: Liregus Modern and Liregus Alfa

Lichtplein carries two ranges of wiring accessories from the Lithuanian manufacturer Liregus (since 1944), each with its own connection system.

• Liregus Modern uses spring clamps. The premium range: flat, matt wiring accessories with slim cover frames in matt white, matt black, matt sand and champagne. 157 items, including dimmers, USB socket outlets and CAT6a network outlets. The earthed socket outlet is also available in Liregus Modern with screw terminals; the connection system is listed per item in the specifications and in the Liregus datasheet on the product page. For homes, hotels and offices where you install right first time and never go behind the plate again.
• Liregus Alfa uses screw terminals. The basic wiring accessories for construction and renovation: 115 items in white and sand, with and without cover frame, flush and surface mounted. Familiar, robust and suitable for solid and flexible conductor.

In price the ranges are close together: a single-pole switch costs around 10 euros in Liregus Alfa and around 12 euros in Liregus Modern excl. VAT, and a single cover frame starts at 1 and 2 euros respectively. The difference is in finish, colour choice and breadth of range, not in the basic switch.

Many installers combine them: Liregus Alfa in storerooms, meter cupboards and plant rooms, Liregus Modern in living and representative spaces. The wiring accessories of both ranges are IP20 for dry indoor areas and ship from European stock within 5 working days, to businesses only, with project prices from 100 pieces.

Frequently asked questions