Why don't electricians use solder?

For fixed household and commercial wiring, UK electricians almost always use mechanical connections — crimp connectors, terminal blocks, or push-fit connectors like Wago — rather than solder. This isn't because solder can't conduct electricity or hold a joint; it's because soldered joints in fixed wiring can crack over years of thermal expansion and contraction as the circuit heats and cools, and a cracked solder joint hidden inside a wall or fitting is far harder to inspect and fix than a mechanical connector.

UK wiring regulations (BS 7671) and standard electrical trade practice favour connection methods that are mechanically robust, easy to inspect, and simple to redo without specialist tools on site — solder doesn't score well on any of those for fixed installation work, even though it's an excellent electrical conductor.

This is entirely separate from electronics and hobby soldering, where a soldered joint on a circuit board or wire isn't subject to the same building-fabric stresses and solder is the standard, correct method. See can I use a soldering iron for automotive wiring for a related case where soldering is the right call, and our best soldering iron UK guide for choosing an iron for that kind of work.