Why industrial sites use different plugs to domestic ones
Standard domestic plugs (BS 1363 in the UK, Schuko/CEE 7 across much of continental Europe, NEMA types in North America) are built for indoor, low-current, single-phase use. Industrial and outdoor sites frequently need connectors rated for higher current, three-phase supplies, and harsher environments — which is what the IEC 60309 ("CEE" or "commando") range of round-pin industrial plugs and sockets is built for, with mechanical keying and colour coding designed specifically to prevent a plug being connected to the wrong voltage.
IEC 60309 colour coding — the fastest way to check voltage at a glance
IEC 60309 connectors are colour-coded by voltage and frequency, and this is one of the few electrical standards designed to be checked visually without a meter: blue is used for 200–250V single-phase (50/60Hz), red for 380–480V three-phase, and yellow for low-voltage 100–130V systems commonly used for site power tools. The pin position within the connector is also physically keyed by voltage range, so a plug genuinely cannot be forced into a socket of the wrong voltage family — a deliberate safety design, not just a colour convention.
What to confirm before specifying a replacement
Beyond voltage and phase, confirm current rating (common ratings include 16A, 32A, 63A and 125A), pin configuration (number of poles including earth and, on three-phase, neutral), and IP rating for the installation environment — outdoor and site connectors typically need IP44 or higher. Where a specific brand or range (such as Sursum) is already in use on site, matching that range avoids introducing a second, incompatible connector family into the same installation.