Steel and GRP are the two serious candidates for an outdoor electrical enclosure in the UK, and both have decades of service behind them. We sell GRP, so you know where we stand — but here's the honest comparison, including where steel genuinely wins.
Corrosion and maintenance
This is the decisive one for outdoor duty. Steel enclosures fight a permanent battle with rust: galvanising and powder coat help, but every scratch, drilled gland hole and door hinge is a way in, and coastal or roadside salt accelerates everything. GRP simply doesn't corrode. The colour is pigmented through the gelcoat rather than painted on, so a 20-year-old GRP cabinet by the roadside has typically had no maintenance at all.
Weight and installation
A GRP kiosk weighs a fraction of its steel equivalent. That means smaller crews, no crane on smaller jobs, easier transport and faster installation. For a walk-in kiosk the difference is dramatic — a GRP building arrives in one piece and is craned onto a prepared base in minutes.
Electrical safety
GRP is non-conductive. The enclosure can never become live, never forms part of a fault path, and doesn't need its own earth bonding. A steel enclosure must be earthed and kept that way for the life of the installation.
Security and impact
Here steel takes points: a determined attack with tools gets through GRP laminate sooner than through plate steel, which is why high-security applications still specify steel or steel-lined housings. For ordinary roadside duty, though, GRP's impact resistance is more than adequate — it flexes and recovers from knocks that would permanently dent a steel door — and standard cabinets take padlocks and locking bars all the same.
Fire
Steel doesn't burn — but it does conduct heat to whatever's inside. GRP enclosures built with fire-retardant resin achieve self-extinguishing performance to BS 476 (many of our cabinets exceed a half-hour rating), which satisfies the overwhelming majority of specifications. Where a spec demands strict non-combustibility, steel or concrete wins by definition.
Lifespan and cost
Purchase prices are comparable size-for-size; the divergence is whole-life cost. Steel needs inspection and recoating on a cycle, and a neglected steel cabinet in an exposed spot can need replacing inside 15 years. GRP's realistic service life outdoors is several decades with no maintenance budget at all.
The short version
Specify steel when the threat model is deliberate, tooled attack or the spec demands non-combustible construction. For everything else outdoors — weather, decades of unattended service, electrical safety, ease of installation — GRP is the stronger choice, which is why the UK's roadside infrastructure is overwhelmingly housed in it. New to the material? Start at What is a GRP enclosure?, see the broader case on Why use GRP, or browse the full GRP electrical enclosures range.