A switchgear panel that looks right on the outside can still fail its purpose if the constructional details underneath aren't specified correctly. These are the practical design standards — sheet steel thickness, gland plate material, busbar choice, module sizing and mandatory safety interlocks — that determine whether a panel is genuinely fit for the installation it's going into.
Sheet Steel Thickness by Component
Different parts of a switchgear assembly carry different loads, and the sheet steel gauge should match the job rather than being uniform throughout the panel:
- Load-bearing members and frame — 2 to 3 mm (10, 12 or 14 SWG), depending on the size of the structure and the weight of the components it carries.
- Covers and partitions — 1.6 to 2 mm (14 or 16 SWG); larger doors, or doors carrying multiple relays, instruments and mimic-panel devices, need a thicker gauge or a stiffener at the back to prevent shaking and buckling.
- Base frames — 3 to 4 mm (8 to 10 SWG) MS sheet, or MS channel section such as ISMC-75 or ISMC-100, sized to the weight and footprint of the assembly.
- Gland plates — 3 to 4 mm, in MS or a non-magnetic material depending on the cable configuration passing through (see below).
Why Gland Plates Must Be Non-Magnetic for Single-Core Cables
When all three phases of a cable pass through a common opening in the gland plate, the magnetic field each phase induces is largely neutralised by the others due to phase transposition, and an ordinary MS gland plate is fine. The problem appears when single-core cables must each pass through their own separate gland: each core now produces its own uncancelled magnetic field, inducing eddy currents and hysteresis losses in a ferrous (MS) gland plate. Left unaddressed, this can heat the plate enough to damage cable insulation or trigger a short-circuit. The fix is straightforward — specify the gland plate in a non-magnetic material such as aluminium, SMC/DMC or Bakelite wherever single-core cables are involved.
Aluminium vs Copper Busbars
Busbar material is a genuine engineering trade-off, not a default choice:
- Aluminium — roughly a third of the weight and cost of an equivalent copper bus, with a lower cost-per-amp of current-carrying capacity. The trade-off is conductivity: aluminium has about half the conductivity of copper, so it runs hotter for the same current.
- Copper — higher conductivity means lower resistance and less heat generation for a given load, which matters where thermal margin and long service life under sustained high current are priorities.
In practice, the right material depends on the specific application — aluminium is the common choice for cost-sensitive general distribution, while copper is favoured where heat generation and equipment longevity are the deciding factors.
Stainless Steel Density by Grade Family
Accurately estimating panel weight and raw material cost depends on using the correct density for the specific stainless steel grade, not a rounded average:
- Austenitic grades (201–305, 321) — approximately 7.93 kg/dm³; higher-alloy austenitic grades (309S, 310S, 316, 316L, 317, 347) run slightly higher at 7.98 kg/dm³.
- Martensitic grades (403, 410, 416, 420, 431) — approximately 7.75 kg/dm³; the 440 series is slightly lower at 7.70 kg/dm³.
- Ferritic grades (405, 410L, 444) — approximately 7.75 kg/dm³; the 429/430/434 family runs at 7.70 kg/dm³.
- Austenitic-ferritic (duplex) grades (329 series, 630, 631) — approximately 7.80–7.93 kg/dm³.
- For reference, copper is 8.96 kg/dm³ and aluminium is 2.7 kg/dm³ — the gap that drives the busbar trade-off discussed above.
Module Sizing, Operating Heights & Mandatory Safety Interlocks
A well-designed panel follows established conventions for usability and safety, not just electrical performance:
- Module sizing — for a standard 1800 mm vertical panel, modules are typically sized in ratios of 1/6 (300 mm), 1/4 (450 mm), 1/3 (600 mm) or 1/2 (900 mm). Critical installations — refineries, petrochemical plants, humid or contaminated sites — should avoid modules smaller than 1/6 (300 mm) to keep adequate clearance between live parts.
- Operating heights — breaker handles, switches and pushbuttons should sit no higher than 1900 mm from ground level; indicating instruments like voltmeters and ammeters should be readable between 300 mm and 2000 mm; cable terminals should sit no less than 200 mm from the gland plate.
- Shrouds and shutters — mandatory over any live part that could be exposed when a feeder door is opened during routine operation, rated to withstand up to 200°C without deformation in case a fault occurs at the terminals.
- Door interlocking — a feeder door must not open while the feeder is live, and the feeder must not be switchable ON while its door is open. A defeat mechanism for authorised testing, and padlocking for lockout during shutdown or repair, are standard requirements.
- Grounding — a continuous main ground bus runs the length of the panel, with each feeder separately bonded to it rather than relying solely on the painted frame for continuity; doors should carry their own dedicated ground connection in addition to the automatic bond through their hinges.
Together, these details are what separate a panel built to a real specification from one that merely looks the part — see our guide to switchgear panel construction types for how these standards apply across fixed, cubicle and draw-out assemblies, and our Indian Standards reference for the IS codes governing enclosure and switchgear protection.
