Must an electronic equipment case be metal?

A: No: a plastic case with a conductive coating shields too, provided openings are bonded.

Why must the earth lead be short?

A: Beyond a hundred millimetres impedance rises and interference current stays; short, thick, single point.

Is cooling about thickness or area?

A: Area: mount the equipment against the largest face with a thermal pad.

Is a thicker thermal pad better?

A: No: too thick raises resistance, too thin leaves gaps; match thickness to the surface.

Can it run with the lid open?

A: Not for long: shielding and cooling both fail and the failure rate rises without early symptoms. ---

What Is an Electronic Equipment Case? Shielding, Earthing, Cooling

Quick answer: An electronic equipment case differs from a protective case in three electrical paths: continuous shielding, low-resistance earthing and a heat path. Break any one and the equipment inside shows errors, drift or throttling — none visible when the case is opened.

Three electrical paths
Shielding: continuity beats material
Earthing: short, thick, single point
Cooling: pad and wall area
Selection and acceptance
FAQ

1. Three electrical paths

Shielding needs a continuous conductive surface. A metal case conducts through its body but openings break continuity; a plastic case needs an internal coating. Judge by whether openings are bonded, not by whether the body is metal.

Close-up of the foam cavity holding a rectangular instrument

Earthing needs low resistance between equipment shell, case and the external earth point. Its job is to divert interference current, and a lead longer than a hundred millimetres raises high-frequency impedance enough to matter.

Cooling needs an exit. A sealed case sheds heat through the wall only; without a thermal pad between equipment and wall the heat stays inside and the case runs twenty degrees above ambient.

Path	Structure	Test	If broken
Shielding	continuous surface or coating	surface resistance	errors, interference
Earthing	stud with short lead	earth resistance	static build-up, discharge
Cooling	thermal pad and wall area	internal temperature loaded	throttling, crashes

2. Shielding: continuity beats material

Shielding fails at seams and openings: lid rim, hinge, cable port. Without a conductive gasket there, thickness only shields half the problem. Measure resistance across each opening; it should read near zero.

Close-up of the earth bonding stud inside the case

Gasket type matters: braided mesh shields well but oxidises, conductive rubber seals well but takes a set, finger stock suits frequently opened doors. Life differs, so choose by opening frequency.

3. Earthing: short, thick, single point

Three rules: short, thick, single point. Keep the lead under a hundred millimetres, use at least four square millimetres, and earth the case to the external ground at one point only to avoid a ground loop.

The case closed on a shelf beside a plain plastic bin

The common error is earthing equipment and case separately, creating two points. The loop introduces low-frequency interference that shows as slow drift, usually misdiagnosed as ageing equipment.

4. Cooling: pad and wall area

Cooling capacity follows wall area rather than thickness. Thicker walls conduct a little better but the area does not change, so mount the equipment against the largest face with a pad between.

Close-up of the lid gasket and pressure valve

Pad thickness must match the surface: half to one millimetre on a flat base, one to two with thirty percent compression over raised components. Too thick raises resistance, too thin leaves air gaps.

5. Selection and acceptance

Check three things on a sample: conductive coating or metal body, an earth stud with a short path, and whether the largest wall face has enough area to cool the load. No instruments needed.

Accept with three actions: resistance across openings, earth resistance, and a two-hour loaded temperature run. Forty minutes covers shielding, earthing and cooling, and none of the three appears in a quotation: three items a datasheet almost never states and the three most often found wanting on site, which is why a sample test beats a specification sheet.

One usage note: do not run an electronic equipment case with the lid open. Shielding and cooling both fail, dust and interference enter, and the failure rate rises without any early symptom.

These three paths can be verified with a multimeter and one loaded run, no laboratory required, which is the sharpest difference between an electronic equipment case and a protective case.

Conclusion

Three paths: continuous shielding, short thick single-point earthing, and cooling through wall area with a pad. All three are electrical and thermal, so wall thickness and outer size never reveal whether the case is adequate.

This article covers container-side specifications and design implications only, not the handling, loading or use of the contents.