Should the cavity of an equipment protection case include service room?

Answer: Yes, but only on the operating face. Allow forty millimetres there, twenty elsewhere.

Is thicker foam always safer?

Answer: No. Thicker foam shrinks the cavity and eats side margin. Keep the two numbers separate.

What should the empty case weigh?

Answer: About 3.1 kilograms for a twelve litre moulded body, within thirty percent of the loaded weight. Rotomoulded bodies are heavier.

Does a wheeled case still need carrying figures?

Answer: Yes. Wheels help only on flat ground; steps still need lifting. Above twenty-five kilograms, fit wheels and two handles.

Is the cavity measured at the opening or the floor?

Answer: At the narrowest point, the floor. Two degrees of draft over 200 millimetres pulls each side in about seven millimetres.

Equipment Protection Case: Sizing Cavity and Shock Margin

Quick answer: Choosing an equipment protection case takes two sums. Build the internal cavity from the device envelope plus foam, cabling and access allowances, then set corner and base margin from the weight. Quote the cavity at its narrowest point and margin against drop height.

Start With the Cavity, Not the Outside
Three Allowances: Foam, Cabling, Access
Shock Margin at Corners and Edges
Weight, Balance and Carrying Method
Filling the Sizing Sheet
FAQ

1. Start With the Cavity, Not the Outside

Every equipment protection case is quoted with three numbers: outside size, moulded cavity and usable cavity. The outside sets stacking volume, the moulded cavity is what the tool produces, and the usable cavity is what remains once foam is in. Quote the wrong one and every allowance after it is wrong.

Measure at the narrowest point: two degrees of draft over 200 millimetres pulls each wall in about seven millimetres. A body that fits at the opening and not at the floor is a draft nobody counted.

Term	Meaning	How it goes wrong
Outside size	Envelope with bumpers and latches	Used to size the load, too generous
Moulded cavity	Space as moulded, draft included	Measured at the opening, too generous
Usable cavity	Space left after foam and ribs	Cabling omitted, too tight

2. Three Allowances: Foam, Cabling, Access

Usable cavity is the envelope plus three allowances. Foam runs twenty millimetres at the sides and fifteen at the top, with the base handled as margin. Below fifteen, a device corner wears through the foam and reaches the shell.

Cabling needs a bend radius: thirty millimetres, or twice the cable diameter. Access needs forty millimetres on any face carrying knobs or ports, or the device comes out for every connection.

Allowance	Direction	Value
Side foam	All round	20 mm
Top foam	Above the panel	15 mm
Cabling	Cable exit	30 mm minimum
Access	Operating face	40 mm

3. Shock Margin at Corners and Edges

Margin is not thickness. Thickness is static space; margin is what is left to compress. Up to six kilograms, use twenty-five millimetres at the base, twelve at each corner and eight along the edges. Double the weight and the base goes to thirty-five, corners to sixteen.

Corners take more because they land first and foam fits worst where three faces meet. A thin corner splits inside the bumper and runs along the parting line. A separate moulded corner block fixes that; a thicker bumper does not.

Device weight	Base foam	Corner margin	Edge margin
Up to 6 kg	25 mm	12 mm	8 mm
10 kg	30 mm	14 mm	10 mm
20 kg	35 mm	16 mm	12 mm

The figures assume a 1 metre drop. For parcel sorting, add five millimetres back, since chute drops often exceed 1.5 metres.

4. Weight, Balance and Carrying Method

Total weight is device plus empty body. A twelve litre moulded case weighs about 3.1 kilograms, so a six kilogram payload lands at 9.1, while twelve kilograms approaches fifteen.

Keep one-handed loads under twelve kilograms, two-handed under twenty-five, with the handle within 150 millimetres of the centre of gravity. Beyond fifteen percent off-centre, the mass lands on one corner and effective margin falls.

Total weight	Carrying method	Handle
Under 12 kg	One hand	Centred, 25 mm grip
12 to 25 kg	Two hands	Symmetric, both sides
25 to 40 kg	Strap or wheels	Wheel 75 mm minimum

5. Filling the Sizing Sheet

Fill the sheet in order: envelope, three allowances, margin by weight, outside from cavity plus wall, then a weight check. Set the outside first and the case starts dictating the device.

Trial fitting confirms the arithmetic. The lid should close without force and should not lift the device when opened. A stiff lid means the top allowance is short; a device riding up means the grip is too tight.

Conclusion

Choosing an equipment protection case is arithmetic: the envelope is known, foam, cabling and access are added, margin comes from a weight table, and the outside is derived from the cavity. Once every step ends in millimetres, trial fitting confirms a decision instead of replacing one. What remains is whether the supplier can hold the tolerance on that equipment protection case.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.