Does the 8 kg divider load refer to one layer or a whole case?

A: One layer. The figure covers a suspended divider over a 300 mm span under distributed load; layers above and below count separately.

Does the 0.3 mm clearance per side reduce divider load?

A: It reduces rattle, not strength. The clearance lets the board shift until deflection passes 2 mm and the edge meets the slot wall. Above 0.6 mm the board walks in transit and the rating drops to 90 percent.

How far apart are distributed and concentrated load?

A: At 8 kg on a 300 mm span, distributed load gives 1.8 mm and a 40 mm contact patch gives 2.4 mm. Quote concentrated cases at 70 percent of the distributed rating.

Is a 5 mm slot deep enough?

A: Up to 300 mm span, yes; at 400 mm span it needs 8 mm. Below 4 mm depth the end counts as a simple support and the rating drops one step.

Why a safety factor of 2 instead of 1.5?

A: Batch scatter in failure load is plus or minus 15 percent, so a factor of 1.5 leaves about 20 percent for creep. A factor of 2 covers both.

Divider Load Rating

Quick answer: Divider load is set by span before board thickness: on 4 mm PP, a 300 mm span carries 8 kg and a 200 mm span carries 18 kg at 1.8 mm deflection.

Span comes before thickness
300 mm and 200 mm: 8 kg to 18 kg
Support type: floor, one side, suspended
Safety factor 2: where the ratings come from
6 mm at 400 mm: 100 mm bought for 2 mm
FAQ

1. Span comes before thickness

One 4 mm PP board carries 8 kg over a 300 mm span with 1.8 mm deflection at the centre. Shorten the span to 200 mm and the same board carries 18 kg.

Span enters the deflection formula to the fourth power, thickness to the third. A 50 percent longer span multiplies deflection by 5.1; going from 4 mm to 6 mm cuts it to a third, so the order matters.

The working limit is 2 mm. Past it the lower edge lifts away from the rib on the case floor, the 0.3 mm clearance per side is used up, and the board goes from surface to line contact. The 2 mm line is a fit limit, not a strength limit.

Thickness mm	Span mm	Support type	Deflection at rating mm	Divider load rating kg
4	200	Slots both ends	1.4	18
4	300	Slots both ends	1.8	8
4	300	One side supported	2.6	12
4	300	Standing on floor	1.2	30
6	400	Slots both ends	2.2	15

2. 300 mm and 200 mm: 8 kg to 18 kg

Scale 8 kg at 300 mm by the cube of the span ratio and 200 mm should give 27 kg. Measured usable is 18 kg.

Those nine kilos are not in the board, they are in the slot mouth: a 4 mm board in a 5 mm slot leaves 4 mm of wall, and 18 kg runs down two 200 mm lines of it.

Divider load test insert: black case open, square recess in lid foam, base foam split by ribs into two rows of six pockets

So the weak point moves with span. Above 300 mm, rate on deflection; below 200 mm, rate on slot crushing.

Span mm	4 mm board usable kg	6 mm board usable kg	Failure mode first
200	18	24	Slot edge crushing
300	8	16	Deflection past 2 mm
400	5	15	Deflection past 2 mm
500	3	9	Lateral buckling

A case often carries both spans: one long divider down the middle, short ones along the sides. Quote the longest and verify the slot mouth on the shortest.

3. Support type: floor, one side, suspended

A floor-standing divider rests its lower edge on the case floor, so load travels along the board and 30 kg produces only 1.2 mm. A suspended divider enters a 5 mm slot at each end and the same board carries 8 kg. One-side support sits between them at 12 kg.

The 5 mm slot depth is the premise of that set of numbers. Shallower than 4 mm, the end behaves as a simple support. At 8 mm the end is clamped and centre deflection drops by a third.

Support type	Boundary condition	Divider load rating kg	Deflection at rating mm
Standing on floor	Lower edge on floor, upper edge in slot	30	1.2
One side supported	One end in slot, one end on rib	12	2.6
Slots both ends	5 mm engagement per end	8	1.8

Change the support once and divider load moves by 3.75 times, far cheaper than changing thickness. The cost lands in assembly: a locating rib in the floor, or a boss on the wall.

4. Safety factor 2: where the ratings come from

The 30, 12 and 8 kg figures already carry a safety factor of 2, against measured failure loads of 60, 24 and 16 kg.

A factor of 2 rather than 1.5 follows from the failure mode. Slot edge crushing is progressive, so after the edge yields the board still carries part of the load, and batch scatter stays inside plus or minus 15 percent. A factor of 2 covers that scatter and creep, and would not suit a brittle board, which PP is not.

Divider load hardware example: black case open, contour pockets in black foam holding metal brackets, pliers and connectors

Three things must be confirmed first: whether the span runs slot floor to slot floor or slot mouth to slot mouth, one slot depth apart; whether the load is distributed or concentrated; whether the case is ever carried past 30 degrees of tilt.

Concentrated load is harsher. Spread 8 kg over a 300 mm span and the centre deflects 1.8 mm; press the same 8 kg onto a 40 mm wide patch and it reaches 2.4 mm, past the 2 mm line.

5. 6 mm at 400 mm: 100 mm bought for 2 mm

A 6 mm board over a 400 mm span deflects 2.2 mm under 15 kg. Scaled by the fourth power from the 4 mm at 300 mm case, the prediction would be 3.2 mm, so the measurement comes in lower. The difference is slot depth: the slot grows from 5 mm to 8 mm, the end shifts toward clamped, and centre deflection drops by a third.

Thickness has a price. Each divider eats 2 mm more width, and six of them take 12 mm out of the internal width, straight out of the compartments.

On short spans the extra thickness stops paying. Below 200 mm the gap between 4 mm and 6 mm shows up at the slot: a thicker board needs a wider slot, the slot wall thins, and crushing arrives earlier. In the table, 6 mm at 200 mm moves from 18 kg to 24 kg while the slot wall loses 2 mm.

The order is: measure the span, fix the support type, then choose thickness.

Conclusion

The answer to divider load is not in the thickness column, it is in span and support type. The same 4 mm board carries 8 kg suspended over 300 mm, 18 kg over 200 mm, and 30 kg standing on the floor. Set the working limit at 2 mm deflection, halve the measured failure load for the rating, then check the slot mouth.