Is V-0 enough to ship a flame retardant case?

Answer: For most indoor sites, yes. With a heater or battery inside, quote 5VA, since the plaque test mirrors real failure better; a shell with no internal ignition is covered by V-0 at 2.0 mm.

Is V-0 at 1.5 mm the same as V-0 at 3.0 mm?

Answer: No. Heat capacity and dripping differ, and 1.5 mm often lands at V-2. Write the thickness into the specification and cut acceptance specimens from the same wall.

Is halogen-free always weaker than bromine?

Answer: On efficiency it trails one step, since phosphorus needs 18% to match bromine at 20% on a 1.5 mm wall. On smoke it wins, with 40% lower density and far less acid gas.

How much more does a 5VA flame retardant case cost?

Answer: Material runs 15% to 25% higher and the wall grows from 2.0 mm to 3.0 mm, so the case lands 30% to 40% up. Above 500 units the gap narrows to about 25%.

How do you stop surface bloom?

Answer: Swap liquid phosphorus for solid phosphinate, cool the mould to 35 °C, add 8 s of cooling, and post-bake 4 h at 60 °C only as a last resort.

Does regrind hurt the rating?

Answer: It does. At 20% regrind afterflame climbs from 3 s to 6 s and drip risk doubles; past 30% a 1.5 mm wall falls to V-2. Retest at the same thickness first.

Flame Retardant Case: UL94 V-0 vs 5VA

Quick answer: A flame retardant case needs 5VA only when the shell is the last barrier: V-0 proves self-extinction at 50 W, 5VA proves no burn-through at 500 W.

Two Rulings, Not One Scale
Specimen Thickness: Why 1.5 mm and 3.0 mm Disagree
Halogen-Free Systems: Phosphorus, Nitrogen, Intumescent
What 5% to 15% Loading Costs
Matching the Rating to the Site
FAQ

1. Two Rulings, Not One Scale

The two ratings sit on different scales. V-0 holds a 20 mm blue flame of about 50 W under a 125 mm by 13 mm bar twice, 10 s each pass; 5VA applies a 500 W flame 125 mm long to a 150 mm plaque five times, 5 s each.

Item	V-0	5VA
Flame energy	about 50 W	500 W
Flame height	20 mm	125 mm
Passes	2, 10 s each	5, 5 s each
Specimen	125 mm by 13 mm bar	bar plus 150 mm plaque
Afterflame	10 s single, 50 s total	60 s after the fifth pass
Dripping	must not light cotton	plaque must not burn through

V-0 also carries a budget buyers forget: five bars must sum to 50 s of afterflame. The 5VA rule is blunter, since a hole reads 5VB. Neither test covers the other, so a flame retardant case order always pairs the grade with a thickness.

2. Specimen Thickness: Why 1.5 mm and 3.0 mm Disagree

Change the wall and the verdict flips. UL94 binds the rating to a thickness, so a card reads V-0 at 1.5 mm, never V-0 alone.

Flame retardant case in white, closed and facing forward, two blue catches at the front edge, a wide curved recess between them

Thin walls fail on dripping. A 1.5 mm bar loses viscosity fast, drops light the cotton 300 mm below, and V-0 becomes V-2; the same compound at 2.0 mm dripped once and held 5 s. Thick walls spread heat sideways, so 3.0 mm settles at 3 s to 5 s of afterflame and an oxygen index 1 to 2 points higher, at the cost of 1.2 mm penetration.

Conditioning decides the rest: 48 h at 23 °C and 50% RH, then 168 h at 70 °C, both of which must pass, or the lost grade returns within two years outdoors.

The process sets the window. Rotomoulded walls run 3.0 mm to 6.0 mm with no weld line. Injection-moulded flame retardant case walls land at 1.5 mm to 2.5 mm, where the weld line opposite the gate is the weak path, so specimens are cut there.

3. Halogen-Free Systems: Phosphorus, Nitrogen, Intumescent

Halogen-free does not mean low loading, and the wrong system doubles the dose without reaching V-0.

System	Loading	Mechanism	Wall	Main cost
Phosphorus	12–18%	gas phase plus char	2.0–4.0 mm	hydrolyses, blooms
Nitrogen	8–12%	dilution, char promotion	1.5–3.0 mm	amide resins only
Intumescent	20–28%	acid chars and foams	above 3.0 mm	brittle char, moisture
Bromine plus antimony	18–22%	radical scavenging	from 1.5 mm	smoke, acid gas

Phosphorus is the most efficient: 15% phosphinate with 3% char promoter gave 2 s of afterflame and no drip at 3.0 mm, yet 7 days at 60 °C and 90% RH pulled the extract pH from 6.8 to 5.4. Nitrogen at 10% reaches V-0 in PA and stalls in PP, which lacks the amide backbone. Intumescent at 20% to 28% foams to 5 mm to 8 mm, then cracks on a 1.2 m drop and lifts Ra from 0.8 to 3.2. Bromine at 18% with 5% antimony still reaches V-0 at 1.5 mm for 30% less material cost, though smoke density of 300 to 500 fails many indoor approvals.

4. What 5% to 15% Loading Costs

A flame retardant is a filler, and the invoice arrives in impact and finish. Each extra 5% takes 12% to 18% off Charpy impact: 25 kJ/m² unfilled, 16 kJ/m² at 10%, 12 kJ/m² at 15%. Haze climbs from 8% to 22%, colour shift reaches ΔE 1.5 to 3, and a pale flame retardant case shows both while a black one hides them.

Flame retardant case in red, closed and flat, two red catches either side of a curved recess, flush lid seam, plain white background

Shrinkage falls with the load, from 1.6% to 1.1%, so a mould cut to the old figure gives a 400 mm case 2 mm short. Three fixes work together: POE at 5% to 8% restores 18 kJ/m², a Ra 3.2 grain hides bloom, and a mould near 40 °C limits skin orientation. All three add 8% to 12%, still less than a thicker wall.

5. Matching the Rating to the Site

Site	Rating	Wall	Why
Charging pillar metering bay	5VA plus V-0	3.0 mm	parts inside can ignite
Storage PACK top cover	5VA plus V-0	3.0 mm	cell runaway, shell is last
Server room battery tray	V-0	2.0 mm	sprinklers cover the room
Forecourt box	V-0 plus static dissipative	2.0 mm	vapour cloud outside
Vehicle tool case	V-2	1.5 mm	no fixed ignition nearby

A flame retardant case earns 5VA only where fire can start inside and the shell is the last barrier. A charging pillar bay and a storage PACK lid both qualify at 3.0 mm, since a component can fail and the wall must survive five passes at 500 W. Where a steel cabinet or a sprinkler already stands in front, V-0 at 2.0 mm carries the job, and a vehicle tool case clears at V-2.

A forecourt box within 3 m of a loading point is the exception, needing V-0 plus static dissipation because the vapour cloud sits outside rather than inside. That clause outranks the yellow card.

Conclusion

A flame retardant case comes down to three numbers: 10 s of single afterflame and 50 s across five bars for V-0, five passes at 500 W with no hole for 5VA, and the grade drop between 1.5 mm and 3.0 mm. Where fire starts inside and the shell is the last barrier, quote 5VA. Where a cabinet or a sprinkler stands in front, V-0 at 2.0 mm carries the job, and 18% halogen-free loading is the price of matching bromine on a thin wall.

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.