Short answer: match the cable flame rating to the safety standard your product is built to, not to UL94 V-0. V-0 grades plastic parts; cable carries its own flame marks. Inside a control enclosure, three marks line up: VW-1 (UL 2556), CSA FT1 and IEC 60332-1. The order line that covers a typical build reads 18 AWG [0.82 mm²] wire, VW-1 flame rating, 90 °C temperature rating, 600 V. Where the product is built to IEC 61010, VW-1 is the rating the standard itself names for internal wiring. FT4 stays on building tray and riser runs; its burner applies roughly 230 times the heat of the small-cable test.
What UL94 V-0 rates, and what it does not
UL 94 grades a plastic specimen, not a cable. V-0 takes two 10 s burner applications to a vertical sample: the specimen must stop burning within 10 s after each application and within 50 s in total, and a flaming drip that ignites the cotton underneath fails the class. V-2 runs the same test, allows up to 30 s of afterflame per application and tolerates flaming drips.
A cable is copper, insulation and jacket built to a wire specification, and its flame behavior is judged on a full cable sample under a cable test. So the useful question is 'what does my product standard ask of the wire', and the standard answers it with a cable test, not a plastic class. For the parts themselves the bar is lower: IEC 61010 asks a printed wiring board for V-2 or better, so your V-0 plastic already outruns what that standard calls for.
The three cable tests that line up
VW-1, FT1 and IEC 60332-1 all burn a single cable, mounted vertically, under a small flame, then judge how far the damage climbs. That is why the safety standards treat the three as interchangeable marks for internal wiring.
- VW-1 comes from UL 2556, the wire and cable test standard. A burner touches the vertical sample twice for 15 s, the flame must die within 60 s of each application, and neither the paper flag above nor the cotton pad below may ignite.
- FT1 is CSA's vertical flame test for one cable, scored on the same three items: afterflame time, flag charring and flaming drips. FT2 is CSA's horizontal version and the weaker of the pair.
- IEC 60332-1-2 holds a 1 kW premixed flame on the vertical cable for 60 s; the sample passes when the burnt length stays near the burner. A companion part, IEC 60332-1-3, covers small cables and ribbon types the main sample size misses.
| Marking | Test standard | The burn | Pass looks like |
|---|---|---|---|
| VW-1 | UL 2556 vertical flame test | 2 x 15 s flame applications | Afterflame stops within 60 s per application; flag and cotton untouched |
| FT1 | CSA vertical flame test | One small-flame application to one cable | Afterflame, flag charring and flaming drips stay inside limits |
| FT2 | CSA horizontal flame test | Cable lying flat | Weaker than FT1; use it where the standard names it |
| IEC 60332-1-2 | IEC 60332-1 series | 1 kW flame for 60 s | Burnt length stays near the burner instead of climbing |
Any of the three marks answers a call for flame-retardant internal wiring inside a panel.
What the safety standards ask of internal wiring
IEC 61010, the safety standard for test and measurement equipment, asks that insulated wires and cables retard flame propagation; a note in the standard counts a UL 2556 VW-1 rating, or an equivalent, as meeting it. If your V-0 plastic parts live in a benchtop instrument, VW-1 wire closes the cable question.
IEC 62368-1, the audio-video and IT equipment standard that replaced IEC 60950, handles fire through enclosures and material classes rather than a cable clause. Its explanatory report, IEC TR 62368-2:2015, exempts wire and tubing insulation that complies with the IEC 60332 series or IEC 60695-11-21, so cable marked to 60332-1 answers it there.
NFPA 79 governs industrial machinery, and it points at the same test family. NFPA 79 permits nonmetallic wiring duct inside the enclosure only when the duct is flame-retardant as judged by the IEC 60332-1 test. Our backplate and DIN rail layout guide builds on that rule. The harness follows the same logic, together with the color code and conductor sizing covered in the NFPA 79 and IEC 60204-1 wiring article.
What it changes in a real panel
A flame mark and a water mark come from different tests, so you order both. For a washdown or outdoor site you spec a Type 4X / IP66 box and VW-1 harness wire inside. Our stainless enclosures are rated NEMA 4X / IP66 by the manufacturer; not UL listed. The enclosure rating covers hose-directed water and corrosion; the cable rating covers flame spread from an ignition source such as a mains power supply rated for a 40 °C panel interior. The thermal side of mounting that supply is in the power supply enclosure safety article.
Where cables cross the wall, the entry hardware carries its own component tests. The cable gland standards article explains what IEC 62444 and UL 514B prove, and wiring methods into a Type 4 box covers EMT, PVC and cable entry.
When the finished panel must carry a listing, more than the box feeds it. UL 508A is the standard a listed industrial control panel is evaluated to. The enclosure rating, the wire style markings and the duct all feed that process; how a panel carries a listing with an unlisted enclosure walks that path when the box itself is not listed.
If a burned harness brought you here, lock out the panel and verify absence of voltage before you open the door.
Worked example: why FT4 stays on the building side
FT4 is CSA's tray and riser rating, proven on a bundled vertical sample under a large burner running at roughly 40,000 Btu/h [11.7 kW] for 20 min.
Heat into the sample in that test: 11.7 kW x 1,200 s = 14,040 kJ, about 14 MJ.
IEC 60332-1-2 applies 1 kW for 60 s: 1 kW x 60 s = 60 kJ.
The ratio: 14,040 / 60 = 234, call it 230. The tray test puts about 230 times more heat into its sample than the hook-up-wire test. That is why an FT4 jacket is heavier and stiffer than the same copper deserves inside a panel, and why three 18 AWG drops in a 16 x 12 x 8 in [406 x 305 x 203 mm] stainless box are tidy in VW-1 wire and clumsy in tray cable.
You can still stock one type: an FT4 jacket passes the small-flame tests, so it works everywhere at the cost of routing bulk on every internal run. The decision: FT4 or tray-rated cable where the run leaves the enclosure for building tray or riser, VW-1 hook-up wire for everything inside the box.
What to put on the wire order
Write the flame rating and the temperature rating on the same order line, because the maker prints both on the spool:
That line covers 24 V DC I/O, 120 V control circuits and most sensor harnesses in a machine panel; the size call itself is covered in the 16 vs 18 AWG wiring article. Where the product standard is IEC 62368-1, order cable marked IEC 60332-1 instead of, or alongside, VW-1.
Decision by build:
| You are building | What the standard asks of the wire | What to order |
|---|---|---|
| Benchtop or lab instrument to IEC 61010 | Flame propagation retardance; VW-1 or equivalent counts | VW-1, 90 °C wire |
| AV or IT product to IEC 62368-1 | Insulation per the IEC 60332 series or IEC 60695-11-21 | Cable marked IEC 60332-1-2 |
| Machine panel to NFPA 79 | Flame-retardant wire and duct; duct judged by IEC 60332-1 | VW-1 or FT1 wire plus flame-retardant duct |
| Run leaving the panel into building tray or riser | Tray and riser rules take over | FT4 or tray-rated cable |
For the box around that harness, a custom stainless enclosure is built to your size, material and cutouts and delivered in 10 business days. Pick 304 stainless for most washdown and outdoor sites, 316L for salt air, brine and chlorides.
Catalog dimensions to compare
Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 16 × 12 × 8 in | 304 stainless | 16 x 12 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 304 stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 24 × 20 × 8 in | 304 stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Is VW-1 the same as CSA FT1 for wiring inside an enclosure?
Broadly yes: both are vertical small-flame tests for a single cable, and the standards that call for flame-retardant internal wiring treat them as equivalents. VW-1 is the marking US wire carries under UL 2556; FT1 is the Canadian marking; IEC 60332-1 is the international twin, with IEC 60332-1-2 applying a 1 kW flame for 60 s. Order the marking your market recognizes; a spool printed VW-1, 90 °C covers most panel builds.
Does VW-1 wire raise my enclosure's NEMA 4X or IP66 rating?
No, and none is needed: the two ratings test different properties. A Type 4X / IP66 enclosure, rated by the manufacturer and not UL listed, keeps hose-directed water and corrosive washdown off the harness; VW-1 limits flame spread from an ignition source inside. You order them separately: VW-1, 90 °C wire for the harness and a Type 4X stainless box for the washdown site. A V-0 plastic part raises neither property.
Can I run FT4 cable everywhere so I stock one type?
You can, because an FT4 jacket also passes the small-flame tests. The trade is bulk: FT4 proves itself over a 20 min, roughly 14 MJ burner run, about 230 times the 60 kJ an IEC 60332-1-2 sample takes, so the jacket is heavier and stiffer for the same 18 AWG copper. Use FT4 where the run leaves the panel into building tray or riser, and VW-1 hook-up wire inside the box.
How do I find wire styles marked VW-1 with a 90 °C rating?
Filter appliance wiring material listings by two parameters: flame rating VW-1 and temperature rating 90 °C. Machine-tool (MTW) and TEW styles at 600 V commonly carry both. Confirm the marking on the spool print, which repeats the style number, voltage, temperature and flame rating; that print is what an inspector reads. For 24 V DC control harnesses, a VW-1, 90 °C, 600 V order line covers it.
