UL 3321 for Internal Wiring of Appliances
UL AWM Style 3321 is a single conductor with extruded insulation, rated 150°C, 600 Vac and 750 Vdc, with Horizontal Flame. The conductor range is 30 AWG through 4/0 AWG, solid or stranded, with extruded XLPE insulation and an optional treated or untreated braid.
The official Use for Style 3321 is internal wiring of appliances. That wording names the equipment category directly, which is worth noting because many AWM Styles state only “internal wiring” and leave the equipment category entirely to the designer. For Style 3321, appliance internal wiring is the Style-level Use itself.
This page is written for that requirement: sourcing Style 3321 as internal component wiring inside an appliance, at a temperature and voltage level above what general-purpose internal wire covers.
Verified UL Style 3321 Ratings and Construction
| Parameter | Style-level information |
|---|---|
| UL AWM Style | 3321 |
| Construction | Single conductor with extruded insulation |
| Temperature rating | 150°C |
| Voltage rating | 600 Vac / 750 Vdc |
| Flame | Horizontal Flame |
| Conductor size range | 30 AWG–4/0 AWG |
| Conductor form | Solid or Stranded |
| Insulation | Extruded XLPE |
| Optional covering | Treated or untreated braid |
| Marking | General |
| Official Use | Internal wiring of appliances |
Insulation Wall Varies by Conductor Size
Style 3321 does not apply one insulation wall across its whole range. The requirement steps up four times between 30 AWG and 4/0 AWG:
| Conductor size | Minimum average thickness | Minimum thickness at any point |
|---|---|---|
| 30–9 AWG | 30 mils | 27 mils |
| 8–4 AWG | 45 mils | 40 mils |
| 3–2 AWG | 60 mils | 54 mils |
| 1–4/0 AWG | 80 mils | 72 mils |
The span is substantial — the top group requires more than two and a half times the minimum average wall of the bottom group. Describing Style 3321 as having a 30 mil insulation wall is therefore accurate only for the 30–9 AWG group, and wrong for everything above it.
Each group carries two separate requirements, not a range: the first figure governs the average across the wall, the second sets a floor at every individual point on it.
Why AWG Has to Be Identified Before Quotation
Because the insulation requirement changes with conductor size, an enquiry naming Style 3321 without an AWG has not identified which of four constructions is being asked for.
The effect is not marginal. A design moving from 9 AWG to 8 AWG crosses a group boundary and the minimum average wall requirement rises from 30 mils to 45 mils — a construction change sitting behind what looks on a BOM like a single size step. The same happens again between 4 and 3 AWG, and between 2 and 1 AWG.
Required conductor size comes from the appliance electrical design. No ampacity value is published here and no current capacity is inferred from AWG alone, because the Style record establishes neither.
600 Vac and 750 Vdc Are Both Verified Ratings
Style 3321 carries an AC rating of 600 Vac and a DC rating of 750 Vdc. Both appear in the Style record, and both belong in a complete technical table.
They are separate figures for separate conditions. 750 Vdc is not restated here as 750 Vac, as “750V AC/DC”, or as a combined 600/750V cable designation. Where an appliance section operates on DC, the DC figure is the relevant one; where it operates on AC, the AC figure is. State which condition applies in the enquiry.
The 150°C Rating
The verified Style rating is 150°C, and it applies to the wire.
It does not follow that any given appliance location may operate continuously at 150°C without further engineering evaluation. The appliance designer evaluates the actual thermal environment at the wire’s position against the equipment requirements, and the wire rating does not on its own establish service life at that position. No continuous-service-life or thermal-aging figure appears on this page.
Style 3321 is also not compared here qualitatively against PVC, silicone, FEP, PFA or mica constructions. Those are separate Styles and material families with their own verified ratings, and a comparison that matters has to be made between verified figures rather than between material reputations.
The Optional Braid
Style 3321 permits an optional treated or untreated braid as a covering. Optional is the operative word.
Constructions exist with and without it, so a braid is not a feature of every Style 3321 wire and is not described as mandatory here. The base construction is the extruded XLPE insulation; the braid is a separate covering present only where the ordered construction includes it.
Braid material, thickness, colour, mechanical performance, abrasion rating and any temperature effect are not established by the Style record and are not stated here. Where a braid is required, state yes or no in the enquiry and supply whatever the drawing controls about it.
Conductor Requirements Are RFQ Items
The official Style information establishes the 30 AWG–4/0 AWG range and the solid or stranded form. It establishes nothing else about the conductor.
Copper, tinned copper, bare copper, silver-plated copper and nickel-plated copper are none of them established at Style level, and no strand count, individual strand diameter, conductor diameter, lay length, conductor resistance or ampacity is stated here. Where the appliance specification controls conductor material, plating or detailed stranding, each is a confirmation item in the enquiry.
One Style Number, Very Different Conductor Classes
30 AWG and 4/0 AWG are not variants of the same physical product. A fine conductor at one end of this Style and a 4/0 conductor at the other differ in every practical respect that affects procurement — dimensions, handling, termination hardware, packaging and the insulation wall requirement itself.
Nothing on this page should be read as implying that all sizes within the Style share similar physical dimensions. The Style number describes a construction family; the AWG describes the product.
Dimensional Confirmation
No universal finished outside diameter is published for Style 3321, because the Style provides minimum insulation-wall requirements rather than a completed-wire diameter.
Finished OD depends on the AWG, the specific conductor construction, the solid or stranded form, the conductor details, and whether the optional braid is included. Where dimensions matter, the RFQ should specify the AWG, the maximum finished OD, the OD tolerance if controlled, the available routing clearance, the terminal or connector interface, and the optional braid requirement.
Style 3321 is not described here as universally compact, thin-wall or small-diameter wire, and no dimensional value is invented.
Appliance Internal Wiring in Practice
The practical contexts in which appliance manufacturers specify this Style are component-level: internal component-to-component wiring, internal appliance leads, connections between appliance electrical components, protected internal routing within the assembly, and high-temperature internal locations where the equipment specification calls for Style 3321.
These are procurement contexts within the official Use. They do not mean that UL approves any particular appliance type through the Style, and no heater wattage, motor rating, current figure, component temperature, service life or continuous operating load is stated here.
Application Boundary
Internal wiring of appliances is the Use, and it stays inside the appliance.
Style 3321 is not building wiring, field wiring, branch-circuit wiring, premises wiring, facility wiring, tray cable, raceway wiring, conduit wiring, portable cord, an external appliance power cord or general power distribution cable. The distinction between AWM internal appliance wire, field-installed building wire and external flexible cords is a category distinction, not a matter of rating.
Bulk Wire and Finished Leads
This page concerns Style 3321 single-conductor wire. It is not a finished wire harness, a processed appliance lead, a multi-core cable, a terminated power lead or an external appliance cord.
The Style itself defines no cut length, strip length, terminal, connector, ferrule, crimp, wire seal or harness geometry. Where processed leads are required, those requirements are separately specified and confirmed rather than assumed to accompany the wire.
What Style 3321 Does Not Define
- Conductor material and conductor plating
- Strand count, strand diameter and conductor resistance
- Ampacity
- Finished OD and OD tolerance
- Colour
- Terminal, connector, cut length and strip length
- Packaging, reel length, MOQ, stock and lead time
Each comes from the buyer drawing, the ordered construction, a verified SKU specification or separate commercial confirmation.
Common Procurement Errors
- “UL3321 wire” requested with no AWG. Four insulation groups sit inside the range.
- A 30 mil wall assumed for all sizes. It applies to 30–9 AWG only.
- Thicker requirements for larger conductors overlooked. The wall reaches 80 mils minimum average at 1–4/0 AWG.
- Braid assumed to be included. The covering is optional.
- Tinned copper assumed from the Style number. Conductor material is not set at Style level.
- 750 Vdc read as 750 Vac. The AC rating is 600 Vac.
- One universal finished OD assumed. OD depends on size, construction and braid.
- Bulk wire assumed to include terminals. The Style defines no lead assembly.
- Appliance internal wiring confused with building wiring. Different categories.
- Conductor finish left open where the drawing controls it.
Substitution
Different AWM Styles have independent temperature ratings, voltage ratings, conductor ranges, insulation constructions, covering requirements and official Uses. No Style is presented here as automatically interchangeable with Style 3321.
Where an alternative is under consideration, substitution requires separate technical evaluation against the appliance specification across all of those parameters, not a match on one or two of them.
Appliance RFQ Checklist
- UL AWM Style 3321 requirement
- Required AWG from 30 AWG through 4/0 AWG
- Solid or stranded requirement
- Required conductor material
- Required conductor finish or plating
- Detailed stranding, if controlled
- Insulation colour
- Optional treated or untreated braid required: yes / no
- Finished OD or maximum OD, if controlled
- Appliance type
- Internal installation location
- Required AC or DC working condition
- Customer drawing or existing wire specification
- Cut length, if applicable
- Strip length
- Terminal or connector interface
- Marking requirement
- Quantity
- Packaging requirement
- Destination
- Required compliance documentation
These are buyer inputs. No configuration is presented as automatically available.
UL Marking and Documentation
Material is supplied as UL-recognized component wire where supplied under qualified manufacturing scope, and UL marking is applied according to the confirmed ordered construction. The Style-level marking designation is General.
CSA AWM, FT1, VW-1 and dual UL / CSA certification are not claimed here; any additional certification depends on the ordered construction. Applicable RoHS / REACH documentation can be confirmed according to the ordered construction.
Flame Classification
The verified Style-level flame designation is Horizontal Flame. VW-1 and FT1 are separate classifications, are not claimed here, and Horizontal Flame is not rewritten as either. Any separately confirmed vertical-flame construction is order-specific rather than a universal Style 3321 rating.
